Author: Dr. Larry E. Stevens, Consulting Ecologist, P.O. Box 1315, Flagstaff, AZ, 86002
Saltcedar or Tamarisk (Tamaricaceae: Tamarix ramosissima Deneb)
Deciduous, pentamerous saltcedar is a small, exotic tree introduced to the Southwest near the turn of the century from southern Eurasia (Horton 1977; Baum 1978). Saltcedar, now a dominant riparian shrubby tree in the Colorado River basin below 2,000 m elevation, spread rapidly throughout the system via wind-dispersed seeds (Graf 1978). Although saltcedar had reached the Grand Canyon by 1938 (Clover and Jotter 1944), the oldest trees found in the system thus far, date to about 1943 (Hereford personal communication; Stevens, in preparation). Saltcedar occupied pre-dam terraces and tributaries during the pre-dam era, and was the first species to invade the newly stabilized post-dam riparian zone in the Grand Canyon (Turner and Karpiscak 1980).
Mature saltcedar plants are capable of producing 2.5 x 108 tiny, wind-dispersed seeds per year (Stevens, in press). Its seeds are short-lived (less than 2 months in summer), have no dormancy requirements, and germinate in less than 24 hr. Saltcedar seeds require a moist, fine-grained (silt or smaller particle size) substrate for eccesis, such as is found in southwestern riparian habitats after flood waters subside (Stevens 1989a, b). Saltcedar commonly co-occurs with Populus fremontii (Fremont cottonwood), Salix exigua (sandbar or coyote willow), Salix gooddinggii (Goodding's willow), and Tessaria sericea (Marks 1950; Stevens, in press), but the non-native species is more tolerant of harsh environmental extremes than are native species (Warren and Turner 1975; Stevens and Waring 1985; Stevens, in press).
Saltcedars success in riparian environments in the Southwest appears to be a function of its phenomenal reproductive output and its greater drought and flood tolerance, as compared to Salix exigua (Warren and Turner 1975; Stevens and Waring 1985). In an effort to understand the ecological success of saltcedar, experiments on its competitive ability, germination and nutritional requirements, and other aspects of its life history were conducted (Stevens 1986a). Competition experiments with Salix exigua, a common neighbor throughout the Colorado River system, failed to demonstrate competitive superiority of saltcedar over the willow. In fact, at the seedling stage, willow was competitively dominant.
Saltcedar was consumed by several introduced invertebrate herbivores, particularly the cicadellid leafhopper, Opsius stactogalus; however, invertebrate herbivore standing crop was equivalent with Salix exigua during normal (non-flooding) years in the Grand Canyon (Fig. 20; Stevens 1985). Saltcedar was more drought tolerant and inundation tolerant than any native species. Some saltcedar survived more than two years of root-crown inundation in the Grand Canyon during high water events from 1983-85 (Stevens and Waring 1988), a period far exceeding the 90 day record observed in warm, anoxic reservoir waters by Warren and Turner (1975). Saltcedar is extraordinary not only in its persistence, but also in its reproductive output, as mentioned, and seedling densities in excess of 16,000/m2 have been observed in the southwest (Warren and Turner 1975). These life history characteristics make saltcedar highly successful in the harsh, unpredictable channels of unregulated southwestern rivers, but limit its recruitment along the more stabilized channels of regulated streams.
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