Flood flows and dynamics of Sonoran riparian forests

In the Hassayampa River system, recruitment of Fremont cottonwood Populus fremontii and Goodding willow Salix gooddingii, depends on 1) large prior-year floods to remove herbaceous cover; 2) high spring flows or rains to stimulate germination on floodplains above the zone of frequent flood inundation; and 3) reduced post-germination flooding to reduce seedling mortality. Small differences in timing of spring floods influence relative recruitment success of the two species because of differences in emergence phenologies. Recruitment of velvet mesquite Prosopis velutina depends on large (>5-yr) floods to disperse seeds to establishment sites on floodplains 1-2 m above the water table, and small (>2-yr) late-summer floods or rains to inundate germination sites. -from Authors