Effects of Topographical Differences on Macroinvertebrate Access and Litter Decomposition in a Temperate Broad-Leaved Forest

Geodiversity, particularly topographical gradients, significantly influences ecosystem function by creating heterogeneous environmental conditions. This study examined how local-scale microtopography and litter bag perforation affected leaf litter decomposition rates in a humid-temperate secondary forest. We categorized microtopography into ridge, valley, southwest slope, and northeast slope, with relative height differences of around 20 m. Using the litter bag method comparing non-perforated (1 mm mesh) and perforated (with 6 mm holes) bags, we measured leaf litter mass loss and moisture content of Quercus serrata over 6 and 12 months. While microtopography caused only slight differences in leaf litter moisture content, it significantly influenced decomposition rates. Leaf litter mass loss was lower in valley microtopography compared to the southwest slope and ridge microtopography. We infer that topographical differences in unmeasured microclimatic factors, such as solar radiation and soil temperature, may have potentially driven these spatial variations in decomposition. Furthermore, because the litter bag perforation did not significantly promote further mass loss, our results suggest that baseline decomposition driven by organisms capable of passing through the 1 mm mesh (e.g., microbes and meso/microfauna) might have been sufficiently high in this environment. These findings highlight that local-scale microtopographical differences enhance the spatial heterogeneity of leaf litter decomposition in forest ecosystems.