A study of the birds in central Bangkok (Thailand) in order to implement the basis of a long term monitoring
par Camille Calicis
Université de Gembloux Agro Bio-Tech - Master Bioingenieur en gestion des forêts et des espaces naturels 2014
This section aims at setting the general context of this study, using what the literature can offer so far. It will start by a brief recall of the actual worldwide biodiversity crisis, focusing then more on the description of the situation in Southeast Asia. Afterwards, we will provide an overview of the bird taxa situation, starting with the general trend of the evolution of their populations in Bangkok. We will also show the bird's importance as environment indicators as well as the need of monitoring them to explain environmental changes. We will next have a look at the effect of urbanization on birds and the importance of urban green areas, finally giving conservation clues from studies made in other cities.
IMPORTANCE OF BIODIVERSITY
«La caractéristique la plus merveilleuse de
notre planète est la présence de la vie et
The term «biodiversity» is a contraction of «biological diversity» and was defined by the Convention on Biological Diversity (UNCED, 5th of June 1992) as: «The variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems.» First, this term was closely related to nature conservation but has been then associated with more functional and utilitarian notions, especially after the publication of the MILLENNIUM ECOSYSTEM ASSESSMENT (MEA; 2005) which connected interactions between people, biodiversity and ecosystems.
Indeed, despite the fact that most humans consider themselves above everything, the biodiversity that surrounds them is indispensable to their survival. In fact, the changes in human condition leads to changes in biodiversity and in ecosystems and thus, have an ultimate effect on the services provided by the ecosystems which make biodiversity and human well-being entirely linked together (MEA, 2005). Species conservation is not only giving the species the right to exist, it also adds value to human's life by providing supporting, provisioning, regulating and cultural functions as shown in Figure 2.
1 «The most wonderful characteristic of our planet is the presence of life and the most incredible characteristic of life is its diversity»
Figure 2: Functions provided by the ecosystem (MEA, 2005)
Currently, biodiversity is unequivocally declining and some authors even speak about a «6th extinction crisis» (LEAKEY and LEWIN, 1999; MEA, 2005). If the extinction of a species is indeed a natural process (75 to 95% of all species that have ever existed are now extinct), today's biodiversity is disappearing at a 100 to 1000 times higher rate than the mean natural extinction rate that occurred during the fifth previous extinctions. So, the concern is not about the occurrence of extinctions, but rather about the acceleration of the extinction process: if nothing is done, 50% of the actual species will have disappeared before the end of the XXIst century (LEAKEY and LEWIN, 1999) and a world of pests and weeds will remain.
Nowadays, the challenge is to implement a sustainable development ensuring the social and economic viability of human societies while respecting the ecosystems (BROWN, 2001). Protecting those ecosystems requires a good basic knowledge of them, which can be improved by scientific research. As shown before, biodiversity is a quite nebulous and extremely large concept. Nonetheless, it must unconditionally be quantified in order to reach political decisions or to implement management measures or to reach a priority for actions. An important difficulty in quantifying biodiversity is that it is a multifaceted concept (PURVIS and HECTOR, 2000) and it must be done at a defined scale and with a defined and refocused objective (HOSTETLER, 1999).
II.1.2. The case of Southeast Asia
Although Southeast Asia (Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Timor-Leste, Thailand, and Vietnam) incorporates four biodiversity hotspots (BRIGGS, 1996; SODHI et al., 2004; WILLIAMS, 2012) (Figure 3), the region faces several key social, scientific and logistical conservation challenges.
Figure 3: Species Richness and endemism in the four biodiversity hotspots of Southeast Asia. The red bars represent the percentage of species endemic to the respective hotspot. Numbers in parentheses represent total and endemic species known to science, respectively (SODHI et al., 2004)
Among all the world's tropical regions, Southeast Asia has the highest rate of habitat lost with a deforestation rate four times higher than elsewhere in the world (FAO, 2012). This fact is alarming knowing that compared to the other tropical regions, Southeast Asia has the highest mean proportion of country-endemic bird (9%) and mammal species (11%) as well as the second highest rate of country-endemic vascular plant species (25%) (SODHI et al., 2009).
The current major threats to biodiversity in Southeast Asia are predominantly from socioeconomic origin; including population growth, poverty, chronic shortage of conservation resources and corrupt national institutions. Hence, as the regional societies of Southeast Asia attempt to match
the living standards of developed nations, environmental issues are inexorably marginalized (SODHI et al., 2004; SODHI and BROOK, 2006). This is supported by the fact that the economic constraints are much larger in the developing countries like Thailand, than in North America or Europe and therefore it is difficult to find money for environmental management when basic needs and poverty are an immediate bigger concern (FRASER, 2002).
