Decay of deadwood carbon – current knowledge and opportunities for modelling

Deadwood is a prominent part of forest ecosystems. It is important for multiple forest functions, including habitat, water storage, nutrient cycling and carbon storage. Deadwood volume is now routinely measured in many large-scale inventory programs, including the national forest inventory or inventory of nationalparks or nature reserves. Policy changes, increasing climatic stress, more frequent and more intense disturbances and/or abandoning forest management will likely lead to increasing deadwood volumes in the next decades. We will explore here the available knowledge on decay of deadwood in Central Europe, focussing on carbon (C) and nitrogen (N) content and release.

Decay classes can be assessed in the field and provide a potent proxy for deadwood density, pore volume and C:N ratios, based on pilot studies in Eastern Austria. Using C:N as proxy for decomposability suggest that decomposition is non-linear and that advanced decay stages have faster decomposition. Our results highlight that smaller sized deadwood (2-10 cm diameter) can store substantial amounts of C and N. Additional field work, non-destructive methods and modelling can link decay stages with time since death and allow estimating mass and volume loss by decomposing organisms.

For understanding the dynamics between standing and lying deadwood we will need models that are able to predict the disintegration of trees, considering loss of less stable stem parts, like bark or sapwood. We will need continuous deadwood monitoring as well as more complex models to understand the main pathways for deadwood decay, the effects of climate on decomposition and the role of management in deadwood accumulation and dynamics. Complementing available data with new methods and models will allow us to quantify the capacity of managed and unmanaged forests for deadwood, the carbon sequestration in deadwood and its persistance in the future.

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