Ecological consequences of silviculture at variable stand densities. I. Stand growth and development

The main goal of this review was to characterize ecological consequences of growing trees at variable stand densities. We found that the majority of studies were focused on biometry, productivity and mortality of trees, and wood quality and its economic value, while the influence of stand density on biomass allocation, abiotic and biotic factors, chemistry of different tree organs, diversity and biomass of understory plants, ecophysiology of trees and microclimate conditions (e.g. temperature, humidity, light conditions, etc.) were only occasionally addressed. Stand growth and development trajectories are clearly modified by stand density, however the strength of influence depends on the phase of stand development. Lower seedling densities in nursery conditions lead to increases in their height and diameter, thus influencing seedling quality used in afforestation. The positive influence of higher density on diameter and height of trees in younger stages of stand development may be a result of higher probability of seedlings being planted in more favorable microhabitats, improvement of microclimate conditions, earlier crown closure that reduces interspecific competition for nutrient and water resources. Moreover, stand density clearly influences branch diameter and length, and thus knot size. Higher stand density results in earlier crown closure and higher tree mortality, leading to vertical and horizontal changes in stand structure (DBH, height and crown dimensions of trees). In the denser stands slender and flexible trees with small, narrow crowns dominate, and most of the trees belong to the 3rd class according to Kraft' classification of tree social positions in the stand. The influence of stand density on stand structure may lead to changes in biomass partitioning and thus merchantable wood production and nutrient retention in particular tree organs