Lastly, research on Southeast Asian biodiversity over the past 20 years has been neglected in comparison to other tropical regions (SODHI and BROOK, 2006). Indeed, it appears that there is a shortage of local scientists conducting rigorous conservation biology research in Southeast Asia, with the current work dominated by descriptive work, mostly inventories (SODHI and LIOW, 2000). These trends are disturbing and the consequence can be even more severe for that region because of the habitat destruction that occurred during the last century. Some solutions were brought by SODHI and LIOW (2000) to improve the quality of conservation biology research of Southeast Asia. They range from an increased accessibility to the international conservation biology journals to the start of more multinational collaborative projects, more rigorous funds for long-term research, education of local scientists in research design to reach the standards in order to be published in international journals ...
THE BIRDS STATE
«Birds are among the best known parts of the Earth's biodiversity. But nevertheless soundly quantified knowledge is far from complete for most species and regions.» (BIBBY et al., 1998a)
The bird taxa did not avoid the general biodiversity decline, and indeed, according to the IUCN Red List of Threatened Species (IUCN, 2013), 12% of the world avian species are now threatened. For a long time, the major threats for the birds were the variability of climatic events and their effect on vegetation. Those have been lately supplanted by the human impacts on the environment. During the last centuries, the pressure humans put on nature increased substantially with the intensification of urbanization and agriculture that generates the vanishing of many ecosystems.
II.2.1. Evolution of the birds of the Bangkok Area
The study of avian fauna of Southeast Asia reveals alarming trends: if the region hosts the highest mean proportion of endemic bird species at a national level, it also has the highest mean proportion of threatened bird species of all tropical regions. Despite this, the avifauna of Southeast Asia has been one of the least studied in the tropics (SODHI et al., 2006).
Thailand, as a country, holds 971 bird species (IUCN, 2013). 925 are native bird species while 1 has been introduced (Columbia Livia), 40 are vagrant species and 5 species are still uncertain data. Figure 4 shows a pie chart of Thailand bird species distribution through the IUCN Red List Categories.
Figure 4: Bird species distribution into the IUCN Red List
Categories. CR= Critically Endangered, EN=
PHILLIP ROUND (2008) in his book, «The birds of the Bangkok area», reviewed the birds of the Central Plain of Thailand. He also put together existing behavioral, life-history and ecological data on birds around Bangkok. The following paragraphs give a short summary of the evolution of the avian state in Bangkok that ROUND (2008) developed in the introduction of his book.
Once, the Central Plain held a bird and mammal mega fauna that vanished because of the high rate of destruction due to large-scale historical transformations in Thailand. Unfortunately, historic surveys of the wildlife of Bangkok are poor. Some old records inform us about the previous presence of ibises, pelicans, adjutants, vultures and birds characteristic of open forests. All those species are not there anymore, only smaller and ecologically tolerant birds of forests and secondary growth persisted until the seventieth century. The gradual decrease in the number of resident bird species in the Central Plain is clear and keeps happening since the intensification of agriculture and the spread of housing and industry. The Asian Economic Crisis, from mid-1997th onwards, gave the environment of the Chao Phraya Delta a brief respite from land speculation and uncontrolled development. However, today's economy is once again booming with all that is involved and no additional environment safeguards are put in place.
Nowadays, Bangkok's urban green areas are sparse compared with many other capitals and only the most ecologically tolerant species still survive well in inner city gardens and parks (Coppersmith Barbet, Common Iora, Pied Fantail, Oriental Magpie Robin, Streak-eared Bulbul, Common Tailorbird, Scarlet-backed Flowerpecker, Brown-throated Sunbird and Olive-backed Sunbird). Introduced bird species are also often seen in the city while they escape their cages, like the White-Crested Laughingthrush or the Red-Breasted Parakeet. Still, many birdwatchers are constantly amazed at how many species of birds they are able to see in the concrete jungle of Bangkok (pers. obs.).
Parks are of great importance in order to provide habitats for the birds but most of Bangkok's public parks have tended to be too deeply manicured to support many species. Native vegetation is disappearing and even water bodies are polluted with herbicides to prevent the colonization of aquatic vegetation. Though, the direct widespread impacts of pollution can't be estimated because of the absence of any systematic monitoring of the levels of toxic pollutants in birds.
