Canary in the coal mine: what can cottonwoods tell us about our PNW floodplains and waterways

Year: 2023
Presenter/s: Nate Hough-Snee
Symposium Session: 2023 - 10 Charismatic Megaflora: Cottonwoods Restoration
Topics covered: beavers, cottonwoods, floodplain, groundwater, and riparian


Cottonwood (Populus species) are considered an obligate riparian species whose biology and life cycle are tied to the seasonal movement of water and sediment through floodplains. In many large, alluvial rivers, cottonwood forests may be the primary forest ecotone, providing shade, contributing large wood to channels, and creating bars, islands, and other complex fluvial landforms. Given the links between watershed and reach-scale hydrology, sediment transport, and cottonwood establishment, persistence, and regeneration, cottonwood forests can serve as an indicator of reach and watershed-scale processes. Here, I describe where and how cottonwood forests, one of western rivers’ canaries in the coalmine, regenerate along Pacific Northwest rivers and streams, with a focus on Washington State and tributaries of the Columbia River Basin. With an eye to fluvial geomorphology and hydrology in the interior Columbia River, I will discuss where and how cottonwood occur within watersheds and floodplains and what their presence and absence tell us about how our watersheds have evolved and what trajectories they might be on. Providing examples from across the Pacific Northwest, I will discuss the limitations to cottonwood establishment and persistence, and how targeted restoration through environmental flows, invasive species control, planting, grazing management, and reintroduction of keystone species, like beaver (Castor canadensis), may allow practitioners to rejuvenate and restore cottonwood forests. I will synthesize these restoration approaches to introduce the case studies from California, British Columbia, and Washington State to be presented by subsequent speakers within the session.