Carbon flux and forest dynamics: Increased deadwood decomposition in tropical rainforest tree‐fall canopy gaps

Standing dead trees (snags) decompose more slowly than downed dead wood and provide critical habitat for many species. The rate at which snags fall therefore influences forest carbon dynamics and biodiversity. Fall rates correlate strongly with mean annual temperature, presumably because warmer climates facilitate faster wood decomposition and hence degradation of the structural stability of standing wood. These faster decomposition rates coincide with turnover from fungal-dominated wood decomposer communities in cooler forests to codomination by fungi and termites in warmer regions. A key question for projecting forest dynamics is therefore whether temperature effects on wood decomposition arise primarily because warmer conditions facilitate faster decomposer metabolism, or are also influenced indirectly by belowground community turnover (e.g., termites exert additional influence beyond fungal-plus-bacterial mediated decomposition). To test between these possibilities, we simulate standing dead trees with untreated wooden posts and follow them in the field across 5 yr at 12 sites, before measuring buried, soil-air interface and aerial post sections to quantify wood decomposition and organism activities. High termite activities at the warmer sites are associated with rates of postfall that are three times higher than at the cooler sites. Termites primarily consume buried wood, with decomposition rates greatest where termite activities are highest. However, where higher microbial and termite activities co-occur, they appear to compensate for one another first, and then to slow decomposition rates at their highest activities, suggestive of interference competition. If the range of microbial and termite codomination of wood decomposer communities expands under climate warming, our data suggest that expansion will accelerate snag fall with consequent effects on forest carbon cycling and biodiversity in forests previously dominated by microbial decomposers.

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“…2014, Griffiths et al. 2021, Smith and Peay 2021) as also observed in our current study for both interface and buried wood (Figs. 1 and 2).…”

Section: Discussionsupporting

confidence: 90%

Belowground community turnover accelerates the decomposition of standing dead wood

Bradford

Maynard

Crowther

et al. 2021

Ecology

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“…Here, 91% of trees that died in these forests had at least one risk factor 1 yr before being found dead. These results suggest that, typically, tree death is not an immediate event due to unpredictable episodic disturbances, but the result of chronic or lagged mechanisms that take some time to develop and kill the tree (Espírito‐Santo et al ., 2014; Fontes et al ., 2018; Arellano et al ., 2019; Griffiths et al ., 2021). If death is slow and deterministic, rather than sudden and stochastic, then it may be predictable at the individual level.…”

Section: Discussionmentioning

confidence: 99%

Individual tree damage dominates mortality risk factors across six tropical forests

et al. 2021

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Summary The relative importance of tree mortality risk factors remains unknown, especially in diverse tropical forests where species may vary widely in their responses to particular conditions. We present a new framework for quantifying the importance of mortality risk factors and apply it to compare 19 risks on 31 203 trees (1977 species) in 14 one‐year periods in six tropical forests. We defined a condition as a risk factor for a species if it was associated with at least a doubling of mortality rate in univariate analyses. For each risk, we estimated prevalence (frequency), lethality (difference in mortality between trees with and without the risk) and impact (‘excess mortality’ associated with the risk, relative to stand‐level mortality). The most impactful risk factors were light limitation and crown/trunk loss; the most prevalent were light limitation and small size; the most lethal were leaf damage and wounds. Modes of death (standing, broken and uprooted) had limited links with previous conditions and mortality risk factors. We provide the first ranking of importance of tree‐level mortality risk factors in tropical forests. Future research should focus on the links between these risks, their climatic drivers and the physiological processes to enable mechanistic predictions of future tree mortality.

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“…There is a wealth of experimental evidence demonstrating that these invertebrate decomposers contribute significantly to the mass loss of dead plant matter across the globe (e.g. García‐Palacios et al ., 2013; Fujii et al ., 2018; Griffiths et al ., 2019, 2021; Yang & Li, 2020; Guo et al ., 2021). However, few studies look beyond the effects of soil fauna on decay rates to the consequences for plants, and the majority of those investigations has been carried out in temperate regions or laboratories (e.g.…”

Section: Decomposition and Soil Processing By Invertebrates And The Consequences For Plantsmentioning

confidence: 99%

“…dung) are less well understood globally, with tropical deadwood decomposition studies, for example, representing just 14% of the published decomposition literature (Harmon et al ., 2020). However, in tropical and subtropical systems, evidence is mounting that invertebrate decomposers (termites, in particular) are instrumental for the decomposition of coarse woody material, where they have been shown to be equally, if not more, important than free living microbes for deadwood mass loss (Griffiths et al ., 2019; Griffiths et al ., 2021; Guo et al ., 2021).…”

Section: Introductionmentioning

confidence: 99%

The impact of invertebrate decomposers on plants and soil

et al. 2021

Self Cite

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I. Introduction II. Decomposition: chemical breakdown by both microbes and invertebrates III. Decomposition and soil processing by invertebrates and the consequences for plants IV. Outlook Acknowledgements References SummarySoil invertebrates make significant contributions to the recycling of dead plant material across the globe. However, studies focussed on the consequences of decomposition for plant communities largely ignore soil fauna across all ecosystems, because microbes are often considered the primary agents of decay. Here, we explore the role of invertebrates as not simply facilitators of microbial decomposition, but as true decomposers, able to break down dead organic matter with their own endogenic enzymes, with direct and indirect impacts on the soil environment and plants. We recommend a holistic view of decomposition, highlighting how invertebrates and microbes act in synergy to degrade organic matter, providing ecological services that underpin plant growth and survival.

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Carbon flux and forest dynamics: Increased deadwood decomposition in tropical rainforest tree‐fall canopy gaps

Cited by 29 publications

References 55 publications

Belowground community turnover accelerates the decomposition of standing dead wood

Belowground community turnover accelerates the decomposition of standing dead wood

Individual tree damage dominates mortality risk factors across six tropical forests

The impact of invertebrate decomposers on plants and soil

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