There is strong empirical evidence on the importance of the spatial pattern of vegetation in dryland hydrologic and geomorphologic dynamics. However, changes in vegetation cover and spatial pattern are often linked, making it difficult to disentangle and assess their independent hydro-geomorphologic roles. We used synthetic sponges placed on the soil surface to mimic the aboveground structure of vegetation patches, and manipulated patch cover and pattern as well as the sink capacity of the patches on a set of 24 (2 × 1 m) runoff plots. Combining natural-rainfall and simulated-rainfall experiments, we aimed to test that (1) both vegetation cover and pattern independently control runoff and sediment yield; (2) for any given cover, coarsening the vegetation pattern entails increasing runoff and sediment yield; and (3) pattern effect is mostly exerted by modulating the source-sink dynamics of the system. We found that increasing either patch cover or patch density decreased runoff and sediment yields from natural rainfalls, yet the effect of patch density largely disappeared when the effect of the co-varying patch cover was removed. Simulated-rainfall experiments on plots with equal medium-low patch cover showed however that coarser patterns (lower patch density; higher patch size) increased runoff coefficients and reduced time to runoff as compared with finer patterns. The effect of patch density was particularly clear when the sink function of vegetation patches was also mimicked. Rainfall interception and direct soil protection proved to be critical mechanisms underlying the effects of patch cover, yet they barely contributed to the effects of patch pattern. The control of overland flow by patch pattern was exerted through changes in the level of runoff disruption. However, physical obstructions to runoff hardly reduced runoff unless coupled to mimicked soil sinks. Overall this work demonstrates the independent effects of patch cover and pattern on the hydro-geomorphologic functioning of patchy landscapes, with patch cover being the primary hydrologic control factor and patch pattern exhibiting its full potential for low and medium low patch cover values. Our findings provide useful information for modelling and understanding dryland vegetation dynamics, and for designing management and restoration measures that take into account the critical role played by source-sink dynamics and hydrological connectivity in dryland landscapes.

有强有力的经验证据表明植被空间格局在旱地水文和地貌动力学中的重要性。然而，植被覆盖和空间格局的变化往往是相互关联的，因此很难理清和评估它们独立的水文地貌作用。我们使用放置在土壤表面的合成海绵来模拟植被斑块的地上结构，并在一组 24 (2 × 1 m) 径流地块上操纵斑块覆盖和图案以及斑块的汇容量。结合自然降雨和模拟降雨实验，我们旨在测试（1）植被覆盖和模式独立控制径流和产沙量；(2) 对于任何给定的覆盖，粗化植被模式需要增加径流和沉积物产量；(3) 模式效应主要通过调节系统的源汇动态来发挥。我们发现增加斑块覆盖或斑块密度会降低自然降雨的径流和沉积物产量，但当去除共同变化斑块覆盖的影响时，斑块密度的影响在很大程度上消失了。然而，在具有相同中低斑块覆盖度的地块上的模拟降雨实验表明，与更细的斑块相比，较粗的斑块（斑块密度较低；斑块大小较大）增加了径流系数并减少了径流时间。当还模拟植被斑块的汇功能时，斑块密度的影响尤为明显。降雨拦截和直接土壤保护被证明是造成斑块覆盖效应的关键机制，然而，它们几乎没有对补丁模式的影响做出贡献。通过改变径流中断水平来施加斑块模式对地表流的控制。然而，径流的物理障碍几乎不会减少径流，除非与模拟土壤汇相结合。总的来说，这项工作证明了斑块覆盖和图案对斑块景观水文地貌功能的独立影响，斑块覆盖是主要的水文控制因素，斑块图案在低和中低斑块覆盖值方面表现出其全部潜力。我们的研究结果为建模和理解旱地植被动态以及设计管理和恢复措施提供了有用的信息，这些措施考虑了旱地景观中源汇动态和水文连通性所起的关键作用。斑块模式对地表流的控制是通过径流中断水平的变化来实现的。然而，径流的物理障碍几乎不会减少径流，除非与模拟土壤汇相结合。总的来说，这项工作证明了斑块覆盖和图案对斑块景观水文地貌功能的独立影响，斑块覆盖是主要的水文控制因素，斑块图案在低和中低斑块覆盖值方面表现出其全部潜力。我们的研究结果为建模和理解旱地植被动态以及设计管理和恢复措施提供了有用的信息，这些措施考虑了旱地景观中源汇动态和水文连通性所起的关键作用。通过改变径流中断水平来施加斑块模式对地表流的控制。然而，径流的物理障碍几乎不会减少径流，除非与模拟土壤汇相结合。总的来说，这项工作证明了斑块覆盖和图案对斑块景观水文地貌功能的独立影响，斑块覆盖是主要的水文控制因素，斑块图案在低和中低斑块覆盖值方面表现出其全部潜力。我们的研究结果为建模和理解旱地植被动态以及设计管理和恢复措施提供了有用的信息，这些措施考虑了旱地景观中源汇动态和水文连通性所起的关键作用。