Journal of Tropical Forest Research 1 (1) : 58-78 (2017)

Review articles

Ecological Studies of Tropical Seasonally Dry Forest in Continental Southeast Asia: A Review using Thailand as a Case Study

Pongsak Sahunalu*

Forestry Alumni Society, Kasetsart University, Chatuchak, Bangkok, 10900 THAILAND *Corresponding Author, E-mail: [email protected]

Received: Apr 12, 2016 Accepted: May 30, 2016

ABSTRACT

Tropical seasonally dry forest in Continental Southeast Asia has a prominent and similar importance to the region as does tropical rain forest. As there is broad encouragement to protect tropical forest to maintain global biodiversity and remedy global warming, major parts of this forest type are included in the protection system of all countries in Continental Southeast Asia. However, it has been less studied, particularly by ecologists, compared to the tropical wet forest type especially in this region compared to those forests in South and Central America. Ecological studies covering its past and present natural distribution, area cover, nomenclature, and some important aspects were examined using Thailand as a case study as representative of the Continental Southeast Asian region. The history of Thai-Japanese collaborative ecological studies in seasonally dry forests in Thailand is also described briefly. This broad forest community type in Thailand consists of seasonally dry forests of Mixed Deciduous or Monsoon Forest and Dry Evergreen or Seasonal Evergreen Rain Forest with variants occurring in small valleys and along stream banks called Gallery Forest and Dry Dipterocarp or Deciduous Dipterocarp Forest. About 35 topics were found to have been intensively studied and published in scientific papers for these three forest community types in various locations in Thailand. Some of these studies are likely to have not fully covered all ecological aspects and all the details of each approach. Future research needs to fill knowledge gaps and to cover all interesting ecological as well as other related aspects that this study has identified to stimulate interested researchers in this region as well as other scientists to pay more attention to this forest type in the tropics, particularly in Thailand. Trans-boundary studies in neighboring Continental Southeast Asian countries are also encouraged.

Keywords: Continental Southeast Asia, Ecological studies, Thailand, Tropical seasonally dry forest Journal of Tropical Forest Research 1 (1) : 58-78 (2017) 59