An initiative came from the Bird Conservation Society of Thailand, which explored the possibility to implement an urban bird reserve in eastern Bangkok together with the Bangkok Metropolitan Administration (BMA). Regrettably, this effort fizzled out due to a change of BMA governor.
The previous trends highlighted by ROUND (2008) made that BirdLife international decided in 2004 to consider the inner gulf of Thailand (100,000 ha), including the Bangkok Metropolis, as an Important Bird Area (IBA) in order to control the over-exploitation of natural resources and promote compatible forms of land use across the whole area. The function of the IBA program worldwide is «to identify, protect and manage a network of sites that are significant for the longterm viability of naturally occurring bird populations, across the geographical range of those bird species for which a site-based approach is appropriate» (CHAN et al., 2004). However, this applies more to the coastal area where the actions are concentrated than to the Metropolis situation.
II.2.2. Birds as environmental indicators
As there is much concern today about environmental changes, it is essential to know how those changes affect wildlife, and birds offer a great value as biological and environmental indicators (BIBBY, 1999; GOTTSCHALK et al., 2005).
In fact, they reflect well the global health of the surrounding biodiversity because they often have a high position in the trophic chain and also because they respond fast to landscape modifications. They are among the most conspicuous (POMEROY, 1992), indeed, compared to other animal taxa, birds are relatively easy to detect, identify and survey. They have been subject to numerous studies, especially in Europe and America and therefore their eco-ethology is generally well documented. Bird diversity was also found to be correlated with the diversity of other taxa (BLAIR, 1999, SATTLER et al., 2010) which means that they may be reliable indicators of the overall biodiversity. Additionally, many studies have shown that birds are particularly useful to detect unexpected changes, for example, due to the pesticides, as RACHEL CARSON (1962) denounced with her famous book, «Silent spring».
If birds are good environment indicators, it is also and primordially because of the relationship between a bird and its habitat. FULLER (2012) presents a good and recent synthesis of the multiple publications concerning the processes of habitat selection by birds and the following section is a brief description of these.
The habitat is the environment in which an individual lives, including biotic and abiotic features as climate, microclimate, soil type, topography, plant species and vegetation structure as well as the other animal species living in the same environment. The use of a habitat by a bird, meaning the way it uses the free spaces and the various resources it contains, differs obviously between every species but also in between the same species, for example, with the age or the sex of the animal. For birds in particular, the factors affecting the habitat evolve considerably along the year, especially for the migrant species or for the sedentary birds living in latitudes where the seasons are highly contrasted. Usually, it is during the breeding time that birds show the severest association with one habitat.
Mechanisms explaining how a bird chooses its habitat are better and better known. The notions of «ultimate factors» and «proximate factors» in habitat selection have been highly developed in the past (HILDÉN 19652, cited by FULLER, 2012) and are still universal.
- Ultimate factors: Basic factors defining the choice of habitat through its fitness potential (e.g. food-supply, shelter availability, territory space, structural and functional characteristics, other species...)
- Proximate factors: Immediate signs or stimuli that are not automatically of fitness value (e.g. landscape and microhabitat features, vegetation density or height, microhabitats or functional sites like song posts...)
Therefore, in order to allow the birds to select habitat that offers the best fitness, the «proximate factors» have to be correlated with the «ultimate factors». This is all the more important when habitat' quality can't be determined at the time the bird chose is territory, especially in the case of migratory birds which need to quickly select an area to stop.
Furthermore, the spatial scale is important as well to understand how birds select their habitat. Indeed, birds being very mobile animals and generally in need of several types of resources, the mechanisms of selection of their territories are often spatially hierarchized. Certain species start identifying a potential habitat using the general landscape' characteristics, perceived by flying over for example. Then, the exact location of their territory can be elected as a result of a finer scale' analysis. For example, the initial selection of a territory is based on the most common resource but the refinement to the final location will be done on the most limiting resource. In this case, the bird starts to take an interest at a finer scale and then starts checking other factors at a coarser scale. The spatial process encountered at various scales is all equally determinants in order to explain the choice of a habitat by a bird.
2 HILDÉN O., 1965. Habitat selection in birds-a review. Ann. Zool. Fenn., 2, pp. 53-75.
II.2.3. Bird monitoring
Birds are also useful for monitoring and incorporating cumulative changes over long periods of time (BIBBY, 1999; KOSKIMIES, 1989). Birds counts conducted in a systematic and consistent way can provide an early-warning system in order to assess the health of an ecosystem. This is essential for the authorities to ensure that development is truly sustainable (POMEROY, 1992).
