Abstract
Mountain plant species are changing their ranges in response to global warming. However, these shifts vary tremendously in rate, extent and direction. The reasons for this variation are yet poorly understood. A process potentially important for mountain plant re-distribution is a competition between colonizing species and the resident vegetation. Here, we focus on the impact of this process using the recent elevational shift of the sedge Carex humilis in the northern Italian Alps as a model system. We repeated and extended historical sampling (conducted in 1976) of the species in the study region. We used the historical distribution data and historical climatic maps to parameterize a species distribution model (SDM) and projected the potential distribution of the species under current conditions. We compared the historical and the current re-survey for the species in terms of the cover of important potential competitor species as well as in terms of the productivity of the resident vegetation indicated by the Normalized Difference Vegetation Index (NDVI). We found that Carex humilis has shifted its leading range margin upward rapidly (51.2 m per decade) but left many sites that have become climatically suitable since 1976 according to the SDM uncolonized. These suitable but uncolonized sites show significantly higher coverage of all dwarf shrub species and higher NDVI than the sites occupied by the sedge. These results suggest that resistance of the resident vegetation against colonization of migrating species can indeed play an important role in controlling the re-distribution of mountain plants under climate change.
Highlights
In temperate and boreal mountain ecosystems, organisms are shifting their ranges to higher elevations (Gottfried et al 2012; Pauli et al 2012) and these shifts have been accelerating with accelerating rates of climate warming (Steinbauer et al 2018)
Even if the competitive ability of species appears to decrease with elevation (Alexander et al 2015), establishment odds of range expanders may depend on species and trait composition of the communities growing above their range margin (e.g. Dullinger et al 2003, 2004)
We focused on dwarf shrubs because they represent an important growth form in the upper subalpine and lower alpine zone of the region, i.e. those elevational belts where a climate-driven range expansion of C. humilis is most likely
Summary
In temperate and boreal mountain ecosystems, organisms are shifting their ranges to higher elevations (Gottfried et al 2012; Pauli et al 2012) and these shifts have been accelerating with accelerating rates of climate warming (Steinbauer et al 2018). Lenoir et al 2010; Chen et al 2011) The reasons for this variation are not well understood so far. For example, to plant architecture (Guittar et al 2016), seed. Another factor little explored in this context is the resistance of the resident vegetation against plants that move up from below. Competition has known effects on recruitment even in alpine communities (Alexander et al 2018), and even a gradual decrease of this effect with elevation does not contradict the conjecture that resident mountain plant communities may substantially modify the pace of species’ upward shifts under climate warming
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