Potential effects of management practices on nitrogen nutrition and long-term productivity of western hemlock stands

The FORCYTE-10 computer model, developed by J.P. Kimmins and K. Scoullar for Douglas-fir forests in British Columbia, was modified to simulate growth and nutrient cycling of coastalwestern hemlock stands. Initial calibration indicated that predicted yield was extremely sensitiveto the rate of mineralization of soil organic matter ( SOM ), variation in SOM C:N ratio with sitequality, the soil extractable NO3- :NH,' ratio, and the decomposition rate and N mineralizationpattern of large and medium-size roots and woody debris. The predictions suggested that yieldand SOM remain stable under a management system consisting of six successive 90-year rotations.More intensive utilization ( e.g., shorter rotations, whole-tree harvesting and commercial thin-ning) causes depletion of soil and forest floor nitrogen and a small decline in site productivity inlater rotations.