Drivers of soil fauna communities along a successional gradient in upper andean tropical forests

Soils harbor more than half of Earth's biodiversity, with soil fauna representing one of the most diverse groups. However, understanding the drivers influencing their biodiversity remains limited. Upper Andean tropical forests are among Earth's most biodiverse ecosystems, but have undergone large-scale historical transformations, resulting in landscapes with different forest successional stages. In this study, we aimed to analyze soil fauna communities along a successional gradient in Colombia's Eastern Andean forests and identify key microclimatic, soil, and forest structural drivers. We collected soil fauna from 168 samples (30 x 30 x 5 cm), in dry and wet seasons, in 14 permanent plots (20 x 20 m) located in four sites. Data on microclimate, nutrients, productivity, plant diversity, and litter functional richness were gathered from these permanent plots. We observed significant soil fauna biodiversity turnover among Andean montane forest sites, mirroring the distinctive floristic composition between them. We also found that soil fauna richness and abundance increased with succession, attributed to higher productivity and more suitable microclimatic conditions in old-growth forests. Our findings suggest that the primary driver of soil fauna richness in tropical mountain Andean forests is the amount of energy (i.e, forest productivity), while soil fauna abundance is mainly influenced by thermal conditions. Additionally, factors framed within the physiological tolerance hypothesis (i.e., calcium, aluminum) and within the habitat heterogeneity hypothesis (i.e., litter functional richness, plant diversity) also play a role, albeit to a lesser extent. This study emphasizes the importance of examining forest recovery including soil fauna groups to understand successional patterns in tropical mountain forests.