12/16/2023 0 Comments Def ecotoneObserving the vegetation along a gradient, for example, from lower to higher altitudes across an alpine tree line, often reveals a complex pattern of patches. Detecting boundary shifts has been suggested for biomonitoring climate change (Kimball and Weihrauch 2000 but see Zeng and Malanson 2006 and references therein).īecause the geometries of most natural vegetation boundaries are complicated, it is not self‐evident what to measure, that is, which feature of a boundary could be sufficiently general to enable comparisons between years and/or geographic regions. Interest in this topic increased further after reports of significant shifts in vegetation boundaries (e.g., tree lines) due to recent climate changes (Allen and Breshears 1998 Danby and Hik 2007). The distribution of vegetation across environmental gradients has received considerable attention since the beginnings of vegetation science, for example, in gradient analysis (Whittaker and Niering 1965). This offers a new tool for detecting a shift of the boundary due to a climate change. We propose to use the hull edge to define the boundary of a vegetation type unambiguously. To demonstrate that the model is applicable to real data, a hull edge of fractal dimension 7/4 is shown on a satellite image of a piñon‐juniper woodland on a hillside. The result is the same for different spatial models, suggesting that there are universal laws in ecotone geometry. The boundary of connected vegetation delineated by a particular step length is termed the “ hull edge.” We found that for every step length and for every gradient, the hull edge is a fractal with dimension 7/4. Connectivity is characterized from the perspective of various species that use this vegetation type for habitat and differ in dispersal or migration range, that is, “step length” across the landscape. A static (gradient percolation) model is compared to dynamic (gradient contact process) models. We use spatially explicit simulations to study the transition from connected to fragmented vegetation. A change in the environmental conditions across space-for example, altitude or latitude-can cause significant changes in the density of a vegetation type and, consequently, in spatial connectivity.
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