Assessment of urban trees and shrubs using remote sensing technology

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Assessment of urban trees and shrubs using remote sensing technology: A case study on Ramna and Uttara


1.1 Background

Dhaka is one of the fastest growing urban areas in the world and largest city in Bangladesh. It has a population about 9 million within DCC area and over 10 million in the Dhaka Metropolitan area, which seems beyond its ‘carrying capacity’. Historically, the city is the hub of multifaceted activities including commercial, residential and industrial etc. Rapid and unplanned urbanization with poor population characterized it as a chaotic city.

Landscape of the city is characterized by Pleistocene Madhupur tract and depression flood plain deposit whereas most of the built up areas were developed in Madhupur tract. Physiographic nature of the city is bounded by flat land tilted from north-west to south-east. It is also surrounded by four rivers such as Buriganga at the south, Tongi khal at the north, Turag at the west and Balu at the eastern side known as Metropolitan area.

Urban Dhaka is rapidly growing and the mega city is facing various severe environmental problems like wetland loss, biodiversity loss, huge extraction of ground water, unplanned high rise building, discharge of industrial wastes in rivers and water bodies, pollution due to sound and gas emission, water quality degradation and over all vectors of many diseases find a heyday to create health problems

The increasing population exerting pressure on the land cover of greater Dhaka city by converting the lands to built up areas. Thus the landscapes are changing in the form of filling-up wetlands and water bodies together with destroying vegetation cover. These activities are happening mostly unplanned manner which leads the land cover to inundate extensively and to flood vulnerability.

Again, climate change signifies the impact of land use change. As land use change contributes to the global warming by increasing temperature and high rainfall anomaly creates the problem of flood vulnerability. Due to the destruction of vegetation cover and wet lands, the percentage of relative humidity and evaporation is showing undulation over the time period which creates problems to the health of urban population.

For sustainable development of environmentally polluted and hazard prone mega city, an integrated urban planning is very important. The present study will try to seek those problems especially urban greening and its various prospects at Ramna and Uttara.

1.2. General Greening Activities in Dhaka city.

The development of multifunctional urban green structures can be an important contributor to sustainable urban development in terms of improving the quality of life and environment for current urban populations (Konijnendijk et al., 2004). Once the present Dhaka city forest and green areas were managed by the Forest Department, but after the establishment of Dhaka City Corporation (formerly named Dhaka Municipality), it is the main responsible organization for greenery activates. Besides, the Rajdhani Unnayan Kartripakkha (RAJUK) had been emerged in 1987 through the ongoing crisis of planned and controlled development of Dhaka City which prime intension was to develop, improve, extend and manage the city and the peripheral areas through a process of proper development planning and development control. The jurisdiction of RAJUK includes the City of Dhaka and it’s vicinity in the Districts of Dhaka, Narayanganj and Gazipur covering an area of 1528sq. kms. With DCC and RAJUK, a number of state bodies, autonomous bodies, private organizations, NGOs, different societies are involved with greening activities in and around Dhaka city. Of them, the key state and autonomous authorities are Department of Environment (DoE), Local Government and Engineering Department (LGED), Bangladesh Forest Department (BFD), Dhaka Urban Transport Project Authority (DUTP), and Dhaka Transport Coordination Board (DTCB), Department of Archeology, etc. Apart from these, some NGOs like ASHA, PROSIKA, different financial organization, donor agencies such as ADB, World Bank are also taking part in greening activities in Dhaka city. Some social organizations like Society of Arboriculture, Bangladesh National Nursery Consortium (NNC) are also contributing their efforts for promoting greening activities.

The greening activities in Dhaka got impetus during the British regime. The British rulers took several attempts in earlier phase of the previous century to develop Dhaka as a beautiful capital city of Assam and East Bengal with adequate greenery.

Most popular Ramna Park is a successful outcome of their endeavor. Some remarkable improvement was happened during the Pakistan regime. Street and avenue plantation, establishment of gardens, large area allocation tree plantation were the major activities at that time. After the independence in 1971, greening activities have not got any importance rather than other wide variety of urban development projects including sanitation, drainage, housing, and infrastructure. The first Master Plan of Dhaka was prepared in 1959 by a British firm. The Plan covered roughly 830 sq. km (320 sq. miles) with a target population little over 1 (one) million assuming an average annual population growth rate of 1.75% in the city areas. The Plan in general, suggested a broad planning principle and zoned the urban area accordingly for various activities. Protect urban trees, rehabilitate what has been destroyed, and plan for enhancing green resources were some key policies in this plan but unfortunately, there were no mentionable development that happened under this plan due to lack of financial resources, government unwillingness for allocating money, coordination of the activities of different organization etc. Although, the Plan was prepared for a period of 20 years (1959-79) but it lasted almost double till the enforcement of new plan in 1995.

