To investigate plant adaptations across ecoregions, this study investigated the influences of a natural disturbance (flooding) and an artificial disturbance (cattle grazing) on reproductive and population processes of black cottonwood (Populus balsamifera trichocarpa), the dominant tree. Age structure, and viability (% cover, density, etc.) of trees, saplings and seedlings of black cottonwood were measured along two free-flowing, first order streams in three ecoregions (Montane, Parkland, Prairie). Analyses suggest that a healthy cottonwood population displayed a sawtooth shaped 'punctuated progressive age structure' and that cottonwood reproduction processes varied across ecoregions, with increased clonality in the highest montane ecoregion. Cattle grazing impacts on reproduction were most severe in the lowest prairie ecoregion that is treeless except for the riparian zone. Samuelson and Rood conclude that appropriate strategies of instream flow regulation, land-use policies and practices, and conservation and restoration efforts should be refined, according to ecoregion, to recognize the difference in cottonwood reproductive and population ecology.
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