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Effects of Forest Thinning on CO 2 Efflux

Effects of Forest Thinning on CO 2 Efflux. Peter Erb, Trisha Thoms, Jamie Shinn Biogeochemistry 2003: Block 1. Our project…. Measured soil CO 2 efflux at the Catamount Institute in both control and thinned plots, using the Li-Cor 6200. Aim of Study .

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Effects of Forest Thinning on CO 2 Efflux

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  1. Effects of Forest Thinning on CO2 Efflux Peter Erb, Trisha Thoms, Jamie Shinn Biogeochemistry 2003: Block 1

  2. Our project… Measured soil CO2 efflux at the Catamount Institute in both control and thinned plots, using the Li-Cor 6200.

  3. Aim of Study To understand the effects of forest thinning on CO2 efflux at the Catamount Institute.

  4. What is CO2 efflux? • Rate of CO2 released from soil. (gC/m2s) • Caused by microbial, soil animal and root respiration. • Important part of global C cycle.

  5. Why study CO2 efflux? • Soil CO2 efflux produces 10 times more atmospheric CO2 than fossil fuels.

  6. Concern that respiration and decomposition rates will increase exponentially, accompanied by a linear growth rate of plant biomass.

  7. Positive Feedback Cycle Temperature Global Warming Decomposition CO2 efflux

  8. Hypothesis Control plots will have a higher CO2 efflux due to more litterfall and greater root density.

  9. Methods Study site: Catamount upper montane mixed conifer. Plots 1-3 divided into thinned & control. Technique: Li-Cor 6200 (infrared absorption) Field process Statistical analysis: T-test Graphical analysis

  10. T-test: Total plots showed significance, within 90% confidence. P = .08 Hotspots: Plot one is driving total.

  11. Results T-test: Total plots showed significance, within 95% confidence. P=.02

  12. Results Low correlation: .0348 Log scale: .027

  13. Results Importance of slope Correlation significant: .2486

  14. Discussion Results differ from hypothesis: Thinned CO2 efflux is greater than control Investigate major components of CO2 efflux: -Litterfall -Root respiration -Temperature

  15. Litterfall • Soil respiration is directly related to aboveground litterfall • Thinned sites: fewer trees, less litterfall • However… • Thinning occurred ~20 years ago • Time for re-growth • Species composition: higher quality litter in thinned?

  16. Root Respiration • Contributes to efflux: • Site of plant respiration • Highly decomposable fine roots • Thinned sites: fewer trees, less root respiration • Considerations… • Re-growth period • Root expansion due to low nutrient availability • Root density may not differ much

  17. Temperature • Warm temperatures stimulate microbial activity and root respiration • Thinned: open canopy, sunlight warms soils • Temperature seems to have greatest impact in this ecosystem on CO2 efflux

  18. Soil Moisture • Thinned sites are drier • Reduces decomposition, but slows NPP more • Speed decomposition with temperature, while slowing NPP with reduced water… Positive Feedback Loop! -Carbon sinks cannot keep up with C flux to the atmosphere

  19. Spatial and Temporal Heterogeneity Things to Consider • Recently thinned forests v. our study site • Diurnal fluctuations • Slope • Hotspots: - location relative to vegetation - exposure to sunlight - ground cover All these factors contribute to great uncertainty

  20. Conclusion CO2 Efflux higher in thinned: due to high soil temperature Litter quality, quantity, and root biomass may not differ Loss of CO2 sink Future Research Management implications for upper montane mixed conifer

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