Small Mammals in Saltcedar (Tamarix ramosissima)–Invaded and Native Riparian Habitats of the Western Great Basin

Abstract Invasive saltcedar species have replaced native riparian trees on numerous river systems throughout the western United States, raising concerns about how this habitat conversion may affect wildlife. For periods ranging from 2 to 11 yr, I used live-trapping to monitor small mammal populations in paired saltcedar and native riparian woodlands at four sites in western Nevada and eastern California. Heteromyid rodents, such as Merriam's and Ord's kangaroo rats, were more likely to occur in saltcedar habitats, but other rodent species, particularly the montane vole and western harvest mouse, occurred more often in native habitats, and this balanced species richness in habitat comparisons. The most common species at all sites, the deer mouse, did not show any consistent differences in abundance or in mean body mass between the two habitat types. However, the ratio of captured male to female deer mice was higher in saltcedar than native habitats at two sites. Deer mice as well as Ord's kangaroo rats also had higher rates of being recaptured following initial capture in native habitats, which may have been due to fewer transient individuals occurring in these habitats. By contrast, Merriam's kangaroo rats may have been more transient in native habitats because they were more likely to be recaptured in saltcedar. Individuals of two species, pinyon mouse and white-tailed antelope ground squirrel, had greater mean body mass in native habitats than they did in saltcedar, implying that they may have maintained superior condition in native habitats. Nomenclature: Saltcedar, Tamarix ramosissima Ledeb. Management Implications: Invasion of riverside and other riparian vegetation by saltcedar species changes the appearance and structure of riparian habitats in the arid western United States conspicuously. Because riparian environments occupy a small fraction of these arid lands yet support an inordinately high number of animal species, there is considerable concern regarding effects of saltcedar invasion on wildlife. Here, I present results of small mammal monitoring using annual live-trapping for up to 11 years at four sites in the western Great Basin in both saltcedar-invaded and native riparian habitats. Although the total number of species found during the entire monitoring period was equal or greater in native habitat than in saltcedar at all sites, the number of small mammal species sampled did not differ statistically between native and saltcedar habitats. A general effect of saltcedar invasion was an increase in rodents in the family Heteromyidae. This is consistent with well-known adaptations of heteromyid rodents to open, arid environments and conversion of riparian areas to more open, desert-like habitats at many sites invaded by saltcedar. By contrast, rodent species, such as montane voles and western harvest mice, which are typically associated with the greater cover and more mesic conditions provided by native riparian vegetation tended to be uncommon or absent in saltcedar-converted habitat. Such species may benefit at sites where native vegetation can be successfully restored following saltcedar removal.