They keep us cool, we cut them down

Standing forests are our best natural climate solution. So why aren’t we treating them that way?

In terms of climate mitigation, forests are like green gold—working overtime to cool the planet, while also supporting a wealth of biodiversity. But we have not been saving them as one would a precious asset. Despite pledges to end deforestation, old growth forests are being cut down at alarming rates. And planting new trees is widely prioritized and incentivized over protecting existing forests. Across the board, standing forests are vastly undervalued. This has to change if we are to stand a chance of limiting warming to internationally agreed targets.

Forests are global air conditioners

According to a recent study from scientists at Woodwell and the University of Virginia, tropical forests alone are holding back approximately 1 degree Celsius of warming. About 75% of that cooling effect is due to carbon sequestration. Forests grow, trees lock away carbon in their trunks and roots and shunt it into the soil. The other 25% comes from the innate properties of forests that work to cool vast regions of the globe.

Through photosynthesis, plants release water vapor into the air in a process called evapotranspiration. The vapor contributes to cooling near the ground, as well as cloud formation higher in the atmosphere that reduces incoming solar radiation. The shape of the tree canopy also contributes. So-called canopy “roughness” disrupts air flow above the forest. The more uneven the canopy, the more turbulent the air, which disperses heat away from the surface. In the tropics, evapotranspiration and canopy roughness are high, which means that surface temperatures remain relatively low, with the heat dispersed throughout the deep atmosphere.

Forests also naturally produce molecules called biogenic volatile organic compounds (BVOC), which can either contribute to cooling by encouraging the formation of clouds, or to warming by creating ozone and methane. In the tropics, the net effect of these chemicals is cooling.

The cumulative result of these properties is that when forests are removed, the land around them begins to heat up even faster, which can increase the frequency of extreme heat and drought events. Without forests, some regions will become a lot less resilient to sudden shocks. And the release of carbon contributes to global warming which further exacerbates hot, dry conditions.

“Forests act like air conditioners,” says Woodwell Assistant Scientist, Dr. Ludmila Rattis, who studies the impacts of deforestation on agriculture in Brazil. “Deforesting in the face of climate change is like getting rid of your air conditioners before an upcoming heatwave.”

Not all forests are created equally

Protecting forests, and maintaining the cooling services they provide, is vital to limiting warming. But, with forests covering 30% of the Earth’s land, prioritizing protection is a massive task. And when it comes to carbon storage, not all forests are equally valuable. Older, healthier forests tend to have a more secure hold on their carbon.

“Mature forests have higher biodiversity and create their own microclimate,” says Woodwell Associate Scientist, Brendan Rogers. “They’re more resistant to drought and other types of disturbance. And because of that, they tend to be more stable in the face of environmental perturbations over time.”

New research from Woodwell and Griffith University has developed a method of identifying high-value forests using satellite imagery. Estimating the metric of “forest stability” through satellite data on the light reflected by vegetation and a water stress index of the tree canopy, researchers were able to determine gradients of stability within forest patches in the Amazon and boreal forests.

Using a gradient of forest stability allows for a better prioritization of forest protection strategies based on their carbon value.

“The first priority is to protect stable forests from further human disturbance,” says paper co-author Dr. Brendan Mackey. “The second priority is to identify forest areas where restoration efforts will be most cost effective.”

Guarding the forests that guard our future

But if the state of existing forests is any indication, forest protection continues to be deprioritized. Many wildfires are left to burn unless they threaten human settlements. Governments continue to incentivize deforestation for development or agricultural expansion. Indigenous and local communities are not compensated for their work stewarding their territories and keeping forests safe. And the warmer the planet gets, the more susceptible even protected forests become to drought, fire, and disease.

Research has shown that stewarding standing primary forests, and reviving degraded ones, represents the greatest opportunity for near-term carbon storage and removal. A study of global land-based carbon storage potential found that improved management of existing forests alone could store approximately 215 billion metric tons more than they currently do.

Protecting forests is cost effective, too. For example, in the United States, investing in fire fighting in Alaska’s boreal forests would require just $13 per ton of CO2 emissions avoided. That’s easily on par with other mitigation strategies like onshore wind or solar energy generation.

