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Notes From the Field: Cottonwood Galleries

Cottonwoods

The onset of spring is here in Jackson Hole, and a sign of the changing seasons is the greening of the towering sentries of the Snake and Gros Ventre River corridors: the cottonwoods. Stands of cottonwood trees are often referred to as “galleries”. We have always liked this moniker, especially in the fall when these galleries are full of artistic colors as the green chlorophyll of the leaves seeps away. In the habitat map below, this is Cottonwood Riparian Forest land cover type. JHLT easements protect 1,110 acres of this ecologically-significant habitat.

Cottonwood trees are true pioneers. Historically, as floods raged down river, the course of channels would change, leaving deposits of sediment in their wake. As a reproductive strategy in this disruptive system, cottonwoods resprout from the flood’s disturbance, their seeds taking hold in the bare soils left from the receding waters. With the construction of levees to tame the seasonal floods of the Snake and Gros Ventre Rivers, a lack of flood disturbances has left the cottonwoods without open soil to pioneer. As existing cottonwood trees mature and expire, shrublands, meadows, and blue spruce forests will over time replace the majestic cottonwood galleries. Easement donors have noted this change on their lands in the past 30 years.

Riparian woodlands offer passage, shelter, and forage to an astonishing array of wildlife, including moose, deer, ruffed and blue grouse, beaver, marten, mink, muskrat, badger, weasels, coyotes, porcupine, and bobcat. Elk use these cottonwood galleries as primary migration corridors. The open nature of these forests promotes a shrub understory consisting of willow, red osier dogwood, serviceberry, hawthorn, alder, buffaloberry, chokecherry, and common juniper. Crucial habitat often involves the close proximity of forage, provided by open meadows or the river itself, and cover, provided by the cottonwood riparian forests.

In addition to offering prime habitat for a tremendous array of wildlife, the river corridor also offers spectacular views and access for recreation that make it highly prized for residential development. Research on the bird populations of the Snake River riparian corridor has shown a significant reduction in species richness and diversity with increased residential development. Neotropical migrant species, leaf gleaners, and hawkers, such as the Dusky Flycatcher, Dark-Eyed Junco, and Swainson’s Thrush are being replaced with increasing numbers of avian opportunists and predators such as the European Starling and Black-billed Magpie.

The attractiveness of the river corridor for development, combined with its critical habitat value for wildlife, make the cottonwood riparian forest a priority land cover type for private conservation. Thanks to all our easement donors who have helped to protect the pioneering spirit and ecological diversity of the cottonwood galleries!

Photo: Jansen Gunderson

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