|Abstract or Summary
- Successful conservation management requires an understanding of how species respond to intervention. Native and exotic species may respond differently to management interventions due to differences arising directly from their native or exotic origin (i.e., provenance) or from differences in life-history or phylogenetic lineage that are associated with provenance. Thus, selection of a successful management regime requires knowledge of the life history and provenance-bias in the local flora and an understanding of the interplay between species characteristics across existing environmental gradients in the landscape. In my thesis, I examine the Pacific Northwestern upland prairies where the exotic grass flora contains more annual species and species within the Aveneae and Poeae tribes than does the native grass flora, presenting an opportunity to examine how provenance, phylogeny, and life span can interact to determine species distributions along natural gradients of soil chemistry.
I analyze data collected in 2005 and 2006 in ten upland prairie sites from southern British Columbia, Canada to the central Willamette Valley in Oregon, USA for grass species abundance and soil chemistry. I then test the co-structure between grass species characteristics (provenance, phylogeny, and lifespan), patterns of abundance, and underlying soil chemistry. I find that while soil chemistry exerts strong control over community composition, community differences among sites were unrelated to provenance, life span, or phylogenetic grouping.
I performed a greenhouse fertilization study to examine more carefully the biomass and root-to-shoot ratio response of common grass species to nitrogen and phosphorous supply. In this more controlled setting, nitrogen and planting density had the strongest effects on individual plant biomass. As with the field data, species responses to nutrient additions did not vary as a function of provenance, lifespan, or phylogeny.
Thus manipulations of nutrient supplies may have predictable effects on single target species but are unlikely to alter the overall balance between native and exotic species. These results from my thesis work can guide future grassland restoration and management planning.