Graduate Thesis Or Dissertation
 

A study estimating seed potential of Noble fir (Abies procera Rehd.), and several factors affecting its seed production

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h702q872s

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  • Noble fir (Abies procera Rehd.) is an upper elevation timber species native to the Cascade Range and (occasionally) the Coast Ranges of Washington and Oregon. It has always been a commerical species; however, recent changes in forest practices to increase harvests in the elevations where this tree occurs has caused a substantial increase in its importance. Because of this increase, the demand for seed has also risen greatly. However, the species produces few filled and viable seeds, despite an apparently large seed potential. This study reports a new estimate of noble fir's seed potential, and investigates some relatively unknown factors affecting seed production, the objective being to provide useful information to those interested in increasing levels of seed production. The study was carried out at two sites in Oregon in 1977. The primary site was in the Cascade Mountains east of J1olalla, elevation 1100 meters. The secondary site, where corroborative observations were made, was on Marys Peak in ie Coast Range about 20 km west of Corvallis, elevation 1190 meters. Both sites were chosen for accessibility and availability of climbable, cone-bearing trees. A sample of 20 mature cones gathered from eight trees at the Cascade site was used to estimate seed potential and the effect of various seed and cone insects. The relationship of seed potential and cone size characters was also studied, as was the relationship of these characters with insect damage levels. Biological observations of insects were made at approximately weekly intervals throughout the summer, and a weekly bagging experiment was utilized to gain oviposition information. Insect identifications were tentatively established on the basis of previous reports of insects on similar hosts. Final determinations were made by taxonomists at the United States National I1useum. Results of the study showed a seed potential of 133 seeds per cone, which is larger than previous estimates. Cone size differed significantly among trees, and seed potential was positively related to cone size. These results are similar to those for other conifers. The most significant biotic factors reducing seed production were insects. They destroyed 36 percent of sample seed. However, unknown factors, probably including a physiological one related to pollination, had a much greater effect, with 63 percent of sample seed empty or flat. Less than one percent of one seed was filled. Of the nine insects identified as affecting seeds and cones of noble fir, a fir seed chalcid (Megastigmus pinus Parfitt), and two fir cone maggots (Earomyia spp. ficAlpine), caused about 95 percent of total insect damage. The incts showed no preference for any cone portion, which is significant in regard to sampling for insects or damage. Also, except for fir seed chalcids, damage was unrelated to cone size and was not significantly different between trees. A short summary of each insect's activity was prepared, utilizing study results and other literature. Also, a key to the damage for each species was constructed.
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