Relationships between Overstory Structure and Understory Production in the Grand Fir/Myrtle Boxwood Habitat Type of Northcentral Idaho

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Abstract
Relationships between overstory structure and understory current year production on 20 undisturbed sites of the grand fir/myrtle boxwood habitat type were studied in the Clearwater Mountains of north central Idaho. Overstory characteristics measured were tree canopy coverage, sum of the tree diameters, basal area, stand height and stem density. Understory production was divided into 4 vegetation classes: shrubs, forbs, graminoid and total production. Regression models predicting current year production of each understory vegetation class were developed using all possible combinations of overstory parameters as independent variables. Canopy coverage and sum of the tree diameters were the best indices of understory production. Canopy coverage was most significantly correlated with total understory production and shrub production. Canopy coverage and sum of the tree diameters were the most significantly correlated overstory parameters with forb production. Graminoid production was not significantly correlated to any of the measured overstory parameters. Basal area, tree density and stand height were not statistically related to the understory production. Further examination of the models is needed to validate these relationships over the range of the grand fir/myrtle boxwood habitat type. The models are not applicable to areas where recent disturbance such as logging, fire, or disease has affected overstory structure.

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