Portland State University. Department of Geography
Keith S. Hadley
Date of Award
Master of Science (M.S.) in Geography
1 online resource (136 p.) : ill. (some col.), 3 maps
Lodgepole pine -- Oregon, Plant genome mapping -- Oregon, Biogeography -- Oregon
Nurse plant and object facilitation is an important factor mitigating abiotic stress, improving seedling recruitment, and shaping the fine-scale spatial patterns of many plant communities. I investigate the role of facilitation on lodgepole pine regeneration following blowdown in central Oregon. My objective is to examine the importance of nurse objects on seedling recruitment under varying stand conditions. I base my analysis on 1) the mapped locations and attributes of seedlings, saplings, trees, shrubs, snags, stumps, and sound and decomposed logs in each of five, 500 m2 circular plots, 2) water holding capacity estimates of woody and leafy litter and pumice soil, and 3) growing-season air temperatures. My analysis identifies seedling patterns at multiple spatial scales (~0-8 m) using nearest neighbor and Ripley’s K statistics and identifies differences in canopy structure, seedling development, and temperature using non-parametric rank-sum tests.
My results show blowdown severity varies with pre-disturbance stand structure, resulting in a multi-modal stand structure with a wide range of canopy and seedling microhabitat conditions. Stand-wide, post-blowdown regeneration patterns reveal >80% of seedlings grow near nurse shrubs, logs, and woody litter, suggesting preferential germination and survival in these microhabitats. High seedling densities correspond with median shrub diameters, and up to 38% of seedlings grow near recently downed logs, indicating both shrubs and logs serve as important nurse objects. The role of nurse objects in mitigating moisture stress is implicated by the potentially high evaporative stress under extreme growing season temperatures in areas of severe blowdown and by the high moisture-holding capacity of woody litter relative to the pumice soil. Stand-wide, 91% of all seedlings and 87% of all shrubs grow on woody litter, and seedlings growing on woody litter show the greatest development.
The positive spatial correlation of seedlings and shrubs with nurse plants and woody litter supports the assertion that both are important facilitators for seedling regeneration and emerging spatial patterns of stand recovery. These results have important management implications, suggesting that the removal of nurse plants and objects through salvage logging or prescribed burning may have negative long-term impacts on local and regional forest regeneration.
Karps, Jennifer Michelle, "Regeneration Patterns and Facilitation Following Blowdown in a Self- Replacing Lodgepole Pine (Pinus contorta) Stand in Central Oregon" (2006). Dissertations and Theses. Paper 1482.