Application of Spherical Statistics to Change Vector Analysis of Landsat Data: Southern Appalachian Spruce–Fir Forests

Abstract

This study sought to develop a modified change vector analysis (CVA) using normalized multidate data from Landsat TM to examine spruce–fir ecosystems. The introduction of the balsam woolly adelgid ( Adelges piceae) to the Great Smoky Mountains in the late 1950s resulted in widespread mortality of Fraser fir ( Abies fraseri), prompting the need for research on disturbance and regeneration. Drawing from methods in spherical statistics, the extended CVA technique measured absolute angular changes and total magnitude of Tasseled Cap indices (brightness, greenness, and wetness). Polar plots and spherical statistics summarized change vectors to quantify and visualize both magnitude and direction of change. Results separated vectors for forest stands by extent and time interval since infestation, as found along the crest of Smokies Range. Changes in the greenness–wetness plane improved prediction of fir class more than brightness–greenness change. Linear discriminant functions found that magnitude and vector angles combined to predict change class 72% correct with three classes and 57% correct in six spruce-fir classes. The technique demonstrates the ability of change vectors in multiple biophysical dimensions to differentiate forest disturbance and regeneration trends as an alternative to nominal forest or land cover classifications. Introduction High elevation conifer forests in the Southern Appalachians are one of the rarest and most endangered forest types in the eastern United States, encompassing only c. 100 km 2 of which 75% is contained within Great Smoky Mountains National Park (Saunders, 1979; White et al., 1993). These ecosystems, which are dominated by red spruce ( Picea rubens) and Fraser fir ( Abies fraseri), have been impacted by a number of human actions in recent decades, the most serious of which has been the introduction of the balsam woolly adelgid ( Adelges piceae) in the 1950s. Adelgid-caused mortality of mature Fraser firs has surpassed 90% on some mountains (e.g., Mount Mitchell and Mount Collins; Eagar, 1984; Busing et al., 1988; Smith and Nicholas, 1999), and the wave of tree deaths has in turn affected avi-faunal communities (e.g., Alsop and Laughlin, 1991; Rabenold et al., 1998).