Environmental conditions, including climate, strongly influence the distribution of plant species. As temperatures continue to rise around the world, many people are concerned about the possible shifts in distribution of plant species, since plants are immobile, and many of them have a limited ability to disperse. These restrictions to changes in their distribution are particularly severe for plants that are adapted to cold conditions, such as those found in high mountain regions.
Studies by Valenti Rull and others have shown that during interglacial periods in the geological past, alpine plants were able to disperse to microrefugia, small-scale sites which allowed species to persist when most of their ranges became unsuitable for them. Thus, in the current era of warming, such sites, with locally favorable climate, could once again prove to be important for the survival of cold-adapted alpine species. A newly published study by Rodolfo Gentili of the Department of Environmental Sciences at the University of Milan and several co-authors in Ecological Complexity establishes a fresh approach to the study of microrefugia. The authors examined the geomorphological and ecological features of microrefugia during earlier interglacial stages and used these features to identify potential microrefugia areas for alpine plants in and near glaciers, in both the present and the near future.
In general, there are three recognized strategies which alpine plants can adapt to survive under a warming climate. They can migrate to higher elevation, remain at local microrefugia or evolve through genetic differentiation to adapt to new climate. However, there had been no overview to date of how plants in the Alps and other high mountains of Europe could respond to future warming. Gentili and his co-authors conducted a thorough literature review, focusing in particular on geomorphological processes and landforms associated with plant communities in alpine environment. (They found only one study which addressed the genetic evolution of an alpine plant.)
The authors developed a typology of alpine landforms and characterized each one according to its “vegetation features, climatic controls, microclimate features of active landforms and microrefugium functions.” They recognized eight landform types, which differ in terms of the processes that generate them. These landforms are mountain summits, debris-covered glaciers, moraine ridges and deglaciated forelands, nivation niches or snow patches,rock glaciers, alpine composite debris cones (debris slopes and scree), alpine corridors (composite channels, including avalanche channels and tracks), and ice caves.
Taken individually, all of these eight landforms have been documented in the published literature as serving currently as microrefugia, except for the debris-covered glaciers, which nonetheless are promising as future microrefugia because of their relatively cool temperatures which result from the presence of sub-surface ice. The other landforms all have been shown to function as microrefugia. They offer a number of advantages, including suitable sites for colonization (moraine ridges and deglaciated forelands), cooler temperatures (debris-covered glaciers, rock glaciers, nivation niches or snow patches, ice caves), a vertical range that facilitates dispersal (alpine corridors) and a large variety of niches (alpine composite debris cones). Taken together, these landforms provide a very wide range of habitats, increasing the likelihood that any given alpine species could have a favorable spot to which it could disperse. These relations are indicated in the figure from the paper, shown below, which demonstrates that the geomorphological heterogeneity—the diversity of habitats within and across landforms—promotes the survival of species.
The researchers note that these glacial and pre-glacial landforms are potential microrefugia for alpine plants under warming conditions. They recognize that human intervention—purposive translocation of plants—may assist in the survival of species. In addition, they point out that the plant species themselves may adapt genetically to changing environmental conditions. They conclude by suggesting that researchers could profitably direct their attention to evolutionary processes within this geomorphologically complex and climatically dynamic environment, seeing whether species, pressed by climate change, can adapt, or even evolve into new species.