COS 71-9
Comparing habitat change on Horn Island, Mississippi, 1940 versus 2010 using image textural analysis
Barrier islands of the northern Gulf of Mexico are subjected to a continual rise in global sea level, local subsidence and frequent impacts by tropical storms. The ongoing sea level rise coupled with storm-induced erosion may serve to raise water table elevation, thus altering terrestrial plant communities. A recent comparison of 2004 versus 1970 habitat maps indicated a predominance of marsh versus dry-land habitat on Horn Island, Mississippi. However, availability of historical aerial imagery, coupled with innovative image analysis techniques, may allow assessment of such gradual change over periods of more than 5 decades and thus enable the determination of longer-term rates of change. We hypothesize that, as a fraction of total island land area, wetland habitat-types on Horn have increased from 1940 to 2010.The known spectral reflectance of Horn Island beach sand was used to scale brightness values in both 1940 and 2010 aerial imagery to percent reflectance for direct comparison and image classification to habitat-type (ENVI v4.8, ITT Visual Information Solutions). Textural filters applied to image data sets comprised of moving-window spatial coefficient of variation (CV), entropy and correlation were applied to delineate habitat-types. Habitat-type maps and percent coverage were produced via Maximum-Likelihood classification of these filtered data.
Results/Conclusions
Preliminary data suggest a 30% increase in wetland habitats such as marsh characterized by low variations in spectral reflectance which in turn means a decrease in drier habitats such slash pine woodlands characterized by high variations in spectral reflectance. This is indicative of sea level rise affecting habitat structure. Other habitats such as interior ponds and high marsh have increased in area by 15%. An increase in pond size and number of ponds indicates habitat response to sea level rise. Upon reviewing coefficient of variation imagery results there is a mean CV of 13.42 within the 1940 data and a CV 8.9. These differences in habitat structure between slash pine woodlands areas for 1940 and 2010 are most likely due to high tree mortality rates from Hurricane Katrina and other storm events causing salt water inundation of the interior of the island. Further analysis will be conducted using entropy and correlation to delineate differences in habitat structure of slash pine woodland.