Steep slopes with exposed rocks are prone to rock falls and rock slides.
The rock surface is weathered and disintegrates. Rock fragments tumble down and form talus and scree slopes at the foot of cliffs.
Large boulders may be spread singly or in heaps over a large area.

A new rock fall will destroy the vegetation. Subalpine forests often show aisles which have been cut by rock slides.

Why are so few plants and animals found on scree/talus slopes?

Scree is an unstable substrate. Plants living there have to show special adaptations because they are frequently damaged and covered by falling rock material. Many of these plants are able to recover from burial and downslope movement of the substrate by rapid shoot elongation.
For animals scree may not be very favourable due to the unstable substrate and the low availability of food and water.
At the margins of the scree, plants stabilize the substrate and additional species are able to grow.

1 - Scree slope
1 | 2 | 3 (100-150K each)

What are the ecological implications of boulder fields?

Large rocks or boulders provide distinct types of microhabitats. Animals can find shelter between the rocks. The more favourable microclimate of boulder fields (sun-warmed rocks and wind-protected areas) are preferred habitats for marmots (Marmota ssp.) and other animals. Also plant species from lower elevations may be able to extend further upwards when growing in the protection of rocks.
Boulder fields greatly increase the available surface substrate for saxicolous organisms, among them many mosses and lichens, but also higher plants that escape from the stronger competition in closed vegetation and rely only on the low levels of water and nutrients that rock crevices may provide.

2) Boulder field, 1900 m, Biet, Switzerland (99K)
3) Boulder field, closer view (154K)
4) Marmot (Marmota marmota), Biet, Switzerland (141K)
5) Mountain sandwort (Arenaria groenlandica, Caryophyllaceae), growing in a rock crevice, Mt. Washington, NH (67K)
6) Divers cryptogams growing on a boulder, Mt. Washington, NH (122K)

29 August 2011
© ALPECOLe 2002-2007