Graduate Thesis Or Dissertation
 

Impact of insects on seed production in a Douglas-fir seed orchard in Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/th83m2823

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  • The impact of various factors on seed production in a Douglas-fir (Pseudotsuga menziesii) seed orchard in western Oregon was examined by monitoring the fate of seeds in thirty cones, stratified into three crown levels, on each of ten trees during the 1984 growing season. Cones were examined monthly between April and September for mortality or evidence of insect damage. In September, a sample of mature cones was collected and completely dissected. Each seed was examined for extractability, insect damage, or unexplained abortion. Abortion of immature cones was found to start early in the growing season and had a substantial impact on seed production. A newly discovered cone-feeding weevil (Lepesome leconei) caused a large proportion of this abortion. Unexplained cone abortion (possibly frost damage), empty and aborted seed, Douglas-fir cone gall Midge (Contarinia oregpnensis) and Douglas-fir seed chalcid (Megastigmus spermotrophus) were other major causes of seed loss. Crown stratification was found to be important for an accurate estimate of the importance of these various seed loss factors. A basis for an inventory-monitoring system for Douglas-fir seed production is suggested based on early monitoring of immature cones, identifying specific seed loss factors, stratified crown sampling, and an adequate sample size.
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