Effects of different silvicultural measures on plant diversity - the case of the Illyrian Fagus sylvatica habitat type (Natura 2000)

In Slovenia, the Natura 2000 network covers more than 37% of the country. Forests dominate more than 70% of this area, and forest management is a significant driver of diversity. Depending on the options applied, forest management may enhance or decrease forest biodiversity. Dinaric fir-beech forests (part of Natura 2000 habitat type) with remarkable nature-conservation interest and timber production functions were selected for this study. With the aim of testing the effects of different silvicultural measures on plant diversity in these forests, and consequently on biodiversity in a broader sense, three sites in the Slovenian part of a Dinaric fir-beech forest range were studied. The plant species diversity was assessed before and after the implementation of silvicultural measures of three intensities: (1) control plots - no logging; (2) logging of 50% of the growing stock; and (3) logging of 100% of the growing stock. Before the implementation of the silvicultural measures, the mean number of plant species per 400 m² vegetation plots was 48.8, and the mean value of the Shannon’s diversity index was 2.41. Two years after the measures were implemented, different magnitudes of plant species turnover were observed. There were no significant changes in plant diversity status and vegetation composition in the control plots. Two years after 50% of the growing stock was logged, the mean number of species was 73.3, and the mean value of the Shannon index was 3.21. In the plots where all the trees were removed, the mean number of species was 87.4, and the mean value of the Shannon index was 3.42. In parallel with the increases in the diversity parameters, the cover of the herbaceous layer increased significantly with an increase in the silvicultural intensity, indicating that short-term species turnover can mostly be attributed to herbaceous plant species. As a result of changed stand and ecological conditions, an increased plant diversity, a greater biodiversity in a broader sense and an improved habitat suitability for different animal species could be expected