The forrest already faces the problems related to the global climate change. The effects on the vitality of single trees and also the biodiversity of whole wood communities are in the focus of several scientific works. Natural wood communities developed a quite complex system of plant competition related to sustainable balanced geo-chemical and climate parameters due to evolutionary processes. System dynamics on the one hand and stable system conditions on the other provide the plant community with a self generating potential. This potential is quite important in order to create healthy and productive forests. In order to assess geochemical and climate effects on biodiversity the BERN-Model (Bioindication of Ecosystems Regeneration towards Natural conditions) was created by ECO-DATA. The model allows the user a brief look on the possibility range for natural plant community’s existence in dependence on special site parameter ranges. The BERN database contains plant and plant community related information about site parameters with slow dynamic (e.g. relief, exposition, type of soil, soil texture) and with fast dynamic (e.g. base saturation, C/N ratio, soil moisture) also. These parameters represent the ecological niche and are completed by several climate parameters that are quite relevant to the plant development: Length of vegetation period (days of the year with an average temperature above 10°C), climate water balance in the vegetation period (saturation versus potential evaporation) and available energy by solar radiation (sum of solar radiation during vegetation period). So the model’s outcome will be knowledge not only about the fundamental niche width of single plants, but also information about the realized niche width of a whole plant community. The second part of the BERN model first looks for the possibility of a single plant species in a 6-dimensional space of belonging and selects the constant species of a plant community. Then it combines the plant related possibilities by using the Fuzzy Minimum operator to calculate the possibility of the whole plant community. And this is the way to assess the possibility of plant communities for different types of sites and climates. Using future climate scenarios it’s possible to look for tree communities which are stable in vitality now and in the near future (figure). This knowledge allows forest managers to create vital forests using a long term perspective. This is why these processes and the effects should be taken very seriously by the local decision makers and should also be utilized by the forest managers in order to create a sustainable, vital and productive forest.