Survival of plains cottonwood (Populus deltoides subsp. monilifera) and saltcedar (Tamarix ramosissima) seedlings in response to flooding

We examined the response of first year saltcedar (Tamarix ramosissima) and plains cottonwood (Populus deltoides subsp. monilifera) seedlings to flooding in fall (25 days) and spring (28 days) using potgrown plants (12-18 individuals/26.5-liter pot). Seedlings were initially counted in all pots prior to fall treatment. Survival was calculated as the proportion of seedlings in each pot still alive following spring treatment. Mean survival rates of seedlings flooded in fall (saltcedar = 0.8%, cottonwood = 20.8%, n = 14 pots) were lower compared to the spring flooding treatment (saltcedar = 91.1%, cottonwood = 92.2%, n = 13) and control (saltcedar = 93.9%, cottonwood = 98.7%, n = 14). We used multiple response permutation procedures to detect omnibus distributional differences in survival data (total tests = 9) because assumptions of normality and equal variance were not met. Survival distributions differed between saltcedar and cottonwood fall flooding groups (P < 0.0001) and between fall flooding and control groups for both species (P < 0.0001). No differences in survival distributions were detected between species or treatments for the control and spring treatment groups (P > 0.07). Smaller size and consequent lack of energy reserves may account for lower survival of saltcedar compared to cottonwood in the fall treatment and for lower survival of both species in the fall treatment compared to the spring treatment. Fall flooding for controlling first year saltcedar seedlings is suggested as a potentially useful technique in riparian habitat restoration and management in the southwestern United States.