Thesis
Spatiotemporal patterns of conifer encroachment into shrub-steppe habitat in the Sinklahekin Wildlife area, Washington State
Washington State University
Master of Science (MS), Washington State University
2014
Handle:
https://hdl.handle.net/2376/102469
Abstract
A century of fire suppression in the Pacific Northwest has caused shifts in the structure and distribution of conifer forests historically maintained by frequent, low-intensity fires as a shifting mosaic of mixed-age, low-to-moderate-density stands with grass/forb understories. Ponderosa pine forests are now experiencing increases in stand density and are encroaching into adjacent shrub-steppe habitat. In an effort to inform restoration activities, this study examined the effects of topography and climate on ponderosa pine and Douglas-fir encroachment and establishment processes in the Sinlahekin Valley in north-central Washington. Five sampling areas were selected where significant encroachment events could be seen when comparing current and historic aerial imagery. Within each site, sampling plots were established at intervals along transects perpendicular to the perceived encroachment front. Oldest tree age, basal area and stem counts were taken at each plot. Generalized Linear Mixed Models were used to investigate the influence of slope, aspect, profile curvature, soil composition, and slope position on conifer establishment and density. Correlations between annual establishment rates and two climate indices, Pacific Decadal Oscillation (PDO) and the Palmer's Drought Severity Index (PDSI), were also examined. Pre-fire suppression conifer establishment was found to occur primarily at midslope positions on steep slopes and mixed soil textures, while more recent establishment occurred v primarily at toe-slope positions on fine soil textures. Conifer establishment occurred in pulse events and was highest in years with high temperatures and high levels of precipitation. Managers endeavoring to restore ecological integrity in ecotonal ponderosa pine landscapes should consider complete tree removal in toe-slope positions historically dominated by shrub-steppe, thinning around old-growth trees in mid-slope positions, and frequent and flexible applications of prescribed fire
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Details
- Title
- Spatiotemporal patterns of conifer encroachment into shrub-steppe habitat in the Sinklahekin Wildlife area, Washington State
- Creators
- Emily Sutton Haeuser
- Contributors
- Mark E. Swanson (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525068201842
- Language
- English
- Resource Type
- Thesis