Long-term vegetation dynamics mediated by herbivores, weather and fire in a Juniperus-Quercus savanna
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Authors: S. D. Fuhlendorf, and F. E. Smeins
Date: 1997
Journal: Journal of Vegetation Science
Volume: 8
Number: 6
Pages: 819-828
Summary of Methods: At Texas A&M University Agricultural Research Station, Fuhlendorf and Smeins analyzed long-term (45-years) basal area dynamics of dominant graminoid species, across three grazing intensity treatments on the Edwards Plateau, Texas. Taller, more productive mid-grasses were most abundant under moderate or no grazing. Short grasses were most abundant under heavy grazing. Intermediate species were most abundant under moderate grazing and opportunistic weather patterns. The moderately and ungrazed treatments appeared most resistant to short-term weather fluctuations, while the heavily grazed treatment demonstrated significant resilience when grazing intensity was reduced after over 110 years of overgrazing. Significant directional change, which took nearly 20 years, appears to continue in the ungrazed treatment after 45 years of succession. Fuhlendorf and Smeins note that predicting changes associated with a single factor, such as grazing or fire are reasonable in this ecosystem with linear Clementsian models. The primary influence of heavy grazing on increased woody plant dominance is a reduction of fuel from consumption of forage and shifts in herbaceous dominance toward a short-grass community. Less fuel results in lower fire intensities, less uniformity of fires, and lower mortality of woody plants which effectively moves the fire-threshold further into the grassland domain. Thus, when successional changes involve multiple factors, non-linear or multi-scaled linear models may be more appropriate because of interactions between the various factors and feedbacks that create several possible pathways for vegetation change to follow.
Article Summary / Main Points: None
Vegetation Types:
MLRA Ecoregions:
Agrovoc Control Words: Riparian zones Rangelands Wildlife
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: climax community, diversity, grazing, herbivory, scale, stability, succession, vegetation model
Annotation: Three grazing intensity treatments were used in this study.,Two 32-ha units of heavily grazed treatment had a stocking rate of 5.4 ha/AUY in 1948. One of these units was stocked with cattle, sheep, and goats from 1949-present; the other unit was stocked only with sheep from 1949-1969. In 1970, the grazing intensity of both units was increased to 4.8 ha/AUY with cattle, sheep, and goats. The stocking rates of both heavily grazed treatment units were reduced in 1983 to a moderate level that was variable around 8.1 ha/AUY until it was reduced to 10.4 ha/AUY in 1986.,The moderately grazed treatment was a 4-pasture (24-ha each), 3-deferred rotational grazing system (each pasture grazed 1-yr, ungrazed 4-months) with cattle, sheep, and goats at a stocking rate that varied from 6.-8.1 ha/AUY from 1949-1986. Since 1986, stocking rate has been 10.4 ha/AUY. Since 1983, the stocking rates of both the heavily and moderately grazed treatments have been moderate. The ungrazed treatment consists of two 12 ha units that have not been grazed by livestock since 1948. One unit of this treatment also excluded large, free-roaming wildlife. Season of use is not specified.
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