Interesting facts 

That’s how scanty Debris Fields become diverse Habitats

When glaciers retreat, they leave behind an inhospitable landscape of boulders and rocks. Soon afterwards the colonization of the freed terrain begins: the wind carries first plant seeds into the meager rubble fields. In protected niches and places, these first pioneers slowly gain ground and prepare the ground for more sophisticated species - over time a mosaic of different plant communities is created in small places.

The development from ice-free debris fields to alpine grasslands or young forests take a long time: the plants need up to 150 years to colonise such a site completely. The recolonization takes place in typical phases:

Between 5 and 10 years after the retreat of the glacier, the first plants have taken root in the debris fields. The success factors of these pioneers are the many small seeds which are spread by the wind and the long roots, with which they cling in the loose debris and suck water from the ground. Among the pioneer plants are e.g. Fleischer‘s willowherb (Epilobium fleischeri), the mountain sorrel (Oxyria digyna), the yellow mountain saxifrage (Saxifraga aizoides) and the alpine toadflax (Linaria alpina).

After 25 to 30 years, the pioneer plants have prepared the substrate for other plants: On the first humus from decayed plant residues various willow species can settle. These small growing species can well tolerate wind, drought and cold, and with the time they replace the pioneer plants.

After 60 to 100 years: The conditions for the plants become more and more favorable due to the increasing density of the plant cover. For example, the volume and the quality of the soil are increasing and more water is available. Over time, even more sophisticated plants have a chance to settle, e.g. the rust-leaved alpine rose or first low larches and stone pines.

Such colonization processes of inhospitable fields by plants (ecological succession) are taking place and can be observed today in the World Heritage site. They are one of the reasons for the listing of the World Heritage site.