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Abstract

As global climatic and anthropogenic changes bring increasing resource scarcity to ecosystems across the globe, the resiliency of natural communities to these changes can be the determinant in whether or not the population, and the ecosystem as a whole, survives. This is particularly the case in the self- organization of arid vegetation into distinct, periodic patterns in response to resource scarcity, where theoretical models suggest their formations are an “early warning sign” for future catastrophic shifts and sudden ecosystem collapse. These models rely on a “runoff-runon” system of differential infiltration capabilities between vegetated patches and the surrounding bare soil. However, few empirical studies have been conducted to apply this theory to real arid ecosystems, and those that have often reveal unexpected nuances and cast doubt on the applicability of the large, theoretical literature. Accurately predicting catastrophic shifts in real ecosystems is of the utmost importance, but can only be accomplished through site-specific, empirically driven models that consider an assortment of all active mechanisms in pattern formation. Aerial imagery suggests banded pattern formation in an arid ecosystem in Southern Colorado at Chico Basin Ranch over the last 15 years. Infiltration experiments at this site show significantly higher infiltration rates in vegetated areas than in bare soil, suggesting a runoff-runon system may be active. Moreover, statistical analyses of drone imagery at three Areas of Interest (AOIs) reveal non-random, periodic banded vegetation generally in a North-South orientation. However, the orientations of these vegetation bands in relation to slope are not consistent between AOIs, with the expected perpendicular orientation to slope observed in one AOI, an oblique orientation observed in another, and a parallel orientation observed in the third AOI. In this way, this study identifies periodic vegetation bands in Southern Colorado that have orientations that cannot be fully explained by a runoff- runon system, suggesting other mechanisms are also present.

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