Poster Abstract Details

Author(s):
Julia Michalak

Affiliation:
University of Washington

Presentation Type:
Poster

Topic Area:
Human influences on ecosystems (direct and indirect stressors)

Abstract Text:
Numerous studies have found that increased urban development reduces native species richness and increases non-native species dominance and abundance. However, few studies demonstrate how these changes alter ecosystem processes, particularly animal-mediated seed dispersal. Development is likely to alter animal-mediated seed dispersal through two mechanisms: 1) changing the composition of the disperser community and 2) restricting disperser movement between forest patches. Changes to seed dispersal may affect germination and survival because plant recruitment is higher when seeds are dispersed farther from the parent tree. Animal dispersal is especially critical for oak trees which have large seeds and as burying acorns significantly increases survival probability. My research asks: How does landscape context influence the recruitment processes (seed predation, dispersal and germination) of Garry Oak (Quercus garryana)? The study system is located in the rapidly developing Southern Puget Sound region of Washington State. In this region, Garry Oak dispersal species include the state listed native Western Gray Squirrel, non-native Eastern Gray Squirrel, and native Steller’s Jay (Larsen and Morgan 1998). These dispersers vary in their mobility (bird vs. mammal) and landscape preference. EGS may be inferior dispersers as they remove acorn embryos to prolong storage (Fuchs 2001). The behavioral differences of these dispersal agents suggest that dispersal processes will vary depending on landscape characteristics. I selected two oak fragments both located on the Ft Lewis Military Base, one in a developed landscape and the other in a forested landscape. Within each fragment acorns were arrayed in plots located under three different canopy types: oak, non-oak forest, and open. Each plot consisted of 10 acorns planted beneath the soil surface and 10 attached to flags and left on the soil surface. There were six plots per canopy type per site with a total of 720 acorns used in the study. Flags facilitate acorn relocation without significantly influencing dispersal behavior or germination (Xiao et al 2006). Both landscape type and canopy cover influenced seed predation and germination. Seed predation was highest under non-oak forest canopy and higher at the urban site. Germination was higher under oak canopy and at the forested site. Differences in germination appear to be driven by differential seed predation. Garry Oak woodlands are a priority habitat in Washington due to their increasing rarity and the importance of acorns as food resources for rare and threatened wildlife species. Policies to protect oaks often result in “islands” of oak fragments within a matrix of developed land. These policies may be protecting adult oaks but failing to adequately protect regeneration processes. Understanding how development affects Garry Oak function is therefore important to informing both oak protection planning and the management of oaks in developed landscapes.