Environmental Gradients, Community Boundaries, and Disturbance the Darlingtonia Fens of Southwestern Oregon

• Main Author: Tolman, Deborah A.
• Format: Others
• Published: PDXScholar 2004
• Subjects: Darlingtonia californica > Oregon; Fens > Oregon; Fire ecology > Oregon; Boundaries; Plant communities > Oregon; Ecology > Oregon; Environmental Indicators and Impact Assessment; Natural Resources Management and Policy
• Online Access: https://pdxscholar.library.pdx.edu/open_access_etds/3013; https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=4023&context=open_access_etds

The Darlingtonia fens, found on serpentine soils in southern Oregon, are distinct communities that frequently undergo dramatic changes in size and shape in response to a wide array of environmental factors. Since few systems demonstrate a balance among high water tables, shallow soils, the presence of heavy metals, and limited nutrients, conservative efforts have been made to preserve them. This dissertation investigates the role of fire on nutrient cycling and succession in three separate fens, each a different time since fire. I specifically analyze the spatial distributions of soil properties, the physical and ecological characteristics of ecotones between Jeffrey pine savanna and Darlingtonia fens, and the vegetation structure of fire-disturbed systems. Soil, water, and vegetation sampling were conducted along an array of transects, oriented perpendicular to community boundaries and main environmental gradients, at each of the three fens. Abrupt changes in vegetation, across communities, were consistently identified at each of the three sites, although statistical analysis did not always identify distinct mid-canopy communities. Below-ground variables were likewise distinguished at the fen and savanna boundary for two of the three sites. At the third site, discontinuities did not align with the fen boundaries, but followed fluctuations in soil NH4. My results suggest that below-ground discontinuities may be more important than fire at preserving these uniquely-adapted systems, while vegetation undergoes postfire succession from fen to mid-canopy to savanna after approximately 100 years since fire. Although restoration of ecosystem structure and processes was not the primary focus of this study, my data suggest that time since fire may drive ecosystem processes in a trajectory away from the normal succession cycle. Moreover, time since fire may decrease overall vigor of Darlingtonia populations.