Land use not litter quality is a stronger driver of decomposition in hyperdiverse tropical forest

Abstract

In hyperdiverse tropical forests, the key drivers of litter decomposition are poorly understood despite its crucial role in facilitating nutrient availability for plants and microbes. Selective logging is a pressing land use with potential for considerable impacts on plant–soil interactions, litter decomposition, and nutrient cycling. Here, in Borneo's tropical rainforests, we test the hypothesis that decomposition is driven by litter quality and that there is a significant “home‐field advantage,” that is positive interaction between local litter quality and land use. We determined mass loss of leaf litter, collected from selectively logged and old‐growth forest, in a fully factorial experimental design, using meshes that either allowed or precluded access by mesofauna. We measured leaf litter chemical composition before and after the experiment. Key soil chemical and biological properties and microclimatic conditions were measured as land‐use descriptors. We found that despite substantial differences in litter quality, the main driver of decomposition was land‐use type. Whilst inclusion of mesofauna accelerated decomposition, their effect was independent of land use and litter quality. Decomposition of all litters was slower in selectively logged forest than in old‐growth forest. However, there was significantly greater loss of nutrients from litter, especially phosphorus, in selectively logged forest. The analyses of several covariates detected minor microclimatic differences between land‐use types but no alterations in soil chemical properties or free‐living microbial composition. These results demonstrate that selective logging can significantly reduce litter decomposition in tropical rainforest with no evidence of a home‐field advantage. We show that loss of key limiting nutrients from litter (P & N) is greater in selectively logged forest. Overall, the findings hint at subtle differences in microclimate overriding litter quality that result in reduced decomposition rates in selectively logged forests and potentially affect biogeochemical nutrient cycling in the long term.

Litter Inputs, but Not Litter Diversity, Maintain Soil Processes in Degraded Tropical Forests—A Cross-Continental Comparison

“…At both sites, almost 80% of the litter had decomposed after nine months in the forested habitats but <60% had decomposed in the converted habitats ( Figure 2) and soil respiration was consistently higher in the forest habitats (Figure 3). A similar decline in decomposition in degraded tropical forests was also found in an experiment in China, in which open deforested land had significantly lower decomposition rates than old-growth and regenerating forests (Paudel et al, 2015) and similar patterns were found in Sabah (Both et al, 2017). The lower rates of decay and soil respiration in the converted habitats can be explained by a combination of lower soil nutrient content (Table 1), greater variation in soil temperature and water content (Figure 3), and lower soil microbial biomass (Figures 4, 5) compared to the forest habitat.…”

Canopy structure and topography jointly constrain the microclimate of human‐modified tropical landscapes

“…Yet while previous studies have for the most part been limited to making dichotomous comparisons between logged and unlogged forests, using high‐precision ALS data acquired across a landscape where land‐use intensity was manipulated experimentally we were able to characterize the effects of forest degradation on microclimate in terms of quantitative changes in forest structure. In doing so, our results underscore the importance of logged and secondary tropical forests not only for their biodiversity (Chazdon et al, ; Deere et al, ) and carbon storage potential (Martin, Newton, & Bullock, ; Poorter et al, ; Riutta et al, ), but also in terms of their ability to maintain environmental conditions conducive to forest regeneration and nutrient cycling (Both, Elias, Kritzler, Ostle, & Johnson, ; Ewers et al, ).…”

Logging and soil nutrients independently explain plant trait expression in tropical forests

“…FD was more variable among logged forests than among old-growth forests (Fig. 4), probably owing to variation in logging history and intensity, which affect forest structure (Cannon et al, 1994;Berry et al, 2008), microclimatic conditions (Hardwick et al, 2015) and ecosystem functions (Mayfield et al, 2006;Both et al, 2017;Riutta et al, 2018). The substantial variance in FD among the disturbed plots highlights the challenge of predicting the impacts of anthropogenic modification on FD in environments where the outcomes may be highly context-dependent (Costantini et al, 2016).…”