UK Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd, LL57 2UW, United Kingdom.
Victoria University of Wellington, Kelburn, Wellington, 6012, New Zealand.
Ecol Appl. 2020 Mar;30(2):e02046. doi: 10.1002/eap.2046. Epub 2020 Jan 3.
Loss and fragmentation of natural land cover due to expansion of agricultural areas is a global issue. These changes alter the configuration and composition of the landscape, particularly affecting those ecosystem services (benefits people receive from ecosystems) that depend on interactions between landscape components. Hydrological mitigation describes the bundle of ecosystem services provided by landscape features such as woodland that interrupt the flow of runoff to rivers. These services include sediment retention, nutrient retention and mitigation of overland water flow. The position of woodland in the landscape and the landscape topography are both important for hydrological mitigation. Therefore, it is crucial to consider landscape configuration and flow pathways in a spatially explicit manner when examining the impacts of fragmentation. Here we test the effects of landscape configuration using a large number (>7,000) of virtual landscape configurations. We created virtual landscapes of woodland patches within grassland, superimposed onto real topography and stream networks. Woodland patches were generated with user-defined combinations of patch number and total woodland area, placed randomly in the landscape. The Ecosystem Service model used hydrological routing to map the "mitigated area" upslope of each woodland patch. We found that more fragmented woodland mitigated a greater proportion of the catchment. Larger woodland area also increased mitigation, however, this increase was nonlinear, with a threshold at 50% coverage, above which there was a decline in service provision. This nonlinearity suggests that the benefit of any additional woodland depends on two factors: the level of fragmentation and the existing area of woodland. Edge density (total edge of patches divided by area of catchment) was the best single metric in predicting mitigated area. Distance from woodland to stream was not a significant predictor of mitigation, suggesting that agri-environment schemes planting riparian woodland should consider additional controls such as the amount of fragmentation in the landscape. These findings highlight the potential benefits of fragmentation to hydrological mitigation services. However, benefits for hydrological services must be balanced against any negative effects of fragmentation or habitat loss on biodiversity and other services.
由于农业区的扩张，自然土地覆盖的丧失和破碎化是一个全球性问题。这些变化改变了景观的结构和组成，特别是影响了那些依赖景观要素相互作用的生态系统服务（人们从生态系统中获得的利益）。水文缓解描述了林地等景观特征提供的一整套生态系统服务，这些特征可以打断径流向河流的流动。这些服务包括泥沙截留、养分截留和缓解地表水流。林地在景观中的位置和景观地形对水文缓解都很重要。因此，在考察破碎化的影响时，必须以空间显式的方式考虑景观配置和水流路径。在这里，我们使用大量（>7000）虚拟景观配置来测试景观配置的效果。我们在真实地形和溪流网络上叠加了草地中的林地斑块，创建了虚拟景观。林地斑块是根据用户定义的斑块数量和总林地面积组合生成的，随机放置在景观中。使用生态系统服务模型通过水文路径来映射每个林地斑块上游的“缓解区域”。我们发现，更破碎的林地缓解了更大比例的集水区。更大的林地面积也增加了缓解，但这种增加是非线性的，在覆盖率达到 50%时有一个下降，之后服务提供会下降。这种非线性表明，任何额外林地的好处取决于两个因素：破碎化程度和现有的林地面积。边缘密度（斑块的总边缘除以集水区的面积）是预测缓解面积的最佳单一指标。林地到溪流的距离不是缓解的重要预测因子，这表明在种植河岸林地的农业环境计划中，应考虑其他控制因素，如景观中的破碎化程度。这些发现强调了破碎化对水文缓解服务的潜在好处。然而，水文服务的好处必须与破碎化或生境丧失对生物多样性和其他服务的任何负面影响相平衡。
