Forest development in canopy openings in old-growth Pseudotsuga forests of the western Cascade Range, Oregon

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Abstract
Size and age structure, and spatial pattern analysis were used to study the population dynamics of old-growth Pseudotsugamenziesii (Mirb.) Franco forests of the western Cascade Range, Oregon, U.S.A. Tree population structures confirmed that in the absence of fire, Pseudotsuga was replaced by Tsugaheterophylla (Raf.) Sarg. and (or) Abiesamabilis (Dougl.) Forbes. Regeneration patterns of these species reflected establishment in canopy openings or under Pseudotsuga, but not under Tsuga. Abiesamabilis occurred more frequently as seedlings and saplings in openings than did Tsuga because of favourable aspects of its life history. The composition and structure of the pioneer forest developing after fire was a determinant of subsequent regeneration. If Pseudotsuga dominated, Tsuga and Abies invaded the stand at an early stage. Regeneration in stands where Tsuga was a large component, however, was limited by dense canopies and the occurrence of canopy openings. These patterns demonstrate the importance of small-scale disturbances such as tree falls in the dynamics of Pacific Northwest conifer forests.
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