Glacier Forelands: Lessons of Plant Population and Community Development

Abstract

After glacier retreat, the ice-free forelands arise as easily detectable landforms where primary succession starts from the beginning onwards. Here, basic ecological lessons of colonization and community development can be learned. In this review we summarize the results of several case studies from the Austrian and Italian Alps, draw conclusions and highlight research gaps. Glacier foreland species exhibit a considerable intra-population diversity. Actual gene flow was shown to be high enough to maintain the genetic diversity throughout all successional stages. Most seeds of the glacier foreland species are light-weighted and wind-dispersed. Heavier seeds with no specific dispersal traits such as those of certain late successional species will hardly be dispersed to the pioneer stages. In most glacier forelands, a seed bank has to be developed from zero onwards. The already established species are the ones which contribute most to the genesis of a seed bank; an input of seeds by long distance dispersal was hardly detected. A relatively high quantity of glacier foreland species has a deep physiological dormancy. Thus, they will be able to form persistent seed banks. Seedling recruitment is highly governed by drought and seed availability. Additionally, frost and heat might be essential abiotic factors for germination and seedling survival. Growth rates of the glacier foreland species vary considerably among the successional stages and seem to be phylogenetically constrained. Population growth rates are characterised by low seedling recruitment and/or high mortality rates of the seedlings; some species overcome this low reproductive success by clonal growth strategies. From seed sowing experiments we learned that facilitation and competition may occur side by side. However, this topic has to be further explored in the future. By means of plant functional types, the pioneer species were classified as fast-growing ruderal strategists. In contrast, late successional stages harbour mainly stress-tolerant species with dense leaves and low relative growth rates. Phytosociological community descriptions are a challenging topic in glacier forelands. Nevertheless, several communities were described mainly from the Italian Alps. One of the less investigated topics, although being essential in ecology, is the species interaction issue. Among the scarce studies in this context, pollination and flower-visiting insects were studied. Species interactions including different organismic levels as well as species adaptations to changing conditions are still topics to be studied along glacier forelands. Climate warming probably will enhance the speed and the pathway of colonization. If glacier forelands can act as refugia for alpine-nival species remains to be proved. Thus, glacier foreland offer ample ecological questions and further research is highly recommended.