SOIL DEVELOPMENT AND FLORAL COLONIZATION ON RECENTLY EXPOSED LAND SURFACES IN SOUTHERN ICELAND

In the last century, recession of outlet glaciers of the Vatnajökull ice sheet has exposed glacial ground moraine and outwash deposits to pedogenesis and floral colonization. In Skaftafell National Park, the Skaftafellsjökull has retreated over 1000 m in the last 75 years, leaving a broad proglacial plain interupted by recessional morainal ridges. Formation of very young soils on the glacially derived volcanic sediments (andic cryofluvents) comprises the accumulation of organic carbon in the uppermost soil layer and minor root turbation. Organic carbon content in this layer, as measured by Truspec analysis, ranges from a high of ~3% on older (60+ years), more heavily vegetated surfaces, to less than 0.5% on outwash surfaces less than 20 years old. The oldest land surfaces (more than 100 years) are almost completely vegetated, with mats of mosses up to 17 cm thick and birches averaging over 1 meter height. Surfaces less than 65 years old are at most 75% vegetated, with moss thickness averaging ~6 cm. Surfaces that are 25 years old or less are at most 30% covered, with wooly willow dominating the shrub layer. The floral cover on the youngest surfaces is 5% or less, with moss and shrubs mainly on sheltered slopes. The nearby Svinafellsjökull has a history of recession interrupted in the late twentieth century by episodes of surging, and consequently, a more complex periglacial topography. No clear correlation exists between land surface age and soil carbon content for this glacier, possibly, in part, due to the effects of continued livestock grazing in this area.