Tree Patterns in Central Oregon Ponderosa Pine Forests

Four types of pattern in the structure of ponderosa pine forests of central Oregon can be recognized: (1) differences in relative density, dominance, and regeneration of ponderosa pine when competing with other species along a moisture gradient; (2) a mosaic pattern of relatively even-aged reproduction clusters averaging about 2/3 acre in size, produced by periodic fire in the past; (3) variations in stand density within an even-aged group primarily due to chance factors during establishment; and (4) a tendency toward regular dispersion of individual trees in a reproduction cluster produced by competition. The same types of patterns and their causes have been described for the ponderosa pine forests of Arizona. However, the Oregon forests exhibit a much larger scale of pattern in the reproduction clusters.