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A size-gradient hypothesis for alpine treeline ecotones

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Abstract

Research on the stress gradient hypothesis recognizes that positive (i.e. facilitative) and negative (i.e. competitive) plant interactions change in intensity and effect relative to abiotic stress experienced on a gradient. Motivated by observations of alpine treeline ecotones, we suggest that this switch in interaction could operate along a gradient of relative size of individual plants. We propose that as neighbors increase in size relative to a focal plant they improve the environment for that plant up to a critical point. After this critical point is surpassed, however, increasing relative size of neighbors will degrade the environment such that the net interaction intensity becomes negative. We developed a conceptual (not site or species specific) individual based model to simulate a single species with recruitment, growth, and mortality dependent on the environment mediated by the relative size of neighbors. Growth and size form a feedback. Simulation results show that the size gradient model produces metrics similar to that of a stress gradient model. Visualizations reveal that the size gradient model produces spatial patterns that are similar to the complex ones observed at alpine treelines. Size-mediated interaction could be a mechanism of the stress gradient hypothesis or it could operate independent of abiotic stress.

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Correspondence to George P. Malanson.

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http://orcid.org/0000-0001-9527-0086

http://orcid.org/000-0002-5135-1797

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Malanson, G.P., Resler, L.M. A size-gradient hypothesis for alpine treeline ecotones. J. Mt. Sci. 13, 1154–1161 (2016). https://doi.org/10.1007/s11629-016-3984-5

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  • DOI: https://doi.org/10.1007/s11629-016-3984-5

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