Fall in Wyoming is highly variable, often with extreme temperature fluctuations and snowstorms. One may wonder how any plant is able to survive in such variable daily conditions. Oak trees (Quercus Spp.) can, therefore, be presumed to be particularly resilient in order to survive in Wyoming, to withstand temperatures in a state where not so long ago most people struggled to survive the winters.
|Figure 1. Oak tree located at |
N 41º 18.821’ and W 105º 34.837’.
This picture was taken on October 5, 2013.
Using a spectrophotometer, we measured the leaf reflectance across 11 visible and near-infrared wavelengths of light and calculated the Normalized Difference Vegetation Index (NDVI) to assess change over time. NDVI is an index that measures the difference in the absorption and reflection of light across red and near-infrared wavelengths. Healthy leaf absorbs most of blue and red light and reflects green and the near-infrared (NIR) light. Unhealthy leaf reflects more visible light and less NIR. This difference provides important information about plant physiological conditions. In general, normal end-of-season senescence result in NDVI decrease.
Because plants respond to cumulative temperature changes, not just daily events, we incorporated the minimum temperatures for each day in our research and gathered daily temperature from the National Climatic Data Center. During this experiment, there were three winter snowstorms where temperature dipped to below -6º C (20º F).