Climate change and warming will potentially have profound effect on forest growth and yield, especially for the pure stands in the near future. Thus, more and more attention is given to the mixed stands, for example pine and beech mixtures. Yet, interaction of tree species, growing in mixtures it is still remaining question to be answered.
Thus the aim of this study was to investigate the impact of the interspecific and intraspecific competition to diameter, height and crown width of pine and beech trees growing in mixtures and to evaluate the impact of climatic indicators to the beech radial diameter increment.
The data was collected in the mixed mature pine beech double layer stand, located in the western part of Lithuania in 2017. The sample plot of 1.2 hectare was established and tree species, diameter at the breast height, tree height, height to crown base and crown widths as well as position were measured for all 836 trees. Additionally, representative sample of radial diameter increments were estimated only for the beech trees, by taking out core discs at the height of 1 meter, when the stand was partially cut. Competition analysis was based on distance dependent competition index, based on crown parameters. Climatic effect was evaluated by using Classification and Regression Trees (CART) analysis.
It was found almost no intraspecific competition effect to diameter, height or crown width for both tree species. Yet, interspecific competition effect was important for pine as well as for beech trees.
These results show the possible coexistence of these tree species due to niche differentiation.
Analysis of climatic indicators revealed that higher than 48.5 mm precipitation during February-May of current year had very positive effect to radial growth of beech trees as well as mean temperatures from July to September being lover than 16.5 °C.
Contrary, temperatures lover than 5.2 °C during March and April as well as high precipitation during the January, more than 62.8 mm had negative effect to beech radial increment.
Generally, cool summers as well as higher precipitation during the June of current year had positive effect to the beech radial increment. It shows its sensitivity to high temperatures as well as droughts during the summer time under Lithuanian growth conditions.