Epsilon Archive for Student Projects

Abstract

The homogeneous structures of Swedish forest limits and threats biodiversity. To protect and preserve the biodiversity found in the country, land is set aside. In southern Sweden, broadleaf forest is often suitable for such set asides due to their limited abundance and high associated biodiversity values. In order to preserve forests in the long-term, regeneration is a prerequisite. However, old broadleaf forest found in protected areas often are observed to have a limited natural regeneration. Broadleaf forest tree species compositions change along gradients in site conditions due to differences in tree species adaptations. Site conditions are among other things edaphic gradients which are spatial changes in moisture, nitrogen availability, and pH. Other factors which influence broadleaf tree species compositions are variations in light conditions, as well as selective browsing pressure that may alter how the species compositions of tree regeneration changes along these gradients.
This thesis´ aim was to test if browsing affects how the natural regeneration of trees varies along gradients of light and soil in protected broadleaf forests in southern Sweden. This was done by inventorying fenced and unfenced plots in three protected areas in the county Skåne. The collected data was the number of seedlings found, as well as the plots´ light and edaphic conditions indicated by the plots´ ground vegetation. Thereafter, Generalized Linear Models were created to test how the general number of seedlings and the number of beech and ash seedlings shifted with changing gradients of light and site conditions, and how this shift changed when exposed to browsing in un-fenced plots and when browsing was excluded in fenced plots.
The results indicate that the total number of seedlings and beech seedlings increased with increased nitrogen availability and lower pH. Additionally, lower pH was found to increase the total number of ash seedlings. Furthermore, increased light conditions increased both the total number of seedlings and beech seedlings. The results did not clearly indicate that browsing changes the expression of the light and edaphic gradients. There was rather a tendency that the effects of nitrogen availability and pH effect was more pronounced in un-fenced plots on the general number of seedlings and beech seedlings compared to fenced plots. The variable shade index indicated an increased number of beech seedlings with decreasing shade index in un-fenced plots compared to fenced plots. The single effect of fencing on the number of seedlings was not significant in this study but indicated an increase in seedling number in fenced plots.
This research shows tendencies that browsing influences how some edaphic and light gradients are expressed. However, the pattern is not consistent in the created models. The results still show that gradients of light and soil conditions effects natural regeneration. If fencing is implemented, sites which have a high variation of site conditions are expected to yield high variation in tree species regeneration. Research in this field of study is needed to understand how browsing influences natural regeneration expressed by certain site conditions. With a more well-rounded understanding, recommendations to protected areas which struggle with natural regeneration can be given.