As the fall season progresses and the temperature decreases, leaf color of deciduous trees begins to change as a result of changes in the pigments of the leaves. Using the ALTA II reflectance spectrometer, the reflectance values were measured and the Normalized Difference Vegetation Index (NDVI) was calculated for the Eastern Cottonwood (Populus deltoides) and the White oak (Quercus alba). Tree leaves wee collected at the University of Wyoming Campus in order to monitor and understand on a local scale how these trees respond to climate changes during the fall season, and then draw a general picture comparing both trees in terms of phenological events.
The results revealed that the decline in NDVI is consistent with the progression of the senescence of both trees, but different trends regarding change in leaf color and the leaf-out timing were apparent. The NDVI values for the oak tree were associated with the quadratic model with an R**2 = 74%, while the NDVI values for the cottonwood tree lowed a linear trend (R**2 = 73%).