The effect of forest microenvironment on litter decomposition in the Andean tropical mountains

Abstract Upper Andean tropical forests are renowned for their extraordinary biodiversity and heterogeneous environmental conditions. Despite the critical role of litter decomposition in carbon and nutrient cycles, its dynamics in this region remains unexplored at finer scales. This study investigates how microsite conditions influence litter decomposition of 15 upper Andean species over time. A reciprocal translocation field experiment was conducted over 18 months in 14 permanent plots within four sites in Colombian Andean mountain forests. Each plot contained three litterbeds (microsites), each with the 15 species, harvested at 3, 6, 12 and 18 months, totaling 2520 litterbags. Different forest variables, including canopy openness, leaf area index, slope and depth of litter, were measured in each litterbed. ANOVAs and linear mixed models were used to assess variation between sites and plots respectively, while multiple linear regression analyses evaluated the effects of forest variables on decay rates over time at the microsite scale. Results showed differences in absolute decay rates between sites but consistent relative decay rates, indicating varying magnitudes of decomposition, yet maintaining the same order based on their litter quality. Decay rates varied between species, with more variation in labile species compared to recalcitrant ones. Despite substantial variation in forest characteristics within sites, their influence on litter decomposition was minimal and declined over time. This suggests that, at finer spatial scales, the forest microenvironment plays a lesser role in litter decomposition, with litter quality emerging as the primary driver. This study is a step towards understanding the fine-scale dynamics of litter decomposition in upper Andean tropical forests, highlighting the intricate interplay between microenvironmental factors and decomposition processes.