Short-Term Responses to Sheep Grazing in a Patagonian Steppe

VALENTA M.D.; GOLLUSCIO R.A.; FREY A.L.; GARIBALDI L.; CIPRIOTTI P.

RANGELAND JOURNAL

AUSTRALIAN RANGELAND SOC

Lugar: Melbourne; Año: 2020 vol. 42 p. 1 - 8

1036-9872

Grazing modifies ecosystem function through direct effects on plants, but also through indirect effectsmediated by floristic changes induced by grazing. Although both types of effects occur in the long term, only the directeffects are evident in the short term. We evaluated the short-term direct effects of sheep (Ovis aries) grazing on aPatagonian steppe during one growing season.Wemeasured plant aerial cover in permanent transects located at increasingdistances from a watering point in three paddocks with different stocking rates through the growing season. We alsomeasured frequency of defoliation for vegetative and reproductive phases of different plant species located along thesetransects. Sheep grazing directly (a) reduced aerial cover and/or increased frequency of defoliation of certain preferredgrasses and perennial forbs, (b) did not increase the aerial cover of any life form, but only the proportion of bare soil, (c) didnot change the litter aerial cover, and (d) defoliated the flowers of even the least preferred shrub. Result a) was coincidentwith previous plant aerial cover long-term studies; but results (b) and (c) were contrary to long-term studies, probablybecause they resulted from indirect rather than direct grazing effects. Result (d) was not detected by long-term studies,probably because flower defoliation through grazing is undetectable when measuring shrub plant aerial cover. Our studyshowed that grazing has short-term direct effects mainly on the most preferred species. This could be useful for rangelandmanagement and conservation of Patagonian steppes because short-term effects may be more easily reversible than longtermones, and may provide early warning of rangeland condition deterioration.Additional keywords: degradation, defoliation, herbivory, non-preferred species, plant