Saltcedar, also called tamarisk, is an invasive plant originally from Eurasia and Africa. Tamarisks were introduced as windbreaks and to control erosion. They've dominated areas of the arid southwest, outcompeting native cottonwoods and other trees.
Le Wang, Silvan-Cárdenas, Yang, and Frazier used high spatial resolution technology to map these invasive species by identifying them based on visible canopies. This technique has also been used to map other invasive tree species with a good degree of success. This particular study was focused on an area of the Rio Grande near the town of Candelaria. Each pixel on the map was given a value, for example: green saltcedar, brown saltcedar, mesquite, unknown bush, water, road, et cetera. These were consolidated into three categories: invasive, noninvasive, and clear.
When analyzing the accuracy of this mapping technique, the study found that the degree of accuracy definitely correlated with atmospheric conditions, and that the differentiation of different life-stages of the target tree (green saltcedar versus brown, dry saltcedar) greatly improved accuracy.
This sort of technique only works on particular types of species, namely those whose canopies are both visible and easily distinguished from other trees. However, for the species this does work on, this would be a very useful tool for observing and managing invasive species.
Le Wang, José L. Silván-Cárdenas, Jun Yang & Amy E. Frazier (2012): Invasive Saltcedar (Tamarisk spp.) Distribution Mapping Using Multiresolution Remote Sensing Imagery, The Professional Geographer, DOI:10.1080/00330124.2012.679440