Soundscapes of Sumatra: an analysis of the susceptibility of vocal fauna to ecological edge effects within a historically disturbed lowland forest, Sumatra, Indonesia.

Abstract

Globally between 2000 and 2015, 128.4 million hectares of native forest were destroyed through deforestation. Although Indonesia still has one of the highest levels of biodiversity globally, it has seen an increase in deforestation due to increased land-use change. In highly degraded forest areas, edge effects in combination with microclimate variation and anthropogenic disturbance can influence the species composition of both flora and fauna and can cause losses in biodiversity and ecosystem resilience. Soundscape analysis can assess the spatial and temporal variations in biodiversity and species composition within an ecosystem using its bioacoustics. This study modelled the variations in the edge effects of forests structure, microclimate, anthropogenic disturbance, and biodiversity within a historically logged lowland forest in Sumatra. As well as the susceptibility of the diversity of vocal fauna and two endangered gibbon species Hylobates lar and Symphalangus syndactylus to the variations in microclimate forest structure and anthropogenic disturbance. With the aim of understanding the impacts of edge effects in degraded forests and highlighting the key ecological drivers that can aid in the conservation of the gibbon species and general fauna within degraded lowland forests. Data were collected in at 2019 10 sites within a historically disturbed lowland forest in the Sikundur region of Sumatra. Each sites forest structure was visually surveyed and dataloggers and Open Filed Recorders were installed to collect microclimate and bioacoustics data continuously for 3 months. The analyses showed no correlation between forest structure and distance from the forests edge but a relationship between microclimate and distance suggesting presence of the buffer effect of the forest canopy. Anthropogenic disturbance from machine hums decreased further into the forest but had no impact on the acoustic diversity or presence of gibbon species. Maximum acoustic diversity at dawn was negatively correlated with distance to forest edge, but dusk showed no trends. Similarly, no relationship was found between the distance from the forests edge and the diversity at both dawn and dusk. Interestingly, the median daily acoustic diversity showed a positive relationship to distance from forest edge. The presence of the gibbon species was not impacted by distance from the edge but the length of their stay at a site was. The results show a distinct susceptibility of general diversity to temporal variations in microclimate that lead fauna to depend on trees with a large crown area as a shaded microhabitat and source of food. Similarly, call density of both Hylobates lar and Symphalangus syndactylus correlated with the presence of large canopy connectivity. This reflects the importance of large trees for resilient ecosystems and highlights the importance of conserving them in disturbed forests.