SOME TESTS OF FILM TYPES FOR REMOTE-SENSING OF PURPLE LOOSESTRIFE, LYTHRUM-SALICARIA, AT LOW-DENSITIES

Purple loosestrife, Lythrum salicaria, is an exotic plant that has pro ven to be extremely competitive with native wetland and riparian zone species. Current control measures are limited and most effective when infestations are detected at an early stage. The goal of this project was to provide a detection tool (remote sensing) for relatively small loosestrife infestations. Small format (35 mm) aerial photography was acquired over seven sites in central Washington during the peak bloom period of L. salicaria. The sites were selected to provide a variety o f typical background plants and a range of infestation sizes, from a f ew isolated individuals to large, monospecific stands. All sites were photographed at approximately 1:5000 (large) and 1:12,000 (small) scal e with Fuji Velvia 50 and Kodak Kodachrome 64 color transparency films . Sixteen sample slides were ranked by 46 interpreters according to th e ease of finding loosesuife flowers. As expected, the interpreters ra nked massive loosestrife stands as the most easy to identify. However, a large scale image of single loosestrife flowers was ranked almost a s easy to interpret as the high altitude imagery of massive stands. Lo osestrife was most difficult to detect on imagery from sites with few loosestrife plants or with large amounts of dead plant material below the flower heads. Differences in film type were significant, ranking i n order of decreasing ease of interpretation: Fuji > Ektachrome > Koda chrome. Remote sensing using small format aerial photography can be su ccessfully applied to discriminate flowering loosestrife plants from o ther background wetland vegetation. Color slide transparencies taken a t 1:5000 or larger scale can show flowers in sufficient detail for det ection and mapping of isolated plants. Screening of interpreters can e nhance the probability of proper interpretation and detection. Fuji Ve lvia 50 or other films that provide greater saturation of green colors can offer an advantage in detection.