Tree diversity and composition recovery along a logging gradient in Bornean rainforest

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Martin Svátek, Mendel University in Brno, Brno, Czech Republic

Background/Question/Methods
Biodiversity losses from deforestation and selective logging may be partially offset by the recovery and expansion of the secondary forests in the tropics. The recovery of forests from selectively logging is of particular importance for biodiversity conservation especially in South East Asia, where relative deforestation rate is the highest among any major tropical regions and selective logging is a widespread harvest technique. In Borneo, despite the key role of selectively logged forests in human-altered landscape, information on the speed and extent of secondary forest recovery remains scarce.
Using 193 permanent plots (25 x 25 m each) within the Stability of Altered Forest Ecosystems (SAFE) Project in Sabah, Malaysian Borneo, we studied the dynamics of tree diversity and composition along the logging gradient (ranging from heavily, moderately, and lightly logged stands to old-growth forest). To capture annual demographic changes in composition and diversity both for trees in the main canopy and the lowest strata, we recorded growth, mortality and recruitment of all trees with diameter at breast height (dbh) ≥ 1 cm in each plot, yearly in 2011–2020.
Results/Conclusions
While we found that beta diversity increased with the intensity of logging, and the most heavily disturbed plots exhibited the greatest interannual changes in species composition and diversity, despite the highest species turnover in the most heavily logged stands, the trajectory of species composition in these plots has not been approaching the old-growth forest. In heavily logged forests, there were no signs of recovery in terms of species composition and diversity, and pioneers still dominated in the plots whereas dipterocarps (late successional species) failed to increase both its abundance and basal area even after many years since logging. Because the majority of lowland tropical forests has been already affected by logging to some degree, our results emphasized the widespread long-lasting consequences of heavy selective logging for tree composition and diversity in these forests.