Alien plant invasions in a tropical mosaic landscape are related to lower tree diversity and vegetation structure

Abstract

Abstract Plant invasions are one of the most important drivers of global biodiversity change, posing a major threat to ecosystem health and human well-being. Invasion pressure is not uniformly distributed across biomes and ecosystems. Although tropical forests are often considered resistant towards alien plant invasions, the drivers behind this resistance as well as the actual impact require further clarification in tropical contexts, where dynamics often differ from those in temperate regions. This study investigated the role of tree diversity and vegetation structure in influencing plant invasions across four major land cover types in Sumatra, Indonesia: natural forests, fallow land, rubber, and oil palm plantations. We derived vegetation structure metrics such as canopy height, number of gaps, box dimension, skewness from landscape-scale mobile LiDAR measurements collected across 100 plots and analysed these metrics alongside species diversity data, focusing on both native trees and invasive alien plants. Our results reveal that more diverse tree communities were associated with taller (higher canopy height), more structurally complex (higher box dimension), less open (smaller gap area) vegetation. In contrast, a simplified vegetation structure was more prevalent in monoculture plantations, which correlated with a higher abundance and diversity of alien plants. These results underline the critical role of tree diversity and vegetation structure in shaping the invasibility of tropical ecosystems. Our findings support restoration that maintains multi-layered canopies and limit gap area. These practices should be prioritised to enhance ecosystem resilience and mitigate the impact of biological invasions.