Reduction Numbers of Tree Heights in Forest Shelterbelts of the Northwestern Caucasus

Study of regional indicators of the tree canopy of forest shelterbelts, one of which is reduction numbers, is of considerable scientific and practical interest. Such data are not available for the conditions of the Northwestern Caucasus. The goal of this work is to investigate the pattern of change and to calculate the values of reduction numbers of tree heights in the shelterbelts of the region. For this purpose, problems related to measuring tree heights in the inner and outer rows of shelterbelts were solved. The values of reduction numbers were determined using various methods, and models of their change depending on the rank of trees were created. Ten trial plots with 106–141 individuals in each were laid out for the five main species. Reduction numbers were determined using the classical Schiffel method, average values for rank groups, and newly created models. The value of reduction numbers did not depend on the type of tree species (F = 0.011, P = 0.999) or the row of growth in the belt (F = 0.0002, P = 0.995) and changed in parallel in the inner and outer rows (T = 0.058, P = 0.9528). A similar trend was observed when using the method of averaged values for rank groups. The reduction numbers of heights in forest shelterbelts, when compared with the classic ones for massive forest plantations, demonstrated a difference of over 5% in the extreme ranks; with Schiffel’s data, rank 10 at 5.98, rank 100 at 10.4; with Davidov’s data, rank 100 at 10.4%. This indicates the need to clarify the values of reduction numbers for the objects under study. An adequate model (R 2 = 1) was developed, and new values of reduction numbers of heights for trees growing in forest shelterbelts of the Northwestern Caucasus were calculated on its basis.