Historical land use by domestic grazing revealed bythe soil seed bank: a case study from a natural semi-arid grassland of NW Patagonia

Livestock can affect the soil seed bank through various mechanisms associated with changes in vegetation. We sampled vegetation and seed banks of Patagonian grasslands, in areas with different historical use by grazing (exclosure, moderate use and high use) to evaluate to what extent changes in vegetation are reflected in the seed bank. We also evaluated the effect of historical grazing on horizontal spatial seed distribution by sampling under shrubs and in between plant gaps. We focused the study on functional groups, and on the palatable Poa ligularis, an indicator of grassland status. In general, the proportional changes in composition and abundance of functional groups produced in grazed sectors (relative to each exclosure) were bigger for the seed bank than for the aboveground vegetation. Impacts on seed bank were led by a decrease (moderate use), or total disappearance (high use) of perennial grasses, results clearly reflected by P.ligularis. Although shrubs were represented in vegetation, they were undetected in the seed bank through germination, probably due to the lack of the conditions required for breaking seed dormancy. Intensive grazing produced homogenization in seed spatial distribution. Our work revealed a poor contribution of the seed bank to vegetation regeneration at increasing historical use by grazing. We recommend sampling the seed bank when monitoring the conservation status of grasslands to obtain consistent management guidelines.