Release of coarse woody detritus-related carbon: a synthesis across forest biomes

Abstract

Background: Recent increases in forest tree mortality should increase the abundance coarse woody detritus (CWD) and ultimately lead to increased atmospheric carbon dioxide. However, the time course of carbon release from CWD is not well understood. We compiled CWD decomposition rate-constants (i.e., k) to examine how tree species, piece diameter, position (i.e., standing versus downed), canopy openness, and macroclimate influenced k. To illustrate their implications we modeled the effect of species and position on estimates of decomposition-related carbon flux. We examined a subset of currently used models to determine if their structure accounted for these factors. Results: Globally k of downed CWD varied at least 244-fold with interspecies variation at individual sites up to 76-fold. While k generally decreased with increasing piece diameter, under open canopies the opposite occurred. Standing CWD sometimes exhibited little decomposition, but sometimes had k values up to 3 times faster than downed CWD. There was a clear response of k to mean annual temperature of ≈ 2.6 times per 10 ℃; however, there was considerable variation for a given mean annual temperature related to species, diameter, and position. A key feature of carbon release from CWD after disturbance was the "evolution" of the ecosystem-level k value as positions and species mixtures of the remaining CWD changed. Variations in decomposition caused by disturbance (e.g., changes in species, positions, sizes, and microclimate) had the potential to cause net carbon fluxes to the atmosphere to be highly nonlinear. While several models currently being used for carbon accounting and assessing land-use/climate change would potentially capture some of these post disturbance changes in fluxes and carbon balances, many would not. Conclusions: While much has been learned in the last 5 decades about CWD decomposition, to fully understand the time course of carbon release from increased mortality and other aspects of global change a new phase of global CWD research that is more systematic, experimental, and replicated needs to be initiated. If our findings are to be fully applied in modeling, an approach acknowledging how the rate of carbon release evolves over time should be implemented.

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

“…Yet, despite the fact that decomposition has far reaching implications for global carbon budgets (Hubau et al, 2020), it remains poorly understood compared with other key ecosystem processes such as primary production (Harmon et al, 2011). Furthermore, what is known about the factors controlling deadwood decay is geographically biased towards temperate regions, with tropical forest decomposition studies representing just 14% of the published literature (Harmon et al, 2020). This bias means we lack a basic understanding of the factors that mediate the rate and fate of carbon turnover through globally important deadwood stocks in tropical rainforests.…”

Coarse Woody Debris’ Invertebrate Community is Affected Directly by Canopy Type and Indirectly by Thinning in Mixed Scots Pine—European Beech Forests

“…In addition, modifying litterfall composition and production rate with thinning or changes in canopy type [20,56] could also modify CWD mesofauna communities, as they are also directly connected to litter communities and vice versa [57]. Under the current paradigm of moving from pure to mixed Scots pine-European beech forests in Europe [15,16], our results should be taken into account both from the biodiversity perspective and from the carbon and nutrient cycling perspective [2], as invertebrate communities influence CWD decay rates [9,[57][58][59]. Consequently, we recommend considering the ecological role of CWD mesofauna when planning silvicultural practices, particularly in mixed forests.…”

Large-diameter trees, snags, and deadwood in southern Utah, USA

“…This deadwood protocol, designed for angiosperm and gymnosperm species, facilitates comparison of deadwood among forests worldwide. Snags and deadwood are divided into five different decay classes that are congruent with existing studies of biomass and carbon content of the different decay classes (Harmon et al 2008(Harmon et al , 2013(Harmon et al , 2020. See Janík et al 2018for protocol details and Lutz et al (2020) for an example application in temperate forests.…”

“…Deadwood contributes to ecological processes in addition to surface fuel dynamics (Harmon et al 1986;Thorn et al 2020). Between snagfall and deadwood's eventual decomposition or combustion (Stenzel et al 2019), it contributes to biodiversity by changing the microenvironment (Vrška et al 2015), serving as substrate for seedlings and bryophytes (Taborska et al 2015) and regulating carbon cycling dynamics (Harmon et al 1986;Privetivy et al 2018;Harmon et al 2020). Because of the differential effects of large-diameter trees, snags, and deadwood on forest structure (Lutz et al 2012;Lutz et al 2013;Réjou-Méchain et al 2014), it is important to specifically consider the effects and dynamics of larger pieces (sensu Lutz and Halpern 2006), rather than adopting an approach that ignores piece size.…”