INTRODUCTION important points particularly in relation to the

Tropical seasonally dry forest has been ecological studies in Thai forests are not up to less paid attention than humid or wet tropical date and especially there is no categorization forest although its distribution covers many of the ecological research but rather general parts of the world. It has served humans in information has been given with practically various ways since ancient times. Ecological no suggestions on future research needs. The studies of tropical seasonally dry forest have information compiled before the appearance been reviewed by Murphy and Lugo (1986) of that article did not fully cover all available and Mooney et al. (1995). Emphasis on the information in published papers and those danger of the disappearance of tropical dry after 1995 have not yet been included. Then, forest has also been pointed out by Janzen 16 years later, Bunyavejchewin et al. (2011) (1988). There has been enormous scientific published a paper on seasonally dry forest in and public attention toward the effects of Continental Southeast Asia but the contents destruction of wet forests on soil, water, were not complete; rather, they placed emphasis atmospheric, and global changes rather than on the structure, species composition, and on tropical seasonally dry forest. Degradation dynamics of several forest types throughout and conversion of tropical seasonally dry forest Thailand and included no study on ecological is far more advanced than that of wet tropical function especially on productivity and forest and only a small portion remains intact nutrient cycling, which are considered to though it still contributes a great deal to the be more important information guiding the world ecosystems and to human wellbeing. It future management and conservation of those has also been less studied in Southeast Asia forests. The author presented a view point to compared to the tropical seasonally dry forests stimulate study on this forest formation through in South and Central America or even in the a short communication and a presentation at African savanna. an international symposium in 2004 and 2005, About 105 books and 8,000 scientific respectively (Sahunalu, 2004c, 2005) though articles on tropical rain forest are available subsequent new publications have not yet been but there is only one book that deals with the issued. It appears afterward that the results of tropical seasonally dry forest (see Mooney ecological studies on these forest formations et al., 1995). In this book, only one article were newly added but were not exhaustive was published on the tropical seasonally and further studies on various aspects are dry forest in Southeast Asia, especially on still required to formulate precise sustainable seasonally dry forests of Thailand (see Rundel management and conservation strategies. and Boonpragob, 1995). While the recorded This forest type deserves priority information in this article has proved to be research in order to preserve it as a part of generally useful and comprehensive, some maintaining world biodiversity and as insurance 60 Journal of Tropical Forest Research 1 (1) : 58-78 (2017) against global change, while also avoiding 250 to 2000 mm, and the ratio of potential direct exploitation. This paper aimed to evapo-transpiration (PET) to precipitation review the existing information related to this (P) or PET/P is greater than 1 to a maximum important forest ecological study, particularly of 2. Different nomenclatures included in in Continental Southeast Asian countries by Holdridge’s dry forest are: dry or sub-humid using seasonally dry forest in Thailand as an forest, seasonal drought forest, semi-evergreen, example. semi-deciduous and deciduous forest. Earlier, Beard (1955) classified tropical American Distribution of Tropical Seasonally Dry vegetation types as: seasonal formation series Forest which included: evergreen seasonal forest, Tropical seasonally dry forest on cactus scrub, semi-evergreen seasonal forest, the global scale is distributed across three deciduous seasonal forest, thorn woodland; and continents, particularly in South and Central as a dry evergreen formation series including: America, Africa, and Asia. Broad identification dry rain forest, dry evergreen forest, dry of the world’s biome indicates that there are evergreen woodland, dry evergreen thicket two major forest biomes in the tropics: tropical and evergreen bushland. Later Hartshorn forest including seasonal forest and tropical (1988) classified the North American terrestrial savanna grassland. It is widely accepted that vegetation into major forest vegetation types 40% of the Earth’s tropical and subtropical as: lowland sub-humid forest which included landmass is dominated by open or closed forest tropical dry forest and subtropical dry forest, (Murphy and Lugo, 1986). This area is further subtropical thorn forest and low mountain subdivided into dry forest (40%), moist forest subhumid forest which was further classified (33%), and wet or rain forest (25%). These into subtropical thorn woodland, subtropical dry figures are approximate as the exact original forest, subtropical lower montane, subtropical and potential distributions of dry forest are dry forest, and subtropical lower montane dry uncertain because the existing savanna, scrub, forest. Nevertheless, all these classification and thorn woodlands are thought to have been and terminologies were not popularly adopted derived from dry forest disturbance from time for tropical dry forest elements on the Asian to time. continent.

Tropical Seasonally Dry Forest Definitions Nomenclature of Seasonally Dry Forest in According to the life zone classification Continental Southeast Asia proposed by Holdridge (1967), tropical Continental Southeast Asians countries seasonally dry forest is found in frost-free consist of Myanmar, Thailand, Laos, Cambodia, areas with a mean annual bio-temperature of and Vietnam. Tropical seasonally dry forest in about 17OC, the annual rainfall ranges from Continental Southeast Asia was first defined by Journal of Tropical Forest Research 1 (1) : 58-78 (2017) 61

