Soil CO2 Efflux in Response to Forest Disturbances and its Spatial Variation in a Boreal Mixedwood Forest

• Author / Creator

  Akande, Oluwabunmi J

• Soil CO2 efflux is a key component of the terrestrial carbon cycle as it is the second largest carbon flux between the atmosphere and terrestrial ecosystems after photosynthesis. The spatial and temporal variation of soil CO2 efflux can be altered by various disturbancess, which in turn alter forest processes, structure, and biogeochemistry. In the first part of this thesis, I conducted a meta-analysis to assess the effects of disturbances on forest soil CO2 efflux in boreal, temperate and tropical forests by collecting data on soil CO2 efflux and disturbance regimes published between 1900 and June 2018. Boreal forest soil CO2 efflux was increased by elevated CO2 + warming and windthrow but decreased by fire. Temperate forest soil CO2 efflux was increased by elevated CO2, water addition, and warming. Tropical forest soil CO2 efflux was increased by litter addition, thinning, water addition, and elevated CO2 but reduced by litter removal. This study showed that forest management practices may be used to minimize climate change effects on soil CO2 efflux but should not take the place of global warming mitigation strategies. This chapter also revealed the importance of partitioning soil CO2 efflux to better understand the effects of disturbances on soil CO2 efflux.Following the literature review of disturbance effects on forest soil CO2 efflux, I concentrated the second and third chapters of my thesis on quantifying spatial and temporal variation of soil CO2 efflux and its components in a Canadian boreal mixedwood forest. Canada’s boreal forest is dominated in the south by mixedwood forests so a better understanding of soil CO2 efflux within this area will improve our ability to predict the response of the boreal carbon cycle to climate warming. The second chapter was conducted in a 1-ha boreal mixedwood forest located in Alberta, Canada to determine the fine-scale spatial and temporal variation of soil CO2 efflux during three consecutive growing seasons. This site exhibited a moderate degree of spatial variation, mainly influenced by soil temperature, pH and dissolved organic nitrogen while the temporal variation was explained by soil temperature and moisture. Shrub-dominated patches had significantly higher soil CO2 efflux than deciduous-dominated patches within the plot. In the third chapter, I examined the spatial and temporal variation of heterotrophic and autotrophic soil CO2 efflux within the 1-ha plot using a root-exclusion trenching method. The results showed that because heterotrophic soil CO2 efflux dominated total soil CO2 efflux, changes in heterotrophic soil CO2 efflux may lead to significant variations in total soil CO2 efflux. Soil temperature, stand structure and pH influenced the spatial variation of heterotrophic soil CO2 efflux while heterotrophic soil CO2 efflux increased with warmer temperatures and higher water availability. The spatial variation of autotrophic soil CO2 efflux was regulated by stand structure while its temporal variation could not be explained by any of the variables in this study. Autotrophic soil CO2 efflux did not significantly differ among patches within our study but shrub-dominant patches exhibited significantly higher heterotrophic soil CO2 efflux than deciduous-dominated patches. Overall, this research reveals that disturbance effects on soil CO2 efflux and its components need to be studied further to generate better models of carbon cycle response to global warming. It also clarifies the effect of species composition on soil CO2 efflux and provides a recommendation for finer scale sampling protocol within a 1-ha boreal mixedwood forest. This thesis emphasizes that partitioning soil CO2 efflux enhances our understanding of how disturbances may affect total soil CO2 efflux.  

• Subjects / Keywords

  • forest disturbance
  • spatial variation
  • climate change
  • soil respiration
  • CO2 efflux
  • forest management
  • partitioning
  • land-use change
  • autotrophic
  • boreal mixedwood
  • heterotrophic

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-v8dn-8b10

• License

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