According to KOSKIMIES (1989), monitoring corresponds to «continuous and regular quantitative research using standardized methods, which reveal changes in the abundance and ecology of birds». In order to be well studied, the changes need to be clearly divided between those caused by human activities and those caused by the natural dynamics like the climatic changes, the geological processes or the biological evolution. Indeed, the last one affects the bird populations much more slowly than the human-caused ones. The first advantage of biological monitoring in opposition with non-biological monitoring is that environmental changes are detectable, especially for those that can't be observed or forecasted by the measurement of a set of pre-selected physical or chemical parameters. The second advantage is that biological monitoring makes it possible to detect and monitor cumulative and non-linear consequences of various environmental changes acting simultaneously. An integrated monitoring can allow to study cause-effect relationships which are truly important in order to decide the actions to be taken (KOSKIMIES, 1989).
The more changes the environment undergoes, the more it becomes necessary to learn how to manage it in order to take care of species conservation. Many cases need action but without precise data on numbers or trends, no useful recommendation for management action can be made. Furthermore, there is a need for a large ecological knowledge in many situations because we are continually changing our environment and in so doing, the birds with which we share it are inexorably affected (POMEROY, 1992)
In Thailand, assessment of the effect of various construction projects on biodiversity consists of little more than some unauthenticated lists of birds, mammals, or other taxa (ROUND, 2008). Indeed, a regrettably usual scheme in the case of birds is the statement that the impacts of their habitat damages will be minimal because the birds are able to fly to other areas.
«The effect of urbanization can be immense, yet our
understanding is rudimentary»
Rapid urbanization has turned out to be one of the major concerns in conservation ecology (MILLER and HOBBS, 2002) and can be justified by the fact that the world urban population is expected to increase by 72 per cent by 2050 (UN, 2012). Moreover, cities occupy less than 3% of the global terrestrial surface, but account for 78% of carbon emissions, 60% of residential water use, and
76% of wood used for industrial purposes (BROWN, 2001). Still, the intensifying conflict between the economy and the ecosystem of which it is part is evident and undeniably, urbanization will keep having a significant impact on the ecology at local, regional and global scales (SINGH et al., 2010).
II.3.1. Cities as extinction or richness generator?
Uncontestably, urbanization and anthropogenic activities intensification in the landscapes change the ecosystem at many levels which lead to the homogenization of habitat structure and composition (FORMAN, 1995). For example, the urban sprawl is made of redundant artificial infrastructures that homogenize the urban landscape (MCKINNEY, 2002; 2006). This has a major negative impact on biodiversity and on the ecosystem capacity to ensure the expected services (FORMAN, 1995).
However, urban areas seem characterized by a more important species abundance than suburban areas for some biological groups (KÜHN et al., 2004; ARAÚJO, 2003; NIELSEN et al., 2013). Indeed, some species find alternative ecological niches in the cities and are able to develop important populations like it is the case for the well-known Columbia Livia (Rock Pigeon). Urban land-uses represent ideal habitats for the demographic explosion of those urban-exploiter species, able to use the abundant food resources associated to human litter (ORTEGA-ÁLVAREZ and MACGREGOR-FORS, 2009). Therefore, many studies claim the threat of the massive disturbances created by city growth on the habitat of native species (CONOLE and KIRKPATRICK, 2011; DEVICTOR et al., 2008; MCKINNEY, 2006). Indeed, those disturbances create a new habitat for few widespread non-native species that are easily adapting to urban conditions and enrich the local biodiversity while the global diversity is decreasing subsequently to the extinction of non-adapting local species (SAX and GAINES, 2003).
Those apparent contradictions probably result from differences between the geographic scales used, sampling bias, different contexts or else different biological responses (MACDONNELL and HAHS, 2008). Identifying the proximal factor of the urban diversity is relatively difficult as well as studying urbanizations gradients and biological response that are far from being linear (MACDONNELL and HAHS, 2008). Nevertheless, natural populations' extinction in the most urbanized parts of a city seems well established, especially in the new growth tropical cities. The geographic layout of the urban biodiversity hotspots is fundamental and there is a major lack of protected areas in the urban environment (BASTIN and THOMAS, 1999, SANDSTRÖM et al., 2006).
