J. Agrofor. Environ. 5 (special issue): 89-93, 2011 ISSN 1995-6983 Forest structure and species composition of seasonal flood forest along the Se Buy River in Yasothon Province, Northeast Thailand R. Yoneda1, S. Poungparn2, M. Sano3, R. Tabuchi4, P. Patanaponpaiboon2 1Bureau of International Partnership, Forestry and Forest Products Research Institute, (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki 305-8687, 2Faculty of Science, Chulalongkorn University, Bangkok 10900, Thailand, 3Department of Forest Management, Forestry and Forest Products Research Institute, (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki 305-8687 4Forestry Division, Japan International Research Center for Agricultural Sciences (JIRCAS), 1-1 Owashi, Tsukuba, Ibaraki 305-8686, Japan, E-mail: [email protected] (e-maill address of lead author) Abstract: The structure and topography of seasonal flood forest, where was inundated from August to October, was studied at the Se Buy river in Yasothon Province, Northeast Thailand. Tree census has been conducted since 2005. Five hundred and ninety three trees and climbers were recorded and 70 species were identified in the 30m × 150m plot. Stand density, total basal area and the mean diameter at breast height (DBH) were 1317.8 trees/ha, 23.61m2/ha and 11.32cm, respectively. Mallotus thorelii (Euphorbiaceae), Garcinia schomburgkiana (Guttiferae), Hymenocardia punctata (Euphorbiaceae), Dipterocarpus alatus (Dipterocarpaceae) and Vatica harmandiana (Dipterocarpaceae) were abundant species in the plot. Riparian zone forest locating adjacent to the river was inundated for approximately 3 months, and consisted by small DBH trees of M. thorelii, G. schomburgkiana and H. punctata. Seasonal flooding might disturb the riparian zone frequently, and riparian zone forest consisted by pioneer species. Upper part of the plot, where was rarely flooded by special large flow, was mostly consisted by large DBH trees of Irvingia malayana (Irvingiaceae) and Shorea roxburghii (Dipterocarpaceae). Thus, elevation and flooding period would affect the species composition and consequently the dynamics of seasonal flood forest. Key words: Seasonal flood forest, species composition, inundated period, Thailand. Introduction Swamp forests provide source of nutrients to terrestrial monsoon. Forest type is typically Dry Dipterocarp Forest and aquatic organisms. Some studies have reported the (DDF) and Mixed Dipterocarp Forest (MDF). importance of relationships between freshwater fish and A research plot was established from river to inland. The seasonally inundated vegetation. In the tropics, fish - size of the plot was 30m × 150m, and divided into 10m × forest relationships in Amazon River Basin have been 10m subplot. All trees having more than 4cm in DBH studied (Gottsberger, 1978; Kubitzki and Ziburski, 1994; were mapped, tagged, identified, and measured the DBH. Saint-Paul et al., 2000). In Southeast Asia, many Topography of the plot was surveyed by surveying freshwater fish were known to feed on forest fruits and compass. The elevation increased with the distance from other seasonally flooded vegetation (Roberts, 1993; Baird, river line and the difference between the lowest and the 2007). Thus, seasonal flood vegetation is important for highest ground height was approximately 8m (Fig. 2). terrestrial and aquatic ecosystem. A seasonal flood regime Water level logger (HOBO; U20-001) was set in the has a great impact on the vegetation. Inundation period lowest level of the research plot to record the water level might affect seed germination and seedling establishment. during flooded period. The measurement was conducted Litter amount might be also different in seasonal flood in 2007 and 2009. forest because flooding and drying out leads to change microbial activity in the soil (Neill, 1995). A number of researches on forest vegetation have been conducted in Thailand since 1950’s (Ogawa et al., 1961, 1965; Royal Forest Department, 1962). Some of them studied the relationship between the local distribution of tree species and topography in major forest types (Bunyavejchewin et al., 2003; Sri-Ngernyuang et al., 2003). However, only few researches have done in the seasonal flood forest in Thailand. In this study, pattern of tree distribution, and species composition were studied in a seasonally flood forest in Northeast Thailand. Materials and methods The studies were conducted at a seasonal flood forest along to the Se Buy River in Nakae village, Khum Khuang Kaew District, Yasothon Province, Northeast Thailand o o (15 35’ N, 104 27’ E) (Fig. 1). The mean precipitation in Yasothon province is approximately 1600mm/y (Kono et