This indicator measures the position of treeline in the NWT. There have been many attempts to define treeline in northern Canada. The recently adopted treeline definition used by the NWT is of a forest that contains at least 25% crown closure and is at least 5 meters tall at maturity.
The new standard treeline is defined as the extent of forestlands pertinent to reporting under the Kyoto Protocol. The details of the definition were agreed to within the framework of the Marrakech Accord and are reported by the Canadian government under its obligations as a signatory to the Kyoto Protocol. For the first time, the treeline has been surveyed in the NWT using this standard.
The NWT is home to the northern range of boreal forest in Canada, and contains a large extent of treeline. The current position of the treeline has management implications for reporting on forest cover and carbon accounting in Canada.
Current view: status and trend
The position of the treeline has changed since the end the last glaciation period. The cold waters of Hudson Bay have an important impact on the current location of the treeline on the barrens. Cool temperatures have slowed the advance of tree species near the Hudson Bay, and warm waters from the Mackenzie River havecreated conditions for tree growth all the way to Inuvik and the Coppermine River.
Black and white spruce can be found up to the treeline, with white spruce prevailing at higher latitudes and on calcareous soils. Jack pine is not present at the treeline. Aspen distribution is more complex – aspen can occur right up to the Mackenzie Delta and on southerly slopes in the High Subarctic near the tree line.
Treeline in the NWT. Source: unpublished paper: Downing, February 5, 2008; Taiga Plains ELC Report; Taiga Shield ELC Report; UNFCCCC Marrakech COP 7; Timoney et.al. 1992
Factors that could affect treeline position in the future are changing temperature and precipitation patterns. Different site conditions can favour more rapid growth or cause tree mortality in some forest communities at the treeline Trees migrate very slowly and dispersal of seeds is often measured in tens of meters. As well, vegetative expansion moves at a rate of meters per year. The effects of climate change on the treeline in the NWT are not yet well understood.
At this point, there is not enough information at multiple sites to be able to forecast how changing temperature and precipitation will affect the location of NWT’s entire treeline.
Scientists are predicting that the treeline will advance north with rising temperatures. The treeline in Alaska1 and in Yukon2 is changing, but in complex ways, as trees are showing more growth in some areas, and dying in others.
This baseline indicator is useful for any researchers looking to fix a foundation or baseline on the landscape to watch for the effects of a changing climate on the treeline. As they grow, trees take huge amounts of carbon out of the atmosphere, contributing to a reduction in the effects of greenhouse gas emissions. This indicator tracks changes in the extent of the taiga, an important carbon-regulating ecosystem1.
Find out more
Other focal points
- For more information on landscapes, go to the LANDSCAPE CHANGES focal point.
- The High Boreal ecoregionlines can be used as a surrogate for the northerly extent of jack pine in the Taiga Plains. The Low Subarctic ecoregion lines can be used as a surrogate for the northerly extent of jack pine in the Taiga Shield. The High Boreal ecoregions are generally the northward extent of aspen stands on average sites. See the GNWT Ecosystem Classification reports for more information.
Found an error or have a question? Contact the team at NWTSOER@gov.nt.ca.
Ref. 1. Wilmking, M. G.P. Juday, V.A. Barber and H.S. Zald. 2004. Recent climate warming forces contrasting growth responses of white spruce at treeline in Alaska through temperature thresholds. Global Change 10: 1724-1736.
Ref. 2. D'Arrigo, R.D., R.K. Kaufman, N. Davi, G.C. Jacoby, C. Laskowski, R.B. Myneni, and P. Cherubini. 2004. Thresholds for warming-induced growth decline at elevational tree line in the Yukon Territory, Canada. Global Biogeochemical Cycles 18(3): GB3021.
Updated: May 29, 2015