Effective strategies for protecting forests already exist, they’ve just been suffering from a lack of force—and often funding—behind their implementation. For example, forest carbon markets—where landowners and forest stewards are paid to protect standing forests that are otherwise vulnerable to deforestation—have the potential to keep forests safe while offsetting emissions from other sectors. But nascent carbon markets are inefficient, with weak standards for verifying the quality of credits being sold, and lacking the transparency needed to ensure credits are actually reducing overall emissions, rather than greenwashing carbon-intensive business practices.

Credits are also priced incorrectly for their relative climate value—the market currently values reforestation credits more highly, reducing incentive for landowners to conserve standing, old-growth forests when there is a better livelihood to be made in legally deforesting land for  other uses. A truly effective carbon markets system would require large investments in science that can verify credit standards.

Forests are like our global carbon savings accounts—when we cut them down, we’re drawing out money and limiting our ability to collect interest and keep growing our funds. Successful mitigation can’t be accomplished without taking the full value of forests into account and strengthening policies to reflect that. If they aren’t, the planet will pay a far greater price for it as temperatures rise.

“We can’t afford to keep cutting forests. We need to reduce emissions now, and protecting forests is one of our best available solutions. Despite the obstacles, it’s worth the investment,” says Dr. Rogers.

What’s New?

A recent paper offers new insight into the state of global forests. Using remote sensing imagery from MODIS satellites, researchers were able to categorize forest condition in two important biomes—the Amazon and the Siberian Taiga—differentiating between high stability, low stability, and non-forested areas. These “stability classes” provide another metric of assessing the conservation and carbon value of land, as high stability forests tend to be healthier, more resilient, primary forest stands that store large amounts of carbon and contribute to cooling the planet more than lower stability forests.

“Mature forests have higher biodiversity and create their own microclimate,” says paper co-author and Woodwell Associate Scientist, Brendan Rogers. “They’re more resistant to drought and other types of disturbance. And then because of that, they tend to be more stable in the face of environmental perturbations over time.”

Understanding forest stability

To estimate forest stability, researchers analyzed satellite data that combined measures of photosynthetic radiation with a canopy water stress index. That new approach was able to identify whether or not a forest has been disturbed by either human land use (ex. logging) or natural processes (wildfire, insects outbreaks, etc.) and map the degradation level.

Co-author Dr. Brendan Mackey from Griffith University in Australia says that stability mapping is a first critical step in making an inventory of the world’s remaining primary forests which store more carbon, support the most biodiversity, and deliver the cleanest water. 

According to Dr. Rogers, the less interruption in the ecological processes of the forest, the more secure the carbon stored in both the trees and soils are. Further human interference in an unstable forest could tip it into decline. 

“I think one of the problems for primary forest conservation globally has been this idea that it’s either a forest or not a forest. So, internationally agreed upon definitions of what constitutes a forest sets a pretty low bar. You can get away with calling a plantation with very young trees a forest, but that could have been converted from a high biomass mature forest, and they’re simply not the same—not in terms of carbon, biodiversity, or ecosystem services,” says Dr. Rogers.

What this means for forest conservation

Using a gradient of forest stability instead of a black and white definition of forest/not-forest allows for more nuanced decision-making where both carbon monitoring and conservation planning are concerned.

“The first priority is to protect stable forests from further human disturbance, as once an area is deforested, it takes decades to centuries—and in some cases millenia—for it to regrow to a primary state. The second priority is to identify forest areas where restoration efforts will be most cost effective,” says Dr. Mackey.

According to the paper’s lead author, Dr. Tatiana Shestakova, this means places where a small investment could have bigger positive results.

“If you pick a forest that was degraded in some way, but it still keeps patches of more or less healthy forests, you can reinstate ecological processes faster and easier,” says Dr. Shestakova.

Dr. Shestakova said she encourages other researchers to apply the methods to their particular regions of expertise and expand estimates of forest stability globally.

“The benefit of this approach is that it was tested in such contrasting ecoregions, and has been proven to be a simple and efficient way to assess this important dimension of forest condition,” says Dr. Shestakova.

What’s New?

