Vegetation dynamics in Mediterranean forest pastures as affected by beef cattle grazing

The effect of livestock grazing on the under-story vegetation in a Mediterranean Pinus nigra forest pasture in the Pyrenees was studied during 6 years, by comparing changes in herbaceous and shrub vegetation under cattle grazing conditions or in absence of livestock. Cattle grazed the pasture each year at a moderate stocking rate of 0.2 LU/ha, for 3 months in spring and 3 months in the autumn. Four 10 m × 10 m exclosures were set up in different locations in the range. Each year, at the end of the grazing season, herbage height and biomass and shrub number, volume and biomass were measured inside and outside the exclosures. Herbage quality was measured at the end of the study. After 6 years, herbage biomass was much greater inside the exclosures (1730 kg DM/ha versus 679 kg DM/ha, p < 0.001) and had a higher proportion of dead vegetation and lower protein content than the grazed areas. Over the same period, shrub biomass increased substantially in the exclosures (528.3 kg DM/ha/year, p < 0.001), as the result of an increase in both shrub numbers and volume, while it remained constant in grazed areas. It is concluded that in the mountain pastures of the Pyrenees, cattle grazing at a moderate stocking rate can prevent shrub encroachment and the accumulation of dead inflammable herbaceous vegetation. It can not only maintain the quality and availability of the forage resource but also enhance the environmental and recreational value of the forest.