8:00 am - 9:00 am
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Zhengfeng An. This seminar is open to the general public to attend.
Thesis Topic: Soil Organic Carbon Stability, Storage and Response to Heat Wave Events in Agroforestry Systems in Central Alberta, Canada
Seminar Abstract: Agroforestry systems are a typical land-use type in western Canada and play an essential role in mitigating greenhouse gas (GHG) emissions and soil organic carbon (SOC) sequestration. The stability of SOC sequestered in agroforestry systems is critical to the long-term goal of C sequestration. Increasing extreme climate events (e.g., summer heat waves) may threaten the potential GHG mitigation role of agroforestry systems.
Moreover, information on past C losses, current C stocks, and future development potential of agroforestry systems on a regional scale is critical to better understand the value of agroforestry systems. This thesis research investigated SOC structural, thermal and biological stabilities, the influence of heat wave events and their frequencies on GHG emissions and soil labile C in the forest and cropland components (or land-uses) of typical agroforestry system (hedgerow and/or shelterbelt), as well as the regional C stocks (hedgerow, shelterbelt and silvopasture), historical C loss (hedgerow and silvopasture) and the future potential of the forest land-use for C sequestration in shelterbelt system.
In a hedgerow system, cropland SOC had higher structural and thermal stabilities, but a lower quality than forest SOC (p < 0.05). Both SOC structural and thermal stabilities increased with soil depth regardless of the land-use type (p < 0.01), while SOC quality decreased with soil depth (p < 0.01). The hedgerow system had a higher SOC biological stability than the shelterbelt system (p < 0.1), and the biological stability of SOC was higher in the cropland than in the forest (p < 0.01). The thermal stability of SOC was not different between the hedgerow and shelterbelt systems regardless of the land-use type.
Heat wave events increased the CO2 and N2O emissions from both cropland and forest soils within the hedgerow system (p < 0.01), and the more frequent the heat wave event, the higher the cumulative N2O emissions. Forest soils always had higher CO2 and N2O emissions regardless of the heat wave treatment (p < 0.02). Emissions of CO2 and N2O fell quickly after the heat wave treatment, and soil labile C did not decrease significantly by the heat wave treatment.
The forest land-use of the three agroforestry systems (hedgerow, shelterbelt and silvopasture) stored 699.9 M tons C across the central Alberta region (9.5 M ha), which corresponds to a value of $21 billion based on the tax rate of $30 ton-1 CO2 equivalent in Alberta, Canada in the year of 2020. The forest land-use in the silvopasture system (645 M tons C) had the highest C stocks in central Alberta, storing 14.2 and 67.2 times the C held in the forest land-use in the hedgerow and shelterbelt systems, respectively.
Projected increases in C stocks with the expansion of shelterbelt systems in this region, to include all roadside-cropland interfaces, were estimated to be 21.8 M tons C in total, or 2.3 times the C stocks in current shelterbelt forests (9.6 M tons C). The coverage of forest land-use in hedgerow and silvopasture systems declined at an average rate of 2425 ha yr-1 from 2001 to 2020 in central Alberta, corresponding to a decline of 8.5 M tons of C for the past twenty years.
Overall, SOC stability in the forest was not as high as in the cropland of agroforestry systems, while maintaining the hedgerow system may increase SOC stability than the shelterbelt system. Particular attention should be paid to the influence of extreme climate events on agroforestry systems, which may turn agroforestry systems into GHG sources. Maintaining existing hedgerow, shelterbelt and silvopasture systems and establishing more shelterbelt forests are critical for increasing C sequestration in central Alberta, Canada.
Zoom Link: https://ualberta-ca.zoom.us/j/94049722629
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