ABSTRACT: The role of biological soil crusts in the colonisation and facilitation of vascular plants on a high arctic glacier foreland.

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Since the end of the Little Ice Age (ca. 1850), climate warming has led to a decrease in the surface area and mass of many glaciers in the Canadian High Arctic. As glaciers retreat, they expose new terrestrial environments for potential colonisation by microorganisms and higher plants. While the rare vascular plant can colonise terrain immediately following deglaciation, true primary colonisation takes place on the microbial scale. Pioneering organisms such as cyanobacteria and algae are typically the first organisms to colonise the surface and subsurface of soils and may over time create a firm, yet flexible, aggregate organic layer known as a ‘biological soil crust’. The unique physical and biological properties of soil crusts have been shown to increase soil moisture and nutrients, elevate soil temperatures and reduce soil erosion. We hypothesize that in early community development biological soil crusts create a preferential substrate for subsequent plant colonisation. We quantified the potential facilitative effects of biological soil crusts on vascular plants along a 190 m long glacier foreland in front of the retreating Teardrop Glacier at Sverdrup Pass, Ellesmere Island, Nunavut, Canada (79°10’N, 79°45’W). The distribution of crust cover was measured in relation to ecological variables including vascular plant cover, species composition, density, reproduction and soil parameters using 50 x 50 cm quadrats placed randomly within 40 x 5 m bands at increasing distances from the glacier terminus.Biological soil crusts appeared within approximately 10 m of the glacier terminus and soon became the dominant available substrate for plant establishment up to approximately 120 m. Surfaces colonised by biological soil crusts were found to support higher species richness, density and reproductive output than uncrusted substrates, particularly those in the early stages of succession. Preliminary results suggest that biological soil crusts may play a positive role in initial vascular plant establishment, however in older sites the relationship between plants and crusts may be neutral or even competitive. The soil crust and vascular plant cover and species richness found on the Teardrop Glacier foreland is unsurpassed on other forelands surveyed on Ellesmere Island and reveals the potential for biotic interactions between soil crusts and plants in high arctic succession. The Teardrop Glacier is unique compared to many glaciers in the High Arctic in that it supports over 100 small melt water channels evenly distributed across it terminus, as opposed to one or two large discharge channels, resulting in a foreland that can support high colonisation by soil crust microbiota thereby facilitating vascular plants. Increased glacial melt across the Arctic has the capacity to greatly influence, either positively or negatively depending on melt patterns, the development of biological soil crusts and thus of emerging vascular plant communities.

Bibliography of Canadian Geomorphology