Abstract:
Forest communities in the central portion of Oregon's western Cascades are arrayed along moisture and temperature gradients. With the aid of reconnaissance data and a computerized ordination technique, 23 forest communities have been provisionally recognized in two distinct forest zones, the Tsuga heterophylla (300 to 1050 m in elevation) and the Abies amabilis (1050 to 1550 m). The location of these zones is largely a function of temperature (elevation), while distribution of individual communities within a zone is controlled mainly by moisture availability.
Eleven climax or near-climax associations and three seral communities were recognized within the Tsuga heterophylla zone. Associations range from the Pseudotsuga/Holodiscus on very dry sites to the Tsuga/Polystichum-Oxalis on wet sites. In the Abies amabilis zone, nine units were identified--seven climax or near-climax associations and two seral communities.
Driest habitats in the zone are occupied by the Abies--Tsuga mertensiana/
Xerophyllum association and wettest sites support the Chamaeeyparis/Oplopanax association. Characteristics of all 23 forest communities are described and relationships among them are discussed.
