Coarse Woody Debris Decomposition Assessment Tool: Model validation and application

Abstract

Coarse woody debris (CWD) is a significant component of the forest biomass pool; hence a model is warranted to predict CWD decomposition and its role in forest carbon (C) and nutrient cycling under varying management and climatic conditions. A process-based model, CWDDAT (Coarse Woody Debris Decomposition Assessment Tool) was calibrated and validated using data from the FACE (Free Air Carbon Dioxide Enrichment) Wood Decomposition Experiment utilizing pine (Pinus taeda), aspen (Populous tremuloides) and birch (Betula papyrifera) on nine Experimental Forests (EF) covering a range of climate, hydrology, and soil conditions across the continental USA. The model predictions were evaluated against measured FACE log mass loss over 6 years. Four widely applied metrics of model performance demonstrated that the CWDDAT model can accurately predict CWD decomposition. The R2 (squared Pearson’s correlation coefficient) between the simulation and measurement was 0.80 for the model calibration and 0.82 for the model validation (P<0.01). The predicted mean mass loss from all logs was 5.4% lower than the measured mass loss and 1.4% lower than the calculated loss. The model was also used to assess the decomposition of mixed pine-hardwood CWD produced by Hurricane Hugo in 1989 on the Santee Experimental Forest in South Carolina, USA. The simulation reflected rapid CWD decomposition of the forest in this subtropical setting. The predicted dissolved organic carbon (DOC) derived from the CWD decomposition and incorporated into the mineral soil averaged 1.01 g C m-2 y-1 over the 30 years. The main agents for CWD mass loss were fungi (72.0%) and termites (24.5%), the remainder was attributed to a mix of other wood decomposers. These findings demonstrate the applicability of CWDDAT for large-scale assessments of CWD dynamics, and fine-scale considerations regarding the fate of CWD carbon.

A Modelling System for Dead Wood Assessment in the Forests of Northern Eurasia

“…Dead wood is an important component of forest ecosystems. It generates a carbon pool [1,2] with a residence time from decades to centuries, especially for the snags in cold climates [3][4][5]. Fallen dead wood increases the moisture of the soil surface [6] and the nutrient availability [7,8], as well as maintaining biodiversity [9,10], as 20%-40% of organisms in forest ecosystems depend on dead wood [11] during their lifecycle.…”

“…(2) they do not include all the components of dead wood; (3) they are biased because the minimum threshold for the amount of snags and logs in the inventory varies from 5 to 30 m 3 ha −1 depending upon the region and the forest management category; (4) as a rule, they do not account for the final stages of decomposition; and (5) the aggregated data from dead wood inventories have not been published historically, but only presented in forest inventory reports by individual forest inventory enterprises. Overall, this has led to the substantial underestimation of coarse woody debris (CWD) in the forest inventory.…”