Comparison of Autumn NDVI Values for Quaking Aspen (Populus tremuloides) Leaves in Southeastern, Wyoming

--- Matthew Doonan, Colleen Friday, Rowdy Nelson, Kelsey Welter

As one of the most common deciduous trees in the Rocky Mountain West, the quaking aspen is an important member of many ecosystem communities in the state of Wyoming (Populus). The patterns of pigment concentration levels in the leaves of aspens change the rate and efficiency of photosynthesis throughout the year (Castro). Thus, these pigment concentrations impact ramet (individual trees of the aspen clone community) health and survival rates.

Aspen growing in sun (left column) and shade (right column)
in September 10, and November 5, 2015.

This study looked at two quaking aspen ramets of the same group in the University of Wyoming Cheney Plaza garden in Laramie, Wyoming throughout the entire autumn season (September through November) 2015. One tree received full sunlight for the majority of every day, while the other tree was shaded by a significantly larger pine to the west, and received only a few hours worth of sunlight each day.

NDVI values with a linear trend line for the aspen trees growing in sun and shade
in the autumn of 2015 in Laramie, Wyoming

The study tracked the spectral reflectance of individual leaves from each tree that were representative of the entire tree on a weekly basis, and used the spectral reflectance to calculate the NDVI values for the leaves collected. Our results showed that while the sun and shade tree leaves did not have significantly different NDVI values at the beginning of autumn, by November there was a noteworthy difference between the NDVI values, with the shade tree having lower values.