Chapter 01: Introduction
1.1 General background
The world's population is rapidly becoming more urbanized. It is predicted that by the year 2000 over 50% of the people of the world will live in towns or cities (Carter 1993). In developed regions the population is already predominantly urban, but it is in developing countries that a rapid transformation from rural to urban societies is currently taking place. The average annual growth rate of urban populations in developing countries for the period 1990–1995 is calculated to be 4.2% per annum, compared with 0.8% in developed countries (Carter 1993). People are having an ever increasing impact on local, regional, and global environments. This is particularly significant in and around urban areas, where people are often physically or psychologically disconnected from more natural ecosystems.
Urban forestry is defined as the planned, integrated and systematic approach to the management of trees in urban and peri-urban areas for their contribution to the physiological, sociological, and economic well-being of urban society. Urban forestry is multifaceted; it deals with woodlands, groups of trees, and individual trees where dense conglomerations of people live, involves a wide variety of habitats (streets, parks, derelict corners, etc), and is concerned with a great range of benefits and problems. An urban forest is an ecosystem. An ecosystem is an area that contains living (e.g., trees, people, and animals) and nonliving (e.g., soil, buildings, utilities, and roads) things existing together and interacting. Humans play a dominant role in the urban ecosystem. Different components make up urban forests. They may include street trees, park trees, woodlands, riparian areas, manicured lawns, the urban-rural interface, and others (Carter 1993).
Urban forestry is a new and still developing research field. Although it is new but already the practice of urban forestry has started in Bangladesh. The century old trees in Dhaka and Chittagong cities are reminiscences of the past efforts. Unfortunately, most of these trees were cut down in the name of development activities. During the last two decades, there have been large scale plantations of trees in the country including along the roadsides, avenues, highways, railways and other places in the cities. Commendable approaches are establishment of Botanical Gardens at Mirpur and Suhrawardi Uddyan at the old Race Course ground in Dhaka city. Various indigenous and exotic tree species have been planted in the gardens. The establishment of Balda Garden by a private endeavor is a highly praise worthy effort. The Zoos in Dhaka and Chittagong cities have also been covered with trees. All these may be termed as urban forests. It is established mainly for enhancing aesthetic value of the cities. The importance of urban forestry for maintaining healthy environment was rarely perceived in the efforts (Satter 1999).
The importance of urban forestry may be appreciated by knowing the objectives of urban forestry as given by Zabala (1991) are stated below:
1) maintenance and sustenance of natural processes such as water, gaseous, nutrient cycles and support of flora and fauna; and
2) provision of economic and social benefits.
A principal goal of urban forestry is to sustain forest structure, health, and benefits throughout the urban ecosystem over the long term. Comprehensive and adaptive management approaches are needed to do this. Expanding the management focus of urban forests to all trees, associated resources, and their benefits across the urban ecosystem will require nontraditional urban forest management techniques. The overall societal benefits of implementing such management are likely to be substantial.
1.2 Rationale
Trees have been an important part of human settlements throughout history, only recently has their full value to urban dwellers been considered. Trees and green spaces play an important role in improving city living conditions and to save from environmental degradation. In the past, urban forestry in developed countries was considered almost exclusively on the basis of its aesthetic merits. Now, a closer look is being given to the environmental services and quantifiable economic benefits they provide. In most developing countries, like Bangladesh, government and international support for urban forestry has been limited The dramatic urban population increase in these countries, together with a corresponding growth in needs for food, fuel and shelter, calls for the design of strategies in which forestry will play a larger role in providing such commodities and in improving the urban living environment
Moreover, sufficient study and research are not undertaken to improve the Dhaka city plantation. This paper discusses on status of Dhaka city avenue plantation and inquiry the possible solution for the development of roadside plantation. I think my study will be helpful regarding this.
Objectives
- To investigate status and distribution of avenue plantation in Dhaka city.
- To inquire the possible solution for the development of avenue plantation.
Chapter 02: Review of literature
2.1.Urban forestry concept
Urban forestry is not a new concept, but it is one which appears to have growing potential. This is particularly true in developing countries, where urbanization is increasing at a rapid rate and a demographic switch from a predominantly rural to a predominantly urban society is taking place. Although United Nations (UN) (1991) figures indicate that in 1990 only 37% of the total population of developing countries was urbanized, it is predicted that by the year 2025 the proportion will be 61%. Already rapid and uncontrolled urbanization in many developing countries is having fundamental social and environmental consequences. The role of urban trees in ameliorating this situation might, at first thought, appear to be small.
Urban areas in developing and developed countries are often very different. Furthermore, although we know intuitively what is ‘urban’ and what is ‘rural’, there is actually no universally accepted criterion for distinguishing between such settlements. The usual mechanism, common in national censuses, is to take population thresholds. Once a nucleated settlement grows beyond a certain threshold, it becomes ‘urban’. However, the threshold used varies widely from country to country, and may even change in successive censuses (Hardoy and Satterthwaite 1986). The United Nations has attempted to standardize data by defining settlements of over 20,000 people as ‘urban’, over 100,000 as ‘cities’, and over 5 million as ‘big cities’. In contrast, Hardoy and Satterthwaite define any nucleated settlement of more than 5,000 as an urban centre, those having a population of less than 20,000 being ‘small urban centres’, and those having some 20,000 to 100,000 inhabitants being ‘intermediate urban centres’. Whatever the figure used, generalizations are inevitably unsatisfactory. A small Pacific island whose total population is under 20,000 will obviously have a different perspective on urban settlements from a large, heavily populated country such as India. Different national perspectives may well reflect historical, cultural and political differences. This varied concept of an ‘urban settlement’ should be remembered throughout the ensuing discussion. It is also worth noting that the ‘cut off point’ on the ground for an urban centre is interpreted differently in different countries. An obvious example of this is in China, where cities often ‘annex’ a number of adjacent districts into their administrative areas in order to ensure control over the supply of essential urban services, such as reservoirs or power plants. The official population of many Chinese cities thus includes many rural dwellers (Drakakis-Smith 1987).
The definition of urban forestry given by Miller (1988) is of, “An integrated, city wide approach to the planting, care and management of trees in the city to secure multiple environmental and social benefits for urban dwellers.” The definition of urban forestry given by Grey and Deneke (1986) is of, “Urban forestry is the management of trees for their contribution to the physiological, sociological, and economic well-being of urban society. Urban forestry deals with woodlands, groups of trees, and individual trees, where people live - it is multifaceted, for urban areas include a great variety of habitats (streets, parks, derelict corners, etc) where trees bestow a great variety of benefits and problems.”
2.4.Peri-urban forestry as a separate concept
Peri-urban forestry is loosely defined as forestry on the fringe of urban settlements, but given the lack of conformity between countries as to what constitutes ‘urban’, a precise definition of ‘peri-urban’ is impossible. To use the simple definition of the area used by urban residents is inadequate, since this may extend far into rural areas; as theories such as that of Von Thunen have shown the sphere of influence of a city or town may be very wide. To define peri-urban solely in spatial terms is also unsatisfactory, since it can be so variable. Many urban foresters are unwilling to accept peri-urban forestry as a separate concept; they argue that the peri-urban area, or urban fringe, is simply one location for urban forestry. This argument has been accepted in the compilation of this document, so that all further mention of urban forestry may be assumed to include peri-urban locations, unless otherwise indicated. (Carter 1993).
2.5. A new approach to the potential of urban forestry in developing countries:
The potential of forestry in and around urban settlements may be approached from one of two broad perspectives. One is to focus upon the trees themselves; the potential benefits and problems that may be expected from their cultivation in an urban environment; how they may be managed to maximize the former; and what threats an urban environment pose to their survival. An alternative perspective, which this paper attempts, is to focus first on the residents of urban areas, their needs and the nature of their invariably diverse living conditions, and then to consider how trees might be of benefit to them To learn more about the urban dweller, especially in the developing world, it is necessary to consult geographical or other social science texts. These rarely devote much attention to peoples' use of and perceptions of trees, except, to a certain extent, in the case of fuel wood supplies from peri-urban areas (Carter 1993)
2.6. History of urban forestry
The planting of trees in human settlements and as an integral part of landscape architecture is not new; it has its roots in ancient Chinese, western Asian and Greek civilizations (Jellicoe 1985). A number of ancient cities had highly developed parks, gardens and other green spaces - the most notable being Babylon, "the mother city of gardens'', dating back more than 3000 years. The Assyrian civilization and, much later, the classical Persian and Greek civilizations arising in the fifth century BC, also had such a tradition, based on amenity as well as cultural and religious beliefs In Europe in the seventeenth and eighteenth centuries, municipal and crown forests were managed for recreational hunting. Later, the elite developed urban gardens and parks as visual amenities in many European cities, particularly Italy, France, Austria and England. The practice of urban amenity plantings subsequently spread to colonies in Africa and Asia. Spanish colonization introduced into Latin America the concepts of interior patios in houses and public plazas in urban centre.
Just as the rate and extent of urbanization vary considerably in the Third World, the nature and character of urban settlements also vary according to the individual culture, politics and past of different countries. This is reflected in urban forestry practices, with some countries having a long history of urban tree cultivation. For example, it is known from the writings of Marco Polo that extensive roadside tree plantings were a feature of 13th century China (Pollard 1977). In Mexico City, the forest of Chapultepec was first established by the Aztecs as temple gardens (Benavides Menza 1992), while in India a number of urban parks were established by sultans and maharajas (an example being the Lal Bagh park in Bangalore -Sunder 1985).
Many countries of the Third World share a history of colonialism which exerted a profound effect on the process of urbanization. They are an early mercantile period (beginning in the 1500s or later), a period of industrial colonialism (the 1850s onwards), followed by late colonialism (1920s onwards) and then independence (late 1940s to 1960s). The dates are given as an indication, and pertain most closely to Asia.
