The dynamics of the Taxus baccata L. population and the factors affecting its regeneration in the Jasień Nature Reserve

Taxus baccata L. is a relict plant and has a scattered distribution in the entire species range. Yew regeneration may be affected by moisture conditions and tree stand characteristics – variables which change over time and which have not been sufficiently researched to date. The present study determined the size structure of yews, causes of yew mortality, the effects of tree stand characteristics and habitat conditions on yew diameter increment at breast height, the density of yew seedlings and saplings, and the likelihood of yew seedling occurrence. The study was conducted in central Poland, on 22 permanent sampling plots. The paper presents data col- lected in 2017 with reference to previous studies on these plots from 2001 and 2007. Stand volume, basal area, number of trees, canopy cover, and type of forest site were established for the tree layer. Saplings and shrubs were counted. Finally, the parameters determined for yew seedlings included density and percentage of individuals damaged by browsing, as well as soil moisture and percentage cover of herbaceous vegetation in the nearest neighborhood. In 2017, yew density in the tree layer was 70 individuals/ha, having increased by 15 individuals/ha over 16 years. During that period, 6.4 individuals/ha died in that layer. The predominant cause of yew mortality was wind. In the period 2007–2017, the mean diameter increment at breast height was 2.2 mm/year, and indicated a weak relationship only with tree diameter at the beginning of the studied period (R2 = 0.06). In 2017, the mean density of yew saplings and seedlings was 55 individuals/ha and 1005 individuals/ha, re- spectively. Two independent variables were found to be significant in the model of yew seedling occurrence: presence of mature yews on the sampling plot and soil moisture. The condition of the studied yew population is satisfactory, especially in the less moist areas. The number of seedlings is acceptable, but more active protection should be considered due to the scarcity of yew sap- lings. This is all the more important as seed-producing mature yews tend to die as a result of exposure to strong winds and periodic local flooding