Grazing effect on diversity of annual plant communities in a semi‐arid rangeland: interactions with small‐scale spatial and temporal variation in primary productivity

Abstract

Summary 1The interactive effect of grazing and small-scale variation in primary productivity on the diversity of an annual plant community was studied in a semiarid Mediterranean rangeland in Israel over 4 years. The response of the community to protection from sheep grazing by fenced exclosures was compared in four neighbouring topographic sites (south-and north-facing slopes, hilltop and wadi (dry stream) shoulders), differing in vegetation, physical characteristics and soil resources. The herbaceous annual vegetation was highly diverse, including 128 species. Average small-scale species richness of annuals ranged between 5 and 16 species within a 20 × 20 cm quadrat, and was strongly affected by year and site. 2 Above-ground potential productivity at peak season (i.e. in fenced subplots) was typical of semiarid ecosystems (10 -200 g m − 2 ), except on wadi shoulders (up to 700 g m − 2 ), where it reached the range of subhumid grassland ecosystems. Grazing increased richness in the high productivity site (i.e. wadi), but did not affect, or reduced, it in the low productivity sites (south-and north-facing slopes, hilltop). Under grazing, species richness was positively and linearly related to potential productivity along the whole range of productivity. Without grazing, this relationship was observed only at low productivity (< 200 g m − 2 ).3 The effect of grazing along the productivity gradient on different components of richness was analysed. At low productivity, number of abundant, common and rare species all tended to increase with productivity, both with and without grazing. Rare species increased three times compared with common and abundant species. At high productivity, only rare species continued to increase with productivity under grazing, while in the absence of grazing species number in the different abundance groups was not related to productivity. 4 In this semiarid Mediterranean rangeland, diversity of the annual plant community is determined by the interaction between grazing and small-scale spatial and temporal variation in primary productivity, operating mainly on the less abundant species in the community.

How do sheep affect plant communities and arthropod populations in temperate grasslands?

“…This led us to add seven more references to the first dataset, two more to the second dataset and four more to the third dataset. Given the different reactions of plant communities to grazing intensity depending on habitat productivity (Bakker et al, 2006;de Bello et al, 2006) and salinity levels (Olff and Ritchie, 1998), the few data available on semiarid grasslands (Osem et al, 2002;Li et al, 2008;Campbell et al, 2010) and marshland plant communities (Bouchard et al, 2003;Hofmann and Mason, 2006;Milotić et al, 2010) were excluded from this analysis. Assessment of study quality also led us to exclude surveys dealing with mixed grazing, as well as those where stocking rate could not be calculated from plot size and number of grazing days.…”

Plant community dynamics in shortgrass steppe with grazing relaxation and imposition by large and small herbivores

“…Grazing by large generalist herbivores can have from small to very large impacts on plant community composition and diversity, with primary productivity and evolutionary history of grazing determining some of that variability (Milchunas et al, 1988;Olff and Ritchie, 1998;Osem et al, 2002;Cingolani et al, 2005;Díaz et al, 2007). Much less is known about the impacts of small specialist herbivores, although again the effects can vary from small to very large (Brown and Heske, 1990;Hulme, 1994;Edwards and Crawley, 1999;Keesing, 2000;Maron and Simms, 2001;Bakker et al, 2006).…”

Spatial and temporal heterogeneity ofEragrostis curvulain the downstream flood meadow of a regulated river

“…Considering the lower levels of production and species richness in stony subdivisions (Fig. 3), it can be stated that species compete for soil resources (Osem et al, 2002) in this relatively unproductive environment. On the other hand, due to the high availability of nutrients in sandy subdivisions, production is high, thus plants in these areas compete for light (Osem et al, 2002).…”

“…3), it can be stated that species compete for soil resources (Osem et al, 2002) in this relatively unproductive environment. On the other hand, due to the high availability of nutrients in sandy subdivisions, production is high, thus plants in these areas compete for light (Osem et al, 2002). This seems to be the reason E. curvula showed exceptionally high values for HAV, and to some extent, HMAX in sandy subdivisions.…”