Height growth development of Norway spruce, fir and common beech regeneration in uneven-aged mixed species stands

To enhance the modeling of tree recruitment within simulation models a flexible height growth model for juvenile trees (< 1.3 m) in naturally regenerated uneven-aged mixed species stands was developed. Data were obtained from 240 sample plots located in mixed Norway spruce, fir, and common beech stands. On each plot, the number, of trees by species and divided by height class was recorded. For every species and height class a representative tree;was selected to determine the. total tree height and the height increment of the past 5 yr. of growth. The model predicts the actual periodical 5 yr. height increment by adjusting the corresponding potential height increment for a five year growing period using three competition measures: (1) the competition of the remaining overstory, (2) intra- and interspecies competition among the regeneration itself, and (3) a modifier for the edge effected incidence of light.