Hydrologic dysfunction associated with desertification of grazing lands likely depends on two opposing biophysical drivers, compaction by livestock and bioturbation by plant roots and soil biota. To understand which is most important, we conducted a long-term field experiment. We tested the effects of phytobiomass (control vs. herbicide treated) and three ungulate disturbance treatments (none, once, and twice disturbed) on soil water transport in northern mixed-grass prairie. Field-saturated hydraulic conductivity (i.e., infiltration) was primarily reduced by the most severe (twice disturbed) ungulate disturbance treatment. To a lesser degree, ungulate disturbance and phytobiomass interacted, and similar levels of hydrologic dysfunction were detected for plots annually treated with herbicide and disturbed by a single livestock disturbance event (and while soils were dry and resistant to compaction) and naturally vegetated plots that had been twice disturbed (including while soils were wet and susceptible to compaction). Our findings suggest hydrologic dysfunction in grazing lands is mainly due to compaction by ungulates, especially when grazing at high stocking rates and while areas are vulnerable to compaction (e.g., fine soils, wet soils, not well vegetated).

与牧场荒漠化相关的水文功能障碍可能取决于两个相反的生物物理驱动因素，牲畜的压实和植物根系和土壤生物群的生物扰动。为了了解哪个最重要，我们进行了长期的现场实验。我们测试了植物生物质（对照与除草剂处理）和三种有蹄类动物干扰处理（无干扰、一次干扰和两次干扰）对北部混草草原土壤水分输送的影响。田间饱和导水率（即渗透）主要因最严重（两次扰动）有蹄类动物扰动处理而降低。在较小程度上，有蹄类动物的干扰和植物生物质相互作用，对于每年用除草剂处理并受到单一牲畜干扰事件干扰的地块（并且土壤干燥且抗压实）和受到两次干扰的自然植被地块（包括土壤潮湿且易受感染时），检测到相似程度的水文功能障碍压实）。我们的研究结果表明，放牧地的水文功能障碍主要是由有蹄类动物压实造成的，尤其是在放牧率高且容易受到压实的地区（例如，细土、潮湿土壤、没有良好植被的地区）时。