Overstating trophic cascade strength following large carnivore restoration in Yellowstone: A comment on Painter et al. (2025)

Daniel MacNulty, Elaine Brice, Nicholas Bergeron, Eric Larsen

Painter et al. (2025) claim that large-carnivore recovery in Yellowstone National Park has produced a strong trophic cascade compared to other systems, citing a 152 fold increase in aspen sapling density and widespread recruitment of new trees. We show that these conclusions substantially overstate the cascade’s strength because of key methodological and interpretive flaws. First, Painter et al. miscalculated the baseline density in their dataset, inflating the reported log response ratio from a true 17.5 fold increase to 152 fold. Second, they analyzed repeated measurements of the same stands as if they were independent samples, overstating standardized effect sizes by 30–40%. Third, because sapling densities are highly zero-inflated and right-skewed, mean-based metrics (log response ratios and standardized differences) are disproportionately influenced by a small minority of plots, while most plots showed little or no change. Fourth, Painter et al. conflated stand-level occurrence with magnitude, treating the presence of one or a few tall stems (“43% of stands contained small trees”) as evidence of widespread recruitment. Finally, their assumptions that stems ≥ 2 m have escaped browsing and that reduced browsing alone drives height growth are contradicted by long-term data showing substantial browsing through 2–2.5 m and strong height–browsing feedbacks. Taken together, these shortcomings exaggerate the magnitude and pace of aspen recovery. The evidence supports the occurrence of a trophic cascade in Yellowstone, but not the magnitude of strength claimed. Accurate assessment of trophic cascade strength in Yellowstone is vital to ensure that this iconic system reliably informs ecological understanding and restoration practice.