II.3.2. Importance of urban green spaces
The «urban green spaces» comprises all urban parks, forests and related vegetation (SINGH et al., 2010); even cemeteries can be considered so (LUSSENHOP, 1977). According to the WHO (2008), at least 9 m2 of urban green space per capita is recommended to alleviate undesirable
environmental effects and provide other benefits like a healthy population and a sustainable economy in any city (KUCHELMEISTER, 1998). However, the amount of required open green spaces per city dweller has remained controversial (SINGH et al., 2010). Those amounts have been estimated for some developing countries cities like Seoul that has 14 m2 of urban green per capita (KUCHELMEISTER, 1998), Singapore, 10 m2 (CHOW and ROTH, 2006), Beijing, 6 m2 (DEMBNER, 1993), Mexico City, 1.9m2 (DELOYA, 1993) and New Delhi, 0.12 m2 (KUCHELMEISTER, 1998).
This is quite alarming while knowing that within municipal limits of 26 large European cities, the average of urban green space is estimated at 104 m2 per inhabitant (KONIJNENDIJK, 2003). Indeed, urban green spaces are increasingly critical to healthy cities (WHO, 2008), even more in developing countries that include some of the world's biggest metropolitan areas and have the greater rate of urbanization (UN, 2012).
A functional network of urban green spaces can contribute to ecological diversity in a city (SANDSTRÖM et al., 2006). The major benefits of green spaces are (LAGHAI and BAHMANPOUR 2012):
- Assimilation of Carbon dioxide and other toxic gases as well as Oxygen production
- Regulation and improvement of cities climate
- Noise pollution reduction and improvement of human well-being
- Prevention of water and wind erosion
- Diminution of floods hazard
- Prevention of unsuitable urban development and increase of the beautifulness of the city
Green spaces perform important functions and services worldwide (NIELSEN et al., 2013), their development has the potential to moderate the adverse effects of urbanization in a sustainable way, making cities more attractive to live in, reversing urban sprawl, and decreasing transport demand (DE RIDDER et al., 2004).
II.3.3. Conservation keys to reduce the urban effects on birds: state-of-the-art
Despite high stress ensuing from urban life features such as noise (KATTI and WARREN, 2004), air and soil pollution (MCKINNEY, 2002; ROUND, 2008) and high densities of domestic predators (ANDERIES et al., 2007; SORACE, 2002), urban areas throughout the world are characterized by high food resource abundance and high avian population densities but as developed before, lower species diversity is generally observed (MARZLUFF et al., 2001).
Many studies have attempted to determine the impacts of urbanization on birds worldwide together with solutions in order to alleviate the damages done to bird communities. Table 1 brings a state-of-the art giving conservation keys brought from multiple scientific studies.
Table 1: Synthesis table of the publications bringing conservation keys in order to alleviate the effects of urbanization on birds.
Conservation Keys Reference
Identifying the areas of high conservation interest
RAMALHO and HOBBS, 2012; SODHI et al., 2004
SAX and GAINES, 2003;
Integrating social and socio economic processes (e.g. poverty alleviation, public SODHI et al., 2004;
education, work with various stakeholders) SODHI et al., 2006;
Using the habitat island ecological theory as a research framework for the FAHRIG, 2003;
management and conservation of urban birds FERNÁNDEZ-JURICIC and
Understanding better the degree to which species respond to local environmental conditions and landscape patterns
FAHRIG, 2003; FULLER, 2012; GALITSKY, 2012
Identifying species diversity changes across time at multi-scales
Using satellite-based remote sensing together with bird data in a GIS environment
GOTTSCHALK et al., 2005
in order to assess causal effects in species- environment relationships
Using a Community Specialization Index for measuring functional homogenization on both local and global scales across time
DEVICTOR et al., 2008
Greater understanding of people and wildlife interactions SAVARD et al., 2000
III. STUDY AREA
We carried out the study in Bangkok, Thailand's capital, both a city and a province. The metropolis of Bangkok covers a 1,568.7 km2 area in the delta of the Chao Phraya River in Central Thailand. The study area was focused on green areas localized in the most densely urbanized area of the city (Figure 5).
Figure 5: Localization of the study area. a. Geographical location of Bangkok in Southeast Asia, b. localization of the study area
in Bangkok, c. study area
III.1.1. General context
Since the 1960th, Bangkok has known an astonishing physical growth from 6 km2 to the current city area. Its major river, the Chao Phraya, has performed as the central artery of the whole city and has significantly influenced settlement formation and configuration (MATEO-BABIANO, 2012). The population of Bangkok was estimated to be around one million people in 1950 while today it is close to 12 million (FRASER, 2002). This number is continually increasing due to the excellent economic potential of the city that attracts people from the countryside as well as expatriates from all over the world. Furthermore, abundant tourists visit Bangkok every year, adding people in this already overpopulated city (THAIUTSA et al., 2008).