In 1995, Dhaka Metropolitan Development Plan, 1995-2015 was prepared for overall development of the city and its surrounding. The plan addressed Dhaka’s urban planning issues at three geographic levels: sub-regional, urban and suburbs. This plan, indeed, a mile stone, for city greening with the aim of creating green areas compatible and functional for urban design and meeting the basic needs and values of local communities. Another remarkable planning policy is the National Forest Policy, 1994, prepared by the Ministry of Forest, which included multipurpose objectives for afforestation, social forestry, protected area management, etc. through the coordinated efforts of the government and NGOs and active participation of the people in order to achieve self reliance in forest products and maintenance of ecological balance. A 20-year strategic visionary plan then dubbed the ‘Dhaka Environment Programme’ which has been devised by the DoE for the improvement of the city’s environment including strategies and approaches to establish a ‘Green Dhaka’.

Though some form of greening activities were carried out in different times, indeed, it has got priority very recently. DCC has taken initiatives for beautification and greening of Dhaka city by planting trees in existing parks including establish new parks, play grounds, constructing fountains and other installations at various intersections/ roads and maintenance of 67 road medians and islands for a four-year term. Beside, unpaved parts of roads and footpaths are used for the plantation of decorative plants and shrubs. The implementation of the project is running by the Beautification Cell of DCC involved with large number of banks, educational institutions, hospitals and business organizations. Dhaka Urban Transport Project (DUTP) and Dhaka Transport Coordination Board (DTCB) have also taken different actions to make the city roads beautiful and decorated, with the support from different organizations. Another activities are carrying out under the project named ‘Good Governance and Development’ by linking all Ministries, Departments and Agencies. Bangladesh National Nursery Consortium (NNC) and Horticulture wings of Agriculture Ministry are continuously trying to promote nursery and gardening activities in the city. Prime Minister’s Award for afforestation and Tree fair introduced in 1992 and 1994 respectively in nationwide for creating awareness and inspired the people for tree plantation.

Again the Uttara residential area is recent development of RAJUK and City Corporation (North). The large green fields are now converted into residential though most of the place remained untouched.

1.3 Remote Sensing and GIS: Land use and Greening

Remote Sensing and Geographic Information Systems have widely been used for land use mapping (Dewan et al. 2006). Remotely sensed data provides the instantaneous and synoptic view for land use and vegetation cover assessment. The typical spectral reflectance is useful to obtain correct information from the ground objects.

Land use change can be analyzed with the help of Remote Sensing data. Extraction of land cover information can be done by using Land sat ETM and ASTER Images directly. The 15m ASTER image can provide more accurate data than 30m Land sat ETM image. It can be monitored and evaluated the rapid changes of land cover by using RS and GIS mutually.

In contrast to the land use and flood hazard assessment, the 90m Shuttle Radar Topographic Mission (SRTM) data were further re-projected with Survey of Bangladesh (SOB) used projection in order to obtain the land elevation information of Dhaka using Remote Sensing extensively.

1.4 Underlying Principle

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 plantation and inquiry the possible solution for the development of roadside plantation. I think my study will be helpful regarding this.

2. Objectives Of The Study

The aim of this research is to explore some association of population and for that matter land use with vulnerable situation due to floods and environmental disasters. The following are the specific objectives of this study:

1. The determination of land covers change.

2. The delineation vegetation coverage.

3. The analysis of climate change due to vegetation and land cover change.

4. Inquire the possible solution for the development of avenue plantation.

3. Study Area

3.1 Introduction

The study area is the Metropolitan Dhaka city (Uttara and Ramna) having an area of approximately 306 km² (Islam 2005) is surrounded by a network of natural drainage system the Buriganga at the south, Tongi khal at the north, Turag at the west and Balu at the eastern side. The area is gradually sloping towards the east (14m to1 m elevation) and characterized by vast wetlands and agricultural area Figure 2.1.The focused study areas are Uttara and Ramna statistical thana.

It is a low elevated area which has the maximum elevation of 14 m. It is extending through north and south-east and Spatial location is 23° 50’N 90°20’E and 23°40’N, 90°30’E respectively.

3.2 Land cover Situation in Dhaka City

Geologically, Urban Dhaka is a flat land and is located mainly on an alluvial terrace of madhupur tract (most built up areas), younger and old natural levee deposit (western and southern part) and high floodplain and depression (eastern and northern part) deposit (The Daily Star 2011). It has a fascinating history of erosion and deposition, changes of sea level and in climate change. The exceptional uniformity of clay sediments of this area reveals that it frequently undergoes tidal or marine conditions. It is also slightly tilted to the southeast so that the western edge generally stands 3-6 meters above the adjoining flood plains and the southeastern part is low and has been invade upon old Brahmaputra sediments. The elevation ranges from 1 to 14m above Mean Sea Level (MSL) which is shown in Figure 3.2 by using Shuttle Radar Topographic Mission (SRTM)-90m resolution data which shows undulated topographic condition.

