Cassiope heath is a circumpolar Arctic vegetation type predominated by Cassiope tetragona. Cassiope heaths are a widespread plant community occurring from the Subarctic to the High Arctic. C. tetragona (L.) D.Don (Arctic white heather, white Arctic bell heather, fire moss, four-angled Cassiope, Qijooktaik, Iksutit (Inuktitut), Issutit (Greenlandic)) is an evergreen, long-lived dwarf shrub of the Ericaceae family, which reaches 5-20 cm in height. It has four-ranked, dark green leaves with a deep furrow on the back. The solitary campanulate (bell-shaped) flowers are white. Its general distribution is circumpolar. In contrast, the moss heather Cassiope hypnoides (L.) D.Don is an amphi-Atlantic, Arctic-alpine species and more common in Greenland, Scandinavia, and the Eastern Canadian Arctic. Further Cassiope species, such as C. stelleriana (Pall.) DC (Alaska moss heather), C. lycopodioides (Pall.) D.Don (club moss mountain heather), or C. mertensiana (Bong.) D.Don (western moss heather, white mountain heather), are more restricted to alpine environments south of the treeline. The distribution of vegetation communities in the Arctic is closely related to topographic features that affect soil drainage and microclimate. The harsh climate dictates that species diversity is relatively low and plant height is restricted. In the High Arctic where summer and winter precipitation is low, Cassiope heaths can often be found on hummocky and moist terrain in late-melting snowbeds. Here, they are usually associated with Dryas integrifolia M.Vahl (Mountain Avens, White Dryas), a prevalent species of many cushion plant and dwarf-shrub heath communities in the Mid and High Arctic. Toward the Low Arctic where soils are often poorly drained, C. tetragona occasionally remains an important component of some heaths; however, other dwarf shrubs such as Salix spp. (willows), Betula spp. (birch), Vaccinium spp. (e.g., cranberry), Empetrum spp. (crowberry), and Arctostaphylos spp. (bearberry) dominate. In the Low- and Subarctic, C. tetragona is abundant only on well-drained calcareous soils and rock outcrops. Drier soil conditions occur where slight rises in topographic relief provide a rooting zone above the standing water table, for example, on eskers, raised beach ridges, river banks, along the rims of lakes, or on pingos. Dwarf-shrub communities usually grow in these better-drained areas.
C. tetragona has a relatively high resin content and was formerly important to Inuit as a fuel source for outdoor cooking when traveling on the land. Nowadays, it can provide an archival proxy for climate-related plant growth. Although the leaves of C. tetragona die off after 3-4 years, they remain attached on the plant stems for several decades and their number can be compared with annual temperature variations in the Arctic.
Recent studies in the High Arctic have shown that the number of leaves and flowers produced each year is positively correlated with the July mean temperature. C. tetragona is therefore an Arctic analog to tree-ring records from the Subarctic and is potentially useful as a bioindicator in climate change research.
Callaghan, Terry V. et al., "Historical records of climate-related growth in Cassiope tetragona from the Arctic." Journal of Ecology, 77 (1989): 823-837 Havstrom, Mats et al., "Little Ice Age temperature estimated by growth and flowering differences between subfossil and extant shoots of Cassiope tetragona, an arctic heather." Functional Ecology, 9 (1995): 650-654 Johnstone, Jill F. & Greg H. Henry, "Retrospective analysis of growth and reproduction in Cassiope tetragona and relations to climate in the Canadian High Arctic." Arctic and Alpine Research, 29(4) (1997): 459-469 Scott, Geoffrey A.J., Canada's Vegetation—A World Perspective, Montreal and Kingston: McGill-Queen's University Press, 1995
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