Outside influence during the mercantile period was mainly confined to existing urban settlements, particularly ports, where residential areas tended to be already segregated along ethnic or occupational lines. During the industrial period, colonial control was exerted at all levels of the urban hierarchy, and a tendency towards urban primacy emerged (one “primate” city dominating all others). Often laborers from outside the local area were imported to work in assembly or production. Social, economic and spatial separation was generally reinforced, so that different areas of a city took on a particular character. According to Onganga (1992) in the minds of many local Kenyans, at least, this has left urban amenity trees negatively associated with the colonial past.
In some countries, continuing contacts with former colonial powers, then short of labour, resulted in a flow of workers to Europe during the 1960s. This, however, was short lived; by the end of the 1960s, the world economic system began to change radically, and labour in the North was becoming more organized and expensive. Many European and North American companies began to relocate in Third World cities, where labour was cheaper. It is this phenomenon, the New International Division of Labour, which has had the most sweeping effect upon the nature of Third World cities today. For the purposes of the present discussion, a number of key points may be noted.
The vegetation of Prague has been influenced by agriculture since neolithic times. Historical records from the thirteenth century describe a wood shortage which led King Jan to establish a wood marketplace near the city. In 1350, King Charles IV ordered the preparation of strict regulations controlling the use of forest lands.
In 1740, King Charles VI ordered the planting of trees along roadsides; nobles owning land abutting on roads were to care for and profit from the trees. In 1752, Empress Maria Theresa broadened the decree to include the planting of trees on all new roads in order to orient travelers in fog and snow, increase wood production and enhance the appearance of the landscape.
The first major reforestation of Prague was undertaken in 1854 and, between 1897 and 1908; substantial efforts were made by public beautification commissions to revegetate open spaces and eroded hillsides throughout the city (Valesova 1985).
2.7. Why Urban forestry?
The need for urban forestry to be a planned, integrated, and systematic approach to urban tree management should be stressed. Planning is important because trees are very often considered as an afterthought once development has taken place, rather than being incorporated at the original design phase. An integrated approach implies the participation of many different organizations - local councils, municipal and national planning bodies, departments, etc. Systematic management entails regulated tree management; operations such as planting, pruning, and felling must all be conducted in an organized manner, at the appropriate time. In industrialized countries urban forestry is concerned primarily with environmental enhancement. Even in countries (e.g. Germany), where timber is harvested from peri-urban forests, the major management objective is providing recreation/education of the urban dweller, and timber harvesting operations are significantly modified accordingly (Carter 1993).
Urban forestry plays a vital role in the following ways-
2.7.1. Improving the aesthetic quality of urban areas
It is the aesthetic and recreational value of trees, forests and parks that is most directly identified by most urban dwellers, in developed and developing countries alike. Trees fulfill certain psychological, social and cultural needs of the urban dweller (Dwyer Schroeder and Gobster 1991). They play a very important social role in easing tensions and improving psychological health; people simply feel better living around trees. Parks provide easily accessible recreational opportunities for people.
2.7.2. Ecological maintenance
As a result of the predominance of concrete buildings, asphalt and metal as well as the concentration of transport systems and industrial activities in and around urban areas, the median temperature is higher (the "heat island" effect), the air is drier and often polluted, rainfall is less efficiently absorbed and the environment is generally noisier than in a rural setting (Kuchelmeister and Braatz 1991)
2.7.3. Cleaning the air
One of the major problems in urban areas is poor air quality. Plants help remove pollutants from the air in three ways: absorption by the leaves or the soil surface; deposition of particulates and aerosols on leaf surfaces; and fallout of particulates on the leeward (downwind) side of the vegetation because of the slowing of air movement.
Research on the removal of airborne pollutants by vegetation shows that plants are effective sinks for pollution. Trees absorb sulphur dioxide very efficiently. Keller (1979) has quantified an 85 percent reduction in lead behind a shelter-belt of trees. Soil effectively absorbs gaseous pollutants, including carbon monoxide, sulphur dioxide, nitrogen oxides, ozone and hydrocarbons. Trees intercept dust: a belt of trees measuring 30 meters in width has been found to intercept almost all dust in the air.
2.7.4. Modifying temperature extremes
Trees, shrubs and other vegetation help to control temperature extremes in urban environments by modifying solar radiation. The shade of one large tree may reduce the temperature of a given building to the same extent as would 15 air conditioners at 4000 British thermal units (BTU), i.e. 4220 kJ, in a similar but unshaded building. Energy saving through tree-planting around houses ranges from 10 to 50 percent for cooling and from 4 to 22 percent for heating (NAA/ISA 1991).
2.7.5. Noise reduction
Noise is often referred to as invisible pollution. Excessive noise levels in most major cities contribute to both physical and psychological damage. Trees can help both by absorbing and refracting or dissipating noise such as that produced by the heavy vehicular traffic which characterizes urban areas (Kuchelmeister and Braatz 1991).
2.7.6 Meeting resource-poor people's basic needs
Beyond their aesthetic and ecological value, trees can contribute to the satisfaction of energy requirements as well as the daily food requirements of urban dwellers, particularly in the case of the poorest elements of society (Kuchelmeister and Braatz 1991).
2.7.7. Urban forestry provides Fuel wood
Although "high technology" sources of domestic and industrial energy are available in most cities (electricity and petroleum products such as diesel, kerosene, gas), their relatively high price puts them out of the reach of much of the urban population in the developing world. Therefore, people continue to depend on fuelwood and charcoal for their energy needs which are consequently satisfied by uncontrolled collection, often resulting in the extensive degradation of areas around many urban settlements in developing countries. When "free" wood energy supplies are exhausted or are too difficult for people to tap into, fuelwood markets develop. Even this energy source is relatively expensive; studies report expenditures of 30 to 40 percent of total income by low-income groups to meet domestic energy requirements. Wood-based building materials - poles, branches and leaves for thatching, for example - are also in high demand in many urban areas (Kuchelmeister 1991; Ducchart 1989).
2.7.8. Food production
Urban agriculture is common in many cities in Asia, Latin America and Africa (Yeung 1987; Sanyal 1985; Streiffeler 1987; Ninez 1985; Skinner 1981). Who and how many people practice it as well as what form it takes differ greatly from place to place. It is most often practiced in the urban fringe area by low-income families but, in places such as Africa and the Pacific Islands, urban agriculture is widespread within cities. Although in most places the emphasis is not on the production of staple foods, through the production of vegetables, fruits and condiments, urban agriculture can contribute to the improvement of the nutritional value and variety of city dwellers' diets.
Environmental benefits to be gained from urban trees in the developing world include landscape enhancement, recreation, education, and general well-being; a habitat for wildlife; climatic modification; the control of air and noise pollution; erosion control; the protection of catchments areas for urban water supplies; and the productive use or safe disposal of urban wastes. (Carter 1993)
2.8. Potential problems from urban forestry
A number of the potential problems of trees in urban areas are discussed further in section six, with regard to species selection. However, a brief review is of use here, both of the problems and possible means of avoiding them.
2.8.1. Cost
Urban forestry initiatives conducted on a scale beyond small home gardens can cost a large amount of money to implement. This is particularly the case if instant results are wanted in amenity plantings, so large saplings are planted which require intensive after care in the first year or so of establishment. Maintenance costs, in particular irrigation, can be very high in such situations. Poorly run tree planting campaigns can also prove to be very costly, if mortalities are high as a result of inadequate or misdirected support. There are numerous ways in which costs can be minimized and benefits maximized through appropriate technology and careful planning but arrangement for regular maintenance is crucial. (Carter 1993)
2.8.2. Threats to human safety
Poorly planted or inappropriate tree species can serve as a hazard to urban inhabitants, either directly (through falling branches or the falling over of the entire tree) or indirectly. The former may be particularly likely in countries where typhoons or hurricanes are regularly experienced. It is possible that they are also of increasing occurrence in former colonies where colonial tree plantings are now over-mature and in need of replacement. Whereas in many developed countries there is provision for ensuring the removal or treatment of dangerous trees, this may not exist, or fail to be implemented in some developing countries. The general result is that there is probably more cause for genuine concern about the safety of trees in cities of developing rather than developed countries. Onganga (1992) comments that in Kenya, for example, problems with “trees blocking highways and falling on roofs of houses are common in urban areas.” Careful planting and choice of species, regular maintenance and a clear line of responsibility for dealing with dangerous trees would help to increase human safety.
2.8.3. Structural damage
The roots of street trees often cause the cracking of roads and pavements and sometimes water pipes. Urban trees can also cause structural damage to buildings, both at foundation level due to their roots, and through the falling of whole trees or branches. As with human safety, such problems can be minimized by careful species choice and maintenance (Biddle 1987).
2.8.4. Vandalism and browsing
Damage may be inflicted on trees simply out of intent to destroy; out of casual disregard; as a consequence of harvesting tree products; and by browsing livestock. While many foresters and arboriculturalists would classify all these as vandalism, there are clear differences. Only deliberate and casual vandalism are generally a problem in the developed world, whereas all four occur in Third World cities. Apart from any other considerations, this probably renders them a more difficult environment in which to raise trees (Sunder 1985).
The most important issue in combating all forms of human and animal-induced tree damage is gaining local people's support for and active involvement in tree cultivation, a matter discussed in section five. Apart from this, urban amenity plantings can be planned to minimize the likelihood of vandalism. Trees planted within cultivated ground tend to be less susceptible to deliberate or casual damage than ones surrounded by tarmac or concrete, as are ones planted in groups compared with lone trees. This is substantiated by observations of street trees in Bangalore, India. Here it was noted that, the position of tree stakes can also influence vandalism; trees with stakes that reach to breast height are more likely to be snapped off at this point than ones which have lower, less obvious stakes (Sunder 1985).
2.8.5. Access to solar energy
In developing as well as developed countries which receive significant solar radiation, solar power is an increasingly utilized energy source. While trees may be valued for their cooling shade, if this reduces solar radiation falling onto a solar panel, it may be viewed as a nuisance. In many States of the USA, there are now laws regarding access to solar energy which effectively require trees blocking solar radiation to be pruned or removed (Miller 1988). Although such legal difficulties are unlikely to affect urban tree growers in developing countries, the issue of access to solar energy is one which may be of increasing future importance.
