Validating tree litter decomposition in the Yasso07 carbon model

Up-to-date and accurate information of ecosystem state and functioning becomes ever more critical for decision-making and policy. For complex ecosystems such as forests, these demands can in some cases not be met by field observations only, especially at larger scales. Additionally, methodological requirements include comparability and transparency. To satisfy these needs, models can provide an important supplement or alternative. We examined the validity of the litter decomposition and soil carbon model Yasso07 in Swiss forests based on data on observed decomposition of (i) foliage and fine root litter from sites along a climatic and altitudinal gradient and (ii) of 588 dead trees from 394 plots of the Swiss National Forest Inventory. Our objectives were to (i) examine the effect of the application of three different published Yasso07 parameter sets on simulated decay rate; (ii) analyze the accuracy of Yasso07 for reproducing observed decomposition of litter and dead wood in Swiss forests; and (iii) evaluate the suitability of Yasso07 for regional and national scale applications in Swiss forests. From the three examined parameter sets, the set was identified which resulted in the best agreement between Yasso07 results and observed decomposition. No significant differences were found between simulated and observed remaining C in foliage and fine root litter after 10 years and in lying dead trees after 14-21 years. The model overestimated the decomposition of standing dead trees. We concluded that Yasso07 can provide accurate information on temporal changes in C stocks in litter and deadwood in Swiss forests in a transparent manner that is valid for, e.g., reporting purposes under the UNFCCC and the Kyoto Protocol. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.