Characterisation of woody necromass in beech forests with different anthropic accessibility: the case of La Rioja (ES)

The presence of deadwood is undeniably essential in natural environments for its ecological role. In forest ecosystems, deadwood contributes to the protection of biodiversity, mitigation of climate change, soil protection against erosion, and playing an essential role within biogeochemical cycles, contributing to forest productivity by slowly releasing nutrients and moisture. We assessed the amount of deadwood in four macro-areas within two beech forests located on areas of public utility of Enciso (community of La Rioja, Spain). These areas were different in terms of silvicultural management and proximity to reforested stands of Pinus sylvestris. In each macro-area three circular sample plots were placed at an increasing distance from the access road to the forests: from 20 to 60 m, 60 to 100 m and 100 to 140 m. Dendrometric data and qualitative and quantitative characteristics of deadwood (snags, logs and dead stumps) were collected, and analyzed with respect to the degree of accessibility to the forest 1) to reconstruct past management history of the two stands, and 2) to determine the effect of different levels of forest accessibility on deadwood volume and carbon stocks, estimated using coefficients established by the Intergovernmental Panel on Climate Change (IPCC).
The amounts of deadwood and carbon stored per ha were higher than the values reported in the Spanish and Italian national forest inventories, including the one developed for the Riojan beech woods. Deadwood volume was on average 22.5 m³ ha^-1, showing an unequal distribution depending on the distance from the access roads. Deadwood volume decreased dramatically from the areas close to the access roads moving into the forest, passing from 31.6 m³ ha^-1 to 25.7 m³ ha^-1 to only 9.9 m³ ha^-1 (respectively in the first, second, and third class of accessibility). The decomposition classes were all present, indicating the development of natural degradation dynamics. Finally, the carbon sequestrated in the deadwood was 27.9 t ha^-1 in the first accessibility class, 22.7 t ha^-1 in the second accessibility class, and 9.7 t ha^-1 in the third accessibility class, for an average of 20.1 t ha^-1. The distribution patterns of deadwood in beech forests of La Rioja, apparently counterintuitive, were due to a combination of different factors, including slope, cattle grazing, and weather conditions which might have favoured downward movement of the deadwood. Furthermore, the presence of several standing dead trees near the access roads suggests a preference for removal of deadwood from local population in the more distant areas.