Shrub age structure in northern Minnesota aspen stands

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Age data from hazel (Corylus spp.) and total shrub populations of seven aspen stands in northern Minnesota were used to investigate two age-density distribution models: a negative exponential model and a power function model. The negative exponential model, implying a constant mortality rate for all age shrubs, is the better model for describing population dynamics of both hazel and total shrub populations in the study area. The mortality rate within a stand was independent of stem density and age, decreased when overstory basal area increased, and increased as site quality increased. The mortality rate of hazel increased with light availability, but the total shrub population mortality rate decreased with increasing light availability. The regeneration rate of new aerial stems differed among the sampled stands, indicating its importance in regulating shrub dynamics. The regeneration rate was negatively related to overstory basal area, and positively related to light availability and site index. Hazel regeneration was also positively related to overstory age, implying more regeneration of aerial stems in older stands. Coefficients of the negative exponential shrub age structure relationships are estimated from overstory characteristics and site conditions. © 2001 Elsevier Science B.V.

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Forest Ecology and Management