Abstract A lot of studies have been devoted to understanding the underlying mechanism of woody plant encroachment in savanna ecosystems for informed management strategy. However, many of them take their study area as a whole and do not consider the encompassed environmental gradient, which may modulate the role of different factors in the encroachment. This study aims to test the hypothesis that the role of different factors varies over environmental gradient. The test was conducted in the semiarid and mesic regions of the savanna in central Texas, USA. Tentatively, the role of mean annual precipitation (MAP) and woody cover deficit in juniper encroachment was investigated and compared in these two regions. Results suggest that MAP has a positive effect on the encroachment rate in the semiarid region, but not in the mesic region. The encroachment rate increases with woody cover deficit in the semiarid region. In the mesic region, however, the encroachment rate increases with woody cover deficit till a threshold level, then starts decreasing with it. This study demonstrates the varying role of precipitation and woody cover deficit in juniper encroachment across the rainfall gradient of Texas savanna. It furthers our understanding of the underlying mechanism of woody plant encroachment.

中文翻译：

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降水和木质覆盖不足在德克萨斯大草原杜松侵占中的作用

摘要 大量研究致力于了解热带稀树草原生态系统中木本植物侵占的潜在机制，以制定明智的管理策略。然而，他们中的许多人将他们的研究区域视为一个整体，并没有考虑包围的环境梯度，这可能会调节不同因素在侵占中的作用。本研究旨在检验不同因素的作用随环境梯度而变化的假设。该测试是在美国德克萨斯州中部热带稀树草原的半干旱和中湿地区进行的。初步调查并比较了这两个地区的年平均降水量 (MAP) 和木质覆盖不足在杜松侵占中的作用。结果表明，MAP 对半干旱地区的侵占率有积极影响，但在中地区则没有。在半干旱地区，随着木质覆盖的减少，侵占率增加。然而，在中部地区，侵占率随着木质覆盖不足而增加，直到阈值水平，然后开始下降。这项研究证明了降水和木质覆盖不足在杜松侵占德克萨斯稀树草原降雨梯度中的不同作用。它进一步加深了我们对木本植物侵占的潜在机制的理解。