Facilitation and competition on gradients in alpine plant communities

• Main Authors: Choler, P., Michalet, R., Callaway, R. M.
• Other Authors: Laboratoire d'Ecologie Alpine (LECA), Université Joseph Fourier - Grenoble 1 (UJF)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Station alpine Joseph Fourier - UMS 3370 (SAJF), Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Division of Biological Sciences, University of Montana
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2001
• Subjects: alpine tundra; competition; elevation gradient; facilitation; log; response ratio (LRR); niche theory; ordination; plant communities; plant interactions; relative competitive index (RCI); removal; experiment; topography gradient; Positive interactions; continuum concept; timberline conifers; ecosystem engineers; clonal integration; marsh plants; availability; balance; tundra; envir; geo; Tundra
• Online Access: https://doi.org/10.1890/0012-9658(2001)082[3295:FACOGI]2.0.CO;2; https://hal.archives-ouvertes.fr/halsde-00295049

International audience We conducted a neighbor removal experiment in natural alpine plant communities of the southwestern Alps to test for the relative importance of competitive and facilitative interactions along elevational and topographical gradients. The experimental sites were chosen to encompass most of the floristic diversity observed along gradients of elevation and topography, which are the two main ecological gradients associated with alpine plant communities in the western Alps. The effects of neighbor removal on the survival, aboveground biomass, and reproduction of five target species were tested at each of six experimental sites. Using biomass data, we calculated relative competitive index (RCI) and log response ratio (LRR) as measures of interaction strength and direction. We found highly significant shifts from strong competitive effects in low and sheltered sites to strong facilitative responses in high and exposed sites. When experimental results were integrated with gradient analyses, we found that the responses of particular alpine plant species to neighbor removal generally depended on the species' position on elevational and topographical gradients. When neighbors were removed from around target species at experimental sites that were lower in elevation than the distributional mean of the target species, biomass generally increased. When neighbors were removed from around target species at experimental sites that were higher in elevation than the distributional mean of the target species, biomass decreased. In other words, facilitation appeared to allow species from lower elevations to move up the gradient, but competition at low elevations appeared to restrict species from higher elevations from moving down the gradient. In high and exposed sites, experimental evidence for facilitation was coupled to small-scale spatial associations among species, but spatial disassociation was not coupled to experimental evidence for competition at any sites. We conclude that the distribution and ...