Abstract
Norway included English yew in the Norwegian Red List as this species is threatened and is protected by Norwegian law. Thus, the aim of my study was to reveal the underlying factors for yew regeneration and recruitment in two sites with roe deer, being moderately and highly browsed areas. Specifically, the following hypotheses were tested: (a) The stand structure diversity of yew do not differ among moderately and highly browsed areas of Høgåsen and Fagerliåsen, (b) The stand age of yew do not differ among the two study sites, (c) The yew regeneration is similar among the moderately and highly browsed areas, and (d) The morphological growth forms of individual yew trees differ based on browsing intensity. The two transects of 250 × 15 m2 were laid down on the forest floor in each study site. A total 20 circular plots of radius 5.64 m were established within two transects by maintaining 15 m distance between the plots in each study sites. The all yew plants within a circular plots were investigated. Moreover, dendrochronological analyses were performed to reveal the stand age of each sites. Furthermore, mingling index (Mi) were determined to reveal the interspecific competition within each sites.
My findings revealed that there was no significant difference between Fagerliåsen and Høgåsen in terms of tree density, basal area, volume, DBH and height classes distribution. The average stand age of Høgåsen was older than Fagerliåsen but this difference was not significant. The higher interspecific competitions were observed in both study sites. The balance sex ratio was observed in Fagerliåsen. Similarly, male-biased sex ratio was found in Høgåsen. The regeneration and recruitment of yew were higher in Høgåsen compared to Fagerliåsen. The higher browsing pressure was observed in Fagerliåsen and moderate browsing pressure was observed in Høgåsen. The highly browsed trees developed hourglass shape, highly browsed saplings and small trees were suppressed to growth, whereas light to moderate browsed trees formed ordinary tree shape. Hence, it can be concluded that heavy browsing from roe deer reduced the regeneration and growth of yew.
Evidently, previous studies suggested that herbivory from ungulates negatively impact on regeneration and recruitment of yew. For the long term conservation of yew species, management should reduce the roe deer population to a level where browsing damages is acceptable for a healthy and viable yew forest stand. Therefore, increasing the number of yew nature reserves along with fencing the area around small young trees against ungulates could be better management strategy to protect and conserve the yew population.