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Secondary autogenic succession in the southern Rocky Mountain Trench

University of British Columbia

The patterns and rates of forest regeneration on a critical wildlife winter range on the floor of the trench, known locally as Premier Ridge were examined in this study. A nearby western wall of the trench was also investigated to ascertain the effect of elevation on forest regeneration and understory productivity. Forest regeneration in a community which has remained unforested for several as years has pronounced effects on the floristic dynamics and productivity of the understory. On Premier Ridge the greatest floristic change was a rapid increase in pinegrass and a. corresponding decrease in the abundance of all other grass species as the forest regeneration progressed. Forbs varied widely in abundance while shrubs were slower to react to changes in the overstory. Similar trends were observed on Estella Mountain. Productivity of the grass component on the unforested sites was four times that of the forested sites. The production of forbs and some species of shrubs also declined as forest regrowth began. One species, bearberry, increased under light forest canopies. The reduction in productivity and the changes in species composition of-the understory which occur in regenerating forest communities, appear to be detrimental to foraging populations of wild and domestic ungulates. Cattle seem to prefer to graze the open, unforested areas, and as regeneration proceeds, the acreage which they will readily use diminishes. Since there have been few reductions in stock numbers to compensate for this range shrinkage, local overgrazing has become more widespread. The regrowth of the forest reduces the grass, both in terms of quality and quantity. This is the most important component in the diet of cattle and most of the wildlife species using the Premier Ridge area. In addition, bitterbrush, used in the summer by cattle and during the winter by big game species, is quickly eliminated by forest regeneration. Bearberry, which may be used by wildlife to some extent, increases under forest cover. This component does not approach in value or usefulness, the losses that the other components represent to grazing animals. The trees of the south and southwestern aspects are characterized by relatively slow growth rates. Forage production on these slopes is modest; if grazing animals are deemed desirable in the future economy of the East Kootenay, these areas should remain treeless. Growth rates are more favourable on the north and northeast aspects, which are less frequently used as foraging areas by winter wildlife, but may be used as shelter or bedding areas.

Text

2011-04-29

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http://hdl.handle.net/2429/34141

Plant Science

University of British Columbia

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