1. Effects of Forest Thinning on CO 2 Efflux Peter Erb, Trisha Thoms, Jamie Shinn Biogeochemistry 2003: Block 1

2. Our project… Measured soil CO 2 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 CO 2 efflux at the Catamount Institute.

4. What is CO 2 efflux? Rate of CO 2 released from soil. (gC/m 2 s) Caused by microbial, soil animal and root respiration. Important part of global C cycle.

5. Why study CO 2 efflux? Soil CO 2 efflux produces 10 times more atmospheric CO 2 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 Decomposition CO 2 efflux Global Warming

8. Hypothesis Control plots will have a higher CO 2 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 CO 2 efflux is greater than control Investigate major components of CO 2 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: 1.Site of plant respiration 2.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 CO 2 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 CO 2 Efflux higher in thinned: due to high soil temperature Litter quality, quantity, and root biomass may not differ Loss of CO 2 sink Future Research Management implications for upper montane mixed conifer