The influence of stand structure on European yew Taxus baccata populations in its natural habitats in central Poland

摘要

Taxus baccata is a rare species throughout its entire natural range and is often categorized as nationally threatened in countries where it occurs. In Poland yew is under protection and almost all sites with yew occurrences are subject to reserve protection. The aim of the study was to answer the following questions: What is the tree diameter structure of stands in three yew reserves? What is the stand biodiversity of three yew reserves in central Poland? How does the stand species composition influence natural regeneration of yew? What shall be done in the future to protect yew in its natural habitats? The study was conducted in three yew reserves in central Poland. Based on a detailed research on 30 circular sample plots established in each reserve we found high stand diversity in all investigated areas. Shannon-Weiner index (H ') was high in general and ranged from 1.50 to 1.69, and the Shannon's index of evenness (E) ranged from 0.51 to 0.64. The diameter structure of two studied reserves was similar to natural multi-layered stand structure. The number of yew trees and their vitality was low. The species diversity of natural regeneration in all reserves was very high. However, the quantity and quality of yew regeneration in multi-layered diameter structure was significantly lower than in one-layered stand structure. To protect yew, appropriate conservation measures should be undertaken, including silvicultural treatments for in situ species conservation. We found that passive conservation is an inappropriate strategy for yew because of its weak competitiveness ability. We recommend active conservation approach, including silvicultural treatments. i.e. cutting broad-leaved trees in places where the basal area is the highest, removing some trees in the upper layer of stand which compete with yews. Individual protection of yew seedlings and saplings is also necessary because of damages caused by herbivores.