Populus spp. (cottonwood) and Salix spp. (willow), the dominant overstory trees in many western riparian forests, are disturbance-adapted species with short seed dispersal periods. Changes to flood cycles often lead to a decrease in recruitment success and survival of these species, and may increase the recruitment success of Tamarix spp. (saltcedar), an introduced riparian tree species that has a longer seed dispersal period. This investigation compared Populus, Salix, and Tamarix stem density in 63 stands on unregulated and regulated reaches of the Verde River. Populus and Salix stem density were not different between the unregulated and regulated reaches in sapling (1–10 year) stands. However, Populus stems showed a trend towards higher density in mature stands (11–40 year) in the unregulated reach, and Populus density was significantly higher in old-growth (41 year) stands in the unregulated reach. Tamarix stem density was higher in the regulated reach for the sapling class (4.75 ± 1.83 stems/m2 versus 0.03 ± 0.03 stems/m2). Analysis of flow conditions during a recent recruitment year (1995) suggests that water release patterns in the regulated reach created favorable conditions for Tamarix. Results from this study suggest that where major flooding still occurs in regulated reaches, or where managed flooding is an option, recruitment of Populus and Salix is possible at similar levels to unregulated reaches. However, careful attention to later season water releases may be important in managing Tamarix recruitment opportunities.
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Vol. 27 • No. 2