By Mara Trushell
With a height that can reach 130 feet and a trunk that can span over four feet in diameter, Fremont Cottonwoods (Populous fremontii) are giants within riparian ecosystems. These glorious trees are common along lake shores, rivers, and streams in Arizona from 150 – 6,000 feet elevation. The grayish bark is thick and furrowed at maturity and massive trunks support extensive branches that spread into broad, open crowns. Cottonwoods not only have a noteworthy visual presence; they also have a significant ecological role. Whether an individual tree or an expansive forest, it’s the entire tree, from root tip, to canopy structure, to seed capsule, that supports a rich habitat, complete with food and shelter.
The life of a cottonwood begins within moist soils. With substantial amounts of consistent water, these fast growing trees soon reach their full potential. Intricate root networks stabilize the soil along stream beds, and saplings offer leaves that are a food source for many mammals.
As cottonwoods reach maturity a multitude of flowers are produced in long-stranded catkins, just before the leaves fully emerge from their buds each spring. Both male and female flowers are obscure but develop into long catkins. Female flowers develop seeds with attachments of soft cotton-like puffs that catch the wind and carry them off to spread the next generation further afield.
Summer brings dense foliage that attracts a wide assortment of insects while hefty branches become ideal nesting sites for both song birds and birds of prey. The insects are gleaned by flycatchers, warblers, and hummingbirds, to name only a few, creating a symphony of movement and interaction that is only heightened by wind.
With additional years, the branches become twisted and sculptural while the trunks gnarl and cavities begin to form. This only increases the tree’s value as a resource, because cavity nesters (including mammals such as bats and raccoons) can use it as a home. With fall comes, glorious colors of golden yellow and as leaves drop they envelop the earth below with layers that are rich in fragrance and nutrients.
The Fremont Cottonwoods are a tree worthy of admiration. Not only do they play a key role within riparian ecosystems; throughout the seasons, they provide a magnificent and dramatic focal point in our picturesque southwestern landscapes.
Visit the Highlands Center for Natural History at 1375 Walker Road, 928-776-9550, or HighlandsCenter.Org.
Mara Trushell, education director at the Highlands Center for Natural History, grew up in Prescott surrounded by its natural wonder and now teaches through science and nature to inspire new wonder in current and future generations.