**Primary Succession in Glacier Forelands: How Small Animals Conquer New Land Around Melting Glaciers**

Sigmund Hågvar

*Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Aas, Norway* 

## **1. Introduction**

An easily observed effect of global warming is the gradual melting of glaciers in different parts of the world. Large areas of barren, pristine ground are left open for colonisation of various life forms (Fig. 1). From an ecological point of view, glacier forelands are interesting because they illustrate nature's ability to recover from severe disturbance. Since the successive development of communities starts without previous life forms, it is a primary succession. In contrast, a secondary succession starts with a species assemblage already present, for instance on a forest patch after clear-cutting. While the botanical succession in glacier forelands has been well studied, the parallel zoological succession is less described and understood. Which animal species are pioneers, what properties make them pioneers, how fast does species number increase, and how do plants and animals interact during succession? An ecological understanding of primary succession is not only of scientific interest, but also helps us to predict future ecosystems in areas freed from the ice cover.

#### **2. Glacier forelands: Nature's ecological laboratory**

In some glacier forelands, glaciologists have followed the varying position of the ice edge during long time, sometimes supported by old photographs. The age of certain characteristic moraines can, for instance, be well dated, and the age of sites between may be estimated. Several European glaciers had a maximum size at the end of the "Little Ice Age", which in Norway ended around A.D. 1750 with well-marked moraines. Forelands with dated sites up to 250 years age represent unique ecological laboratories for understanding nature's ability to conquer new land.

Ideally, a primary succession should be studied by following the gradual changes in flora and fauna in a fixed site over long time, from being newly freed from the ice cover, to having achieved a stable community structure. This is rarely possible, and the usual way is to substitute time with space, using plots with known age to estimate the future biological status of newly exposed land. The sequence of dated study plots in the foreland, illuding the succession on a given site over time, is called a chronosequence.

Primary Succession in Glacier Forelands:

differences, and mechanisms.

succession in a glacier foreland in Central Italian Alps.

How Small Animals Conquer New Land Around Melting Glaciers 153

al., 2002; Kaufmann & Raffl, 2002). In Italy, Zingerle (1999) studied spiders and harvestmen in the Dolomites, and Gobbi et al. (2006a,b, 2007) have described epigean arthropod

From southern Norway, three master/PhD theses based on pitfall trapping in glacier forelands focused mainly on surface active beetles and spiders (Alfredsen, 2010; Bråten & Flø, 2009; Vater, 2006). The other Norwegian faunistic studies in glacier forelands dealt with soil living mites (Acari) (Hågvar et al., 2009; Seniczak et al., 2006; Skubala & Gulvik, 2005) or springtails (Collembola) (Hågvar, 2010). Time has come to summarize and compare the invertebrate succession in these different geographical areas, looking for similarities,

Fig. 2. Midtdalsbreen glacier snout in Norway, August 2010: Behind the author, a 20 m broad belt of barren ground was freed from ice during this summer. Photo: Daniel Flø.

Several invertebrate groups are present on barren, vegetation-free ground close to the glacier boarder (Figs. 2-3). Typical representatives are springtails (Collembola) and mites (Acari), which are collectively named microarthropods, as well as beetles (Coleoptera), spiders (Araneae) and harvestmen (Opiliones). Since there is no organic layer, the pioneer invertebrates are surface active species, but they can find shelter in the crevices among

**3. Life on barren ground: The pioneer animals** 

stones, gravel and sand grains.

Fig. 1. Foreland at the Midtdalsbreen glacier snout, a part of the Hardangerjøkulen glacier in central south Norway. Photo: Sigmund Hågvar.

The ideal situation in a chronosequence is that the glacier has retreated at a constant speed, that climate conditions have been stable, and that the exposed ground has not been subject to reworking, for instance by glacier rivers. If temperature has been especially high during the last decades, the youngest sites may have developed faster than older sites did in their early phases of succession. Also, the source sites from which colonising organisms derive, can be influenced by climate change. A perfect chronosequence in all respects is hard to find, but certain forelands contain good historical information and well dated sites.

The botanical changes from a pioneer flora to a closed and stable plant community has been described in various glacier forelands, both in Norway (Matthews & Whittaker, 1987; Matthews, 1992; Vetaas, 1994, 1997), in the Austrian Alps (Moreau et al., 2005; Raffl, 1999; Raffl et al., 2006), and in Alaska (Chapin et al., 1994). Especially during the last decade, increased insight has also been given in the zoological succession along receding glaciers, from three different geographical areas in Europe: Svalbard, the Alps, and Norway. The invertebrate succession in two glacier forelands in Svalbard was described by Hodkinson et al. (2004). In Austria, early faunistic studies in glacier forelands by Janetschek (1949, 1958) and Franz (1969) were followed by Gereben (1994, 1995) on carabid beetles, and Paulus & Paulus (1997) on spiders. Recently, the foreland of the Austrian Rotmoos glacier has been under intense study, including invertebrate succession (Kaufmann, 2001, 2002; Kaufmann et

Fig. 1. Foreland at the Midtdalsbreen glacier snout, a part of the Hardangerjøkulen glacier in

The ideal situation in a chronosequence is that the glacier has retreated at a constant speed, that climate conditions have been stable, and that the exposed ground has not been subject to reworking, for instance by glacier rivers. If temperature has been especially high during the last decades, the youngest sites may have developed faster than older sites did in their early phases of succession. Also, the source sites from which colonising organisms derive, can be influenced by climate change. A perfect chronosequence in all respects is hard to

The botanical changes from a pioneer flora to a closed and stable plant community has been described in various glacier forelands, both in Norway (Matthews & Whittaker, 1987; Matthews, 1992; Vetaas, 1994, 1997), in the Austrian Alps (Moreau et al., 2005; Raffl, 1999; Raffl et al., 2006), and in Alaska (Chapin et al., 1994). Especially during the last decade, increased insight has also been given in the zoological succession along receding glaciers, from three different geographical areas in Europe: Svalbard, the Alps, and Norway. The invertebrate succession in two glacier forelands in Svalbard was described by Hodkinson et al. (2004). In Austria, early faunistic studies in glacier forelands by Janetschek (1949, 1958) and Franz (1969) were followed by Gereben (1994, 1995) on carabid beetles, and Paulus & Paulus (1997) on spiders. Recently, the foreland of the Austrian Rotmoos glacier has been under intense study, including invertebrate succession (Kaufmann, 2001, 2002; Kaufmann et

find, but certain forelands contain good historical information and well dated sites.

central south Norway. Photo: Sigmund Hågvar.

al., 2002; Kaufmann & Raffl, 2002). In Italy, Zingerle (1999) studied spiders and harvestmen in the Dolomites, and Gobbi et al. (2006a,b, 2007) have described epigean arthropod succession in a glacier foreland in Central Italian Alps.

From southern Norway, three master/PhD theses based on pitfall trapping in glacier forelands focused mainly on surface active beetles and spiders (Alfredsen, 2010; Bråten & Flø, 2009; Vater, 2006). The other Norwegian faunistic studies in glacier forelands dealt with soil living mites (Acari) (Hågvar et al., 2009; Seniczak et al., 2006; Skubala & Gulvik, 2005) or springtails (Collembola) (Hågvar, 2010). Time has come to summarize and compare the invertebrate succession in these different geographical areas, looking for similarities, differences, and mechanisms.

Fig. 2. Midtdalsbreen glacier snout in Norway, August 2010: Behind the author, a 20 m broad belt of barren ground was freed from ice during this summer. Photo: Daniel Flø.
