A measurable effect of feral grazing on pasture accumulation rate

Abstract

Feral animals such as possums are known to utilise pasture as a substantial part of their diet, with individual animal intake rates well quantified. The objective of this study was to quantify this effect in terms of pasture accumulation rates, in areas where these animals are likely to occur in high densities; i.e. the boundaries between native forest and pastoral farms. Pasture accumulation rate was measured in small plots open to feral grazing and plots excluded from grazing with electrified flexinets, at six sites throughout the Waikato. Three further sites, within possum control schemes, were established as controls. Pasture accumulation rates were significantly greater within the exclosure plots at all six uncontrolled sites, by ~3 kg DM/ha/d in late-winter and ~7 kg DM/ ha/d in late spring. In contrast there were no significant differences between open and exclosure plots at the three sites where there was active possum control. This effect is quite substantial in the context of livestock consumption, though is not entirely reconcilable with predictions based on possum intake and diet studies. It nevertheless represents a source of loss which is easily countered, with additional benefits in terms of lowered Tb risk and improvement of native vegetation condition. Keywords: feral grazing, grazing exclosure, pasture accumulation rate, possum diet