6. The climax stage of succession does not change into a different
successional stage because the plants that live there are adapted to living
under those environmental conditions. In this case, the fir, spruce, and birch
trees all are tall as adults so they easily can get plenty of sunlight. In addition,
all have wide-ranging root systems to find water and minerals. More importantly,
their seedlings need shade (not light) to survive. Since all these conditions
are met, the older climax species are constantly replaced by their same species.
------ ------ 
Long & Slichter