At the end of the glacial maximum, 20 000 years ago, the climate began to warm. This resulted in the retreat of the glaciers and a subsequent "opening" of fresh unvegetated land.

There are numerous factors affecting the movement rate of vegetation onto this barren ground:

Original ground conditions, prior to glaciation (E.C. Pielou, 1991)

If the ice had originally advanced over unfrozen ground it may have remained unfrozen throughout glaciation due to the insulating effects of the ice sheet. In such a case forests are able to establish themselves relatively rapidly.

If permafrost is present the vegetation types which can be established are limited, and extensive forest development cannot begin until the ground has thawed.

Soil development (E.C, Pielou, 1991)

In situ soil development is a very slow process, and will therefore affect the rate at which vegetation appears

If ready made soil is blown into the area, the rate of soil development will increase. This is very dependent on the strength of the winds and the proximity of a dry soil source.

Initial plant development will also help soil development. After the establishment of the first few plants, they may act as drift fences to build up more soil. Their death will also contribute to the soil as compost.

Texture of new ground

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