Semiarid karst landscapes are often the source areas for regionally important groundwater supplies. Like savannas across the globe, these landscapes are experiencing an increase in woody plant cover—often referred to as woody plant encroachment. Although this phenomenon is commonly viewed as leading to increased transpiration and reduced groundwater recharge, this may not be true of all ecosystems. For example, in the Edwards Plateau region of central Texas—where the underlying geology is karst—dramatic increases in baseflows have occurred concurrently with the expansion of woody plants. It has been suggested that in this context woody plants, especially juniper (Juniperus spp.), are partially responsible for boosting recharge by improving soil infiltrability, but this hypothesis has not been systematically evaluated. Our study examined the effects of an important encroaching shrub (Redberry juniper) on soil infiltrability in the Edwards Plateau. We carried out a large number of infiltration tests to determine soil infiltrability and used a dye tracer followed by soil profile excavation to estimate the potential for deep percolation. Tests were performed at increasing distances under juniper shrubs of five size classes, ranging from young seedlings to mature shrubs. We found that in soils underlying shrubs, infiltrability was quintupled and percolation depth almost tripled compared with soils in intercanopy zones. Surprisingly, shrub size was not a significant factor. Even the soils beneath the smallest shrubs had much higher infiltrability than intercanopy soils, showing that these woody plants modify soil properties at very early stages. We also found that both infiltrability and percolation depth gradually increased with proximity to the trunk and showed a strong correlation with litter thickness. Our results provide support for the hypothesis that in semiarid karst landscapes, woody plant encroachment—especially the invasion of juniper—can play an important role in enhancing groundwater recharge by improving the soil infiltrability.

半干旱喀斯特地貌常常是区域重要地下水供应的来源地区。就像全球的热带稀树草原一样，这些景观的木本植物覆盖率也在增加，通常被称为木本植物侵占。尽管通常认为这种现象导致蒸腾作用增加，地下水补给减少，但并非所有生态系统都如此。例如，在得克萨斯州中部的爱德华兹高原地区（其潜在的地质是喀斯特地貌），基流的急剧增加与木本植物的扩张同时发生。已经提出，在这种情况下，木本植物，特别是杜松（杜松属）），部分原因是通过改善土壤的渗透性来增强补给作用，但是尚未对该假设进行系统地评估。我们的研究检查了爱德华兹高原上一种重要的入侵灌木（杜松）对土壤渗透性的影响。我们进行了大量的渗透测试以确定土壤的渗透性，并使用了染料示踪剂，随后进行了土壤剖面挖掘，以评估深层渗滤的潜力。在五种等级的杜松灌木丛中，从年轻幼苗到成熟灌木丛，以增加的距离进行测试。我们发现，在灌木丛下的土壤中，与冠层间区域的土壤相比，其渗透性增加了五倍，渗透深度几乎增加了两倍。出人意料的是，灌木大小并不是一个重要因素。即使是最小灌木丛下的土壤，其渗透性也比冠间土壤高得多，这表明这些木本植物在很早的阶段就改变了土壤的特性。我们还发现，渗透性和渗透深度都随着靠近树干而逐渐增加，并且与垫料厚度呈强相关。我们的研究结果为以下假设提供了支持：在半干旱喀斯特地貌中，木本植物的入侵（尤其是杜松的入侵）可以通过改善土壤的渗透性而在提高地下水补给中起重要作用。我们还发现，渗透性和渗透深度都随着靠近树干而逐渐增加，并且与垫料厚度呈强相关。我们的研究结果为以下假设提供了支持：在半干旱喀斯特地貌中，木本植物的入侵（尤其是杜松的入侵）可以通过改善土壤的渗透性而在提高地下水补给中起重要作用。我们还发现，渗透性和渗透深度都随着靠近树干而逐渐增加，并且与垫料厚度呈强相关。我们的研究结果为以下假设提供了支持：在半干旱喀斯特地貌中，木本植物的入侵（尤其是杜松的入侵）可以通过改善土壤的渗透性而在提高地下水补给中起重要作用。