The extent of mutilation is clearly inversely proportional to the extent of tree cover in a locality. The fewer the trees, the more insidious the process of destruction, we have either very little, or almost total mutilation in any locality it seems as if there is a psychological threshold involved: once people get over the inhibitions and into the habit of hacking trees, they go and hack every one of them(Gadgil and Parthasarathy 1977).It is common in Kenya, during funerals of important people or when a home team wins a prestigious cup, for people to cut trees and carry branches as a sign of sorrow or victory. One day's riot can leave an entire park stripped of thousands of trees (Onganga 1992).
2.8.6. Unorganized waste disposal
Rather than being a means of recycling urban waste, urban forests may be used as dumping grounds in manner that is wholly deleterious to the environment. Urban forests are considered by many people as the most ideal place to dump industrial waste. This is a major problem which is not easy to solve in Kenya because it involves very rich and influential people. Waste from tires, bottles, and other industrial by-products quite often covers several acres that otherwise could be used for tree planting. These waste products have also become a health hazard to the urban dwellers (Onganga 1992).
2.9. Changes in Urban Forests through Time
The structure of the urban forest changes through time in response to a wide range of powerful forces. These changes originate from diverse human and natural actions operating directly and indirectly on the urban forest and its management. The impacts of these forces for change vary over time and across and among urban systems; they contribute to different urban ecosystems and rates of change across urban areas. By understanding how human and natural forces interact within urban systems to create change, management can minimize negative forest changes and facilitate positive changes (Dwyer Nowak Noble and Sisinni 2000). Human forces for change in urban forests include:
• Urban resident involvement in tree planting, maintenance, and management
• Plant community and species preferences or fads
• Influx of funds to plant trees and other vegetation
• Management of urban infrastructure
• Urban development and land use change
• Development of new urban forest management techniques and tools
• Increased interest in quality of the urban environment and urban life
• Changing character of the urban population (race, ethnicity, and age structure)
• Byproducts of urbanization (for example, air and water pollution)
Natural forces that can lead to changes in urban forest structure include:
• Extreme precipitation or temperature events
• Storms and other natural disasters
• Fire
• Natural regeneration
• Aging of the existing forest
• Insect and disease outbreaks
(Dwyer Nowak Noble and Sisinni 2000)
What most distinguishes the urban forest from exurban forests is the dynamic influence of people. Human activities not only change urban forest structure to meet design and functional needs but also try to minimize and prevent detrimental changes due to natural forces (for example, controlling insects and diseases or altering structure to reduce the risk of wildfires) to sustain desired forest structure
A combination of human actions and natural forces will continue to shape the urban forests in the years ahead. These interacting forces highlight the need to coordinate urban forest resource management with many other urban activities (for example, land use planning, environmental protection, residential development, infrastructure development and maintenance, community empowerment and revitalization, and environmental education). Management of these complex, dynamic systems requires involvement of many disciplines, organizations, owners, users, and managers to sustain ecosystem health and desired functions.
A principal goal of urban forestry is to sustain forest structure, health, and benefits throughout the urban ecosystem over the long term. Comprehensive and adaptive management approaches are needed to do this. Expanding the management focus of urban forests to all trees, associated resources, and their benefits across the urban ecosystem will require nontraditional urban forest management techniques. The overall societal benefits of implementing such management are likely to be substantial (Dwyer Nowak Noble and Sisinni 2000).
Management also must be comprehensive in terms of its process, and it must be adaptive to allow for adjustments in management activities based on new situations and information. To attain comprehensive and adaptive management, urban forest managers should consider:
• The desires and needs of the community
• What urban forest structure is necessary to best address community needs?
• Periodically reassessing community needs and urban forest structure to ensure that management plans remain appropriate
To facilitate comprehensive and adaptive management to sustain the entire urban forest ecosystem, the following topic areas need to be emphasized:
• Improving inventory and assessment
• Improving dialogue among owners, managers, and users
• Fostering collaboration among agencies and groups
(Dwyer Nowak Noble and Sisinni 2000)
2.10. Opportunities for Improving Urban Forest Resource Management
• Improving the understanding of how forest configurations influence forest use and benefits
• Increasing knowledge about factors that influence urban forest health
• Improving the dissemination of information about urban forests and their management
With improvements in the above areas, urban forest resources can become a more highly valued component of large-scale and long-term environmental and community planning. Facilitating the effective management of urban forest ecosystems in the United States requires forging partnerships and collaborative efforts across resources, disciplines, organizations, and geographic areas. One continuing issue is to understand the relation between the management of urban and exurban resources, such that collaborative management efforts across these areas can be fostered. This assessment is the first step in developing a comprehensive understanding of the national urban forest resource and can assist in development of comprehensive adaptive management plans in both urban and exurban environments. As an increasingly urban population continues to play a key role in the social and political structure, understanding and managing of urban forest resources will be a critical mechanism for improving forest benefits and connecting people with ecosystems in the 21st century (Dwyer Nowak Noble and Sisinni 2000).
2.11. Urban Forestry Round the World
Most of the country practices urban forestry around the world. We discuss here into two ways- outside Asia and within Asia.
2.11.1. Urban forestry in the United States
The beginnings although the term did not come into common usage until the 1960s, urban forestry has been around as long as people have been planting trees in towns and villages where they live. In North America, early settlers cut the virgin timber to clear building sites and farm fields, construct their buildings and heat their houses, but it was not really until the late 1700s and early 1800s that Americans began to plant trees in towns and villages. In fact, Philadelphia, a historic city in Pennsylvania, did not have street trees until the late 1700s, partly because insurance companies would not insure houses with trees in front of them (Zube 1973).
Community groups of all kinds participated in the planning and development of these forests, including schools, local governments and churches. Their activity marks the beginning of the American people's involvement with their forest resources. By 1953 a census of community forests recorded a total of 1752815 ha (Duthie 1953). Today, few people who benefit from these forests realize their size or value. One common problem for the urban forests of American cities is the creeping crisis that sets in as city trees grow and mature while budgets and programmes shrink. In 1984, the delegates at the national meeting of the directors of parks and recreation identified trees as their biggest maintenance problem, a problem they have yet to communicate effectively to the public or their political leaders (Moll and Gangloff 1886)
2.11.2. Green space in metropolitan Prague today
Today, fully 10 percent of metropolitan Prague is covered with forest vegetation. There are marked differences among the tree compositions of streets, parks, private yards and courtyards. Vegetation structure is influenced by several factors but the age and structure of buildings appear to have had the greatest influence. The density and type of tree tends to reflect the management choices and species preferences at the time of neighborhood establishment. In Stare Mesto (the old town), which retains a medieval character, vegetation is almost absent, but in sections of another old zone, Mala Strana (the lesser side), where palace gardens are common, green space may be as high as 20 percent of total land area(Profous and Rowntree1990 ). The densely constructed apartment blocks which were common at the turn of the century also have very little green space, while newly constructed residential areas may have as much as 60 percent, largely because of the presence of undeveloped city blocks (Jelen 1985).
2.11.3. Urban forestry in Debre Birhan, Ethiopia
Debre Birhan is situated on the high plateau 140 km north of Addis Ababa. In Ethiopia, over 90 percent of all energy consumed is for domestic needs, and fuelwood supplies 40 percent of the total. The rest comes from animal dung, crop residues and kerosene. The consequences of this rapid deforestation are severe, especially for urban centres, fuelwood when it is available at all, can cost as much or more than kerosene. A recent effort to meet the problem of urban fuelwood supply is the FAO Debre Birhan fuelwood Plantations Project, started in 1986. Financed by a US$2555690 grant from the Danish international Development Agency, the project's major goal is to increase the fuelwood supply on a long-term basis. It also aims to strengthen Ethiopia's capacity to plan and manage similar projects in some 50 urban areas already identified as facing critically low supplies of wood.
Studies indicated that an adequate, sustainable fuelwood supply for the city would require at least 3200 ha of plantations, mostly of fast-growing eucalyptus. However, such plantations would require 25 percent of all land in the area, land now used for crops and grazing. Since a sudden change in land use on this scale would have drastic economic and social consequences, only 1100 ha have been scheduled for planting over the next three years (Haque 2003).
2.11.4. Urban forestry in Tashkent, USSR
Tashkent, lying at the western end of the Tien-Shan mountain range in Soviet Central Asia, is the capital of Uzbekistan and the site of a large textile industry. The present centre's open plan combines decorative modern buildings with attractive landscaped areas. Tree canopies shade many of the streets from the intense summer sun. The most common street species by far is the western variety of maple (Acer negundo var. californicum), with its bold and very hairy foliage. Other frequently seen North American species are white ash, honey locust and Osage orange. English oak, with its luxuriant foliage, provides excellent shade (Haque 2003).
2.11.5. Urban forestry in Colima, Mexico
In Colima, Mexico citizen groups at times can play a decisive role both in heightening public awareness of the value of trees in the urban environment and teaching people how to care for them. One example is the recent work of the Pro-Ecologia de Colima, a non-governmental organization based in Colima, a town near the Pacific Coast directly west of Mexico City. To encourage citizens to take the initiative in planting and tending trees, the guide gives illustrated instructions as to where and when to plant trees, how to prepare the soil, how to plant to ensure maximum chances of survival and the care needed for good growth (Haque 2003)
2.11.6. Milton Keynes, UK - Trees as investment
In Milton Keynes, however, urban forestry is seen not just as a social investment but as a commercial one as well. Established and financed by the national government, Milton Keynes is intended to be one of several model communities which will repay the initial investment by enhancing rental income from housing and industrial sites. In Milton Keynes, these woodlands include: three natural "parks", the largest of which is 40 ha and the smallest 20 ha: 1200 ha of "linear parks” or major green belts which run across the city; and some 22 small spinney and coppices. All of these have been developed from existing tree stands augmented by selected planting of exotics and regeneration planting of native oak, ash, field maple, cherry and hazel. All street and park planting and maintenance are carried out by the Landscape and Forestry Division of the town's Recreation Unit (Haque 2003).
