**8. Succession patterns after the pioneer stage**

The succession from a pioneer stage to a mature, stable community goes through various phases which are more or less predictable. Not surprisingly, both the botanical and the zoological succession can be related to three more or less interrelated factors: Time since glaciation, distance to glacier and vegetation cover (e.g. Bråten & Flø, 2009; Gobbi, 2007; Hågvar, 2010; Hågvar et al., 2009; Hodkinsen et al., 2004; Kaufmann, 2001; Matthews, 1992; Vater, 2006). In the zoological succession, an obvious element is that herbivores like Chrysomelidae and Curculionidae have to wait for their host plant to be established. Furthermore, certain microarthropods and saprophagous beetles depend on a certain thickness of the soil organic layer (Bråten & Flø, 2009; Hågvar, 2010; Hågvar et al., 2009). Different taxonomic groups may show different succession patterns in the same foreland. For instance, at the Midtdalsbreen glacier foreland in south Norway, springtails colonised faster than oribatid mites. After 70 years, 84 % of the springtail species in the chronosequence were present, but only 57 % of the oribatid mites (Hågvar, 2010; Hågvar et al., 2009). Beetles followed a pattern similar to springtails, while spiders colonised more gradually, similar to oribatid mites (Bråten & Flø, 2009). The general rate of succession can also differ between geographical sites. In the foreland of the Rotmoos glacier in Austria, most beetle and spider species were present after only 40-50 years (Kaufmann, 2001). This is

Primary Succession in Glacier Forelands:

profound long-term effects in this alpine ecosystem.

How Small Animals Conquer New Land Around Melting Glaciers 167

Since the first effects of climate change are likely to be observed in terrestrial habitats at northern latitudes (IPCC, 2007), Norwegian studies may be especially relevant. Alpine areas of southern Norway have both had a marked temperature increase during the last 2-3 decades, and been subject to deposition of long-distance transported atmospheric nitrogen (Hole & Engardt, 2008; Ytrehus et al., 2008). Fertilization effects are most probable in nutrient-deficient ecosystems, such as alpine habitats with poorly developed soils. In a nutrient poor alpine *Dryas* heath in south Norway, experimental plots were artificially heated and/or fertilized to study the combined above-ground (plants) and below-ground (soil animals) effects (Hågvar & Klanderud, 2009). Nutrient addition and nutrient addition combined with warming resulted in several effects below ground on microarthropods as previously shown above ground on plants: Increased biomass, high dominance of a few rapid-growing species, contrasting responses of closely related species, and a reduction in species numbers. An earthworm (*Dendrobaena octaedra*) which was very rare in control plots, seemed to be favoured by the changes. These short-term responses (after 4 years) may have

Fig. 14. Pitfall trap on a three year old moraine with several specimens of the predatious and very active Carabidae species *Bembidion hastii*. But what is the density of the species, what

does it eat, and does it reproduce here? Photo: Sigmund Hågvar.

a faster colonisation rate than observed in alpine south Norway (Bråten & Flø, 2009; Vater, 2009). The difference is probably due to a milder climate in the Austrian site, since certain taxa absent in the Norwegian sites were present there, e.g. Lumbricidae, Formicidae, and Diplopoda.

In an extensive study of eight different glacier forelands in south Norway, Vater (2006) demonstrated how altitude and local climate influenced colonisation rate, even within a small geographical area. In the forested sub-alpine zone the colonisation rate of macroarthropods was high, while the succession was very slow in a high alpine foreland. A "geoecological model" was proposed by Vater (2006) to explain three distinctive pathways of succession, representing the subalpine, the low/mid-alpine, and the high alpine zone, respectively. Certain characteristic species could, however, be pioneers at very different altitudes.

Although the colonisation rate may vary considerably between sites due to climatic differences, the sequence between different taxa or ecological groups may show striking similarities. We see that both within south Norway, and in comparison with the Alps (Bråten & Flø, 2009; Kaufmann, 2001; Kaufmann & Raffl, 2002; Vater, 2009). Among beetles, surface active predators within the family Carabidae are typical pioneers, while the speciesrich family Staphylinidae dominates later. This family contains many small species which are favoured by the development of an organic soil layer. Most herbivorous species are also relatively late colonisers, except for the moss-eating genus *Simplocaria* (Byrrhidae), which can inhabit pioneer moss patches. An interesting aspect is that herbivore beetles do not necessarily colonise promptly when the food plant is established. In the Midtdalsbreen foreland, *Chrysomela collaris* (Chrysomelidae) was found after about 80 years, while the food plant *Salix herbacea* belonged to the pioneer species. The explanation may partly be that the beetle is a slow disperser, partly that a certain cover of the food plant is needed.