The Cerrado is a tropical savanna located just southeast of the Amazon rainforest. This biome is a patchwork of forests, savannas, and grasslands, nearly as biodiversity rich as the Amazon yet suffering more due to lax environmental protections. Over 46% of its original land cover has already been cleared for crops or pastures. A recent study assessed the impacts of this conversion on the temperature and water cycling in the region.

The study found that clearing of natural ecosystems resulted in increased land surface temperatures and reduced evapotranspiration — water evaporated to the atmosphere both from soils and as a byproduct of plant growth. Across the biome, land use changes caused a 10% reduction in water being cycled into the atmosphere annually, and almost 1 degree C of warming. Where native savanna vegetation was cleared, temperatures increased by 1.9C and the water recycled to the atmosphere decreased by up to 27%. These changes don’t take into account the additional effects of atmospheric warming from greenhouse gas emissions. 

The study also projects forward three potential future scenarios based on different levels of environmental protection. The worst-case scenario assumes an additional 64 million hectares of both legal and illegal deforestation, which would leave just 20% of native vegetation in the Cerrado by 2050. If illegal deforestation is prevented but legal deforestation still advances, an additional 28 million hectares of deforestation would continue to warm and dry out the region. Only in the most optimistic scenario, with enforced zero deforestation policies and restoration of over 5 million hectares of illegally cleared vegetation, would the impacts of past clearing begin to reverse.

“If we continue down this path of weakening environmental policies, we’re probably heading towards an uncontrolled increase in deforestation,” says Ariane Rodrigues, researcher at the University of Brasilia and lead author on the paper. “As a result, we could reach almost 1 C of temperature increase by 2050 from land use change alone. If we add the estimated temperature increase from global greenhouse gas emissions, we will have a critical situation for food production, biodiversity, water and wildfire risk, affecting areas located way beyond the biome’s limits.” 

Understanding Land Use in the Cerrado

Incentives for large-scale commercial agriculture in the Cerrado date back to the 1970s. Despite its high biodiversity, only 11% of the Cerrado is protected and technological advancements provided favorable conditions for agriculture to expand rapidly. 

The half of the biome that remains unconverted is considered prime agricultural land. The Cerrado alone is responsible for 12% of global soybean production and 10% of global beef exports. Growing demand for these agricultural products is pushing farmers and ranchers to expand into the Matopiba region in the Northeast Cerrado — one of the largest remaining areas of undisturbed native vegetation. 

Hotspots of reduced evapotranspiration and increased temperatures can already be seen in areas of Matopiba with intensifying agricultural activity. This means that farms will rely even more heavily on irrigation to combat drought, a strategy made less viable by the warming and drying caused by agriculture itself.

“That is the driest portion of the Cerrado, where there’s the most climate risk already,” says paper co-author and Woodwell Water program director, Dr. Marcia Macedo. “You can see that in the data — it’s getting hotter, and there’s less evapotranspiration, so we are really intensifying conflicts in areas that are already on the edge.” 

What this Means for Protecting the Cerrado

The results of the paper highlight the urgent need for a paradigm shift that values the additional services the Cerrado provides beyond just crop production. Not only does it house unique ecosystems, but it plays a pivotal role in modulating the climate of the region. In the best-case scenario evaluated by the paper, zero-deforestation and restoration policies could avoid extensive warming and drying and begin compensating for the past transformation of Cerrado landscapes. Continued conversion of natural vegetation will jeopardize both biodiversity and agricultural stability in the Cerrado, as crops struggle to be productive under hotter and drier conditions. 

Already, conflicts over water usage and irrigation are occurring in western Bahía state. As the region warms and dries, competition for a scarce resource will become more common and large-scale agriculture will become much less viable.

“We’re making some risky decisions in terms of land use,” says Dr. Macedo, “We’re losing a lot for short term gains in crop production, often in areas that will struggle to sustain large-scale agriculture as climate changes.”

