Do shrubs reduce the adverse effects of grazing on soil properties?

Abstract

Increases in the density of woody plants are a global phenomenon in drylands, and large aggregations of shrubs, in particular, are regarded as being indicative of dysfunctional ecosystems. There is increasing evidence that overgrazing by livestock reduces ecosystem functions in shrublands, but that shrubs may buffer the negative effects of increasing grazing. We examined changes in water infiltration and nutrient concentrations in soils under shrubs and in their interspaces in shrublands in eastern Australia that varied in the intensity of livestock grazing. We used structural equation modelling to test whether shrubs might reduce the negative effects of overgrazing on infiltration and soil carbon and nitrogen (henceforth ‘soil nutrients’). Soils under shrubs and subject to low levels of grazing were more stable and had greater levels of soil nutrients. Shrubs had a direct positive effect on soil nutrients; but, grazing negatively affected nutrients by increasing soil bulk density. Structural equation modelling showed that shrubs had a direct positive effect on water flow under ponded conditions but also enhanced water flow, indirectly, through increased litter cover. Any positive effects of shrubs on water flow under low levels of grazing waned at high levels of grazing. Our results indicate that shrubs may reduce the adverse effects of grazing on soil properties. Specifically, shrubs could restrict access to livestock and therefore protect soils and plants beneath their canopies. Low levels of grazing are likely to ensure the retention of soil water and soil carbon and nitrogen in shrubland soils. Copyright © 2015 John Wiley & Sons, Ltd.

Microsite and grazing intensity drive infiltration in a semiarid woodland

“…Bhark & Small, 2003;Eldridge, Beecham, & Grace, 2015;Eldridge, Wang, & Ruiz-Colmenero, 2015;Gómez et al, 2015;Madsen, Chandler, & Belnap, 2008), we demonstrated substantially greater sorptivity and infiltration under the canopies of long-lived vegetation patches such as shrubs, trees, and perennial grasses than in the interspaces. Bhark & Small, 2003;Eldridge, Beecham, & Grace, 2015;Eldridge, Wang, & Ruiz-Colmenero, 2015;Gómez et al, 2015;Madsen, Chandler, & Belnap, 2008), we demonstrated substantially greater sorptivity and infiltration under the canopies of long-lived vegetation patches such as shrubs, trees, and perennial grasses than in the interspaces.…”

“…Similarly, long-term livestock removal has been shown to reduce soil compaction and increase rates of water infiltration (Castellano & Valone, 2007). Although these sites had sparse levels of perennial vegetation and were heavily grazed by livestock, they still had macropore indices of~10, consistent with information from well managed sites on loamy-textured Haplargid and Durargid soils in nearby national parks (Eldridge, Beecham, et al, 2015). Although these sites had sparse levels of perennial vegetation and were heavily grazed by livestock, they still had macropore indices of~10, consistent with information from well managed sites on loamy-textured Haplargid and Durargid soils in nearby national parks (Eldridge, Beecham, et al, 2015).…”

Biotic communities cannot mitigate the negative effects of grazing on multiple ecosystem functions and services in an arid shrubland

“…Important biotic components such as biocrust cover, bare soil, shrub size and plant richness had only a very small role in mediating the grazing effects in our study site (~0.07 for multifunction; 0.09 for multiservice). The direct effects of grazing on multifunctionality and multiservices may also be driven by other important factors that were not measured in this study such as shifts in soil microbial communities (Eldridge et al 2015). that can influence soil N content and mineralisation through consumption and deposition of plant material or through impacts on plant litter quality.…”

“…For example, dense patches of litter associated with perennial shrubs are associated with higher concentrations of organic matter and soil nutrients (Soliveres et al 2014). and greater infiltration and soil moisture (Colloff et al 2010;Eldridge et al 2015), leading to patches of enhanced microbial, invertebrate and vertebrate activity (Schlesinger et al 1990). Similarly, biocrusts have been shown to be associated with enhanced functions such as soil stabilisation, water infiltration, nitrogen mineralization and organic matter-rich soils compared with areas of bare soil (Eldridge et al 2010;Bowker et al 2013;Delgado-Baquerizo et al 2015).…”

“…Previous studies have highlighted how grazing reduces specific functions (e.g. soil respiration; Eldridge et al 2010;Thomas 2012;Daryanto et al 2013a, b;Eldridge et al 2015Eldridge et al , 2016 or services (e.g. soil stability; Eldridge et al 2013).…”