Remote Census of Ailanthus altissima (tree of heaven) in West Virginia Using High Spatial Resolution Color Imagery

Rick Landenberger, Department of Biology, West Virginia University, rlanden@mail.wvu.edu

Ailanthus altissima is a highly invasive central Asian tree introduced into U.S. urban areas in the late eighteenth and early nineteenth centuries. Although previously confined primarily to parks, vacant lots, and road embankments, it is now spreading rapidly along highways, power lines, railroad grades, and other disturbance corridors in fragmented suburban landscapes. Capable of producing 500,000 wind-dispersed seeds per mature female (Ailanthus is a dioecious species), it is poised to invade native forests at the suburban-rural interface, with potentially devastating consequences to native biodiversity. To successfully control its range over large areas, it is necessary to accurately and efficiently identify individuals and small populations located at the leading edge of the invasion front where control is most effective. From above, however, Ailanthus is very difficult to distinguish from native deciduous trees during much of the growing season. Fortunately, the species appears to express a unique series of phenological traits that may be exploited by remote sensing. First, for approximately one week in the spring, canopies show an unusual degree of anthocyanin expression in young leaves as they flush, providing a signal that may allow detection and classification of crowns in high-resolution imagery. In the late summer, large clusters of ripening seeds are visible on mature females. By acquiring and co-registering images from early May and late August, it should be possible to identify all crowns and census reproductive females, thus identifying populations at the leading edge of the invasion front. Furthermore, given the spatially explicit nature of remotely sensed data, relationships between specific land uses and Ailanthus presence and density can be determined, leading to a better understanding of the species' ability to invade the suburban-rural interface landscape where much of the development in West Virginia is currently occurring.