Once thought to be natural refuges, old-growth forests are warming faster than we imagined.
by Zachary Perry, graduate student in water resource sciences science at OSU and the Andrews Forest LTER site
A Cool Journey Through an Old Forest
Walking into an old-growth forest feels like stepping through a threshold into another world. The heat of the day lingers outside, but here, the air is cooler, heavy with the scent of firs and moss. Sunlight filters through towering conifers in dappled patterns, painting the forest floor in shifting shades of green. Every sound—the rustle of leaves, the distant trill of a bird, the slow drip of water from a mossy branch—feels amplified in the quiet. It’s easy to forget the world beyond the trees, the one racing toward warmer temperatures and faster changes. For decades, ecologists have assumed these shaded, damp understories act like natural refuges, safe harbors that shield delicate ecosystems from the worst of climate change. But nature, it turns out, is rarely that simple.
A new study of long-term air temperature data beneath old-growth canopies challenges the idea that understory microclimates are shielded from warming. They used a unique dataset of multi-decadal air temperature measurements taken from within the forest understory at the Andrews Forest LTER.
These records were compared with temperature trends from 88 meteorological stations across Oregon and Washington over the same time period. The team’s findings reveal that although forests generate spatial variability in temperature – such as cooler understories compared to clearings – these differences do not shield against the broader forces of climate warming. As such, we cannot rely on forest understories to protect species from the impacts of a rapidly warming climate.
Credit: Greg Cohn, CC BY-SA 4.0.
Throwing Shade: Changing Perceptions
While localized cooling from shade and cold-air pooling still shape daily and seasonal microclimates, they don’t counteract the increase in longwave radiation from anthropogenic climate change. In fact, during the summer months of July and August—when warming is most pronounced—temperature increases in the forest understory equaled or even exceeded those in clearings. The warming observed in these shaded zones suggests that microclimate refugia may be more temporary than once thought.
“We were surprised by the results,” says Dr. Julia Jones, a professor of Geography at Oregon State University. She and her collaborators, Dr. Christopher Daly, Dr. Chris Still, and Andrews Forest Director Dr. Mark Schulze, were expecting to see less warming within the forest canopy, as well as in the depressions where cold air tends to settle.
This research holds important implications for how we understand ecosystem vulnerability in mountainous, forested regions. It suggests that even these shaded, damp environments are not insulated from global climate trends. Land managers and conservationists have historically viewed these areas as protected from warming. This study emphasizes the need to account for long-term warming even in landscapes traditionally viewed as climate resilient. Forests may still provide short-term buffers, but over decades, they are clearly feeling the heat.
Credit: Chris Daly, CC BY-SA 4.0.
Lessons from the Long View: Forests Feeling the Heat
“Well, the obvious message is—there is no escaping climate change,” says Dr. Jones when asked about the key takeaway from their study. “The notion that some parts of the landscape or forest might be less susceptible to climate change is not correct. Climate change is a shift in the global energy balance, which manifests in different ways in different regions. It’s not possible to escape it.”
Credit: Mark Schulze, CC BY-SA 4.0.
This study underscores the power of long-term, place-based science to reveal how ecosystems respond to a changing climate. “[This study is] interesting because it’s a reflection of what the LTER can provide”, says Dr. Jones. “In the LTER, you have a community where climatologists and ecologists can talk to one another and span their different time scales and approaches.” A collaborative, interdisciplinary approach facilitates research such as this, where global environmental conditions are linked to hyperlocal microclimates using data that span decades. By fostering communities of scientists across disciplines, long-term ecological research creates space for new questions, collaborative insights, and innovative approaches to understanding environmental change.
These efforts provide not only deep, process-based knowledge of the natural world, but also the foundation for models that guide how we manage forests, protect biodiversity, and prepare for future change. In a warming world, long-term research doesn’t just show how forests are changing; it also equips us with the foresight to respond to that change and reminds us what we stand to lose if we stop paying attention. LTER research such as this builds an important foundation which can help protect these ecosystems and benefit the human communities connected to them.
