Natural disturbance and soils drive diversity and dynamics of seasonal dipterocarp forest in Southern Thailand

Abstract

In 2000, we established a 24-ha plot in Peninsular Thailand to investigate how forest composition, structure and dynamics vary with spatial heterogeneity in resource availability. Detailed soil and topographic surveys were used to describe four edaphic habitats in the plot. Disturbance history was inferred from historical records and floristic analysis. The plot included >119 000 trees ≥1 cm dbh in 578 species, and was recensused in 2010. Species distributions, floristic turnover, stand structure, demographic rates and biomass dynamics were strongly influenced by heterogeneity in soils, topography and disturbance history. Over 75% of species were aggregated on specific edaphic habitats leading to strong compositional turnover across the plot. Soil chemistry more strongly affected species turnover than topography. Forest with high biomass and slow dynamics occurred on well-drained, low fertility ridges. The distribution and size structure of pioneer species reflected habitat-specific differences in disturbance history. Overall, above-ground biomass (AGB) increased by 0.64 Mg ha−1 y−1, from 385 to 392 Mg ha−1, an increase that was entirely attributable to recovery after natural disturbance. Forest composition and stand structure, by reflecting local disturbance history, provide insights into the likely drivers of AGB change in forests. Predicting future changes in tropical forests requires improved understanding of how soils and disturbance regulate forest dynamics.

ForestGEO: Understanding forest diversity and dynamics through a global observatory network

“…6). This finding, first documented on BCI and several plots in Asia (Condit et al, 2000;Harms et al, 2001), has now been confirmed in many plots across the network (Davies et al, 2005;Gunatilleke et al, 2006;Lai et al, 2009;Chuyong et al, 2011;Lan et al, 2012;Bunyavejchewin et al, 2019). With the obvious exception of the distribution of pioneer species in relation to light gaps, the details of what specific resource requirements, e.g., water availability, soil nutrients, wind exposure, constrain species distributions across these topographic and edaphic gradients remains poorly understood, as many factors covary (John et al, 2007;Baldeck et al, 2013;Kupers et al, 2019).…”

“…Analyzing the dynamics of over 4000 species in 12 ForestGEO FDPs, the largest and most comprehensive sample of species-level population dynamics from tropical forests across Africa, Asia and the Americas, found that the abundance of a majority of species is increasing or decreasing more than expected under a neutral model of community change. Natural disturbances, including fires, landslides, droughts, and hurricanes are a major cause of temporal fluctuations in species composition on decadal timescales in many tropical forests (Hubbell and Foster, 1992;Hogan et al, 2018;Bunyavejchewin et al, 2019). Species-level studies across many ForestGEO FDPs have demonstrated differential sensitivity to drought (e.g., Condit et al, 1995;Engelbrecht et al, 2007;Itoh et al, 2012;Zuleta et al, 2017).…”

Increasing calcium scarcity along Afrotropical forest succession

“…As such, these results reiterate that more work (including more elements and more regions) is needed to fully develop a thorough biogeochemical understanding of this biome. Indeed, as many tropical regions beside central Africa exhibit similar extremely low Ca concentrations (Borneo 53 , southern Thailand 54 and the central Amazon 55 ), there is no reason why Ca limitation could not be widespread on old, deeply weathered land surfaces.…”

Individual tree damage dominates mortality risk factors across six tropical forests

“…Being at lower elevations than the average for a given species was associated with a higher risk of mortality than being at higher elevations. Variation in below‐ground resources, in contrast with light limitation, is largely determined by topography and leads to variation in individual‐level performance among topographically defined habitats (Bunyavejchewin et al ., 2019; Zuleta et al ., 2020). Although lower elevation locations or valleys are generally wetter than slopes or ridges, trees in valleys face flooding more frequently (Margrove et al ., 2015; Moser et al ., 2019) and are sensitive to extreme water shortage because they tend to prioritise efficient water transport over hydraulic safety (Cosme et al ., 2017; Zuleta et al ., 2017).…”