Chinese tamarisk is an invader of riparian sites in the southwestern United States and northern Mexico. Plant canopy light reflectance measurements showed that Chinese tamarisk had higher visible (0.55- and 0.65-μm wavelengths and 0.63- to 0.69-μm waveband) reflectance than did associated woody and herbaceous plant species in the late fall-early winter period when its foliage turned a yellow-orange to orange-brown color prior to leaf drop. Chinese tamarisk had a yellow-orange color on conventional color (0.40- to 0.70-μm) aerial photographs during this phenological stage that made it distinguishable from other plant species. Computer analyses of conventional color film positive transparencies showed that Chinese tamarisk populations could be quantified from associated vegetation. This technique can permit area estimates of Chinese tamarisk infestations on wildland areas.

Riparian habitats are important components of an ecosystem; however, their hydrology combined with anthropogenic effects facilitates the establishment and spread of invasive plant species. We used a maximum-entropy predictive habitat model, MAXENT, to predict the distributions of five invasive plant species (Canada thistle, musk thistle, Russian olive, phragmites, and saltcedar) along the North Platte River in Nebraska. Projections for each species were highly accurate. Elevation and distance from river were most important variables for each species. Saltcedar and phragmites appear to have restricted distributions in the study area, whereas Russian olive and thistle species were broadly distributed. Results from this study hold promise for the development of proactive management approaches to identify and control areas of high abundance and prevent further spread of invasive plants along the North Platte River.

Vegetative propagules of an invasive riparian weed, giant reed, were collected monthly from two Southern California sites and planted in a greenhouse from August 1998 to July 1999. Rooting and emergence frequency of planted pieces and time to emergence, growth rate, and number of developing shoots were recorded; soluble carbohydrates were analyzed. Response variables were regressed against climatic, seasonal, and site effects using a stepwise model. Rhizomes established much more frequently than stems in all months. Time of year of collection was found to be the most important factor determining establishment of all propagule types. The interaction of maximum daily temperature and precipitation at the field sites had a lesser, but significant effect on rooting frequency. The lack of a consistent correlation between any of the response variables and climate or site may indicate broad environmental tolerance. Seasonal patterns in emergence, growth, and soluble carbohydrates suggest that control by shoot removal would be most effective in fall when rhizome carbohydrate reserves are the lowest, resulting in the greatest reduction in regrowth. Chemical control with phloem-mobile herbicides would be most effective in late summer or early fall, when carbohydrates are moving from leaves to belowground structures but prior to natural leaf senescence.

Giant reed is one of the most widespread invasive species in riparian habitats in California and other coastal states of the United States. This species is thought to spread primarily asexually by flood dispersal of stem and rhizome pieces; viable seeds have not been found in the United States. Research was conducted to quantify genetic variation in giant reed along the Santa Ana River in California and to investigate the pattern of distribution of variation along this watershed. Populations at least 3.2 km apart were collected along the length of the Santa Ana River from the headwaters to the Pacific Ocean. One additional population from a different watershed was collected to serve as an out-group. Genetic analyses were conducted using both starch gel electrophoresis for isozyme analysis and random amplified polymorphic DNA (RAPD) analysis. Both isozyme and RAPD analyses revealed levels of genetic diversity comparable with those in the literature for clonal species, suggesting that asexual reproduction is the primary means of spread of giant reed. Most phenotypes were spread along the Santa Ana River, which is expected if water is the primary means of spread of vegetative propagules. Among the unique phenotypes found, two isozyme phenotypes and one RAPD phenotype were dominant and were found spread along the river, which may indicate greater fitness or competitive superiority to the other phenotypes that were less common. The dominant phenotypes were also found in the out-group population, possibly because of spread by humans. Because spread occurs mainly asexually, management efforts should focus on preventing establishment and spread of vegetative propagules. A moderate level of genetic diversity also suggests that biological control of this weed could be successful.