Effects of Stress and Defence Allocation on Tree Growth: Simulation Results at the Individual and Stand Level

Based on the eco-physiological, individual tree-based growth model BALANCE effects of defoliation and drought stress on growth, allocation and opportunity costs are analysed for pure and mixed stands of beech and spruce. Opportunity costs were incurred by beech trees in mixed stands that invested in stress defence. The losses due to competition varied with the proportion of available resources and were altered by investing and non-investing trees. Productivity of dominant beech and spruce trees was influenced more by decreasing resource availability (e.g. water) when compared to dominated trees. Under severe drought stress, however, for spruce a nearly constant loss of productivity for all size classes was obvious. Additionally, drought stress clearly changed the allocation patterns of beech and spruce trees. Overall, BALANCE is a useful tool for analysing influences of environmental changes on productivity and efficiency. It can help to map out adaption strategies to avoid negative consequences of environmental changes.