Patch dynamics under rotational and continuous grazing management in large, heterogeneous paddocks
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abstract
Overoptimistic stocking rates are the leading cause of rangeland degradation. The phenomenon of patch-selective grazing means that the stocking rate on heavily used patches is much higher than that intended for the area as a whole. In addition, the differential use of preferred areas in the landscape results in uneven distribution of animal impact. Landscape heterogeneity increases as grazing unit size increases, resulting in heavier impact on preferred areas. Such phenomena compound over time and have a major long-term impact on the environment and primary and secondary production. This study investigates whether rotational grazing allows reduction of, and recovery from, degradation caused by patch-selective grazing in large (1800-2100 ha) paddocks by providing adequate rest between grazing events. From 1995 through 1998, herbaceous basal area and bare ground changes were measured on adjacent heavily and lightly grazed patches in rotationally and continuously grazed paddocks. Although weather was a dominating influence (p0.0001), the eight-pasture rotation system resulted in greater perennial herbaceous basal area (p = 0.0987) and lower proportions of bare ground on bottomland soils (p = 0.03) and clay-loam soils (p = 0.052) than the continuously grazed control. The increases in basal area with rotational grazing were primarily due to increases in perennial C4 mid- and shortgrasses. Grazing treatment did not influence species aerial biomass composition (p>0.1). This study provides evidence that in large paddocks, rotational grazing allows recovery from and reduces degradation caused by patch overgrazing. Planned rotational grazing addresses the root cause of patch overgrazing and deterioration. It is, therefore, a key tool in managing for sustainable use and restoration of rangeland. 2002 Elsevier Science Ltd.