From the Alps, Kaufmann (2001) concluded that faunal colonisation and succession in alpine glacier forelands, to a large extent, followed predictable and deterministic assembly rules and that stochastic effects were of minor importance. Studies in Norway and Svalbard support this general picture. However, Kaufmann (2001) also stressed that favourable sun and light conditions may facilitate successional progress in local patches.

A general question in succession studies is the turnover rate of species. To answer this, most species have to be identified. Based on a limited taxonomical resolution, Vater (2006) concluded that most macroinvertebrates remained after colonisation. However, in the Alps, several pioneer species of spiders and beetles were absent in later successional stages (Gobbi, 2006b, 2007; Kaufmann, 2001). Bråten & Flø (2009) found that most spiders remained after colonisation, while beetles showed a certain turnover of species. Within mites and springtails, most species remain after colonisation, although their abundance and relative dominance may vary throughout the chronosequence (Hågvar, 2010; Hågvar et al., 2009).

#### **9. Climate change and succession pattern**

A gradually warmer climate will make it more difficult to use dated sites as a substite for time. Kaufmann (2002) concluded that an increase of 0.6oC in summer temperatures approximately doubled the speed of initial colonisation, whereas later successional stages were less sensitive to climate change. It is also possible that the surrounding source habitats may be influenced and increase their dispersion of species into the foreland.

a faster colonisation rate than observed in alpine south Norway (Bråten & Flø, 2009; Vater, 2009). The difference is probably due to a milder climate in the Austrian site, since certain taxa absent in the Norwegian sites were present there, e.g. Lumbricidae, Formicidae, and

In an extensive study of eight different glacier forelands in south Norway, Vater (2006) demonstrated how altitude and local climate influenced colonisation rate, even within a small geographical area. In the forested sub-alpine zone the colonisation rate of macroarthropods was high, while the succession was very slow in a high alpine foreland. A "geoecological model" was proposed by Vater (2006) to explain three distinctive pathways of succession, representing the subalpine, the low/mid-alpine, and the high alpine zone, respectively. Certain characteristic species could, however, be pioneers at very different

Although the colonisation rate may vary considerably between sites due to climatic differences, the sequence between different taxa or ecological groups may show striking similarities. We see that both within south Norway, and in comparison with the Alps (Bråten & Flø, 2009; Kaufmann, 2001; Kaufmann & Raffl, 2002; Vater, 2009). Among beetles, surface active predators within the family Carabidae are typical pioneers, while the speciesrich family Staphylinidae dominates later. This family contains many small species which are favoured by the development of an organic soil layer. Most herbivorous species are also relatively late colonisers, except for the moss-eating genus *Simplocaria* (Byrrhidae), which can inhabit pioneer moss patches. An interesting aspect is that herbivore beetles do not necessarily colonise promptly when the food plant is established. In the Midtdalsbreen foreland, *Chrysomela collaris* (Chrysomelidae) was found after about 80 years, while the food plant *Salix herbacea* belonged to the pioneer species. The explanation may partly be that the

beetle is a slow disperser, partly that a certain cover of the food plant is needed.

and light conditions may facilitate successional progress in local patches.

**9. Climate change and succession pattern** 

From the Alps, Kaufmann (2001) concluded that faunal colonisation and succession in alpine glacier forelands, to a large extent, followed predictable and deterministic assembly rules and that stochastic effects were of minor importance. Studies in Norway and Svalbard support this general picture. However, Kaufmann (2001) also stressed that favourable sun

A general question in succession studies is the turnover rate of species. To answer this, most species have to be identified. Based on a limited taxonomical resolution, Vater (2006) concluded that most macroinvertebrates remained after colonisation. However, in the Alps, several pioneer species of spiders and beetles were absent in later successional stages (Gobbi, 2006b, 2007; Kaufmann, 2001). Bråten & Flø (2009) found that most spiders remained after colonisation, while beetles showed a certain turnover of species. Within mites and springtails, most species remain after colonisation, although their abundance and relative dominance may vary throughout the chronosequence (Hågvar, 2010; Hågvar et al., 2009).

A gradually warmer climate will make it more difficult to use dated sites as a substite for time. Kaufmann (2002) concluded that an increase of 0.6oC in summer temperatures approximately doubled the speed of initial colonisation, whereas later successional stages were less sensitive to climate change. It is also possible that the surrounding source habitats

may be influenced and increase their dispersion of species into the foreland.

Diplopoda.

altitudes.

