Date of Award:

2001

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Department name when degree awarded

Forest Resources

Advisor/Chair:

David W. Roberts

Abstract

T his research investigated the successional status of treeline whitebark pine (Pinus albicaulis) populations on 14 stands in central Idaho and used empirical statistical models to determine the principal factors affecting recruitment and mortality. The longest lived whitebark pines from four additional high-elevation sites were used to develop a tree-ring chronology to reconstruct over 1,000 years of average April-May temperature.

The assessment of stand structures using size-frequency distributions generally provides evidence that treeline whitebark pine populations are currently self-sustaining in areas of low to nonexistent incidence of white pine blister rust (Cronartium ribicola). However the presence of subalpine fir (Abies lasiocarpa) in all size classes on sample plots suggests potential replacement of, or codominant climax with whitebark pine.

Inference from Poisson regression models suggests that stand structure variables are important to whitebark pine establishment, which may be constrained by interference competition and available growing space. Subalpine fir establishment appears to be constrained by distance to seed source at lower elevations and by favorable site water-balance effects on northly aspects.

Inferences from logistic regression models calibrated from pre-epidemic stand conditions and post-epidemic mortality levels surrounding a historic mountain pine beetle (Dendroctonus ponderosae) outbreak suggest that density and tree size variables are significant predictors of stand and individual tree attack. The significance of the predictor variables in these models corroborates the susceptible host characteristics identified in other pine-mountain pine beetle system risk assessments.

A composite whitebark pine tree-ring chronology from 24 trees from four sites was used to develop a 1028-year long reconstruction of spring temperature for the Sawtooth-Salmon River region of central Idaho. The chronology was calibrated against Ketchum and New Meadows, Idaho US Historical Stations, April-May average monthly temperature using half-sample calibration-verification tests for the period that contained historic climate data, 1909-1992. The chronology accounted for 41% of the variability in the climatic data and successfully simulated medium to high frequency trends. A 19th century cold period coincides with the "Little Ice Age." Neither the instrumental nor the proxy temperature records show evidence of warming in the 20th century.

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