It was supposed to be a quiet season, but only two months into summer and Alaska is already on track for another record-setting wildfire season. With 3 million acres already scorched and over 260 active fires, 2022 is settling in behind 2015 and 2004 so far as one of the state’s worst fire seasons on record. Here’s what to know about Alaska’s summer fires:

2. Historic fires are Burning in Yukon-Kuskokwim Delta and Bristol Bay

Southwestern Alaska, in particular, has been suffering. The season kicked off with an unseasonably early fire near Kwethluk that started in April. Currently, the East Fork Fire, which is burning near the Yup’ik village of St. Mary’s, AK, is among the biggest tundra fires in Alaska’s history. Just above Bristol Bay, the Lime Complex— consisting of 18 individual fires— has burned through nearly 865,000 acres. One of the longest lasting fires in the Lime Complex, the Upper Talarik fire, is burning close to the site of the controversial open-pit Pebble Mine.

2. Seasonal predictions showed a low-fire season

For Dr. Brendan Rogers, who was in Fairbanks, AK for a research trip in May, the explosive start of the fire season contrasts strongly to conditions he saw in late spring.

“It was a relatively average spring in interior Alaska, with higher-than-normal snowpack. Walking around the forest was challenging because of remaining snow, slush, and flooded trails,” said Dr. Rogers.

Early predictions showed a 2022 season low in fire due to heavy winter snow. But the weather shifted in the last ten days of May and early June. June temperatures in Anchorage were the second highest ever recorded. High heat and low humidity rapidly dried out vegetation and groundcover, creating a tinderbox of available fuel. This sudden flip from wet to dry unfolded similarly to conditions in 2004, which resulted in the state’s worst fire season on record.

3. Climate Change is accelerating fire feedback loops

The conditions for this wildfire season were facilitated by climate change, and the emissions that result from them will fuel further warming. The hot temperatures responsible for drying out the Alaskan landscape were brought on by a persistent high pressure system that prevents the formation of clouds— a weather pattern linked to warming-related fluctuations in the jet stream

“With climate change, we tend to get more of these persistent ridges and troughs in the jet stream,” says Dr. Rogers. “This will cause a high pressure system like this one to just sit over an area. There is no rain; it dries everything out, warms everything up.” 

The compounding effects of earlier snowmelt and declining precipitation have also made it easier for ground cover to dry out rapidly under a spell of hot weather. More frequent fires also burn through ground cover protecting permafrost, accelerating thaw that releases more carbon. According to the Alaska Center for Climate Assessment and Policy, the frequency of big fire seasons like this one are only increasing— a trend expected to continue apace with further climate change.

Additionally, this summer has been high in lightning strikes, which were linked to the ignition of most of the fires currently burning in Alaska. Higher temperatures result in more energy in the atmosphere, which increases the likelihood of lightning strikes. On just one day in July over 7,180 lightning strikes were reported in Alaska and neighboring portions of Canada.

4. Communities are Being Affected Hundreds of Miles Away

The destruction from these wildfires has forced rural and city residents alike to evacuate and escape the path of burning. Some residents of St. Mary’s, AK have elected to stay long enough to help combat the fires, clearing brush around structures and cutting trees that could spread fire to town buildings if they alight. 

But the impact of the fires is also being felt in towns not in the direct path of the flames. Smoke particulates at levels high enough to cause dangerously unhealthy air quality were carried as far north as Nome, AK on the Seward Peninsula.

“Even though a lot of these fires are remote, that doesn’t preclude direct human harm,” says Woodwell senior science policy advisor Dr. Peter Frumhoff.

Recent research has shown that combatting boreal forest fires, even remote ones, can be a cost effective way to prevent both these immediate health risks, as well as the dangers of ground subsidence, erosion, and loss of traditional ways of life posed by climate change in the region. 

5. The season is not over yet

Mid-July rains have begun to slow the progression of active fires but, according to Dr. Frumhoff, despite the lull, it is important to keep in mind that the season is not over yet.

“The uncertainty of those early predictions also applies to the remainder of the fire season — we don’t know how much more fire we’ll see in Alaska over the next several weeks.”

The Amazon rainforest is one of the planet’s best natural climate solutions. Roughly 123 billion tons of carbon are estimated to be stored in the trees and soils of the Amazon and, if protected, it has the power to continue sequestering billions of tons of carbon each year.

But that irreplaceable carbon sink is under steady threat from a cycle of deforestation, fire, and drought that is both exacerbated by and contributing to climate change. Preliminary analysis from Woodwell of last year’s data has outlined that the most vulnerable regions of the Amazon are where drought and deforestation overlap.

