Grazing or Not Grazing: Implications for Ecosystem Services Provided by Biocrusts in Mediterranean Cork Oak Woodlands

Abstract

Livestock grazing is one of the most common practices in managed woodlands affecting the abundance and diversity of plant and soil communities. While grazing effects have been studied thoroughly in vascular plants, little is known about grazing consequences for soil lichens and mosses ("biocrusts") in managed woodlands. However, these complex communities have critical contributions to soil functioning in drylands. We evaluated grazing effects on biocrust abundance and functional composition in Mediterranean cork-oak woodlands under long-term grazing and after 7 and 17 years of grazing exclusion. We found 4 main groups in the region regarding the functional trait "growth form": fruticose and foliose lichens, and short and tall mosses. Each group presented different water absorption and retention capacity, and showed group-specific effects on soil water and temperature.Fruticose lichens were the most sensitive group to grazing, decreasing dramatically in cover with grazing (~7 times). Also, this group presented higher water retention capacity (~19 h), together with a consistent reducing effect on soil temperature along the grazing gradient (up to 0.9º C). The shift in biocrust abundance and functional composition under grazing pressure have direct consequences in microclimate regulation, and is likely to influence other ecosystem processes such as CO 2 fixation, soil surface protection and habitat provision. In particular, microclimate regulation may affect cork-oak regeneration processes, which is one of the main concerns in managed woodlands.

Dual community assembly processes in dryland biocrust communities

“…In our model we predicted that grazing would have direct effects on individual crust attributes (e.g. functional composition, richness; Bowker et al, ; Concostrina‐Zubiri et al, ; Eldridge et al, ) but also indirect effects via changes in intransitivity (Bowker, Soliveres, et al, ; Soliveres et al, ) and biocrust cover (as larger patches are more likely to support more species which are likely more competitive, therefore modulating biotic interactions). Similarly, the changes in heterogeneity and productivity induced by shrub patches and increasing density at the plot scale should directly affect the composition of biocrust communities (Maestre et al, ), but also their cover and how they interact.…”

“…Finally, to assess the interactions among different biocrust species, we used the four dominant species. Concostrina-Zubiri et al, 2017;Eldridge et al, 2013) but also indirect effects via changes in intransitivity (Bowker, Soliveres, et al, 2010;Soliveres et al, 2015) and biocrust cover (as larger patches are more likely to support more species which are likely more competitive, therefore modulating biotic interactions).…”

“…Grazing can dramatically alter the composition and functioning of biocrust communities in contrasting directions. Intensive livestock grazing can foster local extinctions of functional groups such as fruticose lichens, which enhance soil water retention and reduce soil surface temperature (Concostrina‐Zubiri et al, ), but are sensitive to trampling. Conversely, overgrazing can also create gaps necessary for pioneering taxa such as cyanobacteria and cyanolichens (Bowker et al, ; Concostrina‐Zubiri, Huber‐Sannwald, et al, ; Eldridge et al, ).…”

“…Together with the widespread phenomenon of shrub encroachment, livestock grazing is the most common land use in drylands worldwide. As with increasing aridity or shrub influence, livestock grazing affects the composition and functioning of biocrust communities (Concostrina-Zubiri, Molla, Velizarova, & Branquinho, 2017;Mallen-Cooper, Eldridge, & Delgado-Baquerizo, 2018;Warren & Eldridge, 2001). Grazing can dramatically alter the composition and functioning of biocrust communities in contrasting directions.…”

Towards a predictive framework for biocrust mediation of plant performance: A meta‐analysis

“…As such, biocrusts enhance soil fertility by increasing the availability of C (Li, Zhang, Su, & Jia, ; Tucker et al, ) and N (Barger, Weber, Garcia‐Pichel, Zaady, & Belnap, ) as well as other mineral nutrients (Belnap & Harper, ; Concostrina‐Zubiri et al, ; Guo, Zhao, Zuo, Drake, & Zhao, ; Jafari et al, ). Biocrusts additionally modify soil microclimate via alteration of soil hydrology (Belnap, ; Chamizo, Belnap, Eldridge, Cantón, & Issa, ; Concostrina‐Zubiri, Molla, Velizarova, & Branquinho, ; Faist, Herrick, Belnap, Van Zee, & Barger, ) and surface temperature (Concostrina‐Zubiri et al, ; Couradeau et al, ). Given this wide range of soil modifications, biocrusts can strongly impact the recruitment and performance of plant species with which they coexist (Belnap, Prasse, & Harper, ; Zhang, Aradottir, Serpe, & Boeken, ).…”