Primary succession on glacier forelands in the subantarctic Kerguelen Islands

Primary succession was studied on recently deglaciated areas in front of the Ampere Glacier, Kerguelen Islands (49 degrees 30' S, 69 degrees 30' E). Vegetation, colonization processes and soil development were investigated on seven sites on the outwash plain over a distance of 5 km and representing a > 200-yr old chronosequence. Seven species are involved in the succession, showing four patterns of change: (1) 'pioneer' (Pea kerguelensis, Poa annua, Colobanthus kerguelensis and Cerastium fontanum); (2) 'intermediate' (Festuca contracta); (3) 'late colonizer' (Azorella selago); and (4) 'fluctuating' (Agrostis magellanica). Two of the pioneers are introduced species (Pea annua and Cerastium). The total plant cover increases significantly with the age of the sites but never exceeds 4.2 %. The plant succession pattern observed in this study appears to be related to soil development. Root architecture and fine particle dynamics in the soil may explain the behaviour of the different species along the chronosequence. The pioneer species have a very shallow root system whereas the intermediate and late colonizers are deeper and longer rooted. The dominance of Azorella selago (Apiaceae) in the oldest community may be attributed to its unique root system in relation to the vertical distribution of silt cappings in the soil.