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Keywords:

  • carbon cycle;
  • coarse woody debris;
  • common-garden experiment;
  • decomposition rates;
  • forest;
  • functional traits;
  • model;
  • plant–soil (below-ground) interactions;
  • protocol;
  • wood decay dynamics

Summary

1. While the importance of wood decay for the global carbon balance is widely recognized, surprisingly little is known about its long-term dynamics and its abiotic and biotic drivers. Progress in this field is hindered by the long time-scales inherent to the low decay rates of wood and the lack of short-term methods to assess long-term decomposition dynamics in standardized field conditions.

2. Here, we present such a method, which relies on the sampling and short-term incubation of wood from several decay stages covering the entire decay process. Together these short-term decay steps are used to model and discriminate between three potential decay dynamics (linear, exponential and sigmoid) using an iterative optimization procedure. We applied this method to analyse long-term wood decay of six subarctic tree species (six stems and two roots) and test the hypotheses that (i) different wood species follow distinct decay dynamics and (ii) interspecific variation in wood traits controls variation in wood decay rates in a standardized environment.

3. We found interspecific variation in long-term wood decay dynamics: decay of Alnus and Salix stems was best described by exponential models, whereas decay of Sorbus stems and Betula and Pinus roots was best fitted by linear models and Betula, Pinus and Populus stems each displayed a sigmoid decay dynamics (up to 5-year initial lag phase). A six-fold variation was observed between the decomposition half-lives of all eight wood types, from 6.8 years (6.1–7.5, 95% C.I.) for Alnus stems to 41.3 years (34.5–51.8) for Pinus roots. Initial wood traits such as pH (R2 = 0.92), dry matter content (R2 = 0.79) and lignin (R2 = 0.73) were good predictors of long-term wood decay rates.

4.Synthesis. Our findings suggest changing decay dynamics across wood species and types that are likely to arise from changing underlying wood decay processes (i.e. varying wood functional traits/decomposer community interactions). Our new method, which combines advantages of direct observations and the chronosequence approach, allows reliable comparisons of species contributions to long-term wood decay rates and provides future opportunities to experimentally disentangle intrinsic and external abiotic and biotic drivers of long-term wood decay processes.