The objective of this project was to monitor the phenology of a young cottonwood tree (Populus deltoides) as the autumn season progressed into winter. We collected leaves from the tree from September 19, 2013 to October 24, 2013 and measured the change in leaf reflectance in 11 spectral regions using a spectrometer.
|Cottonwood tree at Sullivan Plaza at University of Wyo.|
Since this tree and the surrounding trees are regularly irrigated (water stress is common in arid regions such as Laramie), we concluded that the conditions are favorable for healthy tree growth. We started our observations on September 19, 2013 while all the leaves on the tree were still green.
Collection of data from an individual leaf happened in two phases; as a single sampling unit, and after cutting the leaf into pieces. We wanted to quantify whether sample size and leaf orientation (facing up or down) influences the reflectance reading.
We hypothesized as leaves change their color from green to yellow, their reflectance values and NDVI plots would show corresponding changes as well. During the course of the experiment, there were 3 winter storm events but the leaf color did not change from green to yellow as expected.
Although we were not able to visibly see change in leaf color, the NDVI plot shows that the amount of light reflected by the leaf in the red and near infrared regions was changing (Figure 2).