Stamp (1925) and terminologies were adopted and highland more or less open forest that for Thailand, Myanmar, and India (Samapuddhi seem to be relevant to the tropical seasonally 1957, Ogawa et al., 1961, Champion and Seth, dry forest but the scale of each forest type 1968) while those for Laos, Cambodia, and was not precisely indicated to realize the true Vietnam were recognized by Vidal (1960). area extent. These terminologies are still used today and The most up-to-date and probably the are well-known among the regional foresters most useful information on tropical seasonally as they reflect the physiognomy as well as the dry forest in Continental Southeast Asia was dominant tree species element clearly (Table compiled by the World Conservation Monitoring 1). An additional terminology for the forest Center and CIFOR (Iremonger et al., 1997) occurring along river courses or in depressions which included forest types, ecological at lowland altitudes was added gallery forest zones, total forest area cover, protected area (Ogawa et al., 1961) and the extremely open distribution, and population data of each deciduous dipterocarp type was called savanna country. It clearly shows that the dry forests by most geographers. in all countries in Continental Southeast Asia are predominated by and have been identified Tropical Seasonally Dry Forest Distribution as deciduous/semi-deciduous broadleaf forest in Continental Southeast Asia or as semi-evergreen moist broadleaf forest, Based on the definitions and terminologies with other forest types being less abundant. adopted for the region, there is no complete Among the nine ecological zones in the region, map of each forest type available for every the lowland sub-dry zone covers much of the country in Continental Southeast Asia. Each area with the dry zone being the next most country might have published its complete common. The forest area cover as well as set of vegetation map separately, for example, the protected area in each country vary and Thailand (RFD, 1962) and Myanmar (Gyi and are largest in Myanmar and least in Vietnam. Tint, 1998). For some particular forest type, Laos and Cambodia have almost identical such as deciduous dipterocarp forest, a map forest area cover. The protected forest area is showing its distribution in Thailand, Laos, largest in Thailand, followed by Cambodia, Vietnam, and Cambodia has been published but while it is least in Myanmar (Table 2). In the excluding Myanmar (see Blasco, 1983). The whole region, the protected forest area 11 % for recent article of Vidal (2000) on Indochinese deciduous and semi-deciduous forest and 19 % vegetation, with the exception of Myanmar, has for semi-evergreen moist broadleaf forest. As substantially shown a map indicating various the population in each country greatly affects forest types. However, these were classified forest utilization and conservation, the ratio under broad categories as lowland mixed of forest area cover to population reflects an deciduous, lowland dry deciduous dipterocarp important indicator for conservation planning. 62 Journal of Tropical Forest Research 1 (1) : 58-78 (2017)

Table 1 Nomenclature of seasonally dry forests in Continental Southeast Asia.

India and Thailand1,2 Myanmar3 Laos4 Myanmar5 Dry evergreen or Pyinkado/semi- Dense humide Tropical semi- seasonal evergreen evergreen forest semi-décidue evergreen forest rain forest or gallery forêt forest6 Mixed deciduous Moist teak, Mixte décidue Tropical moist forest or Monsoon dry teak, dry forêt deciduous forest forest deciduous without teak forest Deciduous dipterocarp Indaing Claire á Tropical dry or dry dipterocarp forest Dipterocarpacées deciduous forest forest (with exception forêt of a savanna named by geographer)

Notes: 1Samapuddhi (1957). 2Ogawa et al. (1961). 3Stamp (1925). 4 Vidal (1960). 5Champion and Seth. (1968). 6Occurrence of this forest type along the river course or on the depression area is called gallery forest (sensu Ogawa et al., 1961). Note that India is not included in Continental Southeast Asian countries.

Table 2 Forest area cover and population in Continental Southeast Asia1.

Forest area: Population Protected % of Forest area population Country (x1,000 forest area protected (Million ha) ratio (ha/10 people) (Million ha) area people) Thailand 17.11 59,414 2.88 5.13 30 Laos 12.97 5,020 25.81 1.78 14 Myanmar 45.95 47,513 9.67 0.56 1.2 Cambodia 11.64 10,530 11.05 2.99 26 Vietnam 5.01 76,161 0.66 0.50 10 Total 92.67 198,641 - 10.96 11.822 Notes: 1Modified from Iremongeret al. (1997). Data are as at 1996. 2Percentage of total forest area of all countries in the region and represent 11 % of deciduous and semi-deciduous broadleaf forest and 19 % of semi-evergreen moist broadleaf forest. Journal of Tropical Forest Research 1 (1) : 58-78 (2017) 63

