Effect of <i>Prosopis</i> (mesquite) invasion and clearing on vegetation cover in semi-arid Nama Karoo rangeland, South Africa

The Nama-Karoo is the largest of the three biomes that comprise the semi-arid Karoo-Namib ecoregion of southern Africa. Large tracts of Nama-Karoo rangeland have been invaded by alien leguminous trees of the genus <i>Prosopis</i>. We assessed the impact of <i>Prosopis</i> invasion and clearing on vegetation cover in heavily grazed Nama-Karoo rangeland on two sheep farms in the Beaufort West district of the Western Cape province of South Africa. Our results suggest that, below critical threshold cover levels, <i>Prosopis</i> trees do not affect indigenous vegetation and add to overall rangeland vegetation cover. However, once <i>Prosopis</i> cover exceeds critical thresholds, the trees begin to negatively impact on indigenous vegetation (especially grasses) and overall vegetation cover. In addition, our data suggest that vegetation cover recovers after <i>Prosopis</i> clearing, being temporarily higher than pre-invasion levels possibly as a result of enhanced post-invasion soil fertility. Lastly, our results suggest that <i>Prosopis</i> trees reduce rangeland erosion potential at low cover and increase it after they exceed critical threshold cover. Information about thresholds of <i>Prosopis</i> impact can be used to direct clearing efforts for maximum benefit when resources are limited.

纳马-卡鲁（Nama-Karoo）是构成南部非洲半干旱卡鲁-纳米比生态区的三大生物群区中规模最大的一个。目前大片纳马-卡鲁牧场已被牧豆树属（*Prosopis*）的外来豆科树木入侵。本研究针对南非西开普省博福特西区两家绵羊牧场内重度放牧的纳马-卡鲁牧场，评估了牧豆树入侵及其清除操作对植被覆盖度的影响。研究结果显示，当植被覆盖度低于临界阈值时，牧豆树不会对本土植被造成负面影响，反而能提升牧场整体植被覆盖度；但一旦牧豆树的覆盖度超过临界阈值，其便会对本土植被（尤其是草本植物）及整体植被覆盖度产生不利影响。此外，研究数据表明，牧豆树被清除后，牧场植被覆盖度会得以恢复，且会暂时高于入侵前的水平，这一现象可能源于入侵后土壤肥力的提升。最后，研究结果显示，牧豆树在低覆盖度时会降低牧场的土壤侵蚀潜力，而当其覆盖度超过临界阈值后，则会提升土壤侵蚀潜力。当资源有限时，掌握牧豆树影响临界阈值的相关信息，可指导清除工作以实现效益最大化。

搜集汇总

背景与挑战

背景概述

该数据集研究了南非半干旱纳马卡鲁牧场中外来Prosopis（牧豆树）入侵和清除对植被覆盖的影响。研究发现，Prosopis在低覆盖水平下增加总体植被覆盖且不影响本土植被，但超过临界阈值会负面影响本土植被和总体覆盖；清除后植被覆盖可恢复，甚至暂时超过入侵前水平，同时Prosopis覆盖变化还影响牧场侵蚀潜力。