2.11.7. Urban forestry in Canberra, Australia
In Canberra the Australian government has kept to its original vision by passing legislation consistent with that purpose and has overtly encouraged the Imaginative use of the existing natural environment. Urban development has been allowed chiefly in the valleys, preserving the naturally forested hills and ridges which screen it off from most vantage points. River corridors are maintained as green space. In 1975, the concept of "essential landscape foreground areas" was introduced. Half a dozen of these landscapes, examples of typical Australian countryside, have been established along major highways on the south and western urban fringes where they provide a foreground to the seasonally snowcapped mountains in the distance (Haque 2003).
2.11.8. Urban forestry in Windsor, Ontario, Canada
The city of Windsor, just across the river border from Detroit, Michigan, incorporates seven smaller communities interspersed with the remnants of market gardens and abandoned farmlands. Before the municipality hired its first urban forester in 1970, the area's tree cover, predominantly elm and maple, was poorly managed and vulnerable to disease and insect attack. Now, however, Windsor has a carefully planned, well-managed urban forestry system with 600 ha of municipal parks and a closed canopy of mature trees along 1000 km of streets. Trees occupy almost 20 percent of the total space. In Windsor, Ontario tree planting has been a major activity. Since 1968 over 20000 street trees alone have been established. Most municipalities in Ontario use the common "bareroot" planting of trees 2 or 3 m in height. Although this method allows a large number of street trees to be introduced inexpensively, Windsor found that poor establishment and vandalism caused an estimated 30 percent loss (Haque 2003).
2.11.9. Kampala, Uganda - Fuel wood and ornamentals
Urban forest management in Kampala, the capital of Uganda, focuses primarily on the expansion and maintenance of fuel wood plantations to meet the increasing demand for firewood and charcoal as the urban population grows and imported kerosene becomes more expensive. An important but secondary activity is the establishment of ornamental trees. As fuel wood purposes eucalyptus introduced from Australia and New Zealand, although the slower-growing Cassia siamea Lam is also used and as ornamental value include mango, papaya, avocado, guava and cashew nut used. Over a hundred species of ornamentals are being used, including several kinds of cypress and pine, Grevillea robusta, Callistemon citrinus (bottle brush tree), Sterculia acerifolia (flame tree), jacaranda, Delonix regia (flamboyant tree) and Araucaria (Haque 2003).
2.11.10. Urban forestry in Dunedin, New Zealand
Few cities in New Zealand have large forest tracts within or close to their boundaries, and those that do have generally left them unmanaged. A notable exception is Dunedin, on the southeast coast of South Island. Dunedin has over 8300 ha of forest preserve inside the city limits. One tract of 200 ha is unique in that it almost encircles the city only 1 km from the centre. Forest management has been so successful from both an environmental and a financial point of view that the city council recently decided to increase the forest area to 12000 ha (Haque 2003).
2.11.11. Urban forestry in Beijing, People's Republic of China
Driving the 25 km from the airport to the city of Beijing, one is immediately struck by the trees - pines, willows and poplars three or more rows deep - which completely shade the entire route. Once in the city, trees continue to strike the eye, for they line virtually every street, flourish in every residential area, surround most public buildings and fill the many public gardens and parks. In modern China, tree planting is everyone's business. The national goal of "Five Ones" includes, as one of its "Ones", one hundred trees planted by each person. The national slogan of "Four Around Plantation" calls upon people to plant trees around houses (1), villages (2), along roads (3), rivers and canals (4) for production, protection and aesthetics. Urban forestry is taught in schools as part of labour education and the national health movement. However, responsibility for urban forestry is decentralized, and trees in Beijing and other urban centre’s are maintained by the people, not "tree experts"(Haque 2003).
2.11.12. Hong Kong - Maximizing the use of space
When the British first came to Hong Kong, they described it as a "barren" island with practically no trees. While the largest forest in a sense is now the city itself - a forest of concrete, glass and steel - almost 40 percent of the land area is "green space". And over one-half of all existing stands of trees and shrubs were planted in recent years. The concern for urban forestry in Hong Kong is not new. A botanical garden was opened in 1864, and a decade later the forestation of Victoria Peak began. Before the 1950s, however, the city's only outdoor recreational facilities were one major park and a collection of private clubs. After the Second World War, a plan was commissioned which proposed the creation of 30 ha of green recreational space for every 100000 inhabitants. The proposal remained more or less on the drawing board until 1968, when a new recommendation halved that goal to 15 ha of green space per 100000 people in the city and 20 ha for towns in the New Territories. These targets have very nearly been met (Haque 2003).
2.11.13. Urban forestry in Yokohama, Japan
Overlooking Tokyo Bay south of the capital, Yokohama has been an international port since Commodore Perry "opened" Japan to the West some 130 years ago. Yokohama has 1209 parks covering almost 600 ha, with an additional 4500 ha of suburban woodlands. This greenery, one of the striking features of Yokohama's river-fed delta plain and the surrounding hills, has been the result of conscious policy, careful planning and hard work. For years the municipal government has been buying land in the suburbs in order to preserve it as "greenery conservation districts" or "citizens' forests". In 1980, a master plan for greenery activities was drawn up and incorporated into the "21st Century Plan for Yokohama", a comprehensive scheme to ensure an attractive and comfortable urban environment for present and future inhabitants. The plan calls for the protection and expansion of green zones in the city outskirts, the management of urban parks, the development of urban agriculture and forestry, and special protection of over 1000 individual famous trees, it also sets a target of 10 million planted trees by the year 2000, three times the present number (Haque 2003).
2.11.14. Singapore, Republic of Singapore - Aerating a concrete jungle
The early 1960s saw Singapore's population mushroom; they also brought a firm commitment to make this world trade and tourist centre a garden city, a green metropolis. Since there were then relatively few trees within the city proper, the Singapore Parks and Recreation Department had to undertake a massive effort to achieve this goal. Two keys to its success are its massive "aeration" and "screening" programmes. Plants and trees in urban environments, where there is an abundance of concrete and asphalt surface, suffer from a poor distribution of rain-water and an inadequate air supply to their root systems. The "aeration programme" is designed to alleviate these problems. Present tree plantation not only provides growing space for trees and shrubs but also minimize the disturbance to root systems during the laying or repairing of cables, water mains and sewers. Car parks, both old and new, are planted with trees to reduce asphalt surfaces and many have been paved with perforated slabs to allow better air flow and water drainage (Haque 2003).
2.12. Attributes of the urban forestry
2.12.1. Diversity
Diversity is one of the most distinctive attributes of the urban forest. This feature is primarily a function of the many components of the urban forest, including trees and ground covers, soil types, microclimates, wildlife, people, buildings, infrastructure, and other developments. These elements are found in almost unlimited combinations in an intricate mosaic across the urban landscape. The elaborate mixture of natural and human-made resources in complex urban ecosystems broadens the scope of urban forestry beyond traditional forestry, arboriculture, and other natural resource disciplines. The diversity of urban forests is also a function of variations in land uses, land ownerships, residents and visitors, and management objectives across and between urban systems. Urban areas are characterized by multiple land uses and diverse populations; consequently, the management of activities by different individuals and groups creates a complex landscape pattern reflecting an area’s unique combinations of physical, biological, and social attributes. With the diversity of land uses and owners in urban areas, the objectives and issues facing managers of the urban forest are wide ranging, extending from wildlife management to the mitigation of air pollution, enhancing aesthetic value, and providing recreation, flood control, fire prevention, and other benefits.
Several factors serve as catalysts for increased diversity in urban forest ecosystems. Shifts in population, changes in economic activity, improvements in transportation, and other developments increase the range of land uses, broaden the spectrum of people involved, and complicate the mixture of old and new, artificial and natural, and native and exotic natural resources in urban areas (Dwyer Nowak Noble and Sisinni 2000).
2.12.2. Connectedness
Connectedness among resource components, and with other resources, activities, and functions within and beyond the urban environment, is another key attribute of the urban forest. Other elements of urban environments include roads, homes, industrial parks, and downtown centers. Whether connected by the logistics of managing urban infrastructure (for example, coordinating maintenance of urban trees and power lines, sewers, sidewalks, and roads), or by contributing to the overall character of the area, urban forests link “landscape” with “architecture” and become an important component of urban planning.
The connectedness of urban forests is reflected in their contribution to a wide range of urban issues, programs, and initiatives. Urban forests and their management are connected to programs for improving air and water quality, flood control, energy conservation, microclimate control, aesthetic enjoyment, recreational opportunities, environmental education, and other goods and services in the urban environment. With the many benefits that urban vegetation can provide, the management of urban forests may be linked to an array of other urban initiatives, including urban renewal and community revitalization, economic development, community empowerment, and environmental education. Urban forests represent a critical link between people and forest resources. Ownership and use of residential holdings, as well as experience with public parks and forest preserves in urban areas, are how many citizens experience, appreciate, and learn about natural resources (Dwyer Nowak Noble and Sisinni 2000).
2.12.3. Dynamics
Like all forests, urban forests undergo significant change with the growth, development, and succession of their biological components over time. The growth and development of urban forest resources occur, however, in the context of much more powerful and swift human-induced factors. Coupled with the relatively slow rate of tree growth and plant succession, the swift human forces for change make the dynamics of the urban forest particularly challenging for managers and users. The expansion and development of urban areas bring important changes in urban vegetation and other urban resources. Alterations to the distribution of land uses, intensity of urbanization, and population characteristics in urban areas result in different combinations of ground cover, increased or decreased opportunities for tree establishment and growth, changing environmental conditions, different resource-use patterns, and altered management objectives. New developments in transportation technology or manufacturing and service industries can bring considerable change to the condition, function, and management of urban lands and associated resources. The introduction of exotic plants and animals into interstate and international trade centers can have a profound influence on the urban forest, as has been the case with Dutch elm disease, gypsy moth, and the Asian long horned beetle. Changes in the composition of neighborhoods can prompt different approaches to the management of forests in residential areas, parks, and other open spaces. Urban trees are becoming more widely appreciated for their ecological, economic, social, cultural, and historical value throughout the urban environment (Dwyer Nowak Noble and Sisinni 2000).
