Shifting limiting factors for population dynamics and conservation status of the endangered English yew (Taxus baccata L., Taxaceae)

Abstract

English yew (Taxus baccata L., Taxaceae) is a Tertiary relict locally endangered within parts of its large geographic range. In this paper, I seek to synthesise the literature and discuss the limiting factors for population dynamics and conservation status of this endangered tree. The literature was reviewed, focusing on yew fossil records, biogeography, molecular ecology, stand structure (size, age and sex ratios), and regeneration dynamics. The information reviewed illustrates diminishing population viability mainly in southern marginal areas of the geographical range of English yew. Water availability seems to be limiting yew regeneration to a greater extent than that of herbivory and shade at the southern margin, while at the northern margin such factors as light availability and frost and/or herbivory may be more important than water. Habitats with fleshy-fruited shrubs proved to be the best habitat for seed dispersion, seedling establishment and sapling survival and growth in the Mediterranean mountains. The results discussed here reveal a widespread lack of regeneration and evidence of increased genetic drift, elevated inbreeding, and depressed gene flow, mainly in southern European populations. The maintenance of healthy populations of yew in temperate forests seems to depend mainly on selective canopy opening to reduce light competition, while regeneration in Mediterranean mountains is strongly related to herbivory regulation and the conservation of well-developed forests, understories, and their community of avian dispersers. Gaps of knowledge for this species are the implications of life strategy for survival across long time periods, the different management of logging and herbivory across the yew distribution range and the predictions of recruitment under climate change.