Do soil fauna really hasten litter decomposition? A meta-analysis of enclosure studies

We present a meta-analysis of experiments in which researchers used litter bags or similar enclosures to explore three questions: Do soil macrofauna increase the removal of litter from the soil surface? How is this mass loss of litter by macrofauna affected by climate and litter quality? To what extent does litter loss from litter layer by macrofauna correspond with litter mineralization? In total, we found 132 published field experiments in which authors compared litter bags with mesh sizes that did permit or not permit access by soil fauna. Meta-analysis of these experiments indicated that litter removal was significantly greater from bags that did permitted rather than did not permitted soil macrofauna access. When we divided these studies according to climate, a significant positive effect of soil fauna on litter removal was only evident from the warm humid, temperate regions with correspond to deciduous forest zone. When studies from this climate zone were sorted according to litter C:N ratio, the effect of fauna was significant in all cases except when the ratio was low (<20), and the effect of fauna was greatest when the ratio was intermediate (20–30). To assess how litter removal from litter bags corresponds with mineralization, we reviewed 11 published experiments that used litter boxes that were or were not accessible to soil macrofauna and 8 studies where fauna was experimentally removed and added. These boxes contained both litter and a mineral soil layer, which allowed researchers to estimate litter removal from the litter layer, the increase in C content (C sequestration) in the mineral soil, and overall C mineralization (difference of the former and the latter number). Analysis of these experiments indicated that fauna significantly increased litter removal from the litter layer, which agreed with the litter bag meta-analysis, but did not significantly affect overall C mineralization. This is consistent with meta-analysis of seven studies showing that rate of leaf litter decomposition is significantly faster than decomposition of macrofauna feces produced from the same litter.