Despite many studies that have explored the effect of livestock grazing on plant communities, the response of species composition and diversity to livestock grazing in arid rangelands remains ambiguous. This study examined the effects of livestock grazing on plant communities in arid steppe rangelands of North Africa. Plant diversity of annual species, perennial species, and all species combined were measured and compared between grazed and grazing-excluded areas. We also examined the relative importance of species turnover and community nestedness. Moreover, the effects of livestock grazing on beta diversity at local among transects and landscape among sites scales were examined using the multiplicative diversity partitioning. Results revealed that livestock grazing significantly decreased the alpha diversity of all species combined and the diversity of annual plants. Livestock grazing induced a shift in plant community composition where most species composition variation (~74%) was due to infrequent species replacement 'turnover' between the two management types rather than nestedness (~26%). Results revealed also that among transects, beta diversity was higher in grazed steppes than in grazing-excluded steppes. Whereas, among sites, beta diversity was lower in grazed steppes compared to grazing-excluded steppes. These findings suggest that livestock grazing in arid steppe rangelands increases the variation in plant species composition at a local spatial scale and engenders vegetation homogeneity at a landscape spatial scale. Therefore, the implementation of appropriate management practices such as short-term grazing exclusion is mandatory to prevent these ecosystems from large-scale biotic homogenization.

中文翻译：

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地中海干旱草原牧场牲畜放牧引起的大规模生物均质化

尽管有许多研究探讨了放牧对植物群落的影响，但物种组成和多样性对干旱牧场放牧的反应仍然不明确。本研究调查了牲畜放牧对北非干旱草原牧场植物群落的影响。测量并比较放牧区和禁牧区之间的一年生物种、多年生物种和所有物种的植物多样性。我们还研究了物种周转和群落嵌套的相对重要性。此外，使用乘法多样性划分检查了牲畜放牧对局部横断面和场地尺度景观的β多样性的影响。结果表明，放牧显着降低了所有物种的α多样性和一年生植物的多样性。牲畜放牧导致植物群落组成发生变化，其中大多数物种组成变化（~74%）是由于两种管理类型之间不频繁的物种替换“更替”，而不是嵌套（~26%）。结果还表明，在横断面中，放牧草原的β多样性高于排除放牧的草原。然而，在站点中，放牧草原的β多样性低于不放牧的草原。这些发现表明，在干旱草原牧场放牧增加了局部空间尺度上植物物种组成的变化，并在景观空间尺度上产生了植被同质性。所以，