Regeneration changes in tree species abundance, diversity and structure in logged and unlogged subtropical rainforest over a 36-year period

Abstract

The long-term effects of logging treatments on rainforest regeneration are difficult to quantify due to compounding interactions with natural dynamics, site characteristics and tree species. The aim of this study was to examine regeneration differences over a 36-year period in stands subjected to various levels of disturbance ranging from natural, through an increasing intensity of individual tree removal to intensive logging. Multivariate and univariate analyses of trees !10 cm diameter at 1.3 m above the ground (dbh) showed that regeneration responses were generally correlated with disturbance gradient. In the undisturbed controls there were gradual changes that had no significant effects on tree species richness and diversity, stem density, or diameter distribution. Gradual changes were also observed during the early stages of regeneration following logging. However, in logged sites changes in tree species richness and diversity, stem density and diameter distribution became more rapid with time, and significant changes were observed. Similar regeneration events across site and disturbance levels resulted in three identifiable stages. In the first stage, lasting about 10 years, stem density of abundant shade tolerant trees decreased with no discernable changes in tree species richness. In the second stage, also lasting about 10 years, tree species richness and diversity, as well as stem density decreased to minima due to localised species turnover and net mortality. In the third stage, recruitment surpassed mortality and reversed the net loss of both species and stems, as tree species assemblages began to return to pre-disturbance levels. Sites subjected to individual tree selective logging returned to their pre-logging states in all aspects within 35 years of logging, but diameter distribution of trees !40 cm dbh showed low density compared to that observed in the controls. After 15-30 years, sites subjected to more intensive logging returned to their pre-logging levels of stem densities, species abundance and richness, but after 35-44 years of regeneration this sites had low species diversity and high densities of both the small sized stems and shade intolerant tree species. More intensively logged sites also had a low density of shade tolerant tree species compared to the controls. This suggests that the restoration of forest structure takes considerably longer than the restoration of tree species richness and abundance following logging in these forests. A high rate of stand basal area growth and a modest diameter distribution of lager trees !40 cm dbh were observed in moderate tree selection logging. This indicates high timber production potential at moderate tree selection rate in this type of forest. However, if the stem size distribution of larger trees is to be maintained, a logging cycle longer than 50 years is necessary. #

Using tree functional diversity to evaluate management impacts in a subtropical forest

“…On the basis of assuming causal relationships between biodiversity, habitat heterogeneity, and ecosystem function, taxonomic species diversities in woodlands have often have been used to assess logging impacts. Several studies found no differences in species diversity between unlogged and logged forests (Verburg and van Eijk-Bos 2003, Kariuki et al 2006, Berry et al 2008, thereby arguing for compatibility between forest management practices and biodiversity conservation. However, the contrasting patterns of species diversity and functional diversity in the subtropical forest of this study suggest that the compatibility may not be evaluated appropriately by taxonomic diversity measures alone.…”

“…Devising sustainable forest management practices that are based on the retention of original communities and their component organisms is a pressing challenge for forest scientists and managers (Gustafsson et al 2012). Forest biodiversity has mostly been assessed using taxonomic information such as patterns of species richness (e.g., Verburg and van EijkBos 2003, Kubota et al 2004, Kariuki et al 2006, Lindenmayer et al 2006. However, to understand the cascading effects of biodiversity loss during forest conversions and to develop more sustainable management practices, forest ecologists need to determine how individual species contribute to ecosystem properties, such as structure, dynamic processes, and biophysical functioning.…”

Tree Diversity Changes over a Decade (2003-2013) in Four Inland Tropical Dry Evergreen Forest Sites on the Coromandel Coast of India

“…Long-term studies of tree population dynamics are critical for understanding the conservation need of tropical forest ecosystems (Hubbell and Foster 1990;Condit 1995;Sheil et al 2000). Several longterm studies of tree population dynamics are available in both tropical and temperate forests (Lieberman and Lieberman 1987;Kochummen and Manokaran 1987;Foster and Hubbell 1992;Sukumar et al 1992;Balslev and Korning 1994;Bhat et al 2000;Lwanga et al 2000;Battles et al 2003;Takahashi et al 2003;Fashing et al 2004;Kariuki et al 2006;Baithalu et al 2012Baithalu et al , 2013. However, most studies on forest composition worldwide have been conducted on rain forest vegetation, and there are relatively few data available on tropical dry forest communities (Sussman and Rakotozafy 1994).…”

Contrasting taxonomic and functional responses of a tropical tree community to selective logging

“…Recent attention has advanced our focus beyond deforestation to forest degradation (Foley et al 2007;Putz & Redford 2008), especially logging, which impacts at least 15 000 km 2 of Amazonian forests per year (Asner et al 2005). Several authors have argued that the lack of decrease in tree species diversity they observed in selectively logged forests implies that logging activities are compatible with biodiversity conservation (Plumptre 1996;Cannon, Peart & Leighton 1998;Kariuki et al 2006;Berry et al 2008). These findings merit further evaluation given the ongoing development of metrics of functional diversity.…”