Effects of climate, soil, topography, and disturbance on liana prevalence

Lianas (woody vines and climbing palms) are increasing in abundance in many tropical forests with uncertain consequences for forest functioning and their recovery following disturbance. At a global scale, these increases are likely driven by disturbances and climate change.  Yet, our understanding of the environmental variables that drive liana prevalence at regional scales is incomplete and geographically biased towards Latin America. To address this gap, we present a comprehensive study evaluating the combined effects of climate, soil, disturbance, and topography on liana prevalence in the Australian Wet Tropics. We established thirty-one 20 m x 20 m vegetation plots along an elevation gradient in low disturbance (canopy closure ≥ 75%) and high disturbance (canopy closure ≤25%) forest stands. In these plots, all tree and liana stems ≥ 1 cm DBH were measured and environmental data were collected on climate, soil, and topography. Generalised Linear Models were used with multi-model averaging to quantify the relative effects of the environmental variables on measures of liana prevalence (liana–tree basal area ratio, woody vine basal area and stem density, and rattan stem density). Liana prevalence increased with disturbance, and also with increasing mean annual precipitation (MAP) and the associated increases in temperature and decline in elevation. Increase in the liana–tree ratio with MAP was more pronounced for highly disturbed sites. Like other tropical regions, disturbance is an important driver of liana prevalence in Australian rainforests and also appears to interact with climate to increase liana–tree ratios. The observed increase in liana–tree ratio with MAP contrasts findings from elsewhere but is likely an artefact of local topography and disturbance, which highlights the importance of regional studies. Our findings show that forests with high disturbance and climatic conditions favourable to lianas are where lianas most likely to outcompete trees and impede forest recovery.