In Europe, the English yew species (Taxus baccata L.) is endangered. Intensive human land-use, including forest management, has caused a decrease of the yew populations all over Europe. In Austria, gene conservation forests are used for the in situ conservation of populations of this rare tree species by silvicultural treatments. In order to improve the conservation management in these gene conservation forests, this study addresses the relation between competition and viability of yew populations through the use of structural diversity indices. The structural indices, which include mingling, tree-tree distance, diameter, and tree height differentiation, were determined for a structural group of four trees as well as the neighbouring trees of the male and female yews at the monitoring plots on a regular grid in three gene conservation forests. Although the three study sites provided quite different environmental conditions for English yew, the vitality of each individual yew was influenced by the interspecific competition of the neighbouring tree species at all sites. Low vitality was associated with a small mean distance to neighbours and large tree height differentiation. In conclusion, we suggest that a combination of different structural indicators is needed for an integrative assessment of conservation status in the gene conservation forests. This would help improve the evaluation of the impact management has on yew population viability.

English yew Taxus baccata L. has been catalogued as endangered tree species and prone to extinction in Austria as well as many other parts of Europe. The present work is based on the comparison of the natural population of two gene conservation forests from different geographic locations in Austria where the spatial structure, regeneration status and possible conservation measures are examined. The pole stand distribution varied distinctly in each sites. The total no of individuals per ha (DBH ≥5 cm), average DBH and average height were 492 n·hm -2 , 8.8 cm and 6.3 m in Stiwollgraben whereas in Leininger Riese 45 n·hm -2 , 16.3 cm and 7.6 m respectively. Over 79% of the Stiwollgraben population were represented the good health condition, while in Leininger Riese it was less then 49 % which means population of Stiwollgraben is in better condition compared to Leininger Riese. The sites differed considerably in the pattern of regeneration but pattern were consistent with the dynamics depicted by the age distribution. Considering the one-year-old seedlings Stiwollgraben contains 13 019 individuals·hm -2 whereas Leininger Riese only 1 368. Surprisingly there were no any saplings in respect of 51 to 150 cm height classes in both sites and 30 to 50 cm in Stiwollgraben. In that context the conservation of English yew on the forest level may require well-managed reserves and long-term rotations between harvest events, protection from the herbivore and reduction of competition, which will enhance the long-term viability of the species.

ABSTRACT:The amount, variability and quality of coarse woody debris (CWD) in an oak-dominated natural forest reserve in Austria were studied in 2006. The average volume of CWD (snags and logs) was 107.3 m 3 /ha, which accounted for 39% of the total living volume. Among the CWD, on average, 23.4 m 3 /ha (22%) were snags and 83.9 m 3 /ha (78%) were logs. According to quality aspects the CWD displayed a wide range of variation in tree species, tree size, stage of decay, and structural characteristics, creating a high diversity of CWD habitats for microorganisms. Among the three forest associations, the highest amount of CWD was found in the mesic Galio sylvatici-Carpinetum association. The results of this study are discussed as reference values for a close-to-nature management of oak-dominated broadleaved submontane forests emphasizing conservation management.

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