Abstract
Tropical forest degradation is a global environmental issue. In degraded forests, seedling recruitment of canopy trees is vital for forest regeneration and recovery. We investigated how selective logging, a pervasive driver of tropical forest degradation, impacts canopy tree seedling recruitment, focusing on an endemic dipterocarp Dryobalanops lanceolata in Sabah, Borneo. During a mast‐fruiting event in intensively logged and nearby unlogged forest, we examined four stages of the seedling recruitment process: seed production, seed predation, and negative density‐dependent germination and seedling survival. Our results suggest that each stage of the seedling recruitment process is altered in logged forest. The seed crop of D. lanceolata trees in logged forest was one‐third smaller than that produced by trees in unlogged forest. The functional role of vertebrates in seed predation increased in logged forest while that of non‐vertebrates declined. Seeds in logged forest were less likely to germinate than those in unlogged forest. Germination increased with local‐scale conspecific seed density in unlogged forest, but seedling survival tended to decline. However, both germination and seedling survival increased with local‐scale conspecific seed density in logged forest. Notably, seed crop size, germination, and seedling survival tended to increase for larger trees in both unlogged and logged forests, suggesting that sustainable timber extraction and silvicultural practices designed to minimize damage to the residual stand are important to prevent seedling recruitment failure. Overall, these impacts sustained by several aspects of seedling recruitment in a mast‐fruiting year suggest that intensive selective logging may affect long‐term population dynamics of D. lanceolata. It is necessary to establish if other dipterocarp species, many of which are threatened by the timber trade, are similarly affected in tropical forests degraded by intensive selective logging.
Highlights
Vast areas of natural forest are being degraded around the world
Selective logging characterized by unsustainable harvest rates and improper silvicultural practices is a major driver of forest degradation (Asner, Rudel, Aide, Defries, & Emerson, 2009; Martin, Newton, Pfeifer, Khoo, & Bullock, 2015; Putz et al, 2012)
Our results demonstrate how multiple stages of the seedling recruitment process of a canopy tree species may be altered when tropical forests are degraded by intensive “selective” logging
Summary
Selective logging characterized by unsustainable harvest rates and improper silvicultural practices is a major driver of forest degradation (Asner, Rudel, Aide, Defries, & Emerson, 2009; Martin, Newton, Pfeifer, Khoo, & Bullock, 2015; Putz et al, 2012). Seedling recruitment is among the fundamental processes that determine the maintenance of plant diversity in forest ecosystems (Wright, 2002), and is a demographic bottleneck in plant population dynamics (Chambers & MacMahon, 1994; Chesson, 2000; Poulsen, Clark, & Bolker, 2012). In the aftermath of disturbances such as logging, seedling recruitment of canopy trees is vital for forest regeneration and recovery (Bagchi et al, 2011; Chazdon, 2003). Our knowledge of the impact of logging on seedling recruitment is limited (Bagchi et al, 2011; Curran et al, 1999)
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