A Method for Determining the Onset Year of Intense Browsing

Abstract

A survey based on browsing related architectures indicated that browsing level had increased at the Mt. Haggin Wildlife Management Area. We describe a technique for determining the year in which the increase in browsing level occurred. The technique is based on the analysis of stems old enough to have experienced the early period of light browsing; the onset year of intense browsing was determined by using dendrochronology to date the formation of twig clusters produced by intense browsing. Stems from 20 Geyer willow (Salix geyeriana Anderss.) plants were analyzed from each of 6 study sites. Mean onset years at the 6 sites ranged from 1983.1 to 1988.4; the mean onset year for all 6 sites was 1985.4 ± 0.5 SE (N = 120). The reconstructed history was used to evaluate the relationship between moose (Alces alces) number and browse trend. From 1976 to 2000, the winter trend census of moose increased from 7 to 56. The onset of intense browsing in 1985 occurred when 23 moose were counted.

Wolves, elk, willows, and trophic cascades in the upper Gallatin Range of Southwestern Montana, USA

“…Since elk usually consume segments of the stem from the current year's growth, browsing removes the terminal bud causing growth to emerge from a lateral bud. When this happens each year, the stem grows in a zigzag pattern leaving behind stubs representing annual segments that can be measured (Keigley et al, 2003). Thus, to assess elk browsing intensity, we determined whether each annual leader segment had been browsed for as far back in time as possible (typically two to five years).…”

“…Outside each of the exclosures, we utilized ''plant architecture'' assessment techniques for determining past browsing history and height growth on the Booth willows (Keigley and Frisina, 1998;Keigley et al, 2003;Ripple and Beschta, 2003). Since elk usually consume segments of the stem from the current year's growth, browsing removes the terminal bud causing growth to emerge from a lateral bud.…”

Linking wolves to willows via risk-sensitive foraging by ungulates in the northern Yellowstone ecosystem

“…For each willow whose height was measured in 2004, we used ''plant architecture'' assessment techniques (Keigley et al, 2003;Ripple and Beschta, 2003) to evaluate plant height and browsing history during previous years. Since browsing usually removes the terminal bud of a stem, causing growth to emerge from a lateral bud, the stems grow in a zigzag pattern, leaving behind stubs identifying annual segments.…”

Willow on Yellowstone's Northern Range: Evidence for a Trophic Cascade?

“…We recorded percentage of twigs browsed on a stem as an index to browsing pressure by counting the number of browsed and unbrowsed twigs from the previous year's growth (Y tÀ1 ), or second year's growth (Y tÀ2 ) (Keigley et al 2003). At each of the 18 sites at which one or both species were found to grow when visited, we established a 25-m transect oriented parallel to the stream passing through the center of the densest willow patches.…”