Ecological consequences of silviculture at variable stand densities. III. Stand stability, phytoclimate and biodiversity

The main goal of this review was to characterize ecological consequences of growing trees at variable stand densities. We analyzed the influence of stand density on its mechanical and biological stability, diversity and biomass of understory plants and microclimate conditions (e.g. temperature, humidity, light, etc.). Higher stand density results in higher susceptibility to wind and snow damage, due to changes in height to diameter ratio (tree slenderness). The mechanical stability of stands may be promoted by silvicultural activities such as light thinning applied before growth stagnation. In addition, the reduction of stand density during stand development may increase biomass allocation to coarse roots that stabilize trees in the soil. High tree density may increase stand susceptibility to pathogens and insects and thus increase tree mortality. Trees growing at higher density (with higher intraspecific competition) may allocate less assimilates for defense against herbivorous insects and pathogens. The effect of tree density on stability of multi−species stands is inconclusive, since such studies were only occasionally undertaken. Since tree density influences light conditions (mainly before canopy closure), there is a negative relationship between stand density and herbaceous species diversity and biomass. Based on the published data, we summarized consequences of silviculture at different stand densities and proposed future directions of research needed to fill the gaps in current knowledge. Understanding the long−term ecological consequences of variable stand densities is essential for development of sustainable and stable forest ecosystems