Demographic superiority with increased logging in tropical understorey insectivorous birds

摘要

Selective logging is pervasive in the tropics and is among the most urgent threats to tropical biodiversity. The vast areas of logged tropical forest are often vulnerable to relogging, clear-felling, burning or conversion to plantations, despite evidence that logged forests retain a large proportion of tropical forest species at high abundances compared with alternate land uses. However, the demographic processes (e.g. survival, fecundity) that drive community or species properties (e.g. occurrence, density) in response to logging have never been examined. We used a novel capture-recapture-based sampling design to separate insitu reproduction from immigration-fuelled recruitment to investigate the demographic vital rates of six forest-dependent understorey insectivorous bird species along a logging continuum in the Eastern Himalaya Global Biodiversity Hotspot. We expected a positive relationship between forest intactness and reproductive rates, and that intact patches would contribute excess' individuals to logged patches from natal dispersal. Contrary to our expectations, we found: (i) a positive relationship between logging intensity and reproduction, and (ii) evidence of natal dispersal from more logged to less logged and intact forest patches. Our results indicate that for certain forest-dependent species in particular contexts, selectively logged habitats can have surprising and hitherto unrecognized demographic value that might be superior even to primary forest.Synthesis and applications. In most tropical settings, logged forests can not only support a greater subset of forest biodiversity than other forms of land use (for instance, agriculture), but can also play an important role in supporting populations of certain forest-dependent species. The ongoing conversion of large swathes of logged forest to non-forest habitat (such as oil palm plantation) because of their perceived lack of importance for biodiversity is a cause for serious concern for the conservation of tropical biodiversity.