**2. Materials and methods**

#### **2.1. Study site**

possibilities for studying primary succession. Instead of monitoring changes within a fixed plot over time, which indeed would be a very time-demanding approach, successions can be described by studying sites with known ages. Such a gradient in the terrain, where space is

Most studies in glacier forelands have dealt with plant succession, and a thorough and longlasting one has been performed near the glacier Storbreen in Norway [4]. A main conclusion is that age alone cannot predict the plant community. Local variations in microtopography, moisture, nutrients, substrate and exposure contribute in shaping the species composition. Instead of ending up with a 'monoclimax', the succession produces a 'polyclimax' with a mosaic of plant communities. A 'bulk' succession related only to the age of the ground contains 'noise' from a mixture of successional pathways. It has been argued for a 'geo-ecological' view on primary succession, where both biotic and abiotic factors were taken into considerations [4]. A recent study from Nigardsbreen foreland in Norway confirmed the modifying

Studies on animal succession near receding glaciers are fewer, and are mainly focusing on arthropods. In addition to the present case study, there are studies on arthropod succession in glacier forelands from the Alps [5, 7–11], from Svalbard [12–15], from Iceland [16] and from

In the following presentation, we have adopted the geo-ecological perspective. In other recent studies of invertebrate successions in Norwegian glacier forelands, a geo-ecological perspective has been successfully applied, when comparing succession patterns at different altitudes

Hardangerjøkulen glacier in Southern Norway has been receding since the end of 'the little ice age' for about 250 years ago. The melting rate has been especially high during the last two decades, with about 20-m retreat yearly at one glacier snout near Finse (Midtdalsbreen). We have good data on earlier positions of the ice edge in this glacier foreland due to dated moraines. Since 2001, extensive zoological studies have been performed here to describe and understand arthropod succession patterns (**Figure 1**). These studies include soil-living microarthropods [24, 25], surface active beetles, spiders and harvestmen [26, 27], aerial transport of arthropods [28], studies on ancient carbon released by the glacier [29, 30], food choice of

Time has come to combine these fragments into a holistic story about animal succession near a melting glacier. In addition to summing up the main results from these nine papers, the

• Are there alternative succession patterns for arthropods, in the same way as there are alter-

• Is there a strong progressive succession of arthropods on terrain ages of 20–50 years, as in

used as a substitute for time, is called a chronosequence [4, 5].

effect of microtopography on the floral succession [6].

pioneers [31], as well as a special focus on early succession [32].

present syntheses will discuss some general aspects of succession:

• Does animal and botanical successions differ in their early phases?

**a.** *Comparison between botanical and zoological succession*

native succession patterns for vegetation [4–6, 33]?

and climatic conditions [19, 20, 22, 23].

Norway [17–23].

148 Glacier Evolution in a Changing World

plants [33]?

The study site was situated close to the 73-km<sup>2</sup> large Hardangerjøkulen glacier in central Southern Norway, between 1200 and 1400 m a.s.l., in the treeless low- and mid-alpine zone. **Figure 2** shows the foreland of a northern glacier snout named Midtdalsbreen (60°34′N, 7°28′E).

**Figure 2.** Aerial photograph of the glacier foreland, showing the position of moraines from 1750, 1934 and 2005. Beetles, spiders and harvestmen were sampled on the six numbered plots with the following ages: 3, 40, 63, 79, 170 and 205 years. Springtails and mites were sampled from eight plots in zone A (32–48 years), five plots in zone B (52–66 years), seven plots in zone C (72–227 years) and five plots in zone D (10,000 years). The small map shows the position of the foreland in Southern Norway. Modified from Ref. [26].

## **2.2. Microarthropod sampling**

For the study of soil-living microarthopods, which are springtails (Collembola) and mites (Acari), we chose to keep the vegetation factor as constant as possible. All soil samples were taken in *S. herbacea* vegetation, which was found throughout the gradient. This tiny shrub belongs to the pioneer plants and shows no preference for snow cover on relatively young terrain [34, 35]. However, after about 70 years, it is mainly restricted to patches where snowmelt is late (the so-called snow beds), where it forms rather continuous carpets. Plots 1–8 (zone A) were 32–48 years old, plots 9–13 (zone B) were 52–66 years old and plots 14–20 (zone C) were 72–227 years old. Plot nos. 21–25 (zone D) were outside the 1750 moraine which mark the end of the 'little ice age' in Norway, so these five plots had an age of about 10,000 years [24]. In each of the 25 study plots, microarthropods were extracted from 10 to 16 soil cores, 3 cm deep and with a surface area of 10 cm2 [24].
