INSTYTUT DENDROLOGII

The main aim of the present work was to determine: 1) the minimal photosynthetic photon flux density that yew seedlings require in order to emerge and survive; 2) importance of nitrogen fertilization on a development yew seedlings in a various light intensity.

The relationship of seedlings and saplings of number of European yew (Taxus baccata) to the photosynthetic photon flux density (PPFD) reaching the forest floor was analysed under natural conditions. Two permanent plots, subdivided into 1x1 m square plots, were established in a naturally regenerating population of Taxus baccata formed during last decades in the Kórnik Arboretum, Poland. All seedlings in every 1x1 m plots were counted and included into three height categories: to 6,0 6,1-25,0 and 25,1-100 cm. Relative PPFD was measured for every plot at the canopy height of the yew seedlings. The dependence of seedling survival upon PPFD was examined.

Seedlings of Taxus baccata have the best chance for survival and growth under a narrow range of light conditions. Seedlings can survive on deeply shaded sites (below 2% of PPFD) for 1-2 years, but in the following years their light demands increased. In the lowlands of Central Europe, the best light environment conditions are between 3-7% of relative PPFD. The development of herbs and seedlings of more light-demanding trees may induce the elimination of yew seedlings in the understorey environments with higher PPFD. The narrow range of relative PPFD is probably one of the main reasons for the mortality of T. baccata seedlings in natural populations of the species.

In a artificial shading experiment Taxus baccata seeds were sowed to the various light intensity: 2, 8, 30 and 100% of full sunlight and in nitrogen (NH3) fertilization variant. Mortality of seedlings were noted and dry mass, area and length of leaves, stems and roots of Taxus baccata seedlings was measured several times every year.

The highest mortality was noted in deep shade and full sunlight. Direct reason of die yew seedlings was probably low temperature, because most of seedlings died at the time of Winter. The best conditions for survival and growth of yew seedlings were in 30%, and the worst in 2% of full sunlight.

Yew seedlings begun to grow better in higher light intensity (100, 30 and 8 % of full irradiation) between third and fourth month of life. However, seedlings fertilized grew better only between fourth and fifth month in comparison with seedlings without nitrogen fertilization. In a deep shade (2% of full sunlight) seedlings fertilized with nitrogen grew better only in second and third years of their life. The light was the most important factor for survival and growth of young yew seedlings but nitrogen fertlization can co-limit with survival and growth older yew specimens.