A size-gradient hypothesis for alpine treeline ecotones
- 84 Downloads
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.
KeywordsCompetition Ecotone Environmental gradient Plant interaction Stress gradient Facilitation
- Callaway RM (2007) Positive interactions and interdependence in plant communities. Dordrecht: Springer. p 404. DOI: 10.1007/978-1-4020-6224-7Google Scholar
- Wilensky U (1999) NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL USA.Google Scholar