Assessing and modelling the status and dynamics of deadwood through national forest inventory data in Spain

The importance of deadwood in forest ecosystems is undeniable, not only in terms of the biodiversity values it provides but also in terms of carbon sequestration and emission. Its importance is evidenced in the international reporting requirements, which include the need for countries to detail their deadwood stock as an important indicator of sustainable development. In recent years, deadwood stocks have been included within the variables reported in the Spanish National Forest Inventories (SNFI), showing average values for total deadwood stocks of 8 and 10.5 m3 ha−1 for the SNFI3 and SNFI4, respectively. However, SNFI are undertaken approximately every ten years, making it difficult their use for accomplishing international reporting requirements annually or every five years. In this context, the objective of the present study was to attempt to model deadwood occurrence, stocks and dynamics using stand, topographic and climatic variables. The models developed considered different forest types, deadwood categories (standing dead trees; downed dead trees; standing saplings; downed saplings/small dead trees; downed coarse wood pieces/downed branches; stumps; coppice stumps) and decay classes. The data set comprises plots from the SNFI3 (3236 plots) and the SNFI4 (1066 plots) from the Basque Country region. Due to the differing characteristics of deadwood stocks in managed forests, where a large number of plots have no deadwood (from 34% to 98% depending on the deadwood category considered), zero-inflated models were chosen as the modelling technique. From the different zero-inflated models analysed, zero-inflated Poisson model was the one that showed better results. Despite the natural variability inherent in deadwood in the analysed forests, good results were achieved for total deadwood stock models as a function of forest types as well as for deadwood dynamics models. These models provide a promising approach for deadwood estimation in the period between the NFI's and they can also be employed by private forest owners in forest management practices, particularly in the case of forest certification.