To determine the history of browsing by elk (Cervus elaphus) on narrowleaf cottonwood (Populus angustifolia), at a site in northern Yellowstone National Park, Keigley assigned each individual cottonwood plant in the study to 1 of 3 categories: (1) uninterrupted-growth-type, (2) a combined arrested- and retrogressed-type, and (3) released-type. Cottonwoods established prior to 1947 were of uninterrupted-growth type architecture. Trees established between 1947 and 1968 were of uninterrupted- and released-type architectures. With the exception of individuals short enough to be protected from winter browsing by snowpack, all individuals established after 1968 were of arrested- and retrogressed-type architectures. Architecture-based methods can be used to determine the rank order sequence in which elk currently prefer different species of browse. Once determined, that rank order sequence can be used to test competing hypotheses about the declines in woody plants in YNP.
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