Bridging structural and functional hydrological connectivity in dryland ecosystems
Bridging structural and functional hydrological connectivity in dryland ecosystems
复制标题
DOI：
10.1016/j.catena.2023.107322
复制
发表时间：
2023-07-06
期刊：
影响因子：
6.2
通讯作者：
Thompson，Sally E.
中科院分区：
文献类型：
--
作者：
Crompton，Octavia;Katul，Gabriel;Thompson，Sally E.
在旱地山坡上，降雨径流从裸露的土壤（源）重新分配到植被斑块（汇），常常补贴植被的水分供应。在降雨量过低而无法支持植物空间连续生长的地区，裸土和植被区之间的这种功能连通性使旱地生态系统得以建立和持续。增加裸露土壤地区的连通性会加剧径流，增加山坡的水分流失，破坏这种再分配，减少维持生态系统功能的可用水量。从结构景观特征推断功能连通性（从裸地到植被，或在裸地区域内）是一种有吸引力的方法，可以通过远程观测快速、可扩展地表征旱地生态系统功能。然而，这样的推断将依赖于结构连通性的度量，它描述了裸露土壤区域的连续性。一些研究已经观察到，随着降雨条件的变化，功能和结构连通性指标之间的关系具有非平稳性。因此，使用结构连通性为功能连通性提供可靠代理的适用性仍然是不确定的，这激励了这里的工作。基于不同土壤性质和植被模式的山坡降雨径流模型模拟，建立了结构和功能连通性指标之间的关系。这些关系在两个水文极限之间变化——一个是“局部”（斑块尺度）极限，其中功能连通性与结构连通性有关；另一个是“全球”（山坡尺度）极限，其中功能连通性与山坡植被比例最相关，而不管裸露土壤区域的结构连通性如何。模拟中这些极限之间的过渡取决于降雨强度和持续时间，以及土壤渗透性。虽然局部极限可能加强植被和水分供应之间的正反馈，但这些极限对旱地功能的影响需要进一步探索，特别是考虑到暴雨径流产生和植被生长之间的时间尺度分离。
On dryland hillslopes, vegetation water availability is often subsidized by the redistribution of rainfall runoff from bare soil (sources) to vegetation patches (sinks). In regions where rainfall volumes are too low to support spatially continuous plant growth, such functional connectivity between bare soil and vegetated areas enables the establishment and persistence of dryland ecosystems. Increasing the connectivity within bare soil areas can intensify runoff and increase water losses from hillslopes, disrupting this redistribution and reducing the water available to sustain ecosystem function. Inferring functional connectivity (from bare to vegetated, or within bare areas) from structural landscape features is an attractive approach to enable rapid, scalable characterization of dryland ecosystem function from remote observations. Such inference, however, would rely on metrics of structural connectivity, which describe the contiguity of bare soil areas. Several studies have observed non-stationarity in the relations between functional and structural connectivity metrics as rainfall conditions vary. Consequently, the suitability of using structural connectivity to provide a reliable proxy for functional connectivity remains uncertain and motivates the work here.Relations between structural and functional connectivity metrics are established based on model simulations of rainfall-runoff on hillslopes with varying soil properties and vegetation patterns. These relations vary between two hydrologic limits – a ‘local’ (patch-scale) limit, in which functional connectivity is related to structural connectivity, and a ‘global’ (hillslope-scale) limit, in which functional connectivity is most related to the hillslope vegetation fraction regardless of the structural connectivity of bare soil areas. The transition between these limits within the simulations depends on rainfall intensity and duration, and soil permeability. While the local limit may strengthen positive feedbacks between vegetation and water availability, the implications of these limits for dryland functioning need further exploration, particularly considering the timescale separation between storm runoff production and vegetation growth.