Biological Soil Crusts

An important component of grassland and alpine tundra ecosystems in western Canada is a complex community of algae, lichens, mosses, liverworts, and cyanobacteria that grow on the soil surface. Collectively these assemblages of photosynthetic organisms are known as biological soil crusts. They perform many important ecosystem services, from binding soil particles together, to adding new nitrogen and organic matter to surface soil horizons.  


The grasslands of the Caribo0 Chilcotin region support diverse biological soil crusts. Farwell Canyon is shown in the background.

Biological soil crusts are particularly important as an early successional community on recently disturbed substrates. This raises the question as to whether or not they could be used to assist in the restoration of disturbed sites, especially in alpine tundra environments, where cold soils and a short growing season pose severe constraints on growth of higher plants.


UNBC graduate student Kasia Caputa setting up field microclimate station for biological soil crust studies.

Research in the plant ecology laboratory at UNBC has focused on quantifying the ecological role of biological soil crusts, especially their abilities to add newly fixed nitrogen to what are typically nutrient limited ecosystems. Current research is developing protocols for using biological soil crusts to assist restoration of disturbed soils. This is a promising approach for addressing impacts from anthropogenic disturbances such as pipelines and mines in high elevation alpine environments.   


Field camp at Chilcotin Lodge examines biological soil crusts.



Caputa, K., D. Coxson, and P. Sanborn. 2013. Seasonal patterns of nitrogen fixation in biological soil crusts from British Columbia's Chilcotin grasslands. Botany:91:631–641.  

Stewart, K.J., M.E. Brummell, D.S. Coxson, D.S., and S.D. Siciliano. 2013. How is nitrogen fixation in the high arctic linked to greenhouse gas emissions?  Plant Soil 362:215–229. 

Stewart, K.J., E.G. Lamb, and S.D. Siciliano. 2011. Bryophyte-cyanobacterial associations as a key factor in N2-fixation across the Canadian Arctic. 

Stewart, K.J., D.S. Coxson, and P. Grogan. 2011. Nitrogen inputs by associative cyanobacteria across a low arctic tundra landscape. Arctic, Antarctic, and Alpine Research 43: 267–278. 

Stewart, K.J., D.S. Coxson, and S.D. Siciliano. 2011. Small-scale spatial patterns of N2 fixation and nutrient availability in an arctic hummock-hollow ecosystem. Soil Biology and Biochemistry 43:133–140. 

Marsh, J., S. Nouvet, P. Sanborn, and D.S. Coxson. 2006. Composition and function of biological soil crust communities along topographic gradients in grasslands of central interior British Columbia (Chilcotin) and southwestern Yukon (Kluane). Can. J. Bot. 84:717–736.


Rangeland grazing exclosures provide an important tool for examining the impacts of grazing on biological soil crusts, the area on the left has been protected from grazing for a decade.


Free-living and lichenized cyanobacteria dominate dark biological soil crusts in the Chilcotin.


Pinkish squamules of  Sockeye Psora  (Psora decipiens) are lined with calcium oxalate depositions.


Bryophyte and liverwort mats in alpine tundra near Terrace, BC are heavily colonized by free-living cyanobacteria.


Cyanobacteria grow on the surface of liverworts at the edge of a small alpine melt pond.


The nitrogen-fixing lichen Solarina crocea grows intermingled with liverworts in alpine tundra biological soil crust.


Yukon College researcher Katherine Stewart and UNBC student Annie-Claude Letendre  use a gas chromatograph to assess rates of nitrogen fixation in biological soils crusts.