Site quality evaluation models for aspen (Populus tremuloides Michx.) in Wisconsin

Soil and site relationships were studied in 32 mature quaking aspen (Populustremuloides Michx.) communities in north central Wisconsin. Multiple linear regression techniques indicated that soil texture, available water-holding capacity, water-table depth, and stand exposure were the most important factors controlling site index. Two models developed from combinations of these factors accounted for 62% of the variation in site index. Values for soil calcium, magnesium, potassium, and phosphorus were corrected for bulk density and summed to 12-, 24-, 36-, and 60-in. depths. When included in additional models, only magnesium to a 60-in. depth was found to have additional effect on aspen growth over and above that implicit in available water-holding capacity. The models were validated using 10 additional mature aspen stands and then applied to data from 10 stands in early stages of deterioration.