While floating through Brown’s Park of the Green River I slowly began to realize that the periodic drifting fluffs were not the water spots decorating by sunglasses, but were instead recently released cottonwood seeds. On the Green River, cottonwood seed rain begins in mid- June and will often last for 4-5 weeks. Historically, this event would have coincided with the declining spring hydrograph to ensure the presence of fresh sediment and suitable soil moisture for seed establishment. Flaming Gorge Dam releases do not create these inviting surfaces for cottonwood seeds on any geomorphic terrace other than the active floodplain. As a result, seeds may recruit but fail to survive because of the repeated inundation of this post-dam terrace. On any other surface, they will land on dry ground and there they will desiccate.
Below the confluence of the Yampa River, seeds were not only fluttering through the air but were also cruising through water as they pass time on their journey to their newly built homes. Though the increased base flows of the dam still reduce available recruitment area in this region, cottonwoods seeds do not seek an imaginary destination. As evident by the overall increase in relative abundance of mature cottonwoods and recruits, seeds below the Yampa River worry less about their future and spend more time enjoying the adventure.
Lower Brown’s Park. Historical cottonwood recruitment may have occurred greatly in this region. As a result of flow regulations, only remaining mature cottonwoods prevail.