Initial treeline for the Alaska portion of the CAVM was taken from the Major Ecosystems of Alaska 1:2,500,000 map (Joint Federal State Land Use Planning Commission for Alaska, 1973). The Seward Peninsula treeline was obtained from a map produced by the Soil Conservation Service (Swanson, et al., 1985). The boundary in southwestern Alaska is along the watershed between the Kuskokwim (included) and the Nushagak (excluded) Rivers. Treeless areas south and west of this line were too far south, with too much marine influence to be considered arctic tundra. Initial polygon boundaries were then adjusted by Martha Raynolds from photo interpretation of the AVHRR image (AVHRR image reference). Areas with trees appeared darker on the image than those areas without trees.
Treeline for western Canada (Hudson’s Bay to the Alaskan border) was defined by Timoney, et al. (1992) as the northern limit of trees where the ratio of tree cover to upland tundra was less than 1:1,000. We obtained original maps from Timoney showing treeline and major hydrological features, and redrew the treeline over our 1:4,000,000 scale AVHRR basemap (AVHRR image reference) using the Digital Chart of the World (DCW; ESRI 1993) hydrology layer for reference. Treeline for Eastern Canada (Quebec and Labrador) are based on Payette (1983, 1993) and Zoltai (pers. comm.) with the northern limit of spruce redrawn over the AVHRR 1:4,000,0000 baseline map using the DCW (ESRI 1993) hydrologic features for reference. The forest tundra transition is gradual in some regions and interpretation of treeline directly from the AVHRR imagery was not possible.
Treeline in Russia was based on Belov (1990) and the Arctic Atlas (Treshnikov 1985), In addition, Adreev (1987) was consulted for Yakutia, Sochava et al. (1976) for Western Siberia, and Belikovich (2001) for the Anadyr area in Far East Russia.
Treeline in Iceland was determined by Eythor Einarsson and Gudmundur Gudjónsson, The boundary is based on historical records of the extent of woody vegetation when people first settled the island. Deforestation and erosion since settlement make it difficult to determine treeline based on existing vegetation. The true arctic part of Iceland is a low-shrub subzone in North Iceland. The tundra regions of the Central Highlands of iceland are alpine rather than arctic. Our boundary is in agreement with other Icelandic vegetation maps (Einarsson et al. 2000). A full discussion of these issues can be found in Einarsson and Gudjonsson (2002).
Andreev, V.N. et al. (eds.) 1987. Vegetation Map in Agricultural Atlas of Yakutia. Scale 1:5,000,000.
AVHRR image reference....
Belikovich, A.V. 2001. Vegetation cover of the northern part of the Koryak Uplands. Russian Academy of Sciences. Far Eastern Branch, Institute of Biology and Soil Science. Vladivostok, Dalnauka. 415p
Belov, V.A. (ed.) et al. 1990. Vegetation map of the USSR. Scale 1:4,000,000. Moscow, Novosibirsk.
Einarsson, E. and F. Gudjónsson. 2002. The situation of Iceland in the system used the CAVM mapping. Pages 43-48 in Raynolds, M.K and C. J. Markon. 2002. Fourth International Circumpolar Arctic Vegetation Mapping Workshop. Russian Academy of Sciences, Moscow, Russia. 10-13 April 2001. USGS Open-file Report 02-181. http://pubs.usgs.gov/of/2002/of02-181/
Einarsson, E., Gudjónsson, G., Hansen, H. H. & Jónsson, Th. H. (2000) Map of the Natural Vegetation of Iceland. In: Map of the Natural Vegetation of Europe (eds. Bohn, U., Gollub, G. and Hettwer). Bundesamt fur Naturschutz, Bonn.
ESRI. 1993. Digital Chart of the World. September 1993, Ed. 1. Environmental Systems Research Institute Inc. Redlands, CA, USA. http://www.maproom.psu.edu/dcw/
Joint Federal State Land Use Planning Commission for Alaska. July 1973. Major Ecosystems of Alaska 1:2,500,000 map. http://agdc.usgs.gov/data/usgs/erosafo/ecosys/metadata/ecosys.html
Payette, S. 1983. The forest-tundra and present tree-lines of the northern Quebec-Labrador peninsula. Tree-Line Ecology. Proceedings of the Northern Quebec Treeline Conference. (eds. P. Morisset and S. Payette) Nordicana, 47:3-23.
Payette, S. 1993. The range limit of boreal tree species in Quebec-Labrador: and ecological and paleoecological interpretation. Review of Paleobotany and Palynology. 79(0993):7-30.
Sochova, V.B. et al. (eds.) 1976. Vegetation map of the West-Siberian plain. Scale 1:1,500,000. M. GUGK.
Swanson, J.D., Schuman, M., Scorup, P.C. 1985. Range Survey of the Seward Peninsula Reindeer Ranges, Alaska. US Dept. of Agriculture, Soil Conservation Service. 77pp + maps. http://www.ak.nrcs.usda.gov/soil/gis/metadata/veg_site.html
Timoney, K.P., G.H. La Roi, et al. 1992. The high subarctic forest-tundra of northwestern Canada: position, width, and vegetation gradients in relation to climate. Arctic, 45(1):1-9. http://www.aina.ucalgary.ca/scripts/minisa.dll/144/proe/proarc/se+arctic,+v.+45,+no.++1,+Mar.+1992,*?COMMANDSEARCH
Treshnikov, A. F. et al. (eds.) 1985. Arctic Atlas. Head Office of Geodesy and Cartography of the Soviety Ministery of USSR. Moscow. 204pp