Some Conifers Clump, Others Scatter
How three species of conifers become distributed throughout a forest as it ages is mediated by competition.
But because competition plays out differently for each species, trees become unevenly scattered in a Vancouver Island forest.
Douglas-fir trees growing in the Coastal Western Hemlock very dry maritime biogeoclimatic subzone form clumps, concentrated on sites with the most favourable conditions. Shading from other tree species is not enough to kill any Douglas-firs. In determining where individual trees survive, small-scale variations in habitat are more important for this species than competition from neighbours.
Western hemlock distribution on the other hand, is affected primarily by competition from other hemlocks. This tree is more apt to die if located close to its own kind instead of a western red cedar or Douglas-fir.
While cedar establishes later than the other two species in the stand's progression to maturity, its mortality rate is lowest. Cedars grow in clusters, although what trees it has for neighbours has no bearing on a cedar's survival.
As a stand reaches 250 years of age, competition's influence on tree survival declines and morality becomes randomly distributed among overstory trees.
Stephan Getzin, Charmaine Dean, Fangliang He, John A. Trofymow, Kerstin Wiegand and Thorsten Wiegand. 2006. Spatial patterns and competition of tree species in a Douglas-fir chronosequence on Vancouver Island. Ecography. 29(5): 671-682.