Urban Forestry status at Dhaka in Bangladesh 2

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.      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

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).

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).

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.

1.1            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.