Characterizing wetland plant communities: An analysis of hyperspectral and biophysical relationships in three taxa of wetland macrophytes

This research focused on remote sensing of phytophysical parameters of three common wetland plant species grown in outdoor mesocosms during the mid-western temperate growing season. Close range hyperspectral reflectance data were collected over quadrats of common reed (Phragmites australis), hardstem bulrush (Schoenoplectus tabernaemontani) and hybrid cattail (Typha glauca) from May–October, 1999. Leaf area index (LAI), percent canopy cover, stem length, dry weight biomass and leaf chlorophyll were sampled concurrently with hyperspectral data. Results indicate that significant differences among the three species can be detected on various dates and within various broadbands using close range optical data at hyperspectral resolution, at simulated Landsat Thematic Mapper spectral bandwidths and with spectral indices derived from spectral bandwidths. The magnitudes of detected differences among species were greatest during the spring and early summer when bulrush and cattails were flowering simultaneously and reeds had a vegetative canopy, and in late August when reeds were flowering. The greatest spectral differences occurred in the near infrared wavelengths. Results of phytophysical sampling showed that stand attributes were unique among the three species. Canopy development began in late April, and maximum canopy cover occurred from June–September in all three species. Dry weight biomass, stem length and LAI paralleled the canopy closure parameter seasonally, and became asymptotic in mid August. Leaf chlorophyll content was unique among the three species. Although clear seasonal patterns existed for the spectral indices and phytophysical parameters, they were not strongly correlated during the majority of the growing season. Leaf chlorophyll a content scaled to the canopy level was not well correlated with canopy spectral reflectance. LAI was moderately correlated (r 2 = 0.38) with spectral reflectance in senescing canopies during the late growing season between August and October. The results suggested that further refinement of the relationships of phytophysical factors relative to canopy spectral reflectance will be necessary to confidently acquire phytophysical data on temperate wetlands using airborne or satellite remote sensing platforms