Seasonal Patterns of Forage Availability in the Fescue Grasslands Under Contrasting Grazing Histories

Abstract

Grazing by large herbivores has been shown to condition vegetation in a manner that improves grassland quality for subsequent herbivory. Fescue grasslands evolved with disturbance from fire and winter grazing by bison but are now grazed primarily by cattle during summer. We examined the effect of long-term summer grazing on the seasonal forage production and quality of fescue grasslands in an examination of the hypothesis that long-term grazing had conditioned fescue grasslands to benefit livestock. This hypothesis was examined by comparing, between grazed and ungrazed plots, the biomass and composition of herbage components, concentrations of nitrogen (N) and acid detergent fiber (ADF) therein, and the ability of major plant types to maintain their biomass and quality throughout the growing season. The study was conducted in southern Alberta at five sites that had long-term exclosures (20+ yr) on grasslands that had been moderately grazed. Grazing had no effect on the N concentration of associated grasses, but grasses had lower N concentration than forbs. Concentrations of ADF followed a reciprocal trend to N. Grazing increased the mass of forbs from about 10% to 20% as a proportion of total biomass, which in turn, was not affected by grazing history. However, this grazing-induced shift to a higher quality vegetation type was not sufficient to affect total mass of N or total digestible nutrients at the community level. Rather than changes in current growth and quality, the predominant effect of summer grazing was in reducing litter mass, which also had the potential for affecting forage production and selection by herbivores. Finally, grazing reduced the relative contribution of rough fescue to total biomass by about 30%, and despite no significant effect on the potential to support summer grazing, this change could reduce the quality of these grasslands for winter grazing. Resumen El Pastoreo por grandes herbívoros ha demostrado que mejora la vegetación incrementando la calidad de los pastizales para un pastoreo subsecuente. Los pastizales de Festucas evolucionaron con perturbaciones de fuego y pastoreo por el búfalo durante el invierno, pero ahora son pastoreados principalmente durante el verano por ganado dome´stico. Examinamos el efecto a largo plazo del pastoreo de verano sobre la producción de forraje estacional y la calidad de los pastizales de Festuca, y probamos la hipótesis de que el pastoreo a largo plazo ha acondicionado los pastizales de Festuca en beneficio del ganado doméstico. Esta hipótesis se examinó por comparación entre parcelas pastoreadas y no pastoreadas, la biomasa y la composición de componentes del forraje, las concentraciones de nitrógeno (N) y fibra detergente ácido (ADF) y en la capacidad de la mayoría de tipos de plantas para mantener su biomasa y calidad a lo largo de la temporada de crecimiento. El estudio se realizó en el sur de Alberta en cinco sitios que tenían exclusiones a largo plazo (más de 20 añ os) en pastizales ha habían sido pastoreado moderadamente. El pastoreo no tuvo...

Grazing improves C and N cycling in the Northern Great Plains: a meta-analysis

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Impacts from Winter-Early Spring Elk Grazing in Foothills Rough Fescue Grassland

“…Bare ground and litter cover did not differ between HG and LG in our study, but they did differ when grazing occurred during late spring-summer-fall (Naeth et al 1991, Bork et al 2012. Our results indicate that bare ground and litter cover in foothills rough fescue grassland are impacted less by grazing during winter-early spring than by grazing later in the growing season.…”

Szarvasmarhák legelőhasználata és legeléspreferenciája

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