Protected forest area in Thailand includes Irrawaddy River in Myanmar, the national park, wildlife sanctuary, forest park, Chao Phraya River in Thailand, and botanic garden, arboretum, and other specially the Mekong River bordering Thailand, assigned areas such as biosphere reserves and Laos, Vietnam, and Cambodia. some archeological sites scattered throughout As stated above, based on these climatic the country. As most areas are seasonally dry regimes together with edaphic conditions and forest, the percentage of protected area in this physiographic location, Thailand’s seasonally forest type is considerably high. However, dry forest has been identified into three main all forest area in Continental Southeast Asia forest types (Table 1). The recent published is classified by WCMC (1994) as one under information on the Myanmar and Cambodian the 25 hot spots of global biodiversity that is forest classifications has not used the same very species rich and very sensitive to human nomenclature as Thailand. The distribution of disturbance. the seasonally dry forest in Thailand is clearly in the upper latitudes beyond the southern Factors Affecting the Occurrence of Seasonally peninsula where it is the main landmass of Dry Forest in Continental Southeast Asia the country and represents approximately Climatic conditions: three-quarters of the country’s total land - Under the Monsoon climatic regime. area and is of considerable importance to the Being classified as Tropical savanna livelihood of a majority of the Thai population. climate of Köppen (Aw). These three main forest types are composed - High total rainfall but erratic monthly of many valuable tree species, with all of rainfall. these having contributed a great deal to the - Having definite wet and dry season. economic development of this country for Edaphic condition: centuries. Some important tree species are - Lithosols and latosols which are listed in Table 3. For example teak (Tectona poor in fertility status. grandis L.f.) was a major export timber from - Low water holding capacity. Thailand during the last century and also for - Shallow horizon of soil profile. Myanmar. However, the distribution of teak- Physiographic location: bearing forest is largest in India. It is also an - Above the 5º N latitude to approximately endemic tree species found particularly in 20ºN latitude but still within the mixed deciduous forest in countries in the northern belt of the tropical region. region while teak growing in Indonesia are - Most mountain ranges run in a thought to be non endemic and were probably north-south direction providing introduced there during the Hindu period (Gyi three major drainage systems: the and Tint, 1998). 64 Journal of Tropical Forest Research 1 (1) : 58-78 (2017)

Table 3 Major tree species in Seasonally Dry Forests of Thailand1.

Forest type Species Family Deciduous dipterocarp forest Euphorbiaceae intricatus D. tuberculatus ” D.obtusifolius ” Shorea obtusa ” S.siamensis ” S.roxburghii ” Pterocarpus macrocarpus Papilionoideae Sindora siamensis Caesalpinoideae Quercus kerrii Fagaceae Mitragyna rotundifolia Rubiaceae Morinda coreia „ Xylia xylocarpa Mimosoideae Seasonal evergreen rain forest Afzelia xylocarpa Caesalpinoideae Hopea ferrea Dipterocarpaceae H.odorata „ Shorea henryana „ Hydnocarpus ilicifolius Flacourtiaceae Memecylon ovatum Melastomaceae Lagerstroemia calyculata Lythraceae Parkia streptocarpa Mimosaceae Walsura trichostemon Meliaceae Mixed deciduous forest Tectona grandis Labiateae Pterocarpus macrocarpus Papilionoideae Terminalia mucronata Combretaceae Lagerstroemia calyculata Lythraceae Xylia xylocarpa Mimosoideae Note: 1Summarized from Smitinand (1977, 1980).

Present Status of Seasonally Dry Forest in shown and have remarkably high percentages Thailand as the former type dominates the northern and The most up-to-date statistics on the the latter the northeastern region. forest area in Thailand have been published Thailand is at the center of three by the Royal Forest Department, Ministry distributional zones; Himalayan, Indochinese, and of Agriculture and Cooperatives (Table 4). Malaysian elements. Plant species components Although the seasonally evergreen forest range from those called mangrove species growing type was not separately classified from the on mud flats in estuaries or along the coastal tropical evergreen forest type, the two main zone of both sides of the Thai peninsula to the seasonally dry forest types (mixed deciduous sub-tropical and alpine on high altitude and deciduous dipterocarp forest) are clearly mountains in the northern region (Santisuk, Journal of Tropical Forest Research 1 (1) : 58-78 (2017) 65

