Plant community composition and structure under short-term grazing exclusion in steppic arid rangelands

Yacine Kouba,Tewfik Mostephaoui,Saifi Merdas,Badreddine Saadali,Haroun Chenchouni

doi:10.1016/j.ecolind.2020.106910

Abstract

Grazing exclusion has been proved to be an effective approach for naturally restoring degraded rangelands. Still, the effect of this management practice on plant community composition and structure is ambiguous, especially under prolonged and repeated drought events. Here, we investigated the responses of community composition (i.e. incidence-based) and structure (i.e. abundance-based) to short-term sheep grazing exclusion under severe drought episode in the arid steppes of Alfa-grass (Stipa tenacissima L.) with a long evolutionary history of grazing. Individual species responses were tested based on species occurrence and abundance in either grazed or grazing-excluded steppes. Besides, indicator species analysis was used to identify species indicative of grazing-excluded steppes. Likewise, incidence-based and abundance-based α-diversity, β-diversity and functional groups’ diversities were quantified using Hill Numbers and compared between the two steppe managements types. Under severe drought conditions, sheep grazing exclusion allowed the apparition of a large number of increasers, colonizers, and native indicator plant species. It also improved the size of regional species pool and increased overall incidence-based and abundance-based α-diversity. Moreover, grazing exclusion decreased the abundance-based β-diversity at local scale but increased it at landscape scale. The incidence-based β-diversity significantly decreased at the landscape scale. Grazing exclusion enabled a significant spatial structuration of abundance-based β-diversity components by maintaining high balanced variation in species abundance at large spatial scale and greater abundance-gradient at fine-scale. Our results suggest that the implementation of short-term grazing exclusion in arid steppes would be the appropriate management practice for vegetation and habitat during prolonged droughts since it permits the recovery of native plant species and affects positively the size of the regional species pool, the overall incidence- and abundance-based α-diversity as well as the abundance-based β-diversity (chiefly at landscape scale).

Highlights

Rangelands occupy a vast area of terrestrial ecosystems and are a valuable base for livestock production and provide important ecological services such as water infiltration and storage, erosion control, wildlife habitat biodiversity, and carbon sequestration (Reinhart et al 2018, Vecchio et al 2019)
H. salicifolium and A. cyrtolepidioides have increased their abundances in the exclosures to become subordinate and dominant species, respectively
Our study revealed a clear effect of short-term grazing exclusion, under severe drought episode, on plant community diversity in Alfa steppe rangelands with a long-term sheep grazing

Summary

Introduction

Rangelands occupy a vast area of terrestrial ecosystems (ca. 30 %; Ellis and Ramankutty 2008) and are a valuable base for livestock production and provide important ecological services such as water infiltration and storage, erosion control, wildlife habitat biodiversity, and carbon sequestration (Reinhart et al 2018, Vecchio et al 2019). A variety of management strategies have been implemented to restore degraded rangelands worldwide (Neffar et al 2018), but the most fundamental and economic management practice remain a nature-based solution “grazing exclusion”, especially in arid and semiarid regions (Tang et al 2016), due to its low investment, extensiveness, simple implementation, and quick response. The effect of short- or long-term grazing exclusion on plant communities of arid rangelands has been the focus of several recent studies. Drought frequency and intensity may greatly affect vegetation dynamics in arid rangelands and the stochastic nature of precipitation may obfuscate vegetation response patterns to grazing exclusion in these ecosystems (Kakinuma et al 2017)

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