title: Trade-off between competition and facilitation defines gap colonization in mountains.
abstract: Recent experimental observations show that gap colonization in small-stature (e.g. grassland and dwarf shrubs) vegetation strongly depends on the abiotic conditions within them. At the same time, within-gap variation in biotic interactions such as competition and facilitation, caused by distance to the gap edge, would affect colonizer performance, but a theoretical framework to explore such patterns is missing. Here, we model how competition, facilitation and environmental conditions together determine the small-scale patterns of gap colonization along a cold gradient in mountains, by simulating colonizer survival in gaps of various sizes. Our model adds another dimension to the known effects of biotic interactions along a stress gradient by focussing on the trade-off between competition and facilitation in the within-gap environment. We show that this trade-off defines a peak in colonizer survival at a specific distance from the gap edge, which progressively shifts closer to the edge as the environment gets colder, ultimately leaving a large fraction of gaps unsuitable for colonization in facilitation-dominated systems. This is reinforced when vegetation size and temperature amelioration are manipulated simultaneously with temperature in order to simulate an elevational gradient more realistically. Interestingly, all other conditions being equal, the magnitude of the realized survival peak was always lower in large than in small gaps, making large gaps harder to colonize. The model is relevant to predict effects of non-native plant invasions and climate warming on colonization processes in mountains.
authors.affiliation: Centre of Excellence of Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium jonas.lembrechts@uantwerpen.be.
authors.forename: Jonas J
authors.initials: JJ
authors.lastname: Lembrechts
authors.affiliation: Climate Impacts Research Centre, Department of Ecology and Environmental Science, Umeå University, SE-981 07 Abisko, Sweden Research Institute for Nature and Forest INBO, Department of Biodiversity and Natural Environment, Kliniekstraat 25, 1070 Brussels, Belgium.
authors.forename: Ann
authors.initials: A
authors.lastname: Milbau
authors.affiliation: Centre of Excellence of Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
authors.forename: Ivan
authors.initials: I
authors.lastname: Nijs
keywords: Alien plant invasion; cold climates; disturbance; gap invasion; gradients; mountains; plant–plant interactions; stress gradient hypothesis