1988). Thailand is therefore considered to be sanctuaries and various recreational rich in plant species resources and having high sites. biodiversity. However, not all plant species in - Site of numerous endemic and rare mangrove forest grow in the seasonally dry plant species, and the genetic pool forest. Furthermore, although whole plant of several plant species. species components in the seasonally dry forest - Source of most valuable timbers, of Thailand have not yet been completely such as teak (Tectona grandis L.f.), identified, there are several notable landscape Dipterocarpus alatus, Hopea ferrea, diversity and numerous plant association types H. odorata, Pterocarpus macrocarpus, in each forest type of seasonally dry forest. Xylia xylocarpa var. kerrii in India, Tree species composition is also diverse and Myanmar, Thailand, and Laos. constitutes a mixture of various plant life forms - Similar ecological significance as the that result in relatively high species diversity. wet or humid forest type, particularly Many species are endemic, native, and some in countries with seasonal climatic are rare and probably extremely rare species conditions. deserving careful study and strict conservation. Many species play important roles in different Tropical Seasonally Dry Forest Utilization functions associated with environmental Studies to date on the utilization of the stabilization and human wellbeing. forest have emphasized direct forest products that have numerous uses, for example, timber Tropical Seasonally Dry Forest and People and wood products. Less study has been focused - Site of human settlement since on non-forest products and in particular, ancient times. information on utilization by the local people - Source of wood, food, fuel, fiber, is scarce. Among the few studies, a thorough medicinal plants, and non-wood investigation was conducted by Prachaiyo forest products. (2000) and presented a very interesting topic - The habitat for wildlife feeding on emphasizing the utilization of the tropical the ground and as shelter. seasonally dry forests by the local people in - Site for domesticated cattle. Northeast Thailand, whose local knowledge - Major component of watersheds and was comprehensive. Interested researchers on other protected or reserved forests this aspect can refer to this informative article. such as national parks, wildlife 66 Journal of Tropical Forest Research 1 (1) : 58-78 (2017)

Table 4 Thailand forest area distribution by region1.

N NE C E S % of total Total country Forest type M ha % M ha % M ha % M ha % M ha % M ha forest area Mixed deciduous 3.23 44.22 0.71 33.78 0.47 29.28 0.08 10.61 - - 4.49 34.42 Tropical 2.12 24.02 0.63 29.97 0.74 46.11 0.64 84.88 1.07 83.59 5.20 39.87 evergreen2 Deciduous 1.79 24.50 0.74 35.20 0.13 8.10 0.02 2.65 - - 2.68 20.55 dipterocarp Swamp - - 0.02 0.95 - - - - 0.06 4.69 0.08 0.61 Scrub 0.0002 0.003 ------0.0002 0.002 Pine 0.16 2.22 0.002 0.10 - - - - - 0.162 1.24 Bamboo 0.003 0.04 - - 0.26 16.20 0.001 0.07 - - 0.264 2.024 Mangrove - - - - 0.005 0.31 0.013 1.72 0.15 11.72 0.17 1.29 Total 7.305 100 2.102 100 1.605 100 0.754 100 1.280 100 13.044 100 % of total country forest 55.98 16.11 12.30 5.78 9.81 area3 Notes: 1Modified from RFD (2000). Para rubber plantation is excluded. 2Dry evergreen or seasonal evergreen rain forest and montane or hill evergreen forest are included in this forest type. 3Total forest area as at 1998 was 13.044 M ha and 25.42 % of total country land area.

