Productivity of western larch in relation to categorical measures of climate, soil moisture, and soil nutrients

The relationship between western larch (Larix occidentalis Nutt.) productivity, as determined by site index, and estimates of climate, soil moisture and soil nutrients, as delineated within the Biogeoecosystem classification system, was examined. Data was collected from 315 even-aged stands throughout the range of western larch in B.C. Climate, expressed by subzone, showed a significant effect on the site index of western larch; however, significant differences occurred only between two groups: lower precipitation (Interior Douglas-fir) and higher precipitation (Interior Cedar - Hemlock and Montane Spruce ) subzones. The climatic growth optimum for western larch corresponded to the intermediate segment of a regional climatic gradient - wetter temperate climate - that is represented by the Dry Warm Interior Cedar - Hemlock subzone. In relation to edatopes, site index significantly increased from water-deficient to moist sites and decreased from moist to wet sites, and on water-deficient sites, it increased with increasing soil nutrient regime. On water-deficient sites, estimates of both actual soil moisture regime and soil nutrient regimes had both positive significant and consistent effects on site index. On non-water deficient sites, the effect of soil nutrient regime appeared to be marginal. A cross-validated prediction model based on actual soil moisture regime and soil nutrient regime accounted for 83% of the variation in site index of western larch suggesting that there is a strong correlation between ecological site classification and western larch productivity. The developed model, combined with the identification of actual soil moisture regime, and soil nutrient regime can be used to provide reliable site index predictions for western larch throughout its range in B.C. to a level of accuracy required for practical forest management.Forestry, Faculty ofGraduat