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Harvard Forest REU Symposium Abstract 2010
- Title: Digital Imagery Reveals the Effects of Solar Azimuth and Altitude on the Phenology of Deciduous Forests
- Author: Andrea M Garcia (Humboldt State University)
- Abstract:
Phenological life cycles (such as bud-burst, flowering, and senescence) are known to be sensitive to various environmental factors including temperature and climate variability. Understanding other factors and the extent to which they can affect phenology is becoming increasingly important, especially in light of the current concerns of global climate change. We hypothesized that solar azimuth and solar altitude could be influential in the use of webcams as a tool for measuring forest phenology. We used digital images taken by webcams and processed them using R (2.11.1) in order to calculate the RGB values of a select region of interest for the images from two study sites: Harvard Forest (in Petersham, MA) and Morgan Monroe Sate Forest (near Bloomington, IN). We then used these RGB values to calculate an “excess green” index and a “percent green” index and tested the relationship between these values and solar altitude and solar azimuth. Initial linear regression analysis showed a strong correlation between the vegetation indices and solar altitude. However, a Shapiro-Wilk test demonstrated that the data were not normally distributed, disqualifying the initial linear regression results. A statistical test to determine the relationship between the vegetation indices and solar azimuth has yet to be determined. Further tests, including non-parametric regressions, should be conducted to fully determine the relationship between the vegetation indices and solar altitude and azimuth. By examining these variables, it may be possible to reasonably predict the extent to which phenological cycles can be influenced by environmental factors.
- Research Category: Group Projects
