Academic journal article The American Midland Naturalist

Effects of Horning and Rubbing Behavior by Bison (Bison Bison) on Woody Vegetation in a Tallgrass Prairie Landscape

Academic journal article The American Midland Naturalist

Effects of Horning and Rubbing Behavior by Bison (Bison Bison) on Woody Vegetation in a Tallgrass Prairie Landscape

Article excerpt

ABSTRACT.-Horning and rubbing behaviors of American bison (Bison bison) and their effects on woody vegetation were investigated for 2 yr on a herd of 300+ animals reintroduced to a 1973-ha tallgrass prairie site in Oklahoma. Horning and rubbing activity was significantly higher in summer than in other seasons. Whether this increase was associated with rut, shedding of winter pelage, insect harassment, or a combination of these factors was unclear; however, these behaviors did have measurable impacts on the woody vegetation of the area. Bison injury to trees was minimal, although one willow (Salix nigra) was uprooted and killed during the study, and several other trees were seriously damaged. Bison horning had the greatest effect on saplings and shrubs, killing or severely damaging 4% of the woody plants documented within the study area and causing moderate injury to 13% and light injury to 12%. Bison showed a strong preference for small willows, killing or severely damaging 17% of the saplings and shrubs of this species during the study. Bison also used artificial, man-made objects present on the landscape such as utility poles and fenceposts. Results suggest that horning and rubbing by bison, along with fire and drought, may have influenced the historical distribution of woody vegetation in prairie environments.

INTRODUCTION

Bison (Bison bison L.), like many large mammals (Snyder and Janke, 1976; Inouye et al., 1994), are capable of severely impacting woody vegetation. England and DeVos (1969) suggested that herds of bison in North American prairies once influenced the distribution of woody vegetation by horning, rubbing, grazing and trampling. Soper (1941) noted that wood bison (B. b. athabascae) destroyed trees by horning and rubbing against them to reduce insect irritation. Similar behavior has been observed in populations of plains (B. b. bison) bison (McHugh, 1958; Meagher, 1973). Moss (1932) and Campbell et al. (1994) concluded that the near extinction of bison from overhunting in the northern plains contributed to the expansion of aspen (Populus tremuloides) woodland into prairies during the late 1800s.

Few studies have documented quantitatively the effects of bison on woody vegetation. Edwards (1978) found that bison in private midwestern herds destroyed woody plants by horning, rubbing and feeding on bark. In one case, 15 bison in a 36-ha enclosure had debarked 80% of the 600 trees in a 1-ha grove in 1 yr, killing most by the following year. He noted that bison exhibited species preferences in their horning, rubbing and feeding activities. McHugh (1958) found that 14% of a small sample of lodgepole pines (Pinus contorta) horned by bison in Yellowstone National Park (YNP) were girdled and killed. Horning and rubbing of lodgepole pine by an estimated 2500 bison spending the summer of 1992 in the Hayden Valley of YNP resulted in extensive tree mortality (M. Meagher, pers. comm.).

We conducted a study of the effects of bison on woody vegetation in the Nature Conservancy's 15,342-ha Tallgrass Prairie Preserve (TPP) in Oklahoma. Bison were reintroduced to the preserve after an absence from the area of almost 140 yr (Shaw and Lee, 1995). The objectives of our research were to: (1) quantify horning and rubbing activity of bison; (2) characterize objects selected for use by bison during these behaviors and (3) examine effects of bison horning and rubbing on woody vegetation.

MATERIALS AND METHODS

The TPP is located ca. 25 km NW of Pawhuska in northern Oklahoma (3650'N, 96o25'W) in the Osage Hills, an extension of the Flint Hills that lie primarily in Kansas. The Flint Hills have hilly topography and generally rocky soils that historically prevented extensive cultivation. Vegetation of the area is native grassland dominated by big bluestem (Andropogon gerardii), indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum) and little bluestem (Schizachyrium scoparium). …

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