Does the Normalized Difference Vegetation Index explain spatial and temporal variability in sap velocity in temperate forest ecosystems?
<p>Understanding the link between vegetation characteristics and tree transpiration is a critical need to facilitate satellite-based transpiration estimation. Many studies use the Normalized Difference Vegetation Index (NDVI), a proxy for tree biophysical characteristics, to estimate evapotran...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/23/2077/2019/hess-23-2077-2019.pdf |
| Summary: | <p>Understanding the link between vegetation characteristics and tree transpiration is a critical need
to facilitate satellite-based transpiration estimation. Many studies use the
Normalized Difference Vegetation Index (NDVI), a proxy for tree biophysical
characteristics, to estimate evapotranspiration. In this study, we
investigated the link between sap velocity and 30 m resolution
Landsat-derived NDVI for 20 days during 2 contrasting precipitation years in
a temperate deciduous forest catchment. Sap velocity was measured in the
Attert catchment in Luxembourg in 25 plots of <span class="inline-formula">20×20</span> m covering three
geologies with sensors installed in two to four trees per plot. The results
show that, spatially, sap velocity and NDVI were significantly positively
correlated in April, i.e. NDVI successfully captured the pattern of sap
velocity during the phase of green-up. After green-up, a significant negative
correlation was found during half of the studied days. During a dry period,
sap velocity was uncorrelated with NDVI but influenced by geology and aspect.
In summary, in our study area, the correlation between sap velocity and NDVI
was not constant, but varied with phenology and water availability. The same
behaviour was found for the Enhanced Vegetation Index (EVI). This suggests
that methods using NDVI or EVI to predict small-scale variability in
(evapo)transpiration should be carefully applied, and that NDVI and EVI
cannot be used to scale sap velocity to stand-level transpiration in
temperate forest ecosystems.</p> |
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| ISSN: | 1027-5606 1607-7938 |