Abstract. Structural dynamics of a natural tropical seasonal – mixed deciduous – forest were studied over a 4‐yr period at Mae Klong Watershed Research Station, Kanchanaburi Province, western Thailand, with particular reference to the role of forest fires and undergrowth bamboos. All trees > 5 cm DBH in a permanent plot of 200 m × 200 m were censused every two years from 1992 to 1996. The forest was characterized by a low stem density and basal area and relatively high species diversity. Both the bamboo undergrowth and frequent forest fires could be dominant factors that prevent continuous regeneration. Recruitment, mortality, gain (growth of survival tree plus ingrowth) and loss in basal area (by tree death) during the four years were 6.70%/yr, 2.91%/yr, 1.22%/yr and 1.34%/yr, respectively. Mortality was size dependent; middle size trees (30–50 cm) had the lowest mortality, while the smallest (5–10 cm) had the highest mortality. Tree recruitment was observed particularly in the first two years, mostly in the area where die‐back of undergrowth bamboo occurred. The bias of the spatial distribution of recruitment to the area of bamboo die‐back was significant and stronger than that to the forest canopy gaps. Successful regeneration of trees which survive competition with other herbs and trees after dieback of bamboo could occur when repeated forest fires did not occur in subsequent years. It is suggested that both the fire disturbance regime and bamboo life‐cycle greatly influence the structure and dynamics of this seasonal tropical forest.

Question: How do tree seedlings differ in their responses to drought and fire under contrasting light conditions in a tropical seasonal forest? Location: Mae Klong Watershed Research Station, 100–900 m a.s.l, Kanchanaburi Province, western Thailand. Method: Seedlings of six trees, Dipterocarpus alatus, D. turbinatus, Shorea siamensis, Pterocarpus macrocarpus, Xylia xylocarpa var. kerrii and Sterculia macrophylla, were planted in a gap and under the closed canopy. For each light condition, we applied (1) continuous watering during the dry season (W); (2) ground fire during the dry season (F); (3) no watering/no fire (intact, I). Seedling survival and growth were followed. Results: Survival and growth rate were greater in the gap than under the closed canopy for all species, most dramatically for S. siamensis and P. macrocarpus. Dipterocarpus alatus and D. turbinatus had relatively high survival under the closed canopy, and watering during the dry season resulted in significantly higher survival rates for these two species. Watering during the dry season resulted in higher growth rates for five species. All seedlings of D. alatus and D. turbinatus failed to re‐sprout and died after fire. The survival rates during the dry season and after the fire treatment were higher for the seedlings grown in the canopy gap than in the shade for S. siamensis, P. macrocarpus, X. xylocarpa var. kerrii and S. macrophylla. The seedlings of these species in the canopy gap had higher allocation to below‐ground parts than those under the closed canopy, which may support the ability to sprout after fire. Conclusions: The light conditions during the rainy season greatly affect seedling survival and resistance to fire during the subsequent dry season. Our results suggest differentiation among species in terms of seedling adaptations to shade, drought and fire.

We have examined the surface (0-10 cm) soil characteristics of sites after bamboo (Cephalostachyum pergracile) mass flowering and death (DB sites) in comparison with sites with living bamboo (Bambusa tulda) (LB sites) in a seasonal tropical forest in Thailand.One year after bamboo flowering the DB sites were acidic with lower concentrations of exchangeable Ca and Mg and soil nitrogen than the LB sites. Therefore, although leaf and root litter of the dead bamboo was deposited in the DB sites after bamboo flowering, soil nutrient status decreased.

No abstract

No abstract

Soil respiration is a carbon flux that is indispensable for determining carbon balance despite variations over time and space in forest ecosystems. In Kanchanaburi, western Thailand, we measured the soil respiration rates at different slope positions-ridge (plot R), upper slope (plot U), and lower slope (plot L)-on a hill in a seasonal tropical forest [mixed deciduous forest (MDF)] to determine the seasonal and spatial variations in soil respiration on the slope. The heterotrophic (organic layer and soil) and autotrophic (root) respiration was differentiated by trenching. Soil respiration rates showed clear seasonal patterns: high and low rates in rainy and dry seasons respectively, at all plots, and tended to decrease up the slope. Soil respiration rates responded significantly to soil water content in the 0-30 cm layer, but the response patterns differed between the lower slope (plot L) and the upper slope (plots R and U): a linear model could be applied to the lower slope but exponential quadratic models to the upper slope. The annual carbon dioxide (CO 2 ) efflux from the forest floor was also associated with the slope position and ranged from 1908 gC m À2 year À1 in plot L to 1199 gC m À2 year À1 in plot R. With ascending position from plot L to R, the contribution of autotrophic respiration increased from 19.4 to 36.6% of total soil respiration, while that of the organic layer decreased from 26.2 to 9.4%. Mineral soil contributed to 46.3 to 54.4% of the total soil respiration. Soil water content was the key factor in controlling the soil respiration rate and the contribution of the respiration sources. However, the variable responses of soil respiration to soil water content create a complex distribution of soil respiration at the watershed scale.

No abstract

Siri S, Ponpituk Y, Safoowong M, Marod D, Duengkae P. 2019. The natural forest gaps maintenance diversity of understory birds in Mae Sa-Kog Ma Biosphere Reserve, northern Thailand. Biodiversitas 20: 181-189. We compared the species composition and feeding guilds between under closed canopies and forest gaps in the low-elevation montane evergreen forest in Mae Sa-Kog Ma Biosphere Reserve. Monthly mist netting was used to capture birds from January 2015 to December 2017. In total, 958 individual birds belonging to 65 species were captured over 25,920 sampling hours. Of the total number of birds, 475 were from 51 species (Shannon-Wiener index: H' 2.974) under closed canopies and 483 were from 47 species (H' 2.985) in forest gaps. The number of bird species in gaps increased rapidly and constantly through 1 year following gap creation. Forest gap localities contained 48% of the understory birds in the area. Foliage–gleaning insectivores were the dominant bird feeding guild in both areas. Some species such as Erythrura prasina is a nomadic bird were found on first year of the forest gap only. Overall, we found that the forest gaps created by natural disturbances in the Mae Sa-Kog Ma Biosphere Reserve had no negative impact on the diversity of understory bird communities. The natural forest gap are created by intermediate disturbance promotes a relatively high biodiversity of birds in the ecosystem.