Early Detection Is the Best Protection for Old-Growth Forests (U.S. National Park Service)

Despite dire evidence of rising tree death, researchers found resilience and hope deep inside western Washington's forests. But it will take 21st-century monitoring methods to keep that hope alive.

By Hazel Galloway, John Boetsch, Beth Fallon, and Marie Denn

A lush forest with ferns and moss-covered trees — The Hoh Rainforest in Olympic National Park
Image credit: NPS / C. Bubar

Forests are losing ground to the stresses of a warming world. Climate change is implicated in increasing tree death on every continent. Tree death, in turn, limits forests' capacity to store carbon, releasing yet more heat-trapping greenhouse gasses into the atmosphere. This can make for an alarming feedback loop. For example, models suggest that Sierra Nevada forests may transform from net carbon sponges to net emitters by the end of this century.

In keeping with global patterns, a 2009 study painted a grim picture of Pacific Northwest forests. Which is why National Park Service and other scientists were so surprised, as related in a March 2023 paper, when they found no trace of this trend in four Pacific Northwest national parks. As of 2018, these forests were defying global odds in not demonstrating increased mortality.

Global Carbon Stores

Mount Rainier. North Cascades. Olympic. Named for their rugged, glacier-capped peaks, these national parks also protect a living legacy: Washington State’s largest remaining tracts of old-growth forest. All life on planet Earth is based on the element carbon. Every living thing has it. Inside those forests, locked away in towering trees, charismatic banana slugs, delicate oyster mushrooms, and generations of decomposing organic matter, are globally significant stores of carbon.

Western Washington’s old-growth forests guard over 100 tons per hectare of what scientists call “irrecoverable carbon.”

Western Washington’s old-growth forests guard over 100 tons per hectare of what scientists call “irrecoverable carbon.” If lost to the atmosphere, this carbon cannot be recovered in time to avoid the worst impacts of climate change. And their role doesn’t stop there. Old-growth forests also do double duty as refuges for heat-sensitive species, likely thanks to cooler microclimates and a varied buffet of food sources.

Beating the Odds

The 2009 study found tree death rates were doubling every 17 years throughout the Pacific Northwest. To discover if that trend held true in protected forests, researchers set up 45 long-term monitoring plots in Olympic, Mount Rainier, and North Cascades, as well as Lewis and Clark National Historical Park. The 2.5-acre plots were chosen by random sample to represent mature forests at various elevations.

Every year from 2008 to 2013 and once more in 2018, study teams hiked out to each site. At the first visit, they attached small metal tags to trees, recording species, size, and other attributes for each tagged tree. In later years, they recorded any new deaths among the tagged trees, mapping mortality rates over time.

Four people in a lush, mossy forest, measuring a tree with a measuring tape. One is writing on a notebook. — Team members working together to measure a large tree on a monitoring plot at Olympic National Park.
Image credit: NPS

As of the final year of monitoring in 2018, there was no sign of either elevated mortality or a general rise in tree death across the 45 plots. That suggested a measure of ecological stability—coming during a ten-year span that also saw the state’s highest recorded annual average temperature.

A Protective Buffer?

Scientists believe this stability may have deep roots. Mature Pacific Northwest forests are complex and interconnected ecosystems. Decomposing “nurse logs” nurture new saplings alongside mutualistic fungi and lichens. Returning salmon deliver a wealth of nutrients from the sea to forest rivers where they spawn and perish.

In the interior of protected forests, the average tree age was nearly 300 years—many were even older. The physical forest structure itself may offer protection.

In some of the 2023 paper’s study plots located in the interior of protected forests, the average tree age was nearly 300 years—many were even older. The physical forest structure itself may offer protection. In one instance, scientists found that during periods of heat stress, growth at forest edges in New England dropped three times faster than it did in forest interiors.

Even though scientists don’t know exactly why these interior plots didn’t follow regional trends, the fact that mature and old-growth forests remain at all is due to early protections and rough terrain. Federal land designations saved these parks from rampant logging. That left large swaths of forest intact, perhaps offering a buffer against dangers that emerged a century later.

A person in a red suit with a white head cover collects information while standing in a densely vegetated green forest — A member of the monitoring team records data in the summer forest undergrowth at Olympic National Park.
Image credit: NPS

In the Dark

But is this a conservation success story? During the record-breaking summer of 2021, while news outlets reported on dangerously high temperatures in Seattle and Portland, forests were also reaching a breaking point. Foliage temperatures throughout the region climbed above 104°F for at least 26 total hours, effectively cooking important leaf structures. Afterwards, aerial surveys revealed the sheer magnitude of the event: over 340 square miles of scorched and damaged foliage. Within days, there were reports of tree death.

