Graduate Thesis Or Dissertation
 

Aboveground vegetation and viable seed bank of a dry mixed-conifer forest at a wildland-urban interface in Washington state

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m900nz90g

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  • Dry coniferous forests in the western United States are experiencing severe wildfires, insect outbreaks, forest disease epidemics and a growing presence of invasive species. Policies strongly emphasize reducing hazardous fuels at the Wildland Urban Interface (WUI) where communities and forests intersect. However, these areas present restoration challenges as they tend to have existing populations of exotic and invasive species due to frequent human disturbance and the presence of roads. This research examined the patterns and relationships between aboveground vegetation and seed germinant abundance and richness in relation to seed bank layer, distance to road, and herbicide treatments. The study was located on the eastern slopes of the central Cascade Mountains near Liberty, Washington; a high priority WUI area slated for hazardous fuels reduction. In June 2006 and 2007, herbicide was applied to noxious weeds in treatment plots, and aboveground vegetation, ground cover and site characteristics measured. In September 2007 litter and mineral soil samples were collected, cold-moist stratified and grown in a greenhouse. Six hundred and thirty seeds germinated from litter and mineral soil samples and forty three species identified. Most germinants (77%) and species (36 species) emerged from the litter layer compared to mineral soil (15 species) and the majority were annual forbs, followed by perennial forbs, graminoids and exotic species. Overall germinant density, frequency and richness were low regardless of distance to road, herbicide treatment or seed bank layer. Little similarity was found between the vegetation and seed bank floras. Fourteen percent of germinants were exotic and invasive species, and were found in similar abundances regardless of proximity to road or herbicide treatment. No effect of the herbicide treatment was found in the vegetation or the seed bank. Our findings suggest the contribution of forest seed banks for post-disturbance understories may be relatively low. Persistent vegetation and dispersal from off-site sources will likely play a large role in early succession following disturbance. However, post disturbance studies are needed to fully evaluate the role of the seed bank in early succession.
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