Litter decomposition rates across tropical montane and lowland forests are controlled foremost by climate

Abstract

The “hierarchy of factors” hypothesis states that decomposition rates are controlled primarily by climatic, followed by biological and soil variables. Tropical montane forests (TMF) are globally important ecosystems, yet there have been limited efforts to provide a biome‐scale characterization of litter decomposition. We designed a common litter decomposition experiment replicated in 23 tropical montane sites across the Americas, Asia, and Africa and combined these results with a previous study of 23 sites in tropical lowland forests (TLF). Specifically, we investigated (1) spatial heterogeneity in decomposition, (2) the relative importance of biological factors that affect leaf and wood decomposition in TMF, and (3) the role of climate in determining leaf litter decomposition rates within and across the TMF and TLF biomes. Litterbags of two mesh sizes containing Laurus nobilis leaves or birchwood popsicle sticks were spatially dispersed and incubated in TMF sites, for 3 and 7 months on the soil surface and at 10–15 cm depth. The within‐site replication demonstrated spatial variability in mass loss. Within TMF, litter type was the predominant biological factor influencing decomposition (leaves > wood), with mesh and burial effects playing a minor role. When comparing across TMF and TLF, climate was the predominant control over decomposition, but the Yasso07 global model (based on mean annual temperature and precipitation) only modestly predicted decomposition rate. Differences in controlling factors between biomes suggest that TMF, with their high rates of carbon storage, must be explicitly considered when developing theory and models to elucidate carbon cycling rates in the tropics. Abstract in Spanish is available with online material.

Canopy opening increases leaf‐shredding arthropods and nutrient mineralization but not mass loss in wet tropical forest

“…We hypothesize that drought had a stronger effect on mass loss and nutrient mineralization than the canopy treatments and litterbag mesh size. Our results are consistent with previous support for hierarchical control of litter decomposition and mineralization (Djukic et al, 2018; Ostertag et al, 2022). The effect of arthropods on leaf litter decomposition occurs on a smaller scale, not on a mesoscale.…”

“…The effect of arthropods on leaf litter decomposition occurs on a smaller scale, not on a mesoscale. Therefore, our results are aligned with previous studies showing that at the mesoscale level, the predominant factors in litter decomposition are resource quality and environmental conditions (Djukic et al, 2018; Ostertag et al, 2022). Based on evidence from multisite experiments at regional and global scales, while soil animals are considered key regulators of decomposition at local scales, their role at larger scales is still unresolved (Wall et al, 2008).…”

“…In this study, about 20% mass remaining was attained at 6 months as compared to 12–18 months in the first iteration of the CTE (González et al, 2014). Ostertag et al (2022) found in a pantropical leaf decomposition experiment in montane and lowland forests that differences in mass loss between litterbag mesh sizes were highly significant using either the mean data from 3‐ and 7‐month incubation or the 7‐month data alone. As noted previously, litter arthropods have largely indirect effects on litter decomposition via regulation of bacterial and fungal populations.…”

“…A pretreatment drought occurred in 2002 before the first canopy trimming and the litterbag decomposition experiment in 2004, leading to pre‐ versus post‐treatment differences in microbial communities within the control treatment, but rainfall had returned to normal before canopy treatment and the decomposition experiment (Cantrell et al, 2014; González & Lodge, 2017; González et al, 2014). In their pantropical leaf decomposition experiment in montane and lowland forests, Ostertag et al (2022) showed hierarchical control of leaf litter mass loss with climate having a stronger effect on leaf litter mass loss than biotic factors including invertebrate size class.…”

Hail-caused greenfall leaves, litterfall, nutrients, and leaf decomposition in tropical cloud forest and a restoration planting

“…Decomposition of organic matter is one of the main mechanisms for releasing nutrients in terrestrial ecosystems, and this process plays an important role in regulating nutrient cycling rates (Fonte & Schowalter 2004, Smith & Throop 2018. Climate, rather than substrate quality, has been reported to be the principal determinant of leaf decomposition across subtropical rain and dry forests (Ostertag et al 2022).…”