| Abstrakt: |
Sagebrush is a vital habitat component for many endangered grassland species. As the need for sagebrush habitat restoration increases, models that enable restoration practitioners to calculate seeding or planting densities required to obtain desired sagebrush cover within specific time frames are essential. We measured cover and density of naturally occurring silver sagebrush (Artemisia cana)stands, subjected to different grazing management in Grasslands National Park. In 10 × 10 m plots, stem diameter and crown diameter of all individuals were measured; a subset of individuals were photographed to determine canopy cover and sampled (cut) for age determination by ring count. Strong relationships between morphological characteristics and age were found. Age was significantly correlated with stem diameter (r2 = 0.79) allowing nondestructive age estimations to be made for A. cana. Canopy cover was correlated to stem diameter and age (r2 = 0.49 to 0.67) with the relationship best described by reciprocal quadratic and rational models. We accurately modeled plot cover as the product of mean canopy cover, determined from morphological models, and plot density (81% of cover estimates within 10% of measured values). Sagebrush mortality was estimated using age frequencies of the sagebrush stems and outplanted seedling survival rates of other studies. Using mortality rate to determine how sagebrush density would change over time, we made projections of sagebrush cover for outplanted seedlings. These models indicate largest cover increases can occur in areas that are lightly grazed by cattle, but that greatest short-term increases can occur in areas where cattle grazing is heavier. Before this study, maximum canopy cover of sagebrush, and age at which it was achieved, were unknown and estimated for restoration purposes. This study provides essential information for successful restoration of A. cana, by modeling sagebrush cover as a function of density and stand age. |
