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 Arnone III1

1Graduate Program of Hydrologic Sciences, University of Nevada, Reno2Department 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:

• 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

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 Site Elevation (ft) Dominant Vegetation

Sage West 5,870 Sage, Greasewood

PJ West 7,220 Pinyon Pine, Juniper

Montane West 9,220 White Fir, Limber Pine

Subalpine West 11,010 Spruce, Bristlecone Pine

Subalpine East 10,070 Spruce, Aspen

Sage East 6,020 Sage

Salt Desert East 5,120 Greasewood, Shadscale

Sheep Range Site Elevation (ft) Dominant Vegetation

Desert Shrub 2,950 Creosote, Burroweed

Blackbrush 5,480 Joshua Tree, Saltbush

PJ 6,770 Pinyon Pine, Juniper

Montane 7,610 Ponderosa Pine, Juniper

Subalpine 10,190 Bristlecone, 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 Species Sample Size

White Fir 2

Limber Pine 2

Mountain Mahogany 2

Douglas Fir 2

Soil Time Domain Reflectometry (TDR) probes and thermocouples installed beside each tree to monitor soil moisture and soil temperature

RESULTS

SPRING

Date

4/11/11 4/25/11 5/9/11 5/23/11 6/6/11 6/20/11

Sap

Vel

ocity

(cm

s-1

)

0.000

0.002

0.004

0.006

0.008

0.010

Spring Sap Flow

Sap

Vel

ocity

(cm

s-1

)

0.000

0.001

0.002

0.003

0.004

0.005

Date

5/1/11

5/5/11

5/9/11

5/13/11

5/17/11

PA

R ( m

ol m

-2 s

-1)

-2000

-1000

0

1000

2000

Precipitation (m

m)

0

10

20

30

40

50

60

PAR

Precip

Sap

Vel

ocity

(cm

s-1

)

0.000

0.001

0.002

0.003

0.004

0.005

Date

5/1/11

5/5/11

5/9/11

5/13/11

5/17/11

Air

Tem

pera

ture

(°C

)

-20

-10

0

10

20

Vapor P

ressure Deficit (kP

a)

0

1

2

3

4

Air T

VPD

Sap

Vel

ocity

(cm

s-1

)

0.000

0.001

0.002

0.003

0.004

0.005

Date

5/1/11

5/5/11

5/9/11

5/13/11

5/17/11

Soi

l Tem

pera

ture

(°C

)

-15

-10

-5

0

5

10

Soil M

oisture (VW

C)

0.15

0.20

0.25

0.30

0.35

0.40

0.45

Soil T

Soil VWC

4 5

5/1/11

5/5/11

5/9/11

5/13/11

5/17/11

Sap

Vel

ocity

(cm

s-1

)

0.000

0.001

0.002

0.003

0.004

0.005

1

2

3

4

5

1 32

Air Temperature (°C)

-10 -5 0 5 10 15 20

Day

time

Sap

Vel

ocity

(cm

s-1

)

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

Regressions

Variable r2

Air Temp 0.412

Soil Temp 0.361

VPD 0.343

PAR 0.244

Soil VWC 4.18e-3

Precipitation 8.10e-4

Slope= 3.00e-4Y-int= 1.15e-4P<0.001

10-min values

GROWING SEASON

Sap

Vel

ocity

(cm

s-1

)

0.000

0.002

0.004

0.006

0.008

0.010

Date

5/2/11

5/16/11

5/30/11

6/13/11

6/27/11

7/11/11

7/25/11

PA

R ( m

ol m

-2 s

-1)

0

500

1000

1500

2000

2500

Precipitation (m

m)

0

20

40

60

80

100

120

Max PAR

Precip

Sap

Vel

ocity

(cm

s-1

)

0.000

0.002

0.004

0.006

0.008

0.010

Date

5/2/11

5/16/11

5/30/11

6/13/11

6/27/11

7/11/11

7/25/11

Air

Tem

pera

ture

(°C

)

-20

-10

0

10

20

30 Vapor P

ressure Deficit (kP

a)

0

2

4

6

8

Air T

VPD

Sap

Vel

ocity

(cm

s-1

)

0.000

0.002

0.004

0.006

0.008

0.010

Date

5/2/11

5/16/11

5/30/11

6/13/11

6/27/11

7/11/11

7/25/11

Soi

l Tem

pera

ture

(°C

)

-20

-10

0

10

20

Soil M

oisture (VW

C)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Soil T

Soil VWC

Maximum Soil Temperature (°C)

0 5 10 15 20 25

Max

imum

Sap

Vel

ocity

(cm

s-1

)

0.000

0.002

0.004

0.006

0.008

0.010

Regressions

Variable r2

Max Soil Temp 0.713

Max Air Temp 0.649

Max VPD 0.588

Min Soil Temp 0.576

Max Soil VWC 0.519

Min Soil VWC 0.493

Min Air Temp 0.469

Min VPD 0.228

Max PAR 0.169

Precipitation 6.02e-3

Slope= 3.00e-4Y-int= 1.15e-4P<0.001

Daily values

Summary What environmental drivers are responsible for initiating

sap flow in the spring?

Date

4/11/11 4/25/11 5/9/11 5/23/11 6/6/11 6/20/11

Sa

p V

elo

city

(cm

s-1

)

0.0000.0020.0040.0060.0080.0100.0120.0140.016

Tem

perature (°C)

-30

-20

-10

0

10

20

30

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 ofsap flow especially if air and soil temperature patterns are significantly alteredChanges 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???