Thesis
The effects of thinning on maturation-phase Douglas-fir/western hemlock forests in the central Washington Cascades
Washington State University
Master of Science (MS), Washington State University
2010
Handle:
https://hdl.handle.net/2376/103029
Abstract
Young and maturation-phase Douglas-fir (Pseudotsuga menziesii)/western hemlock (Tsuga heterophylla) forests in the central Washington Cascades often lack the structural features required by species dependent on late seral forests. The effects of thinning on maturation-phase forests in the Cowlitz River valley were studied for the accelerated development of structures characteristic of old-growth forests. A total of 21 mature stands (approximately 80 years old) were sampled; 13 of these stands were unthinned and 8 were thinned, where thinning occurred 20 years prior to sampling. Unthinned and thinned stands were paired to create a total of 7 stand pairs. Stand variables were measured and compared between thinned and unthinned paired stands. Development of each paired stand was modeled for a 50- year simulation period using the Forest Vegetation Simulator (FVS) to project changes in average diameter of overstory trees, basal area, density, volume, average snag diameters, and seedling/sapling regeneration. Thinned stands had larger overstory diameter trees, higher live crown ratios and higher mean radial growth rates. Basal area increased by 25 percent in thinned stands and only 13 percent in unthinned stands over the 50-year projection period. Conifer and broadleaf tree regeneration was significantly higher in thinned stands, with notably higher shade-tolerant regeneration in thinned stands. Mean snag diameters were also significantly higher in thinned stands over the 50-year projection period. Thinning showed no significant impact on the number of large standing snags. The accelerated rate of diameter growth, higher live crown ratio of living overstory trees, and enhanced regeneration of shadetolerant trees suggest that thinning in maturation-phase Douglas-fir/western hemlock forests may accelerate the rate of development of structures commonly found in old growth stands of the western Cascades Range.
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Details
- Title
- The effects of thinning on maturation-phase Douglas-fir/western hemlock forests in the central Washington Cascades
- Creators
- Rebecca Lynn Greenwood
- Contributors
- Mark Ellyson Swanson (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Agricultural, Human, and Natural Resource Sciences, College of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525193101842
- Language
- English
- Resource Type
- Thesis