Open Collections

Greenberg, Jeremy

University of British Columbia

Whitebark pine (Pinus albicaulis), a high-elevation species critical to mountain ecosystems in western North America, is endangered in the United States and Canada due to white pine blister rust (Cronartium ribicola), mountain pine beetle (Dendroctonus ponderosae), and fire. Its relationship with fire is complex: while fire-intolerant, fire can reduce competition and promote regeneration. Consequently, prescribed fire and fire surrogates are used by land managers to restore its ecological functions. This thesis examines the role and efficacy of various treatment strategies—thinning, prescribed fire, a combination of thinning and prescribed fire, and wildfire—relative to untreated controls, on mature tree and regeneration dynamics of whitebark pine in the Bald Hills of Glacier National Park, BC. Field data were collected three years after prescribed fire, and five years after thinning and wildfire treatments. Widespread mortality of mature whitebark pine occurred regardless of treatment, with burned treatments showing 40–100% mortality and surviving trees experiencing increased mountain pine beetle infestation. White pine blister rust contributed to background mortality of nearly 20%. Fire severity, measured by Composite Burn Index (CBI), was highest in wildfire plots, followed by prescribed fire, and then thinning × prescribed fire treatments. Analysis of pre- and post-treatment ring widths revealed no significant release events among individual trees within the first four years, nor significant differences among treatments. Regeneration densities were generally higher in unburned treatments (control and thinning) than in fire-affected areas. Single-variable GLMs indicated negative effects of herb and fern cover, while multivariate models showed that shrub and regeneration cover positively influenced regeneration density. The findings underscore the complexity of fire effects on whitebark pine and emphasize the need for nuanced, site-specific management strategies. To optimize outcomes, mixed severity prescribed fire should be applied only in areas with dense overstory but few mature whitebark pine, while thinning should focus on trees clearly suppressed by competition. Additionally, thinning to remove surface fuels can reduce fire severity, and fire-damaged trees should be treated with anti-pine beetle pheromones to mitigate infestation risk. Re-measuring monitoring plots every five years is recommended to assess long-term treatment impacts on survival, growth, and regeneration.

Text

2025-04-04

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90584

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/