**11. Conclusion**

Due to global warming, glaciers are receding in many parts of the world, leaving considerable areas of barren ground. While the botanical succession in such glacier forelands have been well studied, the parallel zoological succession is less described and understood. Glacier forelands illustrate nature's ability to recover from severe disturbance, and it is of considerable ecological interest to understand the succession process. Succession studies also help us to predict future ecosystems in deglaciated terrain.

This chapter summarizes and compares zoological studies in glacier forelands within three main areas in Europa: Svalbard, south Norway, and the Alps. A common technique is to study sites with known age in different distances from the ice. The sequence of dated study plots is called a chronosequence, and the various plots act as a substitute for following the same plot over time. Not surprisingly, time, distance and vegetation cover use to be highly correlated factors in a glacier foreland.

Several invertebrates are present before any vegetation is visible. Typical representatives are springtails (Collembola), mites (Acari), beetles (Coleoptera), spiders (Araneae), and harvestmen (Opiliones). The actual species are surface active animals, but they find shelter in the crevices among stones, gravel and sand grains. Springtails and mites are saprophagous, while species from the other groups are mainly predators. It has been called an ecological paradox that predators preceed both plant-eaters and plants. However, the pioneer ground receives airborne insects (mainly Diptera), on which the predators can feed. This fertilizes the ground and contributes to the gradual establishment of plants. However, chlorophyll-based food chains may start surprisingly early, for instance based on pioneer mosses on which certain springtails and beetles can feed.

In the Alps, most arthropod species colonise during a period of 40-50 years, while the colonisation is slower in Norway. High Arctic forelands on Svalbard have a poor fauna, but springtails, mites and certain spiders are early colonisers even there. Certain invertebrate taxa are typical pioneers in all three geographical areas, or common to Norway and the Alps. It is also concluded that the main pattern of the zoological succession is rather predictable. This indicates that dispersion may not be a serious problem. Herbivorous invertebrates are often relatively late colonisers.

Some pioneers are highly specialised, cold-tolerant species. These may go locally extinct if the glacier melts away. Other are open ground-specialists, and may live also in open habitats in the lowland. Several are generalists, with an extra flexibility to inhabit the harsh conditions close to a glacier. Pioneers may be parthenogenetic or bisexual, or have a short or long life cycle. Although pioneer species form an ecologically heterogeneous group, the pioneer community is often rather predictable.

Some of the remaining questions are: Is dispersal such an easy task? What do the various pioneer species eat? Is the pioneer ground an ecological sink, continuously fed from outside? How do plants and animals interact through succession? More field studies with a high taxonomic resolution, and in various geographical areas, are welcomed. Climate change may generally speed up the succession rate around melting glaciers.