2.13 Constraints and the need for improvement
The preceding sections of this article highlighted the value of urban forestry. A number of important constraints, however, stand in the way of full achievement of this potential. Not all of these constraints can be removed, but they must at least be considered.
2.13.1. Inadequate funding
A lack of funding is a major obstacle to systematic tree management and the promotion of more effective urban forestry programmes. Moreover, the situation is unlikely to improve, as municipal and national budgets continue to suffer economic restrictions, escalating inflation and resource shortages. Urban forestry efforts will therefore increasingly need to demonstrate that their benefits exceed their costs. This places emphasis on the need for quantitative research on the positive results of urban forestry efforts. It will not be acceptable to claim that "trees reduce solar radiation", that "trees can absorb atmospheric pollutants" or that "trees can help alleviate fuelwood shortages"; specific data on costs and benefits will be essential (Nowak and McPherson1991).
2.13.2. Low priority
Decision-makers (at both national and international levels) have tended to consider urban forestry as a low-priority activity and one more easily deferred than other programmes. This is partly a result of inadequate education, information, awareness and understanding regarding the economic, social and biological benefits of trees in the urban environment. Even today, urban forestry still tends to be regarded as a cosmetic, aesthetic amenity issue or as a luxury activity that is not worthy of support. Without political will, due attention to urban forestry and the realization of its full potential are impossible (Kuchelmeister and Braatz 1991).
2.13.3. Dispersal of tree management responsibilities
Responsibility for the management of urban trees and forests is often shared by various administrative structures that have competing and even conflicting responsibilities. Because of the initial focus on aesthetic values, park and recreation departments are the agencies most commonly delegated primary responsibility but public works agencies, utility companies, environmental protection agencies, national forestry and/or agriculture departments may also be involved. Governments will need to establish lead agencies and ensure intersectoral linkages in order to make the best use of scarce financial and human resources (Kuchelmeister and Braatz 1991).
2.13.4. Lack of land
The limited availability of land is a key constraint to urban forestry efforts. Urban sites are complex environments in terms of the availability of appropriate land for planting as well as in terms of ownership and tenure. In some cases, for example in extremely densely populated, unplanned urban fringe areas, the lack of land may be an absolute constraint. In others, people's participation may permit an efficient use even of scarce resources (Kuchelmeister and Braatz 1991).
2.13.5. Environmental stress
The urban environment is generally a harsh habitat for trees. Stress from the environment reduces the vigour of many tree species and increases their susceptibility to disease and pest infestation. Urban trees are subject to poor soils (compacted, low in organic matter, deficient in nutrients and moisture), air and water pollution and vandalism (Beatty and Heckman 1981). Species selection takes on paramount importance in overcoming these constraints.
2.13.6. Lack of training, extension and communication
There are relatively few opportunities for training and education in urban forestry, particularly in developing countries, while a lack of appropriate instructional material is another constraint. As opportunities increase in the use of urban forestry as a tool for development, new skills will be required for urban vegetation managers. Foresters must learn to combine knowledge of trees with an understanding of city government and the needs of society. In addition to training to improve biological knowledge, there is a need for skills in ecological landscape planning, extension, communication and sociology and related subjects. Generally speaking, extension in urban forestry is very weak. Practical approaches are yet to be worked out in order to reach and involve citizens, especially the poor (Burch, Jr and Grove 1993).
Networking has proved an efficient tool in research and development in many sectors, but formal global or regional urban forestry networking activities are extremely limited. One networking structure functioning on a global level is the International Union of Forestry Research Organizations (IUFRO) Project Group on Arboriculture and Urban Forestry. Other possible approaches to information exchange include: "twinning" arrangements between the urban forestry establishment of a city in an industrialized country and its counterpart in a developing country; and special programmes established by professional organizations through which city planning authorities, companies and individuals may contribute to a fund to subsidize the cost of collecting and disseminating information (O'Rourke 1990).
2.14. Management of urban forestry in Bangladesh
The main objectives of managing urban forests in Bangladesh are- To Maintenance and sustenance of natural processes such as water, gaseous, nutrient cycles and support of flora and fauna, Provision of economic and social benefits, To get fuel wood and shade from urban forestry. Many of the general principles of arboriculture are applicable throughout the world, although specific management requirements will be dictated by such factors as the species and climatic regime in question. A poor choice of species can be ameliorated to a certain extent by appropriate arboricultural treatment; for example, a tree which has grown too tall for its surroundings can be pruned. However, this is undesirable for tree health, aesthetically unappealing, and wasteful in terms of maintenance costs. It would have been far better to select in the first place a tree that only reaches a low height on maturity. Important arboricultural principles of general application include site preparation, tree establishment and early maintenance, tree surgery and protection, and the removal of tree waste. Each is discussed briefly here, drawing attention to recent changes in thinking and practice. The extent to which these principles are currently followed in Bangladesh is generally uncertain, although mention is made if any information on this subject was available (Carter 1993).
2.14.1. Site preparation
As noted above, urban soils are often poorly suited to tree growth. Common problems are low levels of available nutrients, and high compaction due to the impact of human and vehicular traffic. This is compounded by low soil organic matter levels. The ‘traditional’ response to this has been radical site amelioration prior to planting. Current thinking entails a more modified approach, depending on site conditions. In general, alleviation of soil compaction is seen as being more important than other soil treatments. This may be achieved in a number of ways, the most important being subsoil ripping of the planting site. Current arboricultural practice also places far more emphasis on choosing a species to fit the given site rather than modifying the site to fit the desired species (Carter 1993).
2.14.2. Tree establishment and early maintenance
Plantation stock it is particularly crucial in urban settings to plant nursery stock of good form and quality, with a healthy root-to-shoot ratio. Saplings without this are unlikely to survive planting in compacted urban soils, but even if they do, they may become a hazard in later life, being more prone than trees with a well-developed root system to being blown over, or to other damage. Similarly, saplings which have damaged stems will grow into trees with an unbalanced branch system; this may not only look unsightly, but could be dangerous. The size of seedlings or saplings planted in urban situations is often considerably larger than those used in normal plantation forestry. However, the use of seedlings of no more than 60 cm height is now considered by many professionals to be sounder practice. They are often so much more vigorous than larger saplings that they catch up in size with the latter after a short period (Carter 1993).
2.14.3. Planting techniques
Following site preparation, it is of course important to ensure that planting pits are dug to an adequate size, and preferable that they are prepared well in advance of, rather than at the moment of, planting. It may also be necessary to take into account the existence of underground utility services (water pipes, etc.) when planning where to plant. In professionally conducted urban plantings, particularly in the case of street trees, a variety of techniques may be employed to ensure good tree establishment and to guard against future problems (Webb 1991).
2.14.4. Watering and mulching
Watering is often considered essential for the establishment of urban trees, but it may be very difficult to provide in some circumstances. One example is provided by tree growing in self-help housing areas where even drinking water is in short supply. Apart from taking the obvious precaution of timing planting to coincide with the beginning of the rains, and ensuring that the pit is at least well watered at the time of planting, various options may be considered. These include the use of drought-tolerant species, regular weeding, the application of mulch, irrigation (possibly using wastewater), and the incorporation at the time of planting of a pipe to facilitate water penetration (Carter 1993).
2.14.5Weeding
Weed control may be affected either by manual weeding or by the use of appropriate herbicides, both before planting and on a regular basis afterwards. While the use of herbicides in the case of UK plantings is often recommended (Davies 1987), this may be less appropriate in developing countries for a variety of reasons, both social (employment generation may be desirable) and technical (herbicides may act differently in warmer, wetter climates).
Weed control may be affected either by manual weeding or by the use of appropriate herbicides, both before planting and on a regular basis afterwards. While the use of herbicides in the case of UK plantings is often recommended (Davies 1987), this may be less appropriate in developing countries for a variety of reasons, both social (employment generation may be desirable) and technical (herbicides may act differently in warmer, wetter climates).
2.14.6Staking
In general, staking is no longer recommended in amenity plantings, as it inhibits the development of sturdy stems and can cause problems when finally removed. Forgotten stakes and ties can also badly damage growing trees. It is now considered preferable to plant seedling/saplings which are small enough to require no support (Patch 1987).
In general, staking is no longer recommended in amenity plantings, as it inhibits the development of sturdy stems and can cause problems when finally removed. Forgotten stakes and ties can also badly damage growing trees. It is now considered preferable to plant seedling/saplings which are small enough to require no support (Patch 1987).
2.14.6. Tree surgery and protection
Since the mid-1980s, arboricultural theory and practice in the Western world has been strongly influenced, if not “revolutionized”, by the work of the American arboriculturalist, Alex Shigo. While his ideas are not universally accepted or even necessarily new, his practical recommendations are now quite widely implemented in North America, Europe, Australia and cities elsewhere with a strong urban forestry programme such as Hong Kong. In Bangladesh these practice need to be started. Possibly the most celebrated of Shigo's theories is that of CODIT, Compartmentalization of Decay in Trees. CODIT is a model that describes a tree's defense system - its response to wounding. It is used to explain why traditional pruning regimes using flush cuts are bad for tree health, and that ‘Natural Target Pruning’ (NTP), cutting off the branch at an angle (leaving the branch collar, if one exists, intact), is better practice. CODIT theory is also used as an argument against treating wounds with a seal to guard against pathogens. In place of sealants, a variety of gel formulations with systemic fungicidal properties are now more commonly recommended (Clifford and Gendle 1987).
It is uncertain to what extent the ideas of Shigo are put into practice in developing countries, although it is unlikely that they are widely known or followed. In general, knowledge and skill in tree surgery varies widely by country. For example, Hill (1992) reports that in Quito, Ecuador, poor pruning practices were attributed to excessive demand for services and poor tools, rather than lack of experience and skill. In South China, Jim (1991) have noted that despite quite high standards of tree selection and planting design, pruning is conducted with very scant regard to tree health. Johnston added that this was certainly not merely a reflection of a lack of suitable equipment. Timely and efficient tree surgery is one of the most important means of preventing the spread of disease in trees once it occurs, but good arboricultural practice also implies minimizing the possibility of pest and disease attacks. Attention to this in the early years of tree establishment, including an appropriate choice of species/provenance/cultivar is clearly important, as is the prompt and complete removal of any infected tree material (which should be duly destroyed).
