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  • Thumbnail for Spatial Structure of Treeline Shows Evidence of Robust Criticality
    Spatial Structure of Treeline Shows Evidence of Robust Criticality by McGarigal, Alison H

    Ecotone transitions offer a rare opportunity to examine these spatial patterns along known stress gradients. This allows us to link specific patterns that exist at the different stages of bifurcation to potential mechanisms that create these complex spatial structures. This paper applied robust criticality theory the alpine forest-tundra ecotone transition to see how treelines can be understood through the framework of critical transitions, and concurrently, how robust criticality theory can be applied to an anisotropic system to predict potential threshold behavior in treeline movement upslope. Spatial structure of an abrupt treeline on Pikes Peak, CO was analyzed using Fragstats and ImageJ. The presence of robust criticality was tested using an AIC model fit test. Model analysis showed that this treeline clearly exhibits a type of robust criticality with the existence of a percolation cluster and deviations of log frequency-size distribution of patches along the elevation gradient from a strict power law. However, it did not conform to the theory perfectly. This likely points to the problem of accounting for multiple stressors that exert their influence over the dynamics of treeline to different extents in different zones. It is this complex matrix of local feedbacks created by endogenous interactions between the harsh environmental conditions and the trees that produces the dynamic spatial structure at this site along the elevation gradient. This has important implications for how the treeline will react in the future to increasing temperatures and decreasing snowpack as predicted by climate change models in the Rock Mountain West.