al., 1994). A rainy season occurs from May to October during the southwest monsoon, followed by a dry season from November to April affected by the northeast Fig. 1. Location of the study site River Y軸 100 110 120 130 140 150 10 20 30 40 50 60 70 80 90 0 0 0 8 7 10 0 4 X軸 1 3 0 5 2 8 7 6 20 0 0 0 0 30 Fig. 2. Illustration of topography of the research plot Results puncutata (Euphorbiaceae) were abundant in this plot. Stand structure and species composition: Five hundred These three species accounted for 35% of total tree and ninety three trees and climbers were recorded in the number and 17% of total basal area. Dipterocarpus alatus plot. Within them, 70 species of 30 families were (Dipterocarpaceae), Syzygium sp. (Myrtaceae) and Irvingia identified. Stand density, the mean DBH and total basal malayana (Irvingiaceae) showed high mean DBH and area were 1318 trees/ha, 11.3cm and 23.6m2/ha, basal area. Basal area of these three species accounted for respectively (Table 1). Mallotus thorelii (Euphorbiaceae), 45% of total basal area. Garcinia schomburgkiana (Guttiferae) and Hymenocardia Table 1. Number of trees, density, basal area and mean DBH of the 15 common species in research plot. Number Density Mean DBH Basal Area Species Family of trees [trees/ha] [cm] [m2/ha] Mallotus thorelii Euphorbiaceae 107 237.8 8.13 1.36 Garcinia schomburgkiana Guttiferae 52 115.6 12.67 1.79 Hymenocardia punctata Euphorbiaceae 50 111.1 9.01 0.78 Dipterocarpus alatus Dipterocarpaceae 31 68.9 26.39 4.82 Vatica harmandiana Dipterocarpaceae 28 62.2 10.91 0.69 Melodorum fruticosum Annonaceae 19 42.2 12.36 0.67 Byttneria echinata Sterculiaceae 18 40.0 7.22 0.18 Syzygium spp. Myrtaceae 18 40.0 22.81 3.39 Melodorum siamensis Annonaceae 17 37.8 6.10 0.12 Dalbergia foliaceae Leguminosae-Papilionoideae 16 35.6 6.68 0.13 Barringtonia acutangula Lecytidaceae 15 33.3 10.93 0.49 Irvingia malayana Irvingiaceae 12 26.7 20.12 2.38 Terminalia cambodiana Combretaceae 12 26.7 9.66 0.24 Shorea roxburghii Dipterocarpaceae 11 24.4 25.04 1.27 Cinnamomum porrectum Lauraceae 10 22.2 10.18 0.22 Other 177 393.3 9.76 5.07 Total 593 1317.8 11.32 23.61 The pattern of diameter distribution for all trees showed a D. alatus, had different distribution pattern with less reverse-J shaped (Fig. 3) That of the abundant tree species frequency of saplings. (M. thorelii, G. schomburgkiana and H. puncutata) also Water level and flooded duration: Mean inundated days showed the reverse-J shaped pattern (Fig. 4). Syzygium sp. in 2007 and 2009 were in a range of 0-83 days (Table 2). and I. malayana had a discontinuous diameter distribution It was obvious that number of inundated days decreased with many small DBH trees. Syzygium sp. and I. with increasing ground level. The highest water level was malayana had the same distribution pattern to the recorded at 6.2m in which means that the river flow came abundant species. One of the abundant species in this plot, up to 6.2m of relative ground height. Then, approximately 70% of the plot area was inundated. The mean flooded 90 period at the highest (6.2m) and lowest point (0 - 0.1m) were 1.5 hours and 91days, respectively. 350 300 250 200 150 Number of trees 100 50 0 0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 DBH [cm] Fig. 3. Diameter distribution of all trees in the plot. 70 20 25 60 Mallotus thorelii Garcinia schomburgkiana Hymenocardia wallichii 15 20 50 40 15 10 30 10 Frequency Frequency Frequency 20 5 5 10 0 0 0 0 12 24 36 48 60 72 84 96 0 12 24 36 48 60 72 84 96 0 12 24 36 48 60 72 84 96 DBH [cm] DBH [cm] DBH [cm] 10 10 10 Syzygium sp. Irvingia malayana 8 8 8 Dipterocarpus alatus 6 6 6 4 4 4 Frequency Frequency Number Number of trees 2 2 2 0 0 0 0 12 24 36 48 60 72 84 96 0 12 24 36 48 60 72 84 96 0 12 24 36 48 60 72 84 96 DBH [cm] DBH [cm] DBH [cm} Fig. 4. Diameter distribution of six tree species in the plot. Species composition and ground level: To compare the 15.00 ± 1.56 and 14.06 ± 1.05cm (Table 3). It was species composition and inundation period, we divided the remarkable that the stand density decreased with plot into three zones based on ground level which were increasing the ground level. The mean DBH of the trees ranged from 0 to 3m (zone I), 3 to 6m (zone II) and more in zone I was smaller than that of zone II and III. Zone I than 6m of ground level (zone III), respectively. forest showed relatively high density with small DBH Respectively for each of zones, the stand density was trees. On the contrary, zone III forest had low density 1553, 1244 and 942 trees/ha, mean DBH was 9.48 ± 0.36, with large-size trees. 91 Table 2. Mean inundated days at the each elevation in the generally distributed in the zone I (Table 4).