Different age and spatial structure of two spontaneous subpopulations of Taxus baccata as a result of various intensity of colonization process

Abstract

The aim of the present work was a comparison of the age and spatial structure of two populations of Taxus baccata in the Kórnik Arboretum, formed spontaneously under different initial conditions. The first of them (plot one) comes from at least 11, while the second (plot two) from only two, potential mother tress at a distance up to about 100 m. The influence of the local climate conditions on the seedlings was also analyzed. Age structure of the population formed from 11 mother trees was found to be typical for young, but developing populations of shade tolerant trees about 40 years after the first cohorts were founded. The youngest seedlings formed the most numerous age class, still without saplings. The class ranking next consisted of tree-like specimens of the highest age. Obviously, the population of the first plot was formed by only few cohorts of seeds, in period of about 20 years. Seedlings may have appeared every year, but most often nearly all of them died. The sub-population on the second plot, developed as offspring from only two close-by growing mother trees, was formed during much a longer period and is characterized by a different age structure. The oldest individuals are less numerous as those in sub-population one. There is also a number of saplings, which are still joining the main stand; such saplings were not found in the other sub-population. The spatial structure of two sub-populations is also different. The first of them, which comes from several mother trees, is characterized as rather uniform, while the second which can be traced back to two mother trees, shows a clump distribution of tree-like yews. The climate parameter limiting the number of surviving seedlings in particular years appears to be a minimal temperature below −7.5 °C in November. Temperatures of winter and spring, as well as the drought/precipitation regime during the vegetation period do not restrict the survival rate of the seedlings. Obviously, the distribution of individuals of the ornithochoric species T. baccata is strongly determined by the availability of mother trees in a distance suitable to be bridged by birds. Long distances limit seed supply heavily and retard and prolong the period of colonization. As a consequence, dispersal distances influence strongly age and spatial structure of cohorts founded from isolated (groups of) mother trees.