The soils are relatively mature. In profile, they consist of a thin brown loamy topsoil overlying a red, friable, clay loam to clay subsoil which at 0.7-1.5 meter grades into a strongly mottled friable to clay substratum with red, brown, drained, but acid in reaction and relatively low in plant nutrients .

The study area also lies in the madhupur tract and younger and old natural levee deposit, which is characteristically different form each other.

Figure 3.1: The Study Area denoting Dhaka Metropolitan Area (Uttara and Ramna)

Hydrologically, the study area is situated in the terminal of the three major rivers – the Jamuna, the Padma, the Meghna and the old Brahmaputra flowing towards southeast (Sultana 2005). It is also closely dissected by a number of rivers and khals which are hydro-dynamically connected to the major rivers. The rivers carry the highest amount of rainfall during the monsoon season which is 90 % of the mean annual rainfall (Huq and Alam 2010). They discharge highest amount of water during the monsoon and reached to the highest level during this season (June-October). The incised drainage system is well developed and floodplains consist of back swamps, depressions and meander lakes which are comparatively ill drained.

The hydro-dynamically mighty rivers and stream-streamlets are strongly interconnected. The Buriganga branching off from Dhaleswari and flows towards south east. The Turag river comes from the north and joins the Buriganga near Mirpur. The Balu river also comes from the north running through the eastern side and joins the Lakhya river near Demra. The Tongi khal takes water from the Turag river and discharge it into the Balu river. The Turag, Balu and Tongi khal all are perennial (Sultana 2005). These rivers shrink during dry season and turn into overloaded during rainy season.

Climatologically, it is characterized by hot and humid subtropical climatic conditions demarked with short and cool winter and hot summer with high rain fall. It is situated at the South-central climatic zone (Banglapedia 2008) with highly variations of temperature, humidity and evaporation etc. The mean annual rainfall is 2147 mm and average relative humidity (70-75%) with 1150mm of evaporation (BMO 2011). The temperature is highly variable than surrounding rural areas.

The city is characterized by increasing trends of population (Figure 2.2) and high density. It is the fourth largest mega city in the world (UNFPA 2009). Average density of population is 7918.43 per km². The annual growth rate is 4.5 % (Islam 2005) showing the increasing trends over the year.

Figure 3.2: Digital Elevation Model (DEM) of Dhaka Metropolitan Area (DMA) by using Shuttle Radar Topographic Mission (SRTM) data.

Figure 3.3: The population growth of Dhaka Metropolitan Area (Source: BBS 2001, 2008; BARC 2004 and BCAS 2005, Islam 2005, UNDP 2010).

3.3 General Landuse Scenario

General land use of the city comprised of commercial and industrial activities mostly occurring in unplanned manner. The land comprising of residential, industrial and commercial are about 33.45% of 208km² and percentage of vacant land is about 3.09 (BCAS 2005).

The physical growth of the city mostly directed to the north-east. Rapid and unplanned urbanization, commercial development and with population pressure have made this city worst in terms of living perspective.

4. Review Of Literature

4.1. 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.

4.2. Definition of the term ‘urban’

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).

4.3. Definitions of urban forestry

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.”

4.4. Concept of Peri-urban forestry

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 unfeasible. 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).

4.5. 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).

4.6. 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).

4.7. Purpose 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—-

4.7.1. 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.

4.7.2. 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).

4.7.3. 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.

4.7.4. 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).

4.7.5. 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).

4.7.6 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).

4.7.7. 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).

4.7.8. 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.

4.7.9. Environmental benefits

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)

4.8. Potential problems from urban forestry

A number of the potential problems of trees in urban areas are discussed with regard to species selection. However, a brief review is of use here, both of the problems and possible means of avoiding them.

4.8.1. 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)

4.8.2. 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.

4.8.3. 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).

4.8.4. 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. 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).

4.8.5. 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).

4.8.6. 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).

4.9. 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)

4.10. 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).

4.11. 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.

4.11.1. 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).

4.11.2. 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).

4.11.3. 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).

4.11.4. 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).

4.11.5. 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)

4.11.6. 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).

4.11.7. Urban forestry in Canberra, Australia

InCanberra 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).

4.11.8. 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).

4.11.9. 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).

4.11.10. 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).

4.11.11. 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).

4.11.12. 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).

4.11.13. 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).

4.11.14. Singapore, Republic of Singapore – Aerating a concrete jungle

The early 1960s saw Singapor