Characterization of wetland plant stress using leaf spectral reflectance: Implications for wetland remote sensing

Abstract

Spectral measurements were recorded for leaves from two monospecific stands ofAcer rubrum in an attempt to characterize leaf reflectance at different stages of flooding. The stands occupied two different soil types possessing different soil moisture regimes. Leaves were excised from different parts of the trees, and their reflectance properties were measured with a hand-held spectroradiometer recording from 400 to 900 nanometers in 3-nm increments. Soil redox potentials were recorded at the sites in an attempt to characterize stress as a function of the soil reducing conditions. Spectral curves, reflectance peaks, soil moisture observations, and redox potentials were plotted and analyzed to document the conditions of the trees during a two-and-a-half month period in the early local growing season. Compared to non-flooded trees, spectral measurements for flooded trees showed elevated reflectance in both the green spectral region at 550 nm as well as the near infrared region at 770 nm. In addition, the reflectance measurements were strongly related (r >- 0.80) to redox potentials recorded during the same period. The results indicated that spectrally detectable changes in visible and near infrared leaf reflectance may be more influenced by prolonged flooding than saturation. This suggests that where remote sensing is used for wetland mapping, there may be optimal times to spectrally separate stands of forested wetlands during the growing season.