Responses of vegetation to different land-use histories involving grazing and fire in the North-east Patagonian Monte, Argentina

Abstract

In arid and semiarid lands around the world, vegetation is distributed in patches within a bare soil matrix. Vegetation in the North-east Patagonian Monte, Argentina is a shrubland steppe, and patches are dominated by shrubs, with grasses, forbs and cryptogams under their canopy. It was hypothesised that grazing increases patchiness; and fires and wind erosion homogenise the distribution of vegetation. It was predicted that there would be: (1) greater cover, specific frequency and richness of shrubs in grazed sites; (2) greater cover, specific frequency and richness of herbs and preferred grasses in ungrazed sites; and (3) a random pattern of distribution in burnt areas. Aerial cover of all perennial species was measured at six sites with different land-use histories: heavily grazed, medium grazed, ungrazed, long exclosure from grazing followed by grazing, burnt and then ungrazed, and burnt and then grazed. Species were grouped into five functional types: shrubs, sub-shrubs, preferred grasses, non-preferred grasses and forbs. The results showed significant differences in the cover of preferred and non-preferred grasses, forbs and total cover with previous grazing but there was no evidence of shrub encroachment. Species frequency and richness decreased especially with increased grazing intensity. The pattern of spatial distribution changed from aggregated in grazed sites to random in ungrazed and burnt sites for all plant functional types. At the population level, the cover of the grass, Poa ligularis, was greatest on ungrazed sites whereas the cover of the shrub, Chuquiraga erinacea, was greatest on burnt sites. It is concluded that, after applying a heterogeneous patchwork of disturbance, such as grazing, or with fire, followed by periods of rest, the plant diversity is increased.

Seed rain alteration related to fire and grazing history in a semiarid shrubland

“…The findings of Peter et al (2013) indicated that this semiarid rangeland is resilient to fire, but not to continuous grazing. The objective was to study the effect of different land use histories (involving grazing and fire) on the composition of the seed rain, and its spatial and temporal distribution in northeastern Patagonia.…”

“…Several studies have pointed out these changes Pel aez et al, 2010), but others did not find any evidence to support this practice (Peter et al, 2013). Once fire has occurred, the wind redistributes the nutrients and propagules accumulated under the shrub canopy (B oo et al, 1996;Ravi & D'Odorico, 2009), homogenizing the distribution of the vegetation .…”

“…Moderate northwesterly wind occurs throughout the year (Godagnone and Bran, 2009 (Cabrera, 1971) are also commonly found in the herbaceous layer. The study area has almost 100 years of grazing history, with an average stocking rate of z0.18 sheep ha À1 (Peter et al, 2013).…”

“…Five areas with different land-use histories related to grazing and fire were selected using the judgment employed by Peter et al (2013):…”

“…Several authors explained how traditional management has caused several changes in the vegetation (e.g., B€ ar Lamas et al, 2013;Bisigato et al, 2005;Bisigato and Bertiller, 1997; Le on and Aguiar, 1985;Peter et al, 2012Peter et al, , 2013. Soil erosion is one of the principal processes of degradation in the Monte region (e.g., Chartier et al, 2011;Chartier and Rostagno, 2006;Parizek et al, 2002), and its continuous and accelerated advance may cause irreversible changes (Gait an et al, 2007) limiting perennial grasses establishment (Bisigato and Bertiller, 2004;Chartier and Rostagno, 2006), although in some cases grazing exclusion has allowed the vegetation to recover .…”