QUANTIFYING ENVIRONMENTAL CONTROLS ON SAP FLOW IN GREAT BASIN TREE SPECIES AND THEIR POSSIBLE SIGNIFICANCE FOR MOUNTAIN GROUNDWATER RECHARGE UNDER ANTHROPOGENIC CLIMATE CHANGE Brittany Johnson 1,2, Richard Jasoni 1, and Jay Arnone III 1 1 Graduate Program of Hydrologic Sciences, University of Nevada, Reno 2 Department of Earth and Ecosystem Sciences, Desert Research Institute, Reno

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

Introduction  Climate/global change is expected to alter the timing and extremity of environmental factors that modulate transpiration of mountain trees such as: 1. Vapor pressure deficit (VPD, air dryness) 2. Photosynthetically active radiation (PAR, light) 3. Soil water availability (VWC) 4. Air and soil temperature  Sap flow measurements allow for the continuous observation of transpiration patterns in response to natural fluctuations in the above variables

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?

METHODS

Site Locations Courtesy of Scotty Strachan Snake Range SiteElevation (ft)Dominant Vegetation Sage West5,870Sage, Greasewood PJ West7,220Pinyon Pine, Juniper Montane West9,220White Fir, Limber Pine Subalpine West11,010Spruce, Bristlecone Pine Subalpine East10,070Spruce, Aspen Sage East6,020Sage Salt Desert East5,120Greasewood, Shadscale Sheep Range SiteElevation (ft)Dominant Vegetation Desert Shrub2,950Creosote, Burroweed Blackbrush5,480Joshua Tree, Saltbush PJ6,770Pinyon Pine, Juniper Montane7,610Ponderosa Pine, Juniper Subalpine10,190Bristlecone, Currant

Site Instrumentation Courtesy of Lisa Wable

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

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 Where V= Sap velocity (cm s -1 )

TDP and TDR Installation  TDPs were installed at the Montane West and Subalpine West and East sites in the Snake Range Tree SpeciesSample Size White Fir2 Limber Pine2 Mountain Mahogany2 Douglas Fir2  Soil Time Domain Reflectometry (TDR) probes and thermocouples installed beside each tree to monitor soil moisture and soil temperature

RESULTS

SPRING

Spring Sap Flow

PAR Precip

Air T VPD

Soil T Soil VWC

Regressions Variabler2r2 Air Temp0.412 Soil Temp0.361 VPD0.343 PAR0.244 Soil VWC4.18e-3 Precipitation8.10e-4 Slope= 3.00e-4 Y-int= 1.15e-4 P< min values

GROWING SEASON

Max PAR Precip

Air T VPD

Soil T Soil VWC

Regressions Variabler2r2 Max Soil Temp0.713 Max Air Temp0.649 Max VPD0.588 Min Soil Temp0.576 Max Soil VWC0.519 Min Soil VWC0.493 Min Air Temp0.469 Min VPD0.228 Max PAR0.169 Precipitation6.02e-3 Slope= 3.00e-4 Y-int= 1.15e-4 P<0.001 Daily values

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

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

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

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

Questions???