2.14.7. The removal of tree waste
Key issues in the removal of tree waste are public safety, utilization of removed material as appropriate, and (as mentioned above) limiting the spread of pests and diseases. In Bangladesh, many urban authorities make use of tree prunings by shredding it for compost or mulch, and such recycling is becoming an increasingly important feature of urban forest management. Inevitably urban trees grow old and must be removed, or parts of them removed, before they cause any damage. Technically, there are often complications in this due to the close proximity of buildings and other urban infrastructure. However, perhaps the most important issue for urban foresters is advance planning - ensuring that removal operations are timed to avoid any public hazard, rather than responding to one (Carter 1993).
2.15. Management, structure, factors of urban forestry in Dhaka city
Urban forestry needs multi-management approach. It does necessitate appropriate planning before embarking upon an urban forestry programme. The goals based on the local needs have to be determined in the planning phase. A management plan should serve to sustain psychological health for human perception as well as to maintain whole some environment (Zabala 1991).
The primary objective of urban forest management is to maintain the health and vigor of the vegetation without undue interference of the city dwellers. Apart from others, urban forest management has three fundamental needs, tree planting, maintenance and removal.
2.15.1. Tree Planting
The followings are the factors which should be considered for urban planting of trees.
2.15.1.1. Species-site selection
The urban site is a complex environment where soil, temperature, moisture availability, pollutants etc. vary from one place to another. The species therefore, selected for planting at a given site must be adapted to it.
2.15.1.2. Species composition
Diversification of species is needed. As a general rule, the species composition promotes species diversification by restricting a species to not more than 15% of the population.
2.15.1.3. Spacing of trees
Determined by the local conditions, species, plant height, spread form and use.
Spacing recommendation
Ø Trees which attain bole dia greater than 30 cm when mature should be planted in space less than 1m
Ø Trees should not be planted within 10 m of an intersection
Ø Trees should not be planted within 3m of utility poles or fire hydrants.
Ø Large trees should be planted 12-18 m apart.
Ø Medium tree should be planted a minimum of 10 m apart
Ø Small trees should be planted a minimum of 8 m apart. (Zabala 1991)
2.15.1.4.Selection of species
Availability of space is the most critical factor in selecting tree species in cities since it is limited by buildings, overhead wires, curbs etc. So, tree species have to be selected considering the available space when these will mature. The following are some of the species which may be used in the urban forestry programme in Dhaka city.
2.15.2. Suggested tree species for a particular use
The following are some of the species which may be used in the urban forestry programme in Bangladesh:
Table2.15.2.1.: List of trees for used Energy conservation
| Local Name | Scientific Name |
| Akashmoni | Acacia auriculiformis |
| Kala koroi | Albizia lebbeck |
| Gamar | Gmelina arborea |
| Eucalyptus | Eucalyptus camaldulensis |
| Sada koroi | Albizia procera |
| Sissoo | Dalbergia sissoo |
| Ipil ipil | Leucaena leococephala |
| Mangium | Acacia mangium |
(SourceSattar1999)
Table2.15.2.22: List of trees used roadside and avenue planting for beautification
| Local Name | Scientific Name | Used parts |
| Sonalu Sonalu | Cassia fistula | Yellow flower |
| Minjiri | Cassia siamea | Yellow flower |
| Krishnachura | Delinix regia | Red flower |
| Polash | Butea monosperma | Red flower |
| Eucalyptus Eucalyptus | Eucalyptus camaldulensis | White flower |
| Jarul Jarul | Lagerstroemia speciosa | Purple flower |
| Jacaranda | Jacaranda mimosa | Blue flower |
| Debdaru | Polyalthia longifolia | White flower |
| Jhau | Casuarina equisetifolia | White flower |
| Neem | Azadirachta indica | White flower |
| Koroi | Albizia procera | White flower |
| Ashok | Saraca asoca | Orange flower |
(Sattar 1999)
Table2.15.2.3.: List of trees used Parks, memorials, etc. for shade
| Local Name | Scientific Name |
| Raintree | Albizia saman |
| Simul | Salmalia malabarica |
| Gora neem | Melia azadirachta |
| Bot | Ficus benghalensis |
| Krishnachura | Delinix regia |
| Sissoo | Dalbergia sissoo |
| Kadam | Anthocephalus chinensis |
(Sattar 1999)
Table2.15.2.4.: List of trees used Screening for hiding undesirable objects
| Local Name | Scientific Name |
| Nageshwar | Mesua ferra |
| Akashmoni | Acacia auriculiformis |
| Shetkanchan | Bauhinia variegate |
| Karamja | Pongamia glabra |
| Hizal | Pongamia glabra |
(Sattar, 1999)
2.15.3. Maintenance of trees
One of the primary concerns of urban forest management is to maintain the health, vigor and compatibility of vegetation with the environment. It involves all practices to control growth, damage from insects and diseases right from the time of planting to removal (Zabala 1991).
2.15.4. Growth control
The objective of growth control are to retard or redirect and accelerate growth of trees, the forest objective may be achieved by pruning and application of growth retardant chemicals. The second one can be met by fertilization, irrigation and control of competing vegetation (Zabala 1991).
2.15.5. Pest and diseases
The insects and diseases that attack the forest trees are also those which attack urban trees as well. The urban trees are generally high valued, and as such pest control is aimed at single tree, rather than simultaneous treatment of as trees as practiced in the forest plantations. Biological, mechanical and chemical controls are used for insect attack. In selecting the insecticides, attention must be given to city animals and human beings (Zabala 1991).
2.15.6. Removal
The purpose of removal of trees from urban forests is to reduce the risk of injury to people and damage to property as well as to clean the surroundings of unsightly debris. Dead trees, hazardous trees, overcrowded trees, pruning debris, storm debris, stumps and leaves must be removed. Debris and leaves need to be collected when these fall on the roads, sidewalls, residential lawns, etc. in the plantations, these are not necessarily taken out as they add to the fertility of the soil once decomposed (Zabala 1991).
Chapter 03: Methodology
3.1. Description of study area
3.1.1. Location
Dhaka is situated between latitudes 23°42' and 23°54'N and longitudes 90°20' and 90°28'E. Dhaka stands on the northern bank of the Buriganga River, about 13 km above its confluence with the Dhaleswari (23° 43' N Lat and 90° 24' E Long). It commands connection by navigable waterways with the Padma, the Brahmaputra and the Meghna river-system that affords the convenience of water carriage to and from any principal place of the Bangladesh (Banglapedia 2006).
3.1.2. Area
Dhaka gained city status in 1947 when it was made the capital of East Pakistan and by that time stretched over an area of about 40 sq km. The importance of Dhaka increased exponentially after 1971, when it became the capital of independent Bangladesh. As a result the city expanded phenomenally and according to the census of 1991 the area and population of Dhaka Megacity or Dhaka Statistical Metropolitan Area (DSMA) were 1,600 sq km and 6.83 million respectively. According to the same census the area under the Dhaka city corporation (DCC) was 360 sq km, with a population of 3.39 million. The present population of DSMA is about 9.0 million (2001) (Banglapedia 2006).
3.1.3. Climate
The city has three distinct seasons: winter (November-February), dry with temperature 10° to 20°C; the pre-monsoon season (March-May), some rain and hot with temperature reaching up to 40°C; and the monsoon (June-October), very wet with temperatures around 30°C. Dhaka experiences about 2,000 mm rain annually, of which about 80% falls during the monsoon (Banglapedia 2006).
Temperature:
From April to October, day time temperature normally remains above 30 degrees and low temperature are below 20 degree from November to March.
Table 3.1: Monthly average maximum Temperature (0c)
| Year | Jan | Feb | Mar | April | May | June | July | Aug | Sep | Oct | Nov | Dec |
| 2005 | 24.5 | 29.1 | 32.2 | 34.4 | 33.2 | 33.4 | 31.4 | 32.0 | 32.7 | 30.5 | 29.0 | 27.0 |
| 2006 | 25.3 | 31.2 | 33.2 | 33.7 | 33.7 | 32.3 | 32.3 | 32.5 | 31.9 | 32.2 | 29.6 | 26.8 |
| 2007 | 24.5 | 27.1 | 31.4 | 33.6 | 34.7 | 32.4 | 31.4 | 32.5 | 32.0 | 31.4 | 29.0 | 25.8 |
Source: Bangladesh Meteorological Department.
Table 3.2: Monthly average Minimum Temperature (0c)
| Year | Jan | Feb | Mar | April | May | June | July | Aug | Sep | Oct | Nov | Dec |
| 2005 | 14.1 | 18.3 | 22.4 | 24.1 | 24.2 | 26.8 | 25.8 | 26.6 | 26.0 | 24.3 | 19.8 | 15.6 |
| 2006 | 13.4 | 19.4 | 21.9 | 13.8 | 24.9 | 26.1 | 26.6 | 26.5 | 25.8 | 24.6 | 19.9 | 15.8 |
| 2007 | 12.4 | 16.7 | 19.6 | 23.6 | 25.9 | 25.5 | 25.7 | 26.4 | 26.4 | 23.8 | 19.9 | 15.0 |
Source: Bangladesh Meteorological Department
Relative Humidity:
Relative humidity remains high (70-84%) most of the year, with the highest during the month of May to October. The average humidity was 72%.
Table 3.3: Monthly average Relative Humidity (%)
| Year | Jan | Feb | Mar | April | May | June | July | Aug | Sep | Oct | Nov | Dec |
| 2005 | 68 | 60 | 66 | 66 | 73 | 79 | 81 | 82 | 81 | 80 | 72 | 66 |
| 2006 | 69 | 65 | 53 | 67 | 72 | 81 | 80 | 77 | 80 | 76 | 68 | 69 |
| 2007 | 68 | 68 | 54 | 69 | 70 | 81 | 84 | 80 | 80 | 78 | 77 | 69 |
Source: Bangladesh Meteorological Department.
