Researchers studying montane forests in the northeastern United States often turn to data from the Hubbard Brook Experimental Forest in New Hampshire, well known for its long-running measurements of temperature, precipitation, and ecological processes. That data set has now played a key role in a new study of American red squirrels, offering an unusually detailed look at how these conifer-loving mammals respond to climate and habitat shifts. By relying on lapse rates calculated at Hubbard Brook—0.6°C per 100 m for temperature and 0.67 mm per 100 m for precipitation—the authors show how warming, precipitation changes, and forest regrowth interact to shape a species’ range in sometimes counterintuitive ways.
The paper, titled “Does habitat or climate change drive species range shifts?” by Toni Lyn Morelli, Michael T. Hallworth, Timothy Duclos, Adam Ells, Steven D. Faccio, Jane R. Foster, Kent P. McFarland, Keith Nislow, Joel Ralston, Mary Ratnaswamy, William V. DeLuca, and Alexej P. K. Siren, focuses on the red squirrel’s distribution in the mountains between upstate New York and Maine. The authors cite evidence that might initially suggest upward movements of many montane mammals under a warming climate. Instead, squirrel populations are actually shifting downward. “We found that American red squirrels are not tracking increasing temperatures upslope, despite substantial warming in recent decades,” the authors note. This surprise underscores the power of long-term data, like that from Hubbard Brook, which allowed them to approximate how far one would expect creatures to shift upslope if temperature were the sole driver.
Rather than climate alone, the team finds forest composition is steering red squirrels lower, where red spruce and other conifer species have begun recovering after decades of landscape disturbances. “Structural equation modeling indicates that red squirrel abundance is primarily influenced by red-spruce forest cover, which has shifted downslope with recovery from historical logging and acid deposition,” the authors write. Their analysis relies on occupancy modeling and open-population abundance estimates spanning nearly three decades of acoustic surveys. By pairing those population patterns with consistent climate measures—like those gleaned from Hubbard Brook—they’re able to disentangle the direct and indirect paths linking temperature, precipitation, and forest habitat.
The significance goes beyond just one squirrel species, of course. Studies of global range shifts often emphasize warming air and receding cold zones. Yet the authors argue that any attempt to forecast future distributions has to account for land-use history and habitat shifts, which can either accelerate or override an uphill scramble. “Accounting for the multiple dimensions of global change will enable better predictions and more effective conservation strategies,” they write. Without integrating local data (both climate and ecological), conservation plans risk oversimplifying how animals actually respond on the ground. The red squirrel’s move downslope, rather than up, demonstrates that climate and habitat don’t always pull in the same direction.
Beyond clarifying the squirrel’s own story, this project highlights how combining climate records from places like Hubbard Brook with thorough habitat surveys can reveal unexpected movement patterns. Thanks to nearly three decades of data, the authors offer a template for decoding the interplay of warming, precipitation changes, and forest regrowth. Their findings may inform land managers that species historically labeled “boreal” can also shift lower, so focusing only on higher elevation refuges could miss essential ground-level conservation opportunities.
Citation: Morelli, T. L., Hallworth, M. T., Duclos, T., Ells, A., Faccio, S. D., Foster, J. R., McFarland, K. P., Nislow, K., Ralston, J., Ratnaswamy, M., DeLuca, W. V., & Siren, A. P. K. (2025). Does habitat or climate change drive species range shifts? Ecography. https://doi.org/10.1111/ecog.07560