Ecological Studies on Tropical Seasonally and were oriented toward timber exploitation. Dry Forest: A Case Study in Thailand Subsequently from 1964 onward, Japanese Ecological studies on seasonally dry ecologists and Thai collaborators published forest in Thailand substantially appeared in several ecological studies on Thai forests the scientific literature during the 1960s being (Ogawa et al., 1965a; 1965b, Ogino et al., pioneered by the work of Ogawa et al. (1961) 1964, Kira et al., 1967, Yoda, 1967). These in which quantitative community analysis studies expanded the horizon for Thai forest focused on all the dominant forest types in ecological research as well as representing the Thailand. Before then, there had been numerous earliest and most significant Thai-Japanese studies on Thai plants by some renowned Thai cooperative research projects. In particular, as well as overseas botanists that contributed these studies set the fundamental research to the species composition of each forest type methodologies for ecosystem studies so being well known in other fields of forest far carried out in this region. Later Thai science and helpful for past and present day investigators and some overseas researchers have ecological studies. Most studies in that period undertaken their own studies independently as were directly for forest management purposes well as collaboratively and these studies have Journal of Tropical Forest Research 1 (1) : 58-78 (2017) 67 expanded to cover various aspects. Examples working in RFD at that time (Sakulmeerit, of Thai research initiatives in ecological personal communication). The large scale research in seasonally dry forests include the and long term study plots in other forest types 52 stands of deciduous dipterocarp and 34 were subsequently enlarged to cover a wider stands of mixed deciduous forests subjected area, for example in Huay Kha Kaeng Wildlife to extensive studies throughout Thailand in Sanctuary and in Doi Inthanon National Park 1975-1976 (Sukwong et al., 1976; 1977). in which 50 and 15 ha plots were set up in One Thai-Japanese collaborative ecological seasonally dry forest and montane forest, study carried out during 1976 that included respectively, and these studies are ongoing, some seasonally dry forest stands scattered in though the details of these studies are beyond North and Northeast Thailand apart from those the scope of this paper. carried out collaboratively between Japanese A recently published paper representing and Indonesian ecologists was published in a long-term Thai-Japanese collaborative 1989 (Yamakura et al., 1989). The author ecological study, particularly in MDF of independently studied the dynamics of seasonal western Thailand was initiated in 1992 (Marod evergreen rain forest by setting up a single, 1 et al., 1999). This study included the roles of ha square plot and in deciduous dipterocarp bamboo undergrowth and fire on the structural forest setting up four, 1 ha square plots in the dynamics of that forest and examined the Sakaerat Biosphere Reserve, Northeastern effects of drought on the phonological events Thailand since 1982 and 1984 that have been of some major tree species (Marod et al., continuously monitored for 19 and 17 years, 2002).These studies demonstrated a good respectively (Sahunalu and Dhanmanonda, example of a long-term, large-scale plot (4 1995, Sahunalu, 2001a, b, Sahunalu, 2004a, ha) manipulated as an elaborate, educational b, Sahunalu, 2009a, b, c, d, 2010 a, b, c, d). venture between two counterparts in TSDF of These studies represent the longest term study CSEA. Nevertheless, there were other similar in large scale plots ever undertaken in Thailand joint research activities undertaken in other as there were no other studies carried out in forest types outside the TSDF in Thailand such permanent plots larger than 1 ha in Thailand as those in mangrove, swamp, and montane and elsewhere during that period. Later Kanzaki or hill evergreen forest. et al. (1995) established a substantially larger Deforestation in the form of slash and plot as a 2. 6 ha belt in the seasonal evergreen burn farming was investigated in another Thai- forest in the same area and this continues to be Japanese collaborative study, particularly in monitored today. However, the author’s studies the mixed deciduous and seasonal evergreen did not include the mixed deciduous forest rain forest ecotone in the Namphrom area, as research on this forest type was claimed Northeast Thailand (Kyuma and Pairintra, 1983) to have been undertaken by some foresters where a group of forest ecologists carried out 68 Journal of Tropical Forest Research 1 (1) : 58-78 (2017) a detailed study on the forest, felling, burning, more detail on each subject from the literature and regeneration as a part of research project cited and listed in this paper. The current (Tsutsumi et al., 1983). Prior to this study, investigations and ongoing research topics Sahunalu et al. (1979) had made an extensive as well as unpublished post-graduate theses study of three forest types in the area where and other forest science researches are not seasonally dry forest widely predominated dealt with here. Attempts have been made to and was found to be seriously disturbed by the identify each topic into three main categories: slash and burn farming of the local inhabitants. ecosystem analysis, ecosystem function, and These were all major contributions by the Thai- miscellaneous aspects. Each category is sorted Japanese collaborative research on seasonally into the various topics so far investigated dry forest ecosystem in Thailand during the in the three main forest types and locations past four decades. There has been some other in Thailand and considered to be related to collaborative research activity but not entirely ecological research (Table 5). Some articles carried out in the seasonally dry forest of this that have been omitted or are not sufficiently country; for instance, wasteland rehabilitation listed here can be referred to at least in the two that involved several kinds of degraded forest papers presented by Rundel and Boonpragob resulting from some deforestation practices, (1995) and Bunyavejchewin et al. (2011). with sites scattered in South, West, Northeast, It has been clearly demonstrated that and North Thailand (Yoda and Sahunalu, there is insufficient detail in each category and 1991). These studies are not dealt with here the gaps in knowledge are relatively numerous. although they are important examples of Each particular topic also has some more detail ecological research collaboration between the to be elucidated if the contents of these published two countries’ counterparts. research results are closely overviewed. The In this paper, only the topics of each opportunity for further research is therefore category of ecological studies are pointed out wide open for all researchers who have a keen and listed for each forest type and location in interest in ecological study in tropical seasonally Thailand. Interested investigators can examine dry forests, particularly in Thailand. Journal of Tropical Forest Research 1 (1) : 58-78 (2017) 69

