A pantropical assessment of vertebrate physical damage to forest seedlings and the effects of defaunation

Abstract

Many of the forces that shape tropical forest plant communities are facilitated by interactions with animals, which can either promote or inhibit plant reproduction and survival across ontogenetic stages. Hunting-induced defaunation can disrupt these interactions, altering tree recruitment, forest structure, and carbon storage, with strong effects at the seed and seedling stages. Research to date has largely focused on how changes to prominent interactions (especially seed dispersal) affect plant species and communities, while concurrent disruptions to less-studied processes may have opposing effects. With a particularly limited understanding of non-trophic interactions – such as physical damage to seedlings by vertebrate trampling, rooting, and digging – it remains difficult to predict the outcomes of defaunation for tropical forest plant communities. We established 1800 artificial seedlings in 18 intact and disturbed sites across the three main tropical forest regions – the Neotropics (Peru), the Afrotropics (Gabon) and the Indo-Malayan tropics (Malaysian Borneo) – to isolate non-trophic vertebrate physical damage from other causes of seedling mortality (herbivory, pathogens, abiotic desiccation, etc.), and to understand its effects in intact and anthropogenically-disturbed forests. We found that vertebrate physical damage is a consistent force in forests across the tropics, and that hunting significantly alters its strength, with a ∼70% decrease in damage in hunted vs. intact sites that resulted in a ∼3.5-fold (350%) increase in artificial seedling survival. Our results reveal an understudied mechanism that may contribute to changes in seedling survival, stem density, and plant community composition in tropical forests subjected to hunting.