An ecologically significant trophic cascade in Yellowstone: Response to MacNulty, et al. (2026)

Abstract

In a recent paper (Painter et al., 2025) we reported results from northern Yellowstone National Park, where quaking aspen recruitment was suppressed by intensive Rocky Mountain elk herbivory during the 20th century. Restoration of large carnivores, including gray wolf reintroduction in 1995–96, resulted in sustained reduction of elk density and elk browsing, benefitting aspen. We reported changes in aspen recruitment between our initial random sampling of aspen in 1997–98 and subsequent sampling in 2012 and 2020–21. Density of young aspen (>2 m tall) increased and new young trees (>5 cm dbh) were documented for the first time since the 1940s. About 30 % of stands had many new saplings, while 38 % continued to be suppressed with few or no saplings, and the remaining 32 % had patches of saplings. In their comment, MacNulty et al. (2026) identified an error in our calculation of log ratio effect strength. The corrected result (log_e ratio 2.9, corrected from 5.0) still indicates a strong trophic cascade compared to published examples, and likely underestimates the amount of change. We compared other ways of calculating log ratio effect strength, and these also indicated a strong effect, but this should not be confused with a total reversal of the factors affecting aspen. MacNulty et al. further challenged our general interpretation of our results with arguments we addressed previously, and we address them again here. The Yellowstone aspen trophic cascade is not a complete restoration of all aspen stands, but it is a strong and ecologically significant effect.