Bangkok presents the case of a dynamic city with competition between its traditions and the Western contemporary influences on its urban spaces. The city shows the same seemingly disorganized quality that characterizes the Asian space and therefore the diversity of the street space is alike the forest environment, where a cacophony of sounds, sights, smells, tastes and touch can be experienced altogether (MATEO-BABIANO, 2012).
Regrettably, the other side of the coin of a megacity like Bangkok is the multiple kinds of pollution that occur which include atmospheric, auditory and visual. Water pollution is also critical on the fact that the canals are like open sewer, the groundwater is therefore in really bad shape. The publications over this subject are countless and won't be developed through this work.
III.1.2. Climate and Altitude
Bangkok has a seasonal monsoonal climate. According to the Köppen classification it is an Aw climate type (KHEDARI et al., 2002). The daily average temperature stays relatively constant over the year with a mean annual temperature of 28.1°C. The monsoonal rainy season stands from July to October while the dry season extends from November to June with the three first months (until February) cooler, making it be called the «cool» season. The last month of the dry season (from March until June) shows high solar intensity as well as high heat and longer days and is therefore called the hot season (Figure 6). The heat in this season is even more felt by the effect of pavement and buildings (THAIUTSA et al., 2008).
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Total rainfall (mm) Average Temperature (°C)
Figure 6: Bangkok Climate Chart3
3 Data from http://fr.climate-data.org/location/6313/ visited on 18/03/2014
Climate change is a significant threat that will create, through the rising of the sea level, profound impacts on the Chao Phraya Delta (ROUND, 2008). As Bangkok is situated only 2 m above de sea level with some important parts of the city that are only at 0.5 m or less, clearly much of the inner city could be flooded by the turn of the century (JARUPONGSAKUL, 20004; cited in ROUND, 2008). Over 14% of the city's total area is seasonally flooded during the wet season (THAIUTSA et al., 2008).
III.1.3. Land use
THAIUTSA et al. (2008) calculated the areas of the main land uses in Bangkok from GIS analysis of satellite imagery. As no more literature was found about the land use in Bangkok, the following information stems from this article.
Bangkok includes a quite large amount of unconstructed areas within its boundaries. As shown in Table 2, just over 50% of the metropolis is made of building, roads and other constructed surfaces, followed by an unexpected 26% of land used for food production, mainly farmland and shrimp farms on the periphery of the city boundaries. Finally, only 4.2 % of the city's total area is green space, if one excludes agricultural land. The green spaces are mostly made of trees found in the streets and naturalized areas with 1.2% of developed green spaces. The developed green spaces are nearly equally split between actual parks accessible to the entire population, sports field and golf courses which are not readily accessible to all the citizens of Bangkok.
Table 2: Area of main land uses in Bangkok (variables source: THAIUTSA et al., 2008)
The land use is very different in the central part of the city in comparison with its eastern and western edges that are adjoined with food producing areas and forest covered provinces. Thus, those districts have the highest rate of tree and food producing areas within Bangkok. On the other hand, the districts situated in the center of the city, have the highest population density with 14,000 persons per km2 and 8000 persons per km2 respectively, these amounts being 2 to 4 times higher
4 JARUPONGSAKUL T., 2000. Potential impacts of sea-level rise and the coastal zone management in the upper gulf of Thailand. pp. 138-151 in SINSAKUL S., CHAIMANEE N. and TIYAPAIRACH S. (eds.), Proceedingsof the Thai-Japanese geological meeting: The comprehensive assessment on impacts of sea-level rise. Geological Survey Division, Department of Mineral Resources, Bangkok.
than in the other districts groups. This is of greater importance as the study will focus on the green patches of this part of the city. Those variations in population density distort the per capita green space values. Hence, the per capita green space averages 2.8 m2 in those two districts while it rises to a mean of 11.8 m2 for the entire city. About 40% of those green spaces are actually park spaces (the rest being tree cover) which represent around 1.2 m2 per inhabitant. The BMA tends to increase the park space per capita so it will reach 2.5 m2 in 2023 with an ultimate goal of 4 m2 per person.