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Journal Article

Livestock Grazing-Fire Regime Interactions within Montane Forests of Zion National Park, Utah

Michael H. Madany and Niel E. West
Ecology
Vol. 64, No. 4 (Aug., 1983), pp. 661-667
Published by: Wiley on behalf of the Ecological Society of America
DOI: 10.2307/1937186
Stable URL: http://www.jstor.org/stable/1937186
Page Count: 7
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Livestock Grazing-Fire Regime Interactions within Montane Forests of Zion National Park, Utah
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Abstract

Major differences were found between the vegetation structure of ponderosa pine-dominanted communities on the Horse Pasture Plateau and those on the nearby but isolated Church and Greatheart Mesas in Zion National Park. The Horse Pasture Plateau was heavily grazed by livestock in the late 19th and early 20th centuries, while the mesas were never grazed. Conditions on the mesas now approximate the pre-European situation of the region as described in the earliest written accounts. Pine, oak, and juniper sapling density and cover were much higher on the formerly grazed plateau than on the relict mesas. Herbaceous species dominated the groundlayer in mesa ponderosa pine savanna stands, while grass and forb cover was low on analogous sites of the plateau. Age-class distributions of major tree species further substantiated that major physiognomic changes have occurred on the plateau since the arrival of European man. Analysis of fire scars showed that prior to 1881, the mean fire-free interval for ponderosa pine stands on the plateau was 4 to 7 yr, while the interval for Church Mesa was 69 yr. Since there were no recorded fires on Church Mesa between 1892 and 1964, and yet no corresponding increase in sapling density, the increased understory density of plateau stands should not be attributed primarily to cessation of fires. Instead, heavy grazing by livestock and associated reduction of the herbaceous groundlayer promoted the establishment of less palatable tree and shrub seedlings, Fire, however, played an important secondary role in maintaining savanna and woodland communities.

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