One of the most widely cited stories about Yellowstone’s wolves is facing new scrutiny.
A new peer-reviewed analysis Earth ecology and conservation claims that a high-profile 2025 study vastly exaggerated the ecological impact of wolf recovery in Yellowstone National Park. Researchers from Utah State University and Colorado State University say earlier studies relied on flawed methodology and led to exaggerated conclusions about how wolves affected the park’s ecosystem.
“Ripple and colleagues argued that carnivore recovery has created one of the most powerful trophic cascades in the world,” said Dr. Daniel McNulty, lead author of the new analysis and a wildlife ecologist at Utah State University. “However, our reanalysis found that their conclusions were invalid because they relied on circular reasoning and violations of fundamental modeling assumptions.”
Results of discussion on willow growth
At the heart of the debate is a claim that willow crown volume increased by 1,500 percent after wolf recovery.
According to the new analysis, this number was derived from a statistical model that used plant height to both calculate and predict willow volume. The researchers argue that this creates a circular relationship that produces powerful results, regardless of whether meaningful biological changes actually occur.
“Because height is used to both calculate and predict volume, this relationship is cyclical and is mathematically guaranteed to appear strong even if no biological changes occur,” McNulty explained.
The authors argue that this issue alone casts serious doubt on the reported scale of willow recovery.
Additional issues identified
The researchers also highlighted several other concerns that may weaken their original conclusions.
Among them, a height and volume model was applied to severely browsed willow with abnormal growth morphology, even though the model was not designed considering such a distorted shape. The authors say this is likely an exaggerated estimate of the growth rate.
They also point out that many of the willow plots compared between 2001 and 2020 were not in the same location. As a result, apparent changes over time may partially reflect sampling differences rather than actual ecological changes.
The analysis further argues that comparisons with trophic cascades around the world rely on equilibrium assumptions, which are not compatible with Yellowstone’s still recovering nonequilibrium ecosystem.
Additionally, the authors say the photos were used selectively and omitted potentially important factors, including human hunting, making it difficult to determine what is really driving the changes in vegetation.
A more modest look at Wolf Impact
Considering these issues, the researchers concluded that the available evidence does not support the claim that wolf restoration has dramatically increased willow growth throughout the park.
“Once these issues are accounted for, there is no evidence that predator recovery caused large-scale or system-wide increases in willow growth,” said Dr. David Cooper, co-author of the analysis and senior research fellow emeritus at Colorado State University. “Rather, the data support a more modest and spatially variable response influenced by hydrology, browsing, and local conditions.”
The researchers stress that their findings should not be interpreted as minimizing the ecological importance of large predators. Rather, they say the study highlights the need for rigorous methods when investigating complex ecological relationships.
“Our goal is to uncover the evidence, not to downplay the role of predators,” McNulty said. “The impact of predators in Yellowstone is real, but it is context-dependent. And strong claims require strong evidence.”
Reconciling inconsistent Yellowstone results
The new analysis also helps explain why scientists who studied the same dataset came to very different conclusions.
Ripple et al. (2025) interpreted this data as evidence that wolf recovery created a strong trophic cascade across Yellowstone. In contrast, Hobbs et al. (2024), researchers who collected data during a 20-year field experiment, 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 much more limited and variable ecological response than the widely publicized Yellowstone wolf story suggests.
