Samstag, 27. Dezember 2008

Vegetation on Alpine rockglacier surfaces

Rockglaciers are widespread in the alpine environment, where they can be regarded as reliable indicators of permafrost. Active rockglaciers are tongue-like debris masses, which show a slowly creeping and on the first view vegetation lacking surface. But anyway still some plants can be found here.
In combination with geophysical methods the vegetation cover can give indications for the recent activity of rockglaciers, or help to reconstruct the temporal development where geomorphological indicators are absent.
For plants they represent an ulterior challenge for colonization and growth. Surface morphology and surface instability, both resulting of the movement of the rockglacier, have been found to exert important effects on vegetation patterns developing on it. Traditional studies addressing relationships between vegetation and surface instability in the alpine environment have been carried out on scree slopes and moraines. In both habitats, plant cover and patterns of surface movement are controlled primarily by slope angle and gravity. Relationships between vegetation patterns and surface instability in arctic and alpine regions have been the object of studies focusing on community typology, growing strategies and adaptations to mechanical disturbance, root mechanical properties, and vegetation dynamics.

Along with the type of rock that composes the rockglacier, the average diameter of debris and the movement velocities influence the type of plant succession and cover that can establish.
Missing fine material, and so missing colonisation niches for plant seedlings, seems to favourite plants that can grow between boulders, like Geum-species or shrubs. Active rockglaciers shows a colonisation by lichens, except for the front where pioneer species like Cerastium, Oxyria and the clubb moss Huperzia can be found.

Cerastium uniflorum (Caryophyllaceae)

Oxyria digyna (Polygonaceae)

Huperzia selago (Lycopodiaceae)

The species poor lichen assemblage develops in the middle of rockglacier,in direction of the rooting zone the lichen cover diminishes, to lack completely in the rooting zone. Lichens can be also used for dating the rockglacier by lichenometry.
A high movement causes a coarse-textured substrate; finer material fell off or between the greater, moving boulders. The resulting mechanical stress prevents the establishment of epilithic lichens on boulders.

Rhizocarpon geographicum

Brodoa intestiniformis

The vegetation patterns on active rockglaciers differed from adjacent stable areas and from inactive rockglaciers, probably because of the stressful conditions associated with substrate movement. Highly unstable sites on active rockglaciers were easily recognized by the absence of mosses and lichens. The distributional pattern of vascular plants is not strictly related to the surface instability, but depend on a combination of environmental factors, mainly substrate texture and movement intensity.

CANNONE, N. & GERDOL, R. (2003): Vegetation as an Indicator of Surface Instability in Rock Glaciers. Arctic, Antarctic and Alpine Research. Vol. 35(3): 384-390

BURGA, C.A.; FRAUENFELDER, R.; RUFFET, J.; HOELZLE, M. & KÄÄB, A. (2004): Vegetation on Alpine rock glacier surfaces: a contribution to abundance and dynamics on extreme plant habitats. FLORA 199: 505-515


SLW hat gesagt…

This is great, David! Alpine ecology is one of my early favorites!

Thanks for submitting it to Berry-Go-Round!

timi hat gesagt…

great, was looking exactly for some papers like this :)!! mille grazie, greetings from Graz.