Rainfall:
Precipitation is highest during the monsoon season (May to September). Pre monsoon rains mainly start in March and post monsoon rains can occur as late as October.
Table 3.4: Monthly Rainfall in Millimeter
| Year | Jan | Feb | Mar | April | May | June | July | Aug | Sep | Oct | Nov | Dec |
| 2005 | 1 | 3 | 155 | 91 | 291 | 259 | 542 | 361 | 514 | 417 | 3 | 0 |
| 2006 | 0 | 0 | 0 | 181 | 185 | 326 | 331 | 167 | 663 | 61 | 5 | 0 |
| 2007 | 0 | 30 | 11 | 163 | 185 | 628 | 753 | 505 | 179 | 320 | 111 | 0 |
Source: Bangladesh Meteorological Department.
3.1.4. Physical feature of the study area
Study site
Figure3.1: Showing the map of the study area (Blue circled)
3. 2 Materials and Methods
3.2.1.Method
The study was conducted in Dhaka city, the capital of Bangladesh. The site was selected purposively as among all the urban areas of Bangladesh Dhaka city is well planned both in it’s structure and organization. A reconnaissance survey was initially made to measure the homogeneity of the study area. To assess the status of avenue plantation, the studied 3 roads (Rokeya Sarani, Mirpur-2, Shanshad Bhaban Link road) were selected using a systematic random sampling method among the roads which have a good mass of plantation and roads without any mass of plantation were left out from the population. In all the 3 roads, I took 20m long strip plots in a 100m interval but the width varied from road to road. A total of two tea garden were studied of which 10 plots from Rokeya Sarani and Shanshad Bhaban Link road each, and 30 plots from Mirpur-2 road within 1Km of each road. From the plots studied, some were found to be out of any trees which were marked as NIL and in which plots where trees were found were counted. In each plot where trees were found, I measured the Height (m) and dbh (cm), and counted the number of trees of different species. A field record book was used to collect the data. Thereafter, the data were figured out and tabulated to be ready for analysis. MS XL was used to analyze the data.
3.2.2. Materials
While conducting the field study the following materials were used for different purposes which are listed below:
| Purpose | Name of the material |
| Height | Haga Altimeter |
| Dbh | Dia Tape |
| Taking plot | Measurement tape |
Chapter 04: Result and Discussion
Table4.1: Showing average plot size (m2); average number of species/plot; average, maximum and minimum height (m); average, maximum and minimum dbh (cm) of different studied locations
| Location | Average Plot Size | Specing (m) | Average No.of species/plot | Average Height (m) | Maxm height (m) | Minm height (m | Average DBH (cm) | Maxm DBH (cm) | Minm DBH (cm) |
| Rokeya Soroni | 20m × 1.8 m | 2 | 5 | 7.08(±2.73) | 13.8 | 4.08 | 5.61(±4.71) | 10.14 | 0.81 |
| Mirpur 2 Road | 20m × 2.4 m | 3 | 4 | 6.33(±5.12) | 20.4 | 1.8 | 12.17(±13.18) | 43.63 | 0.63 |
| Sangshad Bhaban link Road | 20m × 5.3 m | 2 | 3 | 11.1(±13.82) | 34.24 | 2.5 | 21.66(±14.03) | 44.60 | 3.02 |
* The value presents in the parenthesis show the standard deviation.
From the Table 1 it is evident that average tree density varied from 3 species/plot to 5 species/plot with a highest density of 5 species/plot in the Rokeya Soroni location. The highest average height (11.1 m) was found in the Shanshad Bhaban Link Road. Maximum height of the studied location Rokeya Soroni, Mirpur 2 Road and Shanshad Bhaban Link Road were 13.8, 20.4, and 34.24 respectively with the minimum height of 4.08, 1.8, and 2.5 respectively. The highest average dbh (21.66 m) was found in the Shanshad Bhaban Link Road. Maximum dbh of the studied location Rokeya saroni, Mirpur 2 Road and Shanshad Bhaban Link Road were 10.14, 43.63, and 44.60 respectively with the minimum dbh of 0.81, 0.63, and 3.02 respectively.
The presence of large and healthy trees can remove 60 to 70 times more pollution than small trees because of their proportionately greater leaf surface area. Hence, sustaining the health and longevity of mature trees is critical to maximizing air quality benefits. Also, air quality benefits can be increased by planting pollution-tolerant species in areas where concentrations are highest.
(McPherson et al.1997)
Table 4.2: Species found in the studied locations
| Location | Local Name | Scientific Name |
| Rokeya Soroni | Akashmoni | Acacia auriculiformis Willd |
| Babla | Acacia nilotica (Linn) Willd | |
| Boroi | Zizyphus mauritiana Lamk. | |
| Mehogoni | Swietenia mehagani King | |
| Mirpur 2 Road | Bot | Ficus bengalensis Linn |
| Mehagoni | Swietenia mehagani King | |
| Akashmoni | Acacia auriculiformis Willd | |
| Jam | syzygium grande (Roxb) DC | |
| Chapalish | Artocarpus chaplasha Roxb | |
| Nageswar | Mesua ferrea Burn. F.Kos | |
| Debdaru | polyalthia longifolia Benth | |
| Beliphool | Jasminum duplex | |
| Mango | Mangifera indica Linn | |
| Pine | Pinus longifolia Linn | |
| Jhau | Casuarina littorea Linn | |
| Sangshad bhabhan Link Road | Mehagoni | Swietenia mehagani King |
| Krishnochura | Delonix regia (Boj.) Raf. |
The study shows that in location Rokeya Soroni, Mirpur 2 Road and Shanshad Bhaban Link Road there found 4, 10, and 2 different species with the Mehagoni (Swietenia mehagani King) as a common species in the three locations. Due to this diversity of tree species, urban forests can mitigate urban heat island effects and conserve cooling energy by shading buildings and other heat-absorbing surfaces, as well as lowering summer air temperatures through evapotranspirational (ET) cooling (Meier 1990/91). Trees can save space-heating energy by reducing wind speeds, thereby reducing the amount of cold outside air that infiltrates buildings (Heisler 1986). In Dhaka city these diversity of tree species help the tolerance to pollution. For example, the tolerance to pollution and other urban environmental stresses of Platanus acerifolia, a tree widely planted in European cities, is well recognized in China, where it is widely cultivated in warm temperate and to a lesser extent in sub-tropical cities (Jim 1991).
In countries (e.g. Germany), where timber is harvested from peri-urban forests, the major management objective is providing recreation/education of the urban dweller, and timber harvesting operations are significantly modified accordingly. Largely having been conceived initially in terms of landscape improvement and amenity provision, urban forestry is now increasingly concerned with other, additional benefits, such as the control of air and noise pollution, and microclimatic modification (Carter 1993). One of the major problem in the Dhaka city is that air is either of foul odor or contaminated with dust and chemicals emitted by many industries and innumerable vehicles in the city. These diversity species can help to reduce air pollution. One example is provided by Mexico City, where the average level of particulate suspension in the atmosphere has risen from 65 mg/m3 in 1974 to 400 mg/m3 in 1990. Over the same time span, atmospheric sulphur dioxide levels rose from 60 mg/m3 to 120 mg/m3 (Chacalo and Pineau 1991). Air pollution may be compounded by local conditions, notably air inversions (warm air lying over cold air) which trap polluted air over cities or towns for prolonged periods. Examples of this phenomenon include Mexico City and Kathmandu, Nepal.
Again many countries practices urban forestry only few purposes. For example- in Debre Birhan, Ethiopia - Growing trees for fuelwood, Hong Kong - Maximizing the use of space, Tashkent, USSR - An international array of trees, Milton Keynes, UK - Trees as investment, Singapore, Republic of Singapore - Aerating a concrete jungle, Brussels, Belgium - The forest of the sun, Kampala, Uganda - Fuelwood and ornamentals, Dunedin, New Zealand - Logs and loans, Beijing, People's Republic of China - Continuing an ancient tradition (Haque 2003)
Although the potential of these processes has not been well documented in Dhaka city of Bangladesh, studies have been conducted in other cities round the world (Akbari and Taha 1992 McPherson 1993).
Table 4.3: Showing number of species found in the three locations
| Name of the species | Rokeya Soroni | Mirpur 2 Road | Sangshad bhabhan Link Road |
| Akashmoni | 34 (89.47%) | 25 (18.94%) | - |
| Mehagoni | 1 (2.63%) | 32 (24.24) | 8 (30.77%) |
| Babla | 1(2.63%) | - | - |
| Debdaru | - | 39 (29.54) | - |
| Boroi | 2 (5.27) | - | - |
| Bot | - | 8 (6.06%) | - |
| Jam | - | 3 (2.27%) | - |
| Nageswar | - | 13 (9.85%) | - |
| Chapalish | - | 2 (1.52%) | - |
| Mango | - | 4 (3.03%) | - |
| Jhau | - | 2 (1.52%) | - |
| Beliphool | - | 1 (0.75%) | - |
| Pine | - | 1 (0.75%) | - |
| Krishnochura | - | - | 18 (69.23%) |
| Katbadam | - | 1 (0.75%) | - |
| Unknown | - | 1 (0.75%) | - |
| Total | 38 | 132 | 26 |
From the table (3) above, it is observed that in Rokeya Soroni there found a total of 38 tress of which Akashmoni contributed the most (89.47%); in Mirpur 2 Road there found a total of 132 tress of which Debdaru contributed the most (29.54%); in Sangshad bhabhan Link road there found a total of 26 tress of which Krishnachura contributed the most 18 (69.23%).
Among the locations in Mirpur 2 Road the highest number of tress were found with the same limit of area. So there is increased amount of trees in the roads of Mirpur 2. An increase in tree cover by 10% (corresponding to about three trees per building) could reduce total heating and cooling energy use by 5 to 10% ($50–$90) (McPherson, 1994b). On a per-tree basis, annual heating energy can be reduced by about 1.3% ($10, 2.1 GJ), cooling energy by about 7% ($15, 0.48 GJ), and peak cooling demand by about 6% (90.3 kW) (McPherson et al. 1997).
