Using historic management records to characterize the effects of management on the structural diversity of forests

The current structure of managed forests reflects the forest management system and silvicultural treatments applied in each stand, as well as the ecological conditions and natural disturbances which have taken place. This study focuses on forest structural diversity as a key component of biodiversity assessments and aims to analyse the effects of silvicultural management on the structural diversity of forests. The area chosen for this study is Pinar de Valsaín, a Scots pine (Pinus sylvestris L.) forest in the Central mountains of Spain. In Pinar de Valsaín the effects of uniform shelterwood management, individual tree selection and thinning can be assessed. Data from the periodic inventories and historic management records as early as 1889 were complemented by our own calculations, and have been used to characterize the applied silvicultural treatments as well as to determine the time elapsed since each intervention. Data from a sample survey carried out in 1998 was used to characterize current forest structure. Forest structure was defined by the spatial variability of stem density and basal area within the block, tree size variability at microstructure level (coefficient of variation of diameter at breast height, and height differentiation within the sample plots), and species diversity of stems, regeneration and shrub at block level calculated as Shannon index and Simpson index. In Pinar de Valsaín, the application of uniform shelterwood system has lead to a greater heterogeneity in the spatial structure within blocks but also to a more homogeneous microstructure. Thinning resulted in homogenisation at both stand and microstructure level. Potential problems of the presented approach as well as possibilities to include the findings in forestry decision making are discussed.