A comparative study of reflectance spectral indices and digital camera imagery to quantify in-vivo foliar chlorophyll concentration in common New England forest species

Quantifying foliar chlorophyll content is an important procedure in ecosystem studies. Established extraction techniques for quantifying chlorophyll concentration were compared to hyperspectral reflectance indices collected with a GER2600 spectroradiometer, and digital image indices derived from digital camera imagery. Findings show REIP:(R 2=0.52) is a strong indicator reflectance changes associated with plant stress, but RE3/RE2:(R2=0.72), FD715/FD705:(R2=0.77) and CRI red-edge(d) :(R2=0.73) predicted differences in chlorophyll concentration across a range of species more accurately. Many spectral indices predict chlorophyll concentrations more accurately than the REIP, but fail to document the blue-shift associated with foliar stress. Camera imagery results show gray card normalized percent red (R-GC)/( R+GC):(R2=0.63) and percent green (G-GC)/(G+GC):(R 2=0.68) to be strong predictors of chlorophyll concentration across multiple species. For individual species (%Red-%Blue)/(%Red+%Blue) or ( RvB:%R) is a reliable camera index that tracks phenological changes in chlorophyll accurately. Pearson's r across the 2008 growing season for black oak (N=40) was (R2=-0.95), and sugar maple (N=33) was (R2=-0.64).