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UBC Theses and Dissertations

Responses of forest carbon, water and their coupling to climate change and cumulative forest disturbance at the regional scale in the central interior of British Columbia Canada Giles-Hansen, Krysta


Forest carbon sequestration and water regulation are two key ecosystem services, however, changing climate and disturbance regimes threaten their continued provision. Most scientific research has been conducted at fine spatial and short temporal scales, often focused on a single disturbance. However, few studies focus on the coupling of the carbon and water cycles at the landscape scale in response to cumulative forest disturbance. The major research objectives of this study were to quantify how severe cumulative forest disturbance has affected regional carbon, water, and their coupling. The study was in the central interior of British Columbia, Canada, a ~400,000 km2 region with severe disturbance from the Mountain Pine Beetle (MPB) epidemic, timber harvesting, and wildfires. Water use efficiency (WUE); the ratio of carbon uptake (NPP: net primary production) to water consumption (ET: evapotranspiration), was used to quantify the coupling relationship. The carbon, water and coupling responses and sensitivities were examined, compared, and discussed across a wide climatic range, in the context of future forest and climate change. Data characterizing forest condition, historical disturbances, climate, and topography were compiled. The Carbon Budget Model of the Canadian Forest Service was applied to calculate the regional forest carbon balance. Watershed scale data were used to create an annual ET model sensitive to forest disturbance, which was then applied regionally. Results showed that severe cumulative forest disturbance has driven carbon emissions, and the region’s forests continue to be a carbon source with reduced sequestration capacity. Recent wildfires have delayed recovery from the MPB epidemic. Forest disturbance has driven a reduction in ET across most of the region. Cumulative forest disturbance was a key driver of WUE, but the sensitivity to forest disturbance varies with climate. Regional WUE stabilized during the period of high disturbance, mainly due to contrasting responses by distinct climate type and their offsetting effects. In dry climates, WUE decreased with cumulative forest disturbance, while in moderate climates, a higher hydrologic sensitivity to forest disturbance drove an increase in WUE. WUE sensitivity to cumulative forest disturbance depends on disturbance levels, regulated by climatic interactions. The strong dependence and contrasting response suggest it is critical to consider these interactions when assessing the regional forest carbon and water relationship.

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