One of the most widely cited stories about Yellowstone’s wolves is facing fresh scrutiny.
A new peer reviewed analysis published in Global Ecology and Conservation argues that a high profile 2025 study significantly overstated the ecological impact of wolf recovery in Yellowstone National Park. Researchers from Utah State University and Colorado State University say the earlier work relied on flawed methods that led to exaggerated conclusions about how wolves affected the park’s ecosystem.
“Ripple et al. argued that carnivore recovery produced one of the world’s strongest trophic cascades,” said Dr. Daniel MacNulty, lead author of the new analysis and a wildlife ecologist at Utah State University. “But our re-analysis shows their conclusion is invalid because it relies on circular reasoning and violations of basic modeling assumptions.”
Disputed Willow Growth Findings
At the center of the debate is a claim that willow crown volume increased by 1,500 percent following wolf recovery.
According to the new analysis, that figure was derived from a statistical model that used plant height to both calculate willow volume and predict it. The researchers argue this creates a circular relationship that can produce a strong result regardless of whether meaningful biological changes actually occurred.
“Because height was used both to compute and to predict volume,” MacNulty explained, “the relationship is circular — mathematically guaranteed to look strong even if no biological change occurred.”
The authors contend that this issue alone casts serious doubt on the reported magnitude of willow recovery.
Additional Problems Identified
The researchers also highlighted several other concerns they believe weakened the original conclusions.
Among them, the height to volume model was applied to heavily browsed willows with unusual growth forms, even though the model was not designed for such distorted shapes. The authors say this likely exaggerated estimates of growth.
They also note that many of the willow plots compared between 2001 and 2020 were not the same locations. As a result, apparent changes over time may partly reflect differences in sampling rather than actual ecological shifts.
The analysis further argues that comparisons with trophic cascades around the world relied on equilibrium assumptions that do not fit Yellowstone’s still recovering, non equilibrium ecosystem.
In addition, the authors say selective use of photographs and the omission of potentially important factors, including human hunting, made it harder to determine what was truly driving changes in vegetation.
A More Modest View of Wolf Impacts
After accounting for these issues, the researchers conclude that the available evidence does not support claims that wolf recovery triggered a dramatic, park wide increase in willow growth.
“Once these problems are accounted for, there is no evidence that predator recovery caused a large or system-wide increase in willow growth,” said Dr. David Cooper, co author of the analysis and emeritus senior research scientist at Colorado State University. “The data instead support a more modest and spatially variable response influenced by hydrology, browsing, and local site conditions.”
The team emphasizes that their findings should not be interpreted as minimizing the ecological importance of large predators. Instead, they say the study highlights the need for rigorous methods when investigating complex ecological relationships.
“Our goal is to clarify the evidence, not downplay the role of predators,” MacNulty said. “Predator effects in Yellowstone are real but context-dependent — and strong claims require strong evidence.”
Reconciling Conflicting Yellowstone Results
The new analysis also helps explain why scientists examining the same dataset reached very different conclusions.
Ripple et al. (2025) interpreted the data as evidence that wolf recovery produced a powerful trophic cascade throughout Yellowstone. In contrast, Hobbs et al. (2024), the researchers who collected the data during two decades of field experiments, reported only weak trophic cascade effects.
By revisiting the statistical methods and assumptions behind the original study, the new analysis argues that the evidence points to a far more limited and variable ecological response than the widely publicized Yellowstone wolf narrative suggests.
