Little influence of soil fauna on decomposition in successional upper Andean tropical forests

Abstract Soil fauna had little influence on decay rates, but the effect varied by species. Soil fauna richness and abundance did not influence decomposition environment. Body size traits of soil fauna were unrelated to decomposition environment. Limited macrofauna presence explained the lack of soil fauna’s effect on decay rates. Macrofauna contribution to decomposition had weak effects on succession. Recent studies and global meta-analyses suggest that soil fauna is a key driver of litter decomposition. However, most research has focused on lowland ecosystems, leaving tropical mountain regions underexplored. Our study investigated the influence of the taxonomic and functional structure of soil fauna communities on litter decomposition in successional upper Andean tropical forests. We conducted two reciprocal translocation experiments: one examining 15 litter species (2 525 litterbags) and another analyzing macrofauna exclusion (336 litterbags). We also performed extensive soil fauna sampling across four climatic seasons (6 999 individuals) and measured body size traits for 93% of the morphospecies. We analyzed the role of soil fauna attributes (richness, abundance, body size) on litter decomposition at the species and ecosystem levels in four sites of successional upper Andean tropical forests in Colombia. Our findings indicated that soil fauna has little influence on decomposition, yet the effect varies by species, suggesting specific affinities between soil fauna and litter substrates. The lack of influence of soil fauna richness, abundance, and body size can be attributed to the dominance of small-sized fauna in upper Andean tropical forests. The contribution of soil macrofauna to decomposition was higher in mature forests, but this effect was weak over time. Further studies should explore indirect effects and microbial interactions to better understand soil fauna’s role in decomposition. Our study highlights that the influence of soil fauna on decay rates is context-dependent and should not be generalized across all ecosystems.