Weak competitive ability may explain decline of Taxus baccata

Marian J. Giertych,Janusz Szmyt,Karolina Sobierajska,Grzegorz Iszkuło,Yakiv Didukh,Anna K. Jasińska

doi:10.1007/s13595-012-0193-4

Abstract

Abstract Context Taxus woodlands suffer from a lack of natural regeneration across its whole distribution range. Aims In Knyazhdvir Reserve in Ukraine Taxus baccata primarily competes with Abies alba. It has been assumed that in the conditions of deep shade, yews have a greater competitive advantage than firs. Methods To verify this hypothesis, a plot with both species growing under the canopy was established. Wood samples were taken from 20 trees of T. baccata and 20 trees of A. alba. Results There were no differences in the mean tree-ring width, height and age between both species. Due to a lack of spatial separation of both species, yews and firs inhabited the same area in the analysed plot. Fir seedlings (up to 0.5 m) were recorded to grow under yew saplings (above 0.5 m), but the inverse situation of yew seedlings growing under fir saplings was not seen. Conclusion Seedling distribution, tree-ring growth rate, possibility of growth of fir seedlings under yew saplings and greater potential growth suggested that fir was predisposed to having the competitive edge over yew. Our results may confirm the hypothesis that T. baccata has a restricted distribution because of weak competitive abilities and can exist only in habitats where faster growing species are absent. The results call into question the prevailing opinion that human influences are the principal cause for the decline of T. baccata.

Highlights

Taxus baccata is a rare species throughout its entire natural range and is often categorized as nationally threatened in countries where it occurs (Thomas and Polwart 2003; Schirone et al 2010) and the woodlands with Taxus have received priority habitat status under Annex I of the EU Habitats Directive
The crown layer of the studied plot consisted of nine individuals of Fagus sylvatica with a height ranging between 17.0 and 38.0 m, two specimens of A. alba with heights of 24.0 and 25.5 m and an individual of Acer platanoides 27.5 m tall
The seedling distribution, tree-ring growth rate, possibility of fir seedling growth under yew saplings and larger potential growth than Taxus point to the fir tree as the species predisposed to having a competitive edge over the yew

Summary

Introduction

Taxus baccata is a rare species throughout its entire natural range and is often categorized as nationally threatened in countries where it occurs (Thomas and Polwart 2003; Schirone et al 2010) and the woodlands with Taxus have received priority habitat status under Annex I of the EU Habitats Directive. All seedlings die in the first or second year, initially their number is high (Thomas and Polwart 2003). The main reasons for seedling mortality are grazing by deer (Perrin et al 2006), excessive shading (Iszkuło and Boratyński 2006), interaction of low temperature and light availability (Iszkuło 2010) and drought in the Mediterranean region (Sanz et al 2009). Dioecy may adversely affect the mortality of yew (Iszkuło et al 2009; Cedro and Iszkuło 2011). The passive protection of European yew populations and the lack of thinning in the natural reserves have resulted in excessive canopy density and, lack of reproduction success (Dhar et al 2008)

Methods

Results

Discussion

Conclusion