Ground temperatures in permafrost south of treeline, Mackenzie Delta, Northwest Territories

Surface conditions and ground temperatures from 50‐cm to 20‐m depth were measured at 26 forested sites in the Mackenzie Delta, to determine if differences in forest structure and organic cover between four common white spruce forest community types were associated with variations in ground temperature. The mean annual temperature at 1‐m depth was lowest (−4.4°C) in the closed/spruce‐feathermoss (CSF) community associated with a thick canopy and thin snow cover, and highest in the recent permafrost of the spruce/alder‐bearberry (SAB) community (−1.0°C) with an open canopy and deep snow. The open‐canopy spruce/crowberry‐lichen (SCL) forest, with a thick surface organic cover and deep snow, had a higher mean annual temperature at 1‐m depth (−2.1°C) than the CSF forest, indicating the importance of canopy cover for snow accumulation and ground heat loss in winter. Seasonal and inter‐annual variation of 4‐m ground temperatures was greatest beneath the CSF community, highlighting the importance of greater winter cooling due to a thin snow cover and a lower unfrozen water content. Temperatures at 20‐m depth ranged from −0.6°C to −1.5°C in SAB forests, and were significantly lower in CSF, open/spruce‐feathermoss and SCL communities (−1.6°C to −2.9°C). Variation in near‐surface temperatures between spruce forest types diminishes with depth due to the thermal influence of water bodies. There was no significant variation of ground temperatures at 20‐m depth within spruce forest communities in different parts of the delta. Copyright © 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada.