When topography is incorporated into models of barrier dune dynamical states, how it is represented determines the dynamical properties inferred. Bottom-up representations rely on elevation and localized biogeomorphic modification. Top-down representations incorporate constraints imposed by the spatial patterns of topography. These spatial patterns emerge from island morphological context and the extent localized biogeomorphic processes can expand and structure the larger landscape. We compared topographies across 30 sites among seven barrier islands of the Virginia (U.S.A) coast to gauge the importance of elevation, the bottom-up variable often weighted most in dune biogeomorphic models, relative to top-down patch and continuous surface landscape representations of topography. LiDAR-derived digital elevation models of each site were characterized with non-metric multidimensional scaling to assess how these bottom-up and top-down metrics structured dune topographic variability. Multiple response permutation procedures gauged the strength of topographic differences among sites grouped according to island morphology versus groupings defined by clustering of topographic metrics. Elevation was the dominant metric structuring topography for these low relief islands. Spatial structure was weakly developed. Topographic differences were more robust when based on clusters defined largely by elevational properties rather than by island or island morphological type. For the Virginia barrier islands, storm inputs may more directly shape topography and override landscape-extent top-down spatial structure. The dominance of elevation suggests that resistance may be the more relevant dynamical property for this coast. Properties like resilience may be greater on higher islands with longer storm-free intervals in which biogeomorphic elements can configure relief and act as recursive top-down controls.

中文翻译：

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自下而上和自上而下如何控制沿美国弗吉尼亚屏障岛海岸的沙丘地形变化以及沙丘动力特性的推断

将地形合并到障碍沙丘动力状态模型中时，如何表示地形确定了推断的动力特性。自下而上的表示依赖于海拔和局部生物地貌修饰。自上而下的表示法包含了地形空间格局所施加的约束。这些空间格局来自岛屿的形态背景，局部生物地貌过程可以扩展和构造更大景观的程度。我们比较了弗吉尼亚（美国）海岸的七个障碍岛中30个地点的地形，以评估海拔的重要性，沙丘生物地貌模型中自下而上的变量通常权重最大，相对于地形的自顶向下补丁和连续地表景观表示。每个站点的LiDAR派生数字高程模型均采用非度量多维标度进行了表征，以评估这些自下而上和自上而下的度量如何构造沙丘地形变异性。多重响应置换程序评估了根据岛屿形态与地形指标聚类定义的分组而进行的站点间地形差异的强度。高程是这些低浮雕岛屿的主要度量结构地形。空间结构薄弱。当基于主要由高程属性而不是岛或岛形态类型定义的聚类时，地形差异更健壮。对于弗吉尼亚屏障岛，暴风雨的输入可能会更直接地影响地形，并覆盖景观范围自上而下的空间结构。海拔的优势表明，抵抗力可能是该海岸更相关的动力性质。在具有更长的无风暴间隔的较高岛上，诸如弹性等属性可能会更大，在这些间隔中，生物地貌元素可以配置地形并充当递归自顶向下的控件。