An increase in herbivory of cottonwood in Yellowstone National Park
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Authors: R. B. Keigley
Date: 1997
Journal: Northwest Science
Volume: 71
Number: 2
Pages: 127-135
Summary of Methods: In the summer of 1994, five narrowleaf cottonwood stands in northeastern Yellowstone National Park were measured for the effects of elk herbivory. These stands were dated by photographs from different time periods and individual bushes were classified as alive or dead, browsed or unbrowsed and measured for maximum height of live previous-year-growth, browse- killed stem, and other stand parameters. Snow levels recorded from 1954-1994 at the Tower Ranger Station were used to determine if snow depth had affected bush height.
Article Summary / Main Points: Stands one and two were the oldest and had 100% and 82% mortality respectively. Stands three, four, and five (five being the youngest) all had 10% or less mortality. The tallest unbrowsed stem height for all of the stands was 29 cm while the average height for the live previous-years-growth was around 30 cm for stands two and three and 15 cm for stands four and five. The average height for the oldest browse-killed stem steadily decreased from 87 cm in stand one to 9 cm in stand five. Snow depth was not found to be a factor in bush height suggesting that increasing elk numbers in the park reduced cottonwood bush heights in stands over time, thereby decreasing the number of cottonwoods that reached maturity.
Vegetation Types: Other (includes Forest and Eastern) Riparian and Wetlands
MLRA Ecoregions: 43B Central Rocky Mountains
Agrovoc Control Words: Riparian zones Rangelands Wildlife
Article Review Type: Refereed
Article Type: Documented Case History
Keywords: elk, cervus elaphus, narrowleaf cottonwood, populus augustifolia, yellowstone national park, browsing, herbivory
Annotation: Inclusion of climatic and fire data, if available, might have made this study more robust. The data does suggest elk browsing was causing low statured cottonwood bushes; however, it might not be the only factor involved. A combination of overgrazing and poor climatic conditions could be driving this degradation. Though this is a case study specific to Yellowstone National Park these findings could be applicable in areas with very high elk concentrations.
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