Year: 1997
Type: article
Abstract: Browse utilization estimates can be based on relationships between twig diameter at the point it was browsed and initial twig weight (Basile and Hutchings 1966, Lyon 1970) on measurements of percent twigs browsed (Stickney 1966) or on the visual determination of form classes (Schmutz 1983). All of these methods express utilization along a scale ranging from 0 to 100% (0—90% in the case of Schmutz 1983). The ecologic implications of points on such a scale, however, vary among land managers. A survey of browse condition may also be based on tree or shrub architecture. The concept is based on a discrete criterion: Does the level of grazing allow trees and shrubs to attain their normal stature? The concept arose from observations of Douglas fir, spruce, and willow growing on parts of the northern Yellowstone winter range within Yellowstone National Park. Trees less than about 10 years of age were often browsed or hedged to less than 1.3-ft tall. Nearby, trees (up to Ca. 6.5-ft tall) had heavily-browsed stems that had been killed to within about 1.3-feet above the ground (Fig. 1, left center). Trees with this second growth form ranged from about 10—20 years of age. Older trees were highlined, but had live foliage above 6.5-ft (Fig. 1, right center). The ages of these trees spanned a period in which Yellowstone's northern elk herd increased from less than 4,000 to more than 23,000 (Coughenour and Singer 1996). It seemed likely that the age-related growth forms were associated with an increase in grazing, and they formed the basis for the ideas described below. The Method This method recognizes 2 levels of browsing intensity: a) light-to-moderate, and b) intense. Under light-tomoderate browsing, young trees or shrubs may grow to the height typical of their kind. Browsing is defined as intense when it prevents young plants from attaining their normal stature. Four plant architectures are described that correspond with 4 different browsing regimes. The architectures are developed over the period of time that the terminal leaders are within reach of browsing animals. Uninterrupted-growth-type architecture is produced under light-or-moder
Author: Richard B. Keigley
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
SDG: Life on land
Open Access status: green
OpenAlex ID: W86311348