Tundra and Treeline

Treeline

Today, trees grow further north in the Mackenzie Delta than anywhere else in Canada, almost to the shores of the Beaufort Sea. This is because the climate is warmer than other places at the same latitude. Summer warmth sets the northern limit to tree growth, and there are indications trees are gradually creeping north. There is evidence that the treeline extended well north of Inuvik and the Arctic coast some 9000 years ago; but it was pushed many hundreds of miles to the south by the continental glaciers.

Tundra

Tundra is located north of the treeline, where sub soils are permanently frozen. Tundra is a treeless area with dwarf shrubs and miniature wildflowers adapted to a short growing season. There are two main types of tundra: moist and dry, with numerous gradations in between. Moist tundra may contain sedges, cottongrass and dwarf shrubs. On dry tundra, plants seek the protection of rocks and grow close to the ground in their own microclimate. Tundra wildflowers provide stunning summer displays, and tundra plants offer important food for wildlife. In late August, the grasses turn gold, while leaves of the various bushes take on the purple and crimson hues of their summer berries.

Permafrost

Permafrost is the name for ground that remains below freezing, year-round. About one fifth of the earth, including half of Canada, is underlain by permafrost. At its simplest, permafrost is caused by lack of heat from solar radiation. In permafrost regions, summers are only long and warm enough to thaw the surface of the ground, known as the active layer. The active layer can vary from 0.3 - 3 meters thick. In 1962, measurements in a borehole drilled on Melville Island showed that the ground was frozen to a depth of at least 450 metres.

Where the permafrost or frozen ground is close to the surface, the active, or seasonally thawed soils may be too thin to hold roots. A tree's height is limited by the depth and holding power of the soil, which is why the trees are shorter and smaller close to the treeline. Along our northern highways the trees may sometimes lean strangely. This is the price they pay for spreading their shallow roots on active permafrost.

Although permafrost is a solid base on which to build, it can easily be damaged or destroyed by the presence of heat. In the north, thick gravel pads are placed on undisturbed vegetation to build roads and buildings. Where excavations must be made, they are made in winter to avoid a muddy mess that rarely re-freezes successfully.

Pingos

Nearly 1400 pingos, the world's highest concentration, are located on the Tuktoyaktuk Peninsula. Ibyuk pingo is the second highest pingo in the world. A pingo is created by the expansion of underground ice. Pingos grow in a permafrost environment and can reach heights of 150 feet – small mountains on the flat coastal tundra. They are found in shallow or drained lakes, and are believed to grow as the result of the penetration of permafrost into a thawed lake basin.