Using Remote Sensing Techniques to Distinguish and Monitor Black Mangrove (Avicennia germinans)

Abstract

Black mangrove │ Avicennia germinans (L.) L.│ is found at several locations along the Texas gulf coast. A hard freeze in December 1983 severely damaged the populations, but the extent of damage has not been determined. Color-infrared (CIR) aerial photography was evaluated to determine the current distribution of black mangrove. Ground reflectance measurements were made on black mangrove and associated plant species and soil to help interpret CIR photographs. Ground surveys were conducted to verify aerial photos. Black mangrove had a distinct red to dark red CIR image response that made it easily distinguishable from other vegetation and soil. Ground reflectance measurements showed that black mangrove had lower visible red (0.63-0.69 µm) reflectance than associated plant species and soil, which contributed greatly to its image response. The low visible reflectance of black mangrove was attributed to its dark green leaves. Major concentrations near Port Isabel-South Bay and Port Aransas, on the Lower and mid Texas coast, respectively, had largely recovered from the freeze and were actively growing, producing flowers and seed. Major populations near Port O'Connor on the upper Texas coast were killed by the 1983 freeze, but many young plants that had grown from seeds or that survived the freeze due to the protection provided by taller plants were producing flowers and seed. Computer-based image analyses of CIR film positive transparencies showed that black mangrove populations could be quantified accurately. This technique can permit 'percent area estimates' of black mangrove which can be useful to monitor changes in its distribution over time. These results showed that remote sensing techniques can be useful to distinguish black mangrove and determine its extent along the Texas gulf coast.