Small-scale positive response of terrestrial gastropods to dead-wood addition is mediated by canopy openness

Abstract

Terrestrial gastropods can benefit from coarse woody debris, even though they are not saproxylic because dead wood maintains suitable microclimatic conditions and provides food resources and essential nutrients, e.g. calcium. Effects of dead wood on terrestrial gastropods have been studied mostly for coarse woody debris at intermediate and advanced stages of decomposition. However, it remains unclear whether dead wood at an early stage of decomposition and of small diameter has similar positive effects on terrestrial gastropods and how effects of dead wood are mediated by canopy openness. We experimentally exposed different amounts of fresh coarse and fine woody debris on 190 temperate forest plots with either high or low canopy openness and studied terrestrial gastropod activity three years after. Plots with high canopy openness had dense herb layers. Feeding activity of gastropods was higher close than distant to dead wood. This effect was stronger on shady plots. The amount of both fine and coarse woody debris positively affected the feeding activity of gastropods, but only on shady plots. The effect of coarse woody debris amount might be partly due to increased leaf litter accumulation. Our results indicated that dead wood plays a stronger role for terrestrial gastropods in shady than in sunny forests with a dense herb layer and that terrestrial gastropods benefit from both coarse and fine woody debris already at an early stage of decomposition. Thus, conservation strategies that aim at maintaining biodiversity of saproxylic assemblages by retaining or adding dead wood are also beneficial for gastropods, especially in shady forests.