Bright light in a dark night. Light comes from behind a tree in dense forest. A tent or blanket is on a rope between trees — 1916 photo by L.D. Lindsley of a light in the forest at night in North Cascades National Park.
Image credit: NPS / L.D. Lindsley. Courtesy of North Cascades NPS Complex Museum Collection. Assembled Collections, Series II: Stehekin Area Photographs, File 001 - Mary Roberts Rinehart Album

Inside national parks, scientists anecdotally report increasing mortality among forest trees near campgrounds and roadsides, raising the specter of a more widespread decline.

Since then, summer droughts, additional heat extremes, and related risks of long-term changes in wildfire regimes have dialed up the stress on Washington forests. Inside national parks, scientists anecdotally report increasing mortality among forest trees near campgrounds and roadsides, raising the specter of a more widespread decline. But ever since monitoring concluded in 2018, they don’t have definitive answers.

Monitoring in Stop-Motion

The conservationists who shielded these forests may have also preserved their ability to bounce back from stress—up to a point. But park boundaries can’t keep out heat waves, drought, or other extreme events. Today, our best way to track and confront climate change impacts is information. A lot of information.

Field-based monitoring is a vital first step, but it has drawbacks. It can take field crews weeks to reach those 45 monitoring plots, and visits are limited by the demands of the brief field season. In effect, this data collection is the monitoring equivalent of watching a stop-motion film. At one frame per year and a 45-pixel resolution, we’ll grasp the main plotline—but will it be in time?

Detecting light reflected by vast tracts of forest, sensors mounted on satellites can pick up subtle changes before they become apparent on the ground.

Modern remote sensing tools would be an invaluable supplement to field-based monitoring. Detecting light reflected by vast tracts of forest, sensors mounted on satellites can pick up subtle changes before they become apparent on the ground. Some tools, using wavelengths invisible to the naked eye, can even “see” early stress markers—from a distance of over 400 vertical miles. In contrast to field-based monitoring, modern tools similar to ones already used in other areas would offer managers the equivalent of an HD film, live-streamed at the speed of light.

A river surrounded by mountains and lush forest — Dense forests line the banks of the Stehekin River in North Cascades National Park.
Image credit: NPS

Passing the Baton

As the National Park Service confronts emerging climate impacts across more than 400 units, ecosystems showing signs of stability may take a backseat to those in crisis. Our collective human tendency to focus resources on emergencies can lead to neglected preventative care. But for threatened forests, skipped checkups have real consequences. Once underway, forest declines can be swift and devastating.

Remote sensing tools would allow park managers to respond proactively to the earliest signs of decline.

Western Washington’s old-growth forests seem to be resilient—so far—in the face of increasing stresses. But we shouldn’t underestimate the importance of monitoring them more frequently and comprehensively. Remote sensing tools would allow park managers to respond proactively to the earliest signs of decline. If we want to pass the baton to the next generation, let’s modernize our methods and protect our forests and their vast carbon stores before the trees fall.

About the authors

^{Hazel Galloway is a science communicator with the National Park Service’s North Coast and Cascades Network.}

^{John Boetsch is an ecologist with the National Park Service’s North Coast and Cascades Network.}

^{Beth Fallon is an ecologist at Mount Rainier National Park.}

^{Marie Denn is an aquatic ecologist with the National Park Service, Regions 8, 9, 10, and 12.}

Early Detection Is the Best Protection for Old-Growth Forests

Despite dire evidence of rising tree death, researchers found resilience and hope deep inside western Washington's forests. But it will take 21st-century monitoring methods to keep that hope alive.

Global Carbon Stores

Western Washington’s old-growth forests guard over 100 tons per hectare of what scientists call “irrecoverable carbon.”

Beating the Odds

A Protective Buffer?

In the interior of protected forests, the average tree age was nearly 300 years—many were even older. The physical forest structure itself may offer protection.

In the Dark

Inside national parks, scientists anecdotally report increasing mortality among forest trees near campgrounds and roadsides, raising the specter of a more widespread decline.

Monitoring in Stop-Motion

Detecting light reflected by vast tracts of forest, sensors mounted on satellites can pick up subtle changes before they become apparent on the ground.

Passing the Baton

Remote sensing tools would allow park managers to respond proactively to the earliest signs of decline.

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Despite dire evidence of rising tree death, researchers found resilience and hope deep inside western Washington's forests. But it will take 21st-century monitoring methods to keep that hope alive.

Global Carbon Stores

Western Washington’s old-growth forests guard over 100 tons per hectare of what scientists call “irrecoverable carbon.”

Beating the Odds

A Protective Buffer?

In the interior of protected forests, the average tree age was nearly 300 years—many were even older. The physical forest structure itself may offer protection.

In the Dark

Inside national parks, scientists anecdotally report increasing mortality among forest trees near campgrounds and roadsides, raising the specter of a more widespread decline.

Monitoring in Stop-Motion

Detecting light reflected by vast tracts of forest, sensors mounted on satellites can pick up subtle changes before they become apparent on the ground.

Passing the Baton

Remote sensing tools would allow park managers to respond proactively to the earliest signs of decline.

You Might Also Like

Tags