Table 5 Ecological studies on tropical seasonally dry forests: Case studies in Thailand.

Forest type/location Seasonal Deciduous Category/topic Mixed deciduous evergreen rain dipterocarp forest forest forest A. Community analysis 1. Structure and floristic or species Pingkong1 Namphrom2 Pingkong1 composition Namphrom2 Sakaerat4 Namphrom2 Doi Inthanon3 - Doi Inthanon3 - - Sakaerat5 2. Mosaic structure - Sakaerat6 - 3. Vegetation pattern - Sakaerat7 - 4. Community dynamics Maeklong WS32 - Sakaerat5,8 5. Species diversity Namphrom2 Namphrom2 Namphrom2 Doi Inthanon3 Sakaerat4 Sakaerat5,9 B. Ecosystem function 1. Biomass production Pingkong1 Namphrom10 Pingkong1 - Sakaerat11 Sakaerat11 52 stands12 2. Litter production Lampang13 Namphrom10 Sakaerat17 - Sakaerat14,15,16 Nongteng18 3. Biomass increment - Namphrom10 Sakaerat11 - Sakaerat11 - 4. Net primary production - Namphrom10 Sakaerat11 - Sakaerat11 52 stands12 5. Community respiration Pingkong19 - Pingkong19 - - 52 stands12 6. Gross primary production - - 52 stands12 7. Nutrient cycling - Namphrom10 Sakaerat20 C. Miscellaneous 1. Nutrient use efficiency - Sakaerat21 - 2. Soil properties Doi Chiangdao22 Sakaerat23 Sakaerat23 3. Forest fire - - Sakaerat24 - - Khao Nangram24 - - Ban Huad24 4. Relative illuminance - Sakaerat25 - 5. Variation in flora along the transect - Sakaerat26 Sakaerat26 6. Phenology Maeklong WS33 - Sakaerat27 7.Growth of tree species - - Sakaerat28 8. Species distribution on limestone hill Lampang29 - - 70 Journal of Tropical Forest Research 1 (1) : 58-78 (2017)

Table 5 (Content) Forest type/location Seasonal Deciduous Category/topic Mixed deciduous evergreen rain dipterocarp forest forest forest 9. Leguminosae trees species in - Sakaerat30 deciduous dipterocarp forest - & various other locations 10. Soil and plant relationships - - Sakaerat31

Notes: Figures above each location refer to list of references below. 1Ogawa et al. (1965a, b). 2Sahunalu et al. (1979).3Teejuntuk et al. (2002).4Sahunalu (2001a) and Visarat et al. (1984a). 5Sahunalu (2009a,b,c,d,2010a,b,c,d) and Dhanmanonda and Sahunalu (1988).6Kanzaki et al. (1995).7Bunyavejchewin (1986). 8Sahunalu and Dhanmanonda. (1995). 9Sahunalu (1995, 1996, 1998, 1999a, b). 10Tsutsumi et al. (1983) and Prachaiyo et al. (1980).11Ogino et al. (1964, 1967). 12Sahunalu and Jamroenpruksa. (1980) and Sahunalu (1994a). 13Thaiutsa et al. (1978). 14Sahunalu (2004a, b). 15Chinsukjaiprasert et al. (1984) and Bunyavejchewin (1997). 16Chunkao and Boonyawat. (1980). 17Paovongsa (1976). 18Wacharinrat (2000). 19Yoda (1967). 20Sahunalu and Jamroenpruksa (1980) and Sahunalu (1994). 21 Sahunalu (2004b, c). 22Khemnark et al. (1972). 23Sakurai et al. (1998). 24 Stott (1986). 25Yoda et al. (1983) and Visarat et al. (1984b). 26Sabhasri et al. (1968). 27Sukwong et al. (1975). 28Sukwong (1982). 29 Sukwong and Kaitpraneet. (1975). 30Sahunalu (1994b, 1997a, b, 1999a, b). 31Sahunalu et al. (1980, 1991, 1993). 32Marod et al. (1999). 33Marod et al. (2002). Only two post-graduate theses were referred to here.

