Forest dynamics in the Bitterroot Canyons, Montana

Both shade-tolerant and shade-intolerant tree species may dominate young stands in canyon-bottom forests of the Bitterroot Range. Subsequent dynamics depend on growth characteristics of the colonizing species. Thus, much of the compositional variation arises at stand establishment (initial floristic composition) rather than through a replacement process (relay floristics). Taxus brevifolia, however, may require shelter from other species for establishment. Vertical similarity increases with stand age towards a maximum value of about 75%. Although the importance of Taxus brevifolia and Thuja plicata tends to increase with stand age, convergence on a common climax composition is thwarted by insularity of the canyon bottoms and an average fire cycle (60 years) that is shorter than the normal longevity (120-140 years) of the shortest lived major tree species (Pinus conforta).