A cooperative agreement between Yale University and the 1970 summer program of the IBM Research Division resulted in a flexible computer program to simulate the growth of the uneven-aged, mixed-species stands of trees on the 10-meter by 10-meter experimental plots of the Hubbard Brook Ecosystem Study in the White Mountains of northern New Hampshire. Annual increments of tree growth are based on species, tree size, and allocation of available light among the competing trees of the plot. Site quality differences between plots are assigned primarily by the concept of tree-growing degree-days, although soil moisture storage during the growing season and plot rockiness are also considered. Species succession, individual tree suppression and release, and other dynamic properties of forest stands have been successfully reproduced using the program. Additional field measurements are needed to further verify the model and to extend its applicability to nutrient cycling and other aspects of the Hubbard Brook Ecosystem Study. We believe that the simulator could readily be extended to include most other tree species of northeastern North America and also to match data from other sites through appropriate adjustment of program parameters.
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