The influence of urban forests on the physical and biological environment, as well as their socioeconomic importance has been compiled in journal articles (Rowntree 1986, 1988; Ulrich 1986; Oke 1989; Dwyer et al. 1992). From above findings, we can infer that the causes behind selecting Akashmoni as one of the major species are: it is a fast growing species; its wood can be used both as fuel wood and timber-that is it has multipurpose uses. Besides, its flowers with great yellow look add some scenic beauties in the urban roads.
Debdaru and Krishnachura both are planted with great emphasize due to their aesthetic values which put some more colour to urban roads. Beisdes, Krishnachura is a member of Leguminosae family, so it has the ability to ameliorate soil quality.
In Prague the most frequently planted street trees are lindens and maples. However, the Division of Road Maintenance in the Department of Transportation (TSK) now avoids the use of lindens because of their sensitivity to salt. Along the Vltava River, trees are planted in containers below street level to reduce salt damage. The containers, which are separated from the surrounding soil by an air gap, range from 8 to 12 m in diameter and are designed to last for at least 30 years. A 5 cm diameter perforated pipe is built into the root area to allow thorough watering. Hedgerow rose (Rosa rugosa), firethorn (Pyracantha spp.), common privet (Ligustrum vulgare L.) sea buckthorn (Hippophae spp.) and tamarisk (Tamarix spp.) are frequently recommended shrubs for salt-resistant planting. (Profous and Rowntree 1987)
Several studies have established relationships between different urban forest structures and specific functions such as visual quality (Schroeder 1986), energy savings (McPherson 1993), removal of atmospheric carbon dioxide (Rowntree and Nowak 1991), urban heat island mitigation (Huang et al. 1987; Oke 1989; McPherson 1994a), sound reduction (Cook and Van Haverbeke 1977), wildlife habitat (DeGraaf and Wentworth 1986), and personal safety (Schroeder and Anderson 1984). However, techniques for evaluating tradeoffs associated with multiple functions from a specific landscape are lacking. (McPherson et al.1997)
Table 4.4: Showing the number of Nil plots in the study area.
| Location | Number of Nil Plots | Total Number of plots |
| Rokeya saroni | 2(20%) | 10 |
| Mirpur 2 Road | 2(20%) | 30 |
| Sangshad bhabhan Link Road | 1(10%) | 10 |
From the above table it is found that in Sangshad bhabhan Link Road the number of Nil plots is minimum 1(10%) whereas in Rokeya saroni and the Mirpur 2 Road number of Nil plots is maximum 2(20%). Sangshad bhabhan Link Road shows the highest density of trees.
Figure 4.1: Showing the family frequency of species found in Rokeya Sarani.
It is observed that in Rokeya saroni, there found different species planted of mainly Leguminosae, Mimosaceae, Rahmanaceae, Meliaceae families among which Leguminosae is the family with highest frequency of 34 whereas Meliace and Mimosaceae both possessed the lowest frequency of 1 (Figure4. 1).
Figure4. 2: Showing the family frequency of species found in Mirpur 2 Road.
It is observed that in Mirpur 2 Road, there found different species planted of mainly Leguminosae, Moraceae, Meliaceae, Myrtaceae, Combretaceae, Guttiferae, Anacardiaceae, Annonaceae and Casuarinaceae families among which Annonaceae is the family with highest frequency of 39 whereas Combretaceae possessed the lowest frequency of 1 (Figure4.2).
Figure4.3: Showing the family frequency of species found in Shansad Bhaban Link Road.
It is observed that in Shansad Bhaban Link Road , there found different species planted of mainly Leguminosae and Meliaceae families among which Leguminosae is the family with highest frequency of 18 (Figure4.3).
If we go through the details of the above figures 4.1, 4.2 and 4.3 it can be found that in all the 3 locations there found that species of the family Leguminosae is present which implies that one of the important purpose of the urban forestry is to ameliorate the soil quality as the family Leguminosae has the capability to fix nitrogen (N).
Direct economic benefits of urban forests
In Bangladesh though budget incurred on the urban forests is tensed to negligible, nevertheless if they can prove their cost-effectiveness their sustainability could draw the kind attention of the policy makers. Though some residents wonder whether it is worth the trouble of maintaining street trees in front of their home or in their yard. Certain species are particularly bothersome due to litterfall, roots that invade sewers or heave sidewalks, shade that kills grass or exudates that foul cars and other objects. Branches broken by wind property, Thorns and low-hanging branches can be injurious. These problems are magnified when trees do not receive regular care, or when the wrong tree was selected for planting.
So for our better understanding of the values of urban forest, we can seek the answer of the following question:
1. Are trees worth it? Do their benefits exceed their costs? If so, by how much?
2. In what locations do trees provide the greatest net benefits?
3. How many years does it take before newly planted trees produce net benefits in Dhaka?
4. What tree-planting and management strategies will increase net benefits derived from Dhaka urban forest?
A Benefit-cost analysis could be used to answer the aforesaid questions. But due to the unavailability of relevant data it was not possible to assess their benefits (McPherson et al.1997). Most literature available on urban forestry concerns trees, rather than the people who might benefit from them. There is a particular dearth of published information about the relationship of Third World urban dwellers (particularly the poor) to urban trees and forests; on whether or not they value, use, or would like to use trees; and how urban trees affect their health and well-being(Carter 1993)
But from a simplified view we can easily understand the worth of urban forest especially of most densely populated and highly polluted Dhaka city.
Urban Forestry for maintenance of wholesome environment
The urban environment is very much different from the rural or countryside environment. Cities are characterized by predominance of concrete structures such as buildings, road, post and also stone, asphalt and metal. These metals absorb and radiate heat easily. The materials have also high reflective power for light and sound (Olembo and Rham 1987). On the top of these, metabolic and industrial activities in the cities produce a great amount of heat and dust. The air thus becomes filled with carbon dioxide, carbon monoxide, sulphur dioxide and many other pollutants and dust. As a result, the climate of a large city is affected adversely resulting in higher temperature and lower humidity. The sunlight is often partially covered by haze, smoke or even fog induced by emissions. If the situations of the cities of six municipal corporations such as Dhaka, Chittagong, Rajshahi, Khulna, Sylhet and Barisal are compared with those of rural areas, a significant difference in respect of temperature, humidity and cleanliness of the air will be observed. The reason is obvious. Apart from the absence of pollutants, the trees around the homesteads and farmlands exert positive effects in ameliorating the wholesome environment. (Zabala 1991)
The major urban centers in the country are the metropolitan cities of Dhaka, Rajshahi, Khulna and Chittagong. Dhaka is one of the most densely populated cities in the world.
Chapter 05: Conclusion and Recommendation
Conclusion
We need to plan for our city and make it a better environment to live in. Whatever determines the fortune of our environment determines also the fortune of our people. We have the power to change our world and everything we do, say and think shapes our reality. Saving the environment is a vital task for all of us. Pollution is increasing in the cities of Bangladesh in spite of government regulations to control it. Parks, squares, street trees, and other greenery and open space in are vital assets of a healthy and livable city. The ecological benefits of these resources are substantial: landscape improves air quality and lowers dust levels, provides vital habitat and corridors for birds and wildlife, reduces water run-off and erosion, and allows groundwater recharge. Trees and other plants absorb carbon dioxide and thus lower the city's contribution to global warming, an important capacity since the phenomenon of global warming has recently passed from theory to confirmed reality. Urban forestry may be practiced to redress the adverse effects of pollution and thus ameliorate the environment. Trees reduce air pollution by filtering air through leaves by the process of sedimentation. Gaseous pollutants and unpleasant odor are reduced either by absorption or masking them with pleasant foliage and floral fragrance. Vehicular noise is also absorbed by the leaves and trees can reduce sound pollution. The vegetation can also provide comfort to the city dwellers by improving the climate like temperature, humidity and air movement. In the wealthier developed countries, urban forestry focuses on amenities and environmental benefits. In poorer countries urban forestry must first pay attention on assisting in fulfilling basic necessities. Much more study is needed to quantify the benefits of urban and peri-urban forestry, to understand the dynamics of demand and flows of forest and tree resources between the rural and urban areas, and to develop a scientific knowledge base for urban forestry.
Recommendation
Human and Natural forces can change urban forestry in our country as well as Dhaka city. By understanding how human and natural forces interact within urban systems to create change, management can minimize negative forest changes and facilitate positive changes. Human forces (e.g. urban resident involvement in tree planting, maintenance, and management) and Natural forces (e.g. Extreme temperature events, Fire). Human activities not only change urban forest structure to meet design and functional needs but also try to minimize and prevent detrimental changes due to natural forces (for example, controlling insects and diseases or altering structure.) to sustain desired forest structure. A combination of human actions and natural forces will continue to shape the urban forests in the years ahead.
To facilitate comprehensive and adaptive management to sustain the entire urban forest ecosystem, the following topic areas need to be emphasized:
ü Improving inventory and assessment
ü Improving dialogue among owners, managers, and users
ü Improving the understanding of how forest configurations influence forest use and benefits
ü Increasing knowledge about factors that influence urban forest health
ü Improving the dissemination of information about urban forests and their management.
With improvements in the above areas, urban forest resources can become a more highly valued component of large-scale and long-term environmental and community planning.
1.3 Limitation of the study
This study should represent the actual condition of the study area. But as the study was conducted for academic interest, the field work was not intensified due to shortage of time and fund. The sufficient secondary data was not available. Sometimes, the people were not interested to help. The time allotted for the study especially for collection and analysis of information, was very short. More time was required for collection of vast information. Moreover no budget is allotted for that purpose.
Only three roads out of whole Dhaka city had been chosen for the study purpose. These are not sufficient. The finding does not represent the overall scenario. It is our empirical study.
There is not enough works, journals and other research related papers in our seminar library or central library in our University.
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Appendix
Questionnaires used in the field work
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