Canopy closure re-establishes ants in young tree plantations, while low soil pH limits ant diversity

Joshua Emil Spitz, Esteve Boutaud, Felix Fornoff, Steffen Seitz, Thorsten Assmann, Xiaojuan Liu, Michael Staab

1. Tree species richness is known to enhance biodiversity and ecosystem functioning, but its effects across trophic levels during forest restoration remain insufficiently understood. In reforestation on complex terrain, habitat complexity may moderate the effect of canopy closure on animal community reassembly, a relationship further shaped by the abiotic environment.
2. Ants, as key functional organisms sensitive to vegetation structure and microclimate, provide an ideal system to test how tree species richness, canopy closure and abiotic environmental variables jointly influence animal communities in young plantations.
3. We examined ground ant diversity, community composition, and functional traits in subtropical tree plantations, using nearby secondary forest as a reference. No ant metric, including incidence, species richness, taxonomic or functional diversity, or community-weighted trait means, responded to tree species richness. Instead, canopy closure and soil pH explained variation in most metrics.
4. Canopy closure and topographical exposure shaped community composition, with canopy closure negatively influencing ant incidence and species diversity, while soil pH consistently had a positive effect on both across the observed range (4.1–5.2). More closed canopies favored leaf-litter-nesting ants, a higher proportion of predators, and communities with increased mandible length, indicating convergence toward forest-adapted predatory assemblages. Soil-nesting ants approached secondary forest values only where both canopy closure and tree species richness were high.
5. Early canopy closure appears to be the primary biotic environmental variable influencing ant community recovery in young plantations, which is further attenuated by the abiotic environment such as soil conditions. This highlights canopy development as a key mechanism of faunal recovery, beyond the effects of tree species richness alone, with increasing predator dominance suggesting potential functional restoration.