DEVELOPMENT AND APPLICATION OF A COMPUTER SIMULATION MODEL TO EVALUATE THE EFFECTS OF DIFFERENT RESIDUAL DIAMETER DISTRIBUTIONS ON 30-YEAR GROWTH OF UNEVEN-AGED NORTHERN HARDWOOD STANDS

A computer simulation model was developed to represent the growth of uneven-aged northern hardwood stands maintained under the selection system. The computer program generates a set of tree data which approximates the initial diameter distribution specified by the model user. Tree data are stored in model plot data lists. Mortality, survivor growth and ingrowth subroutines update the model plot data lists over a 5-year period. By repeatedly calling the three growth subroutines, the model can project stand growth over a longer period of time. Tree data from all model plots are pooled to produce stand-level summary data at the end of each 5-year period.;The model projected the growth of stands having 36 different initial diameter distributions over a 30-year period. The distributions were based on four basal area levels (10, 15, 20 and 25 m('2)/ha), three maximum tree sizes (40, 50 and 60 cm DBH) and three Q ratios (1.2, 1.5 and 1.8 based on a 5-cm diameter class width). Changes in model stand diameter distributions over the 30 years were studied to evaluate how easily the different initial distributions could be recreated at the end of the cutting cycle. Basal area, total volume, sawtimber volume and large sawtimber volume growth data were recorded to determine the effects of the different initial distributions on model stand growth.;Data obtained from the model runs provided some basis information needed to develop marking guides for uneven-aged northern hardwood stands cut at 30-year intervals. Different combinations of Q, maximum tree size and basal area maximized basal area, total volume, sawtimber volume and large sawtimber volume growth. Diameter distributions based on a Q ratio of 1.2 appeared more difficult to recreate at the end of a 30-year cutting cycle than distributions based on Q ratios of 1.5 and 1.8.;The model was developed to study the effects of different diameter distributions on growth of uneven-aged stands during a 30-year cutting cycle. Comparisons between available permanent sample plot remeasurement data and model projections indicated that model stands behave in many respects like real uneven-aged northern hardwood stands. Therefore, the model was judged adequate for satisfying the stated objective.