Brittany Johnson 1,2 , Richard Jasoni 1 , and Jay Arnone III 1

1. Quantifying environmental controls on sap Flow in Great Basin tree species and their Possible significance for mountain Groundwater recharge under Anthropogenic climate change Brittany Johnson1,2,Richard Jasoni1, and Jay ArnoneIII1 1Graduate Program of Hydrologic Sciences, University of Nevada, Reno 2Department of Earth and Ecosystem Sciences, Desert Research Institute, Reno

2. Presentation Outline • Introduction • Research Questions • Methods • Transects • Sap flow • Results • Spring • Growing Season • Initial Conclusions • Ongoing Research

3. Introduction • Climate/global change is expected to alter the timing and extremity of environmental factors that modulate transpiration of mountain trees such as: • Vapor pressure deficit (VPD, air dryness) • Photosynthetically active radiation (PAR, light) • Soil water availability (VWC) • Air and soil temperature • Sap flow measurements allow for the continuous observation of transpiration patterns in response to natural fluctuations in the above variables

4. Research Questions • What environmental drivers are responsible for initiating sap flow in the spring? • How do known environmental drivers of transpiration modulate in situ sap flow in Great Basin tree species during the spring and growing season?

5. Methods

6. Site Locations Courtesy of Scotty Strachan

7. Site Instrumentation Courtesy of Lisa Wable

8. Sap Flow Sensors • Thermal Dissipation Probe (TDP) Figure courtesy of Dynamax.com

9. Sap Flow Sensors • TDPs report differential temperature (dT) • To convert to sap velocity, V (cm s-1), Where dTmax= Maximum pre-dawn dT dT= Raw differential temperature K= Dimensionless variable WhereV= Sap velocity (cm s-1)

10. TDP and TDR Installation • TDPs were installed at the Montane West and Subalpine West and East sites in the Snake Range • Soil Time Domain Reflectometry (TDR) probes and thermocouples installed beside each tree to monitor soil moisture and soil temperature

11. Results

12. Spring

13. Spring Sap Flow

14. PAR Precip

15. Air T VPD

16. Soil T Soil VWC

17. 4 2 3 1 5 2 3 1 5 4

18. Regressions Slope= 3.00e-4 Y-int= 1.15e-4 P<0.001 10-min values

19. Growing Season

20. Max PAR Precip

21. Air T VPD

22. Soil T Soil VWC

23. Regressions Slope= 3.00e-4 Y-int= 1.15e-4 P<0.001 Daily values

24. Summary • What environmental drivers are responsible for initiating sap flow in the spring? Air T Soil T Sap Velocity

25. Summary • How do known environmental drivers of transpiration modulate in situ sap flow in Great Basin tree species during the spring and growing season? Spring • Air temperature • PAR • VPD • Soil temperature Growing Season • Soil temperature • Air temperature

26. Conclusions • Global climate change may cause a shift in the timing and extremity of environmental factors that modulate transpiration • This could affect the start, stop, intensity, and duration of sap flow especially if air and soil temperature patterns are significantly altered • Changes in transpiration will alter the amount of water available for groundwater recharge

27. Ongoing Research • Analyze data from all instrumented trees at this and other sites • Determine if major drivers remain the same or are different among • Tree species • Elevation/latitudes • Weather patterns • Soil type • Develop predictions in response to projected/ possible climate change scenarios

28. Questions???