Fall colors

Fall colors
Trees in Simpson Plaza, UW Campus - Oct 11, 2013 (photo: Ramesh Sivanpillai)

Wednesday, December 7, 2016

Changes in sensecense rates of cottonwood trees under different light conditions

--- Amanda Pennino, Wyatt Good and Tyler Therkildson

In this study, spectral reflectance of leaves from two cottonwood trees (Populus deltoides) grown in full sun and shade conditions were used to measure the rate of senescence, or leaf drop, between trees. Light reflectance was measured using an ALTA II Spectrometer on 3 three leaves for each tree twice a week between September 15 and October 18. Light reflectance was then converted to average reflectance values and then used in a normalized vegetation index (NDVI) to assess for leaf greenness.

Changes in the NDVI values of cottonwood tree (orange - exposed to sun, blue - shaded) leaves

It was found that the tree growing in full sun portrayed lower NDVI values overall compared to the shade tree, insinuating that it’s chlorophyll content breakdown and senescence rate was quicker than the tree in shade. Additional studies should take place over a longer period and to an improved number of trees to further validate these results and to explore similar trends in other deciduous trees.