Tree diversity and liana infestation predict acoustic diversity in logged tropical forests

Logged tropical forests can retain a great deal of biodiversity, but there is substantial variation in the type and severity of habitat degradation caused by logging. Logging-induced habitat degradation can vary significantly at fine spatial scales, with differing effects on plant communities and the growth of lianas, which are woody, climbing vines that proliferate in degraded forests and infest trees by climbing onto them and competing for above and below ground resources. The impacts of such fine-scale variation in habitat structure on faunal diversity is relatively poorly known. We recorded soundscapes and variation in local-scale habitat structure in selectively logged and old-growth primary forests in Malaysian Borneo to examine how changes to logged forest structure predict variation in acoustic diversity indices that are known to correlate with biodiversity indices. We show that acoustic indices relating to higher soundscape diversity increase with liana prevalence but decline with tree species richness and are unaffected by the liana load of adult trees. Our results suggest that acoustic data represent a simple, practicable measure for detecting fine-scale patterns of biodiversity response to post-logging habitat structure. Our findings also suggest that retaining many trees lightly infested by lianas in logged forests is the optimal outcome for biodiversity. This emphasises the need for forest restoration that retains some climbers, rather than blanket-cutting of all stems in projects seeking to return post-logging forest communities towards their primary forest state

Understanding the impacts of tropical selective logging on ecological mechanisms

Selectively logged tropical forests have been recommended for forest protection and restoration initiatives as these forests maintain a substantial amount of biodiversity and ecosystem functions compared to other tropical land-uses. Most work on selective logging impacts on biodiversity examines species richness, abundance and community composition, yet these metrics can conceal underlying impacts. It is important that we examine the impacts of logging on processes that underpin biodiversity changes, including species’ vital rates (i.e. survival, reproductive success and movement) and community function (i.e. mass-abundance scaling). In Chapter 2, I conducted a literature review to examine the state of our current knowledge on how tropical land-use change impacts species’ vital rates. I found that empirical research on species’ vital rates across taxa and regions were greatly lacking and had considerable variation, with some taxa and land-use biases. In Chapter 3, I focused explicitly on tropical selective logging and investigated its impacts on the mass–abundance scaling of avian communities, an underlying response describing the flow of energy through communities, by conducting a meta-analysis to examine pantropical trends. Only the omnivore guild from mist-netting studies and the frugivore guild from point-count studies had mass-abundance relationships affected by selective logging. I then used field data from a capture-mark-recapture mist-netting study of Bornean understory birds to assess species’ vital rate responses (i.e. local movements and survival) to selective logging at the community- and species-level. In Chapter 4, I developed hierarchical Bayesian models, adapting developments from joint-species modelling, to assess local avian movement and found a higher probability of moving shorter distances (below 200 m) in logged forests and higher movement probability at longer distances (above 200 m) in unlogged forests across 71 species. Finally, in Chapter 5, I developed a multi-species hierarchical Cormack-Jolly-Seber model in a Bayesian framework to determine avian survival rates, revealing similar apparent survival probabilities across 71 species in both unlogged and logged forests. Together, these results suggest limited impacts on avian species and communities. This highlights the potential high ecological value of selectively logged forests, lending further support for the protection of these forests for biodiversity conservation. Integrating post-logging management interventions with various restoration funds, long-term commercial investments, and effective governance will drive transformative change for the long-term environmentally sustainable management of logging concessions