Spectral sensing of foliar Spectral sensing of foliar water conditions in conifer water conditions in conifer

needlesneedles

Hugh StimsonHugh Stimson11, David Breshears, David Breshears22, , Shawn KefauverShawn Kefauver11, Susan Ustin, Susan Ustin11

11 University of California, Davis University of California, Davis2 2 Los Alamos National LaboratoryLos Alamos National Laboratory

Ecological Society of America Annual Meeting, Savannah Georgia USA, August 7Ecological Society of America Annual Meeting, Savannah Georgia USA, August 7 thth 2003 2003

goalsgoals

•find relationships find relationships between water and between water and reflectance at the reflectance at the needle levelneedle level

•assess a suite of assess a suite of reflectance indicesreflectance indices

•lay groundwork for lay groundwork for pending aerial pending aerial imaging of water imaging of water statusstatus

systemsystem

protocolprotocolsample gradientsample gradient

• 17 trees selected17 trees selected

• selected from visual selected from visual estimate for wide water estimate for wide water rangerange

water contentwater content

• 3 twigs per sample3 twigs per sample

• 11stst whorl of needles removed whorl of needles removed

•weighed, dried to constant weight, weighed, dried to constant weight, reweighedreweighed

water potentialwater potential

• N = 15N = 15

• average of 2 twigs per treeaverage of 2 twigs per tree

• measured in pressure bombmeasured in pressure bomb

protocolprotocol

spectral reflectancespectral reflectance

• same 3 twigs as water same 3 twigs as water contentcontent

• subset of needles subset of needles removed, racked onto vinyl removed, racked onto vinyl mountsmounts

• measured with ASD full-measured with ASD full-range field spectrometer range field spectrometer via Licor integrating spherevia Licor integrating sphere

• Measured within 15 Measured within 15 minutes of fridge, 5 of minutes of fridge, 5 of instrument calibrationinstrument calibration

•integration time 10sintegration time 10s

protocolprotocol

protocolprotocol

datadata

datadata

datadata

datadata

analysisanalysis

direct water direct water

measurementsmeasurementsv.v. spectral indicesspectral indices

Water contentWater content

(% foliar mass)(% foliar mass)

Water potentialWater potential

(MPa)(MPa)

980nm water absorption

1200nm water absorption

normalized differential water index

normalized differential vegetation index

analysisanalysis

analysisanalysis

970nm

analysisanalysis

1200nm

analysisanalysis

NDWI860-1240

860+1240

analysisanalysis

NDVI880-660

880+660

analysisanalysis

NDWI

970nm1200nm

NDVI

resultsresults

foliar water content (%mass)foliar water content (%mass)

997700

nnm m

RR22=0.91=0.91

p<0.001p<0.001

0% 25% 50% 75%

spectral indices v. water contentspectral indices v. water content

11220000

nnm m

RR22=0.59=0.59

p<0.001p<0.001

NNDDWWII

0% 25% 50% 75%

RR22=0.96=0.96

p<0.001p<0.001

0% 25% 50% 75%

RR22=0.93=0.93

p<0.001p<0.001

NNDDVVII

0% 25% 50% 75%

resultsresults

water potential (|MPa|)water potential (|MPa|)

997700

nnm m

RR22=0.37=0.37

p=0.03p=0.03

spectral indices v. water potentialspectral indices v. water potential

11220000

nnm m

RR22=0.03=0.03

p=0.5p=0.5

NNDDWWII

RR22=0.45=0.45

p=0.006p=0.006

RR22=0.35=0.35

p=0.02p=0.02

NNDDVVII

1.5 2.5 3.5

1.5 2.5 3.5

1.5 2.5 3.5

1.5 2.5 3.5

resultsresults

Water Content Water Potential

R2 p R2 p

#1 NDWI 0.93 <0.00 0.45 0.01

#2 NDVI 0.93 <0.00 0.35 0.02

#3 970nm 0.91 <0.00 0.37 0.03

#4 1200nm 0.59 <0.00 0.03 0.50

resultsresults

•The foliar water content of Piñon pine needles The foliar water content of Piñon pine needles can be reliably predicted from their reflectance.can be reliably predicted from their reflectance.

• A weaker, indirect, relationship exists A weaker, indirect, relationship exists between water potential and reflectance.between water potential and reflectance.

• The most robust measure is NDWI, closely The most robust measure is NDWI, closely followed by NDVI and 970nm absorption.followed by NDVI and 970nm absorption.