Soil nutrient status after bamboo flowering and death in a seasonal tropical forest in western Thailand

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.     

The effects of drought and fire on seed and seedling dynamics in a tropical seasonal forest in Thailand

Seed production and seedling dynamics were studied for 6 years(1992–1997) with particular emphasis on the effects of the drought andfire in a natural tropical seasonal forest at Mae Klong Watershed ResearchStation, Kantchanaburi, western Thailand. The number of seed produced andemerged seedlings varied greatly among years and species. Most tree speciesproduced very few seeds in 1994 and many in 1995 and 1996, particularly,Shorea siamensis Miq. which displayed the most seedinghabit. Some seedlings, Shorea, Dipterocarpus alatus Roxb.,and Dipterocarpus turbinatus Gaertn. f., emerged at theendof the dry season (late April, after the first rain but when soils still have alow soil moisture content), while the majority of seedlings emerged at thebeginning of the rainy season. After a fire disturbed the plot in April 1996,many species increased their seedling emergences, especially Berryaammonilla. Seedlings of most species less than a year old showed arelatively low mortality in the rainy season, but those ofPterocarpusmacrocarpus Kurz had high mortality. The mean survival rate for allseedling species in this forest was quite low (24.1% y^–1), anddifferent values existed for the rainy and the dry season (11.5, and 6.1%month^–1, respectively). This suggests that different specieshave adaptations related to the season of seedling emergence and resistance todrought in this tropical seasonal forest community. The traits of tree speciesare classified in terms of their traits in the early stages of regeneration;seed and/or seedling bank, resprouting, and drought resistance. Most specieshave adapted to fire and/or drought by resprouting, seed bank, and/or seedlingbank, although the few species which occur mainly in mesic evergreen forestshave less adapted to these environments. The demographic variations in seed andseedling stages may contribute to the coexistence of these species in thisspecies-rich dry tropical forest.     

The ecology of conifer persistence in tropical rainforests: Podocarpus neriifolius in northern Thailand

Plant Ecology - A range of hypotheses seek to explain why conifers are infrequent in tropical rainforests. Here, we explore how the conifer, Podocarpus neriifolius, persists at low density in...     

Effects of drought and fire on seedling survival and growth under contrasting light conditions in a 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.     

Structural dynamics of a natural mixed deciduous forest in western Thailand

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.     

Effects of El Niño drought on seedling dynamics in a seasonally dry tropical forest in Northern Thailand

As El Niño is predicted to become stronger and more frequent in the future, it is crucial to understand how El Niño-induced droughts will affect tropical forests. Although many studies have focused on tropical rainforests, there is a paucity of studies on seasonally dry tropical forests (SDTFs), particularly in Asia, and few studies have focused on seedling dynamics, which are expected to be strongly affected by drought. Seedlings in SDTFs are generally more drought-tolerant than those in the rainforests, and the effects of El Niño-induced droughts may differ between SDTF and tropical rainforests. In this study, we explored the impact of El Niño-induced drought at an SDTF in northern Thailand by monitoring the seedling dynamics at monthly intervals for 7 years, including a period of strong El Niño. The effects were compared between two forest types in an SDTF: a deciduous dipterocarp forest (DDF), dominated by deciduous species, and an adjacent lower montane forest (LMF) with more evergreen species. El Niño-induced drought increased seedling mortality in both the forest types. The effect of drought was stronger in evergreen than in the deciduous species, resulting in higher mortality in the LMF during El Niño. However, El Niño increased seedling recruitment only in the DDF, mainly because of the massive recruitment of the deciduous oak, Quercus brandisiana (Fagaceae), which compensated for the mortality of seedlings in the DDF. As a result, El Niño increased seedling density in the DDF and decreased it in the LMF. This is the first long-term study to identify the differences in the impacts of El Niño on seedlings between the two forest types, and two leaf habits, evergreen and deciduous, in Southeast Asia. Our findings suggest that future climate change may alter the species composition and spatial distribution of seedlings in Asian SDTFs.