Der einfluß von bestandeskenngrößen, topographie, standort und witterung auf die entwicklung des kronenzustandes im bereich des forstamtes Rothenbuch

This article tries to evaluate, by different regression models, the data of a visual forest health inventory, which has been carried out since 1983 in the forest district Rothenbuch (Spessart). As explanatory variables (regressors) characteristics of stand, topography, site and weather were considered, as well as the state of tree health of the previous year ("last year value"). Separately for five tree species, sets of regressors are established which are able to determine the degree of defoliation in a significant manner. Within these lists the regressor "last year value" is dominant, explaining (maximum) 61-75% of this year's defoliation. Further, variables related to stand, site and weather play an important role. For beech, oak and spruce there is a highly significant influence of age, with lower damage in younger stands (<50 years old), and greater damage in old stands (>100 years old) for beech and spruce and with high damage in middle aged stands (50-100 years old) for oak. For beech in thinner stands too and after fructification significant higher defoliation can be observed. Unfavourable soil conditions such as thick humus layer, low pH etc. in tendency lead to higher defoliation, but here the tree species do not behave uniformly. With respect to weather, after dry years one has to expect higher tree damage with high transpiration stress due the to dry and hot atmosphere having a greater impact than water deficit in the soil. Topography is of minor importance and indicates higher defoliation at higher elevation (for oak and larch) and less steep slopes (for oak and spruce). In total the regressors related to stand, topography, site and climate explain in addition to the regressor "last year value" only about 4 to 12% of defoliation, depending on tree species.