UBC Theses and Dissertations
Survival of five forage species after aerial seeding on snow Brooke, Barbara M.
In aerial seeding of clearcut-logged sites above 1000 m elevation near Kamloops, British Columbia, mixtures of 5 forage species have been applied; orchardgrass (Dactylis glomerata L.), timothy (Phleum pratense L.), smooth brome (Bromus inermis Leyss.), alsike clover (Trifolium hybridum L.), and white clover (T. repens. L.). Seeding has been done by the B.C. Ministry of Forests during winter when such sites are snow-covered. A survey of stand establishment on operational winter seedings resulted in survival estimates for orchardgrass (2.3%), timothy(1.2%) and bromegrass(1.3%),in contrast to the 0.1% survival observed for clover species. On operational spring seedings, grass survival was 1.3%, 0.5% and 1.9% respectively for the above three species, while clover survival was 2.6%. In high elevation date-of-seeding trials established on a new clearcut winter mortality of clover seeds occurred after all seeding dates. First and second year clover plant establishment averaged 1.5% and 0.2% respectively for winter seedings (Nov. 11 to Mar. 22) compared to 20.5% and 13.2% for the May 2 seeding. Orchardgrass seeds were not damaged during the winter and first and second year survival of winter seedings was 43.8% and 21.9% compared to 37% and 12% for the spring (May) seeding. When broadcast from an aircraft, seed of the five species became lodged in the upper snowpack and soon after deposition were able to imbibe melt water. A model snowpack was developed in the laboratory to show that when the snow melted, pack shrinkage was localized at the top and that grass and clover seeds did not sink into the pack. In the field a similar pattern was observed; shrinkage was localized in the top of the pack so that seed was eventually exposed on the surface of the remaining pack. Therefore, seeds broadcast on any date in winter would eventually be located on the pack surface, regardless of the occurrence of post-seedng snowfalls. Field measurements showed that rapid freezing and thawing could occur in the upper layers of the pack. Laboratory simulation of such freeze-thaw cycling caused significant reductions (r₂=0.71;P<0.05) in alsike clover viability while not apparently affecting that of orchardgrass (r₂=0.10;NS). The effects on viability could not be explained by changes in seed moisture content of the two species. It is concluded that no date during winter is suitable for snow seeding of alsike and white clover on high elevation clearcut sites at Kamloops.
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