A Silent Decline
One of the main stresses is that too often the sprouts and saplings of these water-loving plants are being eaten repeatedly by cattle, elk, deer, and/or domestic sheep. If the topmost branches (the tallest leader and subleaders within about 6 vertical inches of the leader) are repeatedly browsed, then the aspen, cottonwood, and tall species of willow cannot exceed the height of 5 to 6 feet. Eventually, entire willow patches, cottonwood galleries, and aspen stands can — and do — disappear from the landscape.
This is a major loss because they support an unusually high number of native animal species and, especially in the case of aspen, provide habitat for a diversity of understory plants. Willows and cottonwood trees hold riparian banks together with their deep roots, and aspen provide far higher water yields than conifer stands. Aspen stands are second only to riparian areas in the West for supporting the greatest number of native species.
Curiously, the three national forests of southern Utah have only rarely (if at all) been measuring the intensity of browsing or height structure of aspen, and none have been measuring the browsing/height structure of cottonwood or willow, despite the thousands of cattle and sheep that are permitted for 4 or more months each year on these forests. Yet it’s common to see aspen stands with only scattered, tall, old trees and short, repeatedly browsed sprouts; old, hedged willows with no young willows in sight; and grand old cottonwoods with sprouts that are no more than 1 or 2 feet in height. This means no recruitment of youngsters into the overstory, which can replace the older trees and willow as they die.