Graduate Thesis Or Dissertation
 

Ecology of curlleaf mountain-mahogany (Cercocarpus ledifolius Nutt.) in Eastern Oregon and adjacent areas

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  • Cercocarpus ledifolius (curlleaf mountain- mahogany), a small, hardwood evergreen tree, was studied to provide information on germination and initial seedling growth characteristics, and the species' relationship to its environment.and associated vegetation. Exceptional germination for this species resulted from both a wet cold treatment at 4°C for 170 days (88 percent), and a 15-minute soak in a 30 percent solution of H202 (64 percent). Total and partial embryo excision indicated two possible deterrents to germination: mechanical impedance by the seed coat or a gas diffusion block by the membrane surrounding the embryo. The latter was concluded to be the most likely deterrent. Planting techniques must provide for seed coat deterioration by fall seeding (which allows moist winter conditions to do this) or by a brief, strong chemical treatment before spring planting. A pronounced specialization was demonstrated for rapid root growth in relation to top growth of seedlings for at least 120 days following germination. Under optimum laboratory conditions, the six most vigorous seedlings extended roots an average 1. 13 m in 120 days, but developed only 4 cm2 of leaf area and 2. 35 cm of shoot height, indicating a high potential for re-establishment of natural stands after decimation by fire or logging, or in the face of grass and shrub competition. Seedling stem diameter immediately above the root crown was an indicator of root vigor. Seedlings with the largest diameter stems were deepest rooted. Relationships among Cercocarpus ledifolius ecosystems were examined and 12 habitat types with their attendant plant associations, phases, and successional stages were delineated. Associations and their phases occurred due to topo.edaphic influences. No serious competition between C. ledifolius and other tree species existed in associations described. Where conifers occurred they were uncommon and not expanding their territory. Graminoids were the most predominant understory group in all associations based on dominance and constancy, with south slope associations generally having higher values than those on north slopes. Soil development was weak with no significant differences in solum development noted between exposures. However, percent surface stone on southerly exposures was twice that on the northerly, and percent buried stone volume in the solum was almost one-third greater on southerly exposures. The survival of C. ledifolius and the communities in which it was dominant were dependent on fire resistant rocky sites. Trees in these niches were larger and older than those on nearby non rocky sites and provided an available seed source in case fire decimated adjacent stands.
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