Since the first effects of climate change are likely to be observed in terrestrial habitats at northern latitudes (IPCC, 2007), Norwegian studies may be especially relevant. Alpine areas of southern Norway have both had a marked temperature increase during the last 2-3 decades, and been subject to deposition of long-distance transported atmospheric nitrogen (Hole & Engardt, 2008; Ytrehus et al., 2008). Fertilization effects are most probable in nutrient-deficient ecosystems, such as alpine habitats with poorly developed soils. In a nutrient poor alpine *Dryas* heath in south Norway, experimental plots were artificially heated and/or fertilized to study the combined above-ground (plants) and below-ground (soil animals) effects (Hågvar & Klanderud, 2009). Nutrient addition and nutrient addition combined with warming resulted in several effects below ground on microarthropods as previously shown above ground on plants: Increased biomass, high dominance of a few rapid-growing species, contrasting responses of closely related species, and a reduction in species numbers. An earthworm (*Dendrobaena octaedra*) which was very rare in control plots, seemed to be favoured by the changes. These short-term responses (after 4 years) may have profound long-term effects in this alpine ecosystem.

Fig. 14. Pitfall trap on a three year old moraine with several specimens of the predatious and very active Carabidae species *Bembidion hastii*. But what is the density of the species, what does it eat, and does it reproduce here? Photo: Sigmund Hågvar.

Primary Succession in Glacier Forelands:

invertebrates are often relatively late colonisers.

pioneer community is often rather predictable.

Oct 22: 3 (5): 487-490.

149-175.

**12. References** 

How Small Animals Conquer New Land Around Melting Glaciers 169

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

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

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

Alfredsen, A. N. (2010). Primary succession, habitat preferences and species assemblages of

Bardgett, R. D.; Richter, A.; Bol, R.; Garnett, M. H.; Bäumler, R.; Xu, X.; Lopez-Capel, E.;

Bråten, A. T. & Flø, D. (2009)*.* Primary succession of arthropods (Coleoptera and Araneae)

Chapin, F. S.; Walker, L. R.; Fastie, C. L.; & Sharman, L. C. (1994). Mechanisms of primary

Coulson, S. J.; Hodkinson, I. D. & Webb, N. R. (2003). Aerial dispersal of invertebrates over a

Fjellberg, A. (1974). A study of the Collembola fauna at Stigstuv, Hardangervidda.

Fjellberg, A. (2007). The Collembola of Fennoscandia and Denmark. Part II:

Franz, H. (1969). Besiedlung der jüngst vom Eise freigegebenen Gletschervorfelder und ihrer

Gereben, B. A. (1994). Habitat-binding and coexistence of carabid beetles in a glacier retreat

carabid beetles in front of the retreating glacier Midtdalsbreen, Finse, southern

Manning, D. A.; Hobbs, P. J.; Hartley, I. R.; & Wanek, W. (2007). Heterotrophic microbial communities use ancient carbon following glacial retreat. *Biological Letters*

on a newly exposed glacier foreland at Finse, southern Norway. *Master thesis,*

succession following deglaciation at Glacier Bay, Alaska. *Ecological Monographs,* 64,

Abundance, biomass and species diversity. *Master Thesis*, University of Bergen,

Entomobryomorpha and Symphypleona. *Fauna Entomologica Scandinavica*, 42, 1-266.

Böden durch wirbellose Tiere. Neue Forschungen im Umkreis der Glocknergruppe.

zone in the Zillertal Alps. In: *Carabid beetles: ecology and evolution.* Desender, K., Dufrene, M., Loreau, M., Luff, M. L. and Maelfait, J.-P. (eds.), pp. 139-144.

change may generally speed up the succession rate around melting glaciers.

Norway. *Master thesis,* University of Bergen, 83 pp.

Norwegian University of Life Sciences, 85 pp.

*Wissenschaftliche Alpenvereinshefte,* 21, 291-298.

Norway, 141 pp. (In Norwegian.)

Dordrecht: Kluwer.

High Arctic glacier foreland. *Polar Biology,* 26, 530-537.

### **10. Future research**

Although we are beginning to understand several trends and mechanisms in the primary succession of glacier forelands, more field studies with a high taxonomic resolution, and from different geographical areas, are needed. It is a special challenge to explain the ecological mechanisms working in pioneer communities on barren ground. What is the importance of pioneer microflora as food for pioneer microarthropods, and how important are resident microarthropods as food for pioneer beetles and spiders? Gut content analyses based on DNA primers of potential prey items would be highly welcome. And how important are pioneer mosses as a driver in succession?

Another improvement would be to add more quantitative samplings methods. Pitfall trapping favours fast-moving surface species (Fig. 14). Species with low densities may give considerable catches if they are very active, while species with higher densities may be lacking in the pitfall traps if they are rather immobile (for instance web-building spiders or moss-eating beetles).

Long-term monitoring of selected plots can illustrate effects of changed climate on succession. Plots which are already well studied should be re-studied at intervals. A better understanding of primary succession makes it easier to forecast what future ecosystems may be like in areas freed from ice. It can also increase our general insight into ecology, maybe by removing the "predator first-paradox" as a paradox.