Future Prospects and Research Needs in protected areas and their surroundings must be Tropical Seasonally Dry Forest fully and intensively studied as a whole. This Tropical seasonally dry forest still needs to be recognized widely and demands remains important as does wet or tropical urgent attention. Some important points of rain forest and will be attractive for future interest and for which there is still a lack of research. In particular, it serves as a valuable comprehensive information have emerged from the author’s viewpoint, especially in the natural resource for a large number of people three main seasonally dry forests of Thailand in Continental Southeast Asia. It has equal and these are outlined as follows: importance for conservation as for research through the exploration and gaining of deep Community structure and species composition: knowledge on future exploitation and the - Undergrowth or forest floor vegetation formulation of the conservation strategy. It is including vines and climber vegetation especially crucial for maintaining and restoring - Variation in plant life-forms distribution species diversity in this important forest type. and contribution to species diversity The management of protected areas in the Community productivity: 21st and successive centuries will not only - Belowground or root biomass involve the forest area under current control estimation but also management of the forest ecosystem in - Net primary production of various which all components of the ecosystem in the community types Journal of Tropical Forest Research 1 (1) : 58-78 (2017) 71

- Litter production of various community - Minor and non-wood forest products types - Commonness, rarity, and endemism - Community carbon sequestration, in the three forest types circulation, and preservation of three All these proposed aspects of future forest types research have been derived from the author’s Community nutrient cycling: thorough examination of the contents of the - Nutrient cycling of various community references discussed and are thought to have types been ignored or included in such little detail - Decomposition rate of dead plant and so need to be elucidated to gain more parts and litter of various community knowledge on seasonally dry forest ecology, types especially in Thailand. All researchers in this - Soil respiration, fine root distribution, academic society are sincerely welcomed and dynamics in the three forest and all protected forests in Thailand have types facilities that are relatively comfortable and Miscellaneous and related subjects: there are accessible educational and research - Phenology: flowering, fruiting, seed sites in every region throughout the country. production, seed dispersal, seed Moreover, trans-boundary research projects bank, leafing, and growth of tree among neighboring countries using Thailand species as a center are also encouraged to gain more - Soil fauna in the three forest types collaborative academic activities, sharing, and - Fire effects on the three forest types exchanging of experiences and information - Human impacts: shifting cultivation, as well as creating comparative studies on grazing, exploitation, and land-use the regional seasonally dry forests. As five - Secondary forest studies, and countries are on the Continental Southeast Asia regeneration and succession processes region and presently enjoying close cooperation - Rehabilitation and restoration of the under the ASEAN Economic Community degraded forests in the three forest (AEC) agreement, academic collaboration in types this field of study can provide mutual benefit - Ecophysiological studies: drought among them all. response, seedling establishment under adverse condition, water use, REFERENCES and water use efficiency of the three Beard, J.S. 1955. The classification of tropical forest types America vegetation types. Ecology - Plant-animal-microorganism 36: 89-100 interactions: micorrhizae, rhizobia, Blasco, F. 1983. The transition from open forest herbivories, pollinators etc. in the three forest types to savanna in Continental Southeast - Ethnobotany and local indigenous Asia. pp.167-181. In: Bourliere, F. knowledge (ed.). Ecosystems of the World 13. - Paleobiology and palaeoecology Tropical Savannas. Elsevier. Amsterdam. 72 Journal of Tropical Forest Research 1 (1) : 58-78 (2017)

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