2021 data shows deforestation drives fire in the Amazon

Unlike temperate or boreal forest ecosystems—or even neighboring biomes in Brazil— fires in the Amazon are almost entirely human caused. Fire is an intrinsic part of the deforestation process, usually set to clear the forest for use as pasture or cropland. Because of this, data on deforestation can provide a good indicator of where ignitions are likely to happen. Drought fans those flames, producing the right conditions for more intense fires that last longer and spread farther. Examining the intersection between drought and deforestation in 2021, Woodwell identified areas of the Amazon most vulnerable to burning.

Areas of deforestation combined with exceptionally dry weather to create high fire risk in northwestern Mato Grosso, eastern Acre, and Rondonia. Although drought conditions shifted across the region throughout the course of the year, deforestation caused fuel to accumulate along the boundaries of protected and agricultural land.

These areas of concentrated fuel showed the most overlap with fires in 2021, indicating that without the ignition source that deforestation provides, fires would be unable to occur, even during times of drought.

In June of 2021, we identified a dangerous and flammable combination of cut, unburned wood and high drought in the municipality of Lábrea, that put it at extreme risk of burning. Data at the end of December of 2021 confirmed this prediction. The observed fire count numbers from NASA showed that last year, Lábrea experienced its worst fire season since 2012.

Fires and climate change form a dangerous feedback loop

As a result of deforestation in 2021, at least 75 million tons of carbon were committed to being released from the Amazon. When that cut forest is also burned, most of the carbon enters the atmosphere in a matter of days or weeks, rather than the longer release that comes from decay.

This fuels warming, which feeds back into the cycle of fire by creating hotter, drier, conditions in a forest accustomed to moisture. Drought conditions weaken unburned forests, especially around the edges of deforestation, which makes them more susceptible to burning and releasing even more carbon to the atmosphere to further fuel warming.

Fire prevention strategies enacted by the current administration over the past 3 years have been insufficient to curb burning in the Amazon, because the underlying cause of deforestation remains unaddressed. Firefighting crews are not sufficiently supported to continue their work in regions like Lábrea that are actively hostile to combating deforestation and fire. If deforestation has occurred, fire will follow. To ensure the safety of both the people and the forests in these high-risk municipalities, the root causes of deforestation must be addressed with stronger and more strategic policies and enforcement.

The feasibility of land-based carbon mitigation in 4 graphics

Mist over the Amazon rainforest, photo by Chris Linder

The importance of natural climate solutions came to the forefront of climate talks in Glasgow last week as decision makers discussed the “how” of making good on emissions pledges.

One of the most powerful existing solutions we can deploy are land-based mitigation strategies, also known as natural climate solutions.  Forest protection and restoration, agroforestry, and other changes to the way we manage land can boost the amount of carbon ecosystems pull from the atmosphere and could help tackle 20-30 percent of the emissions reductions needed to limit warming to 1.5 degrees C. These graphics, based on a recent study in Global Change Biology, break down the potential and feasibility of land-based carbon mitigation.

Cost-effective mitigation is only 40% of the total technical potential

Cost-effective mitigation is only 40% of the total technical potential

Although there is great potential in land-based mitigation globally, some actions will be cheaper and easier to implement. Roughly 40 percent of the total carbon mitigation potential of land-based strategies can be considered cost-effective, with estimated price tags up to $100 per ton of carbon sequestered. On a global scale, actions like reducing deforestation or improving carbon sequestration on grasslands are incredibly cost effective. Shifting to healthier, more plant-based diets is another, individual, action that can have big impacts.

Agricultural mitigation is as important as forest protection in the Northern Hemisphere

Agricultural mitigation in Brazil vs United States

On a regional level, the value of different actions varies. In Latin America and the Caribbean, as well as Africa, the greatest mitigation power lies in forests, both protecting existing forests and restoring degraded ones. In Brazil, which holds 60 percent of Amazon forests, the feasible benefits are striking. For developed nations, like the United States, improving sequestration on agricultural lands is a much larger piece of the equation, almost equal to forest-related measures. This is because developed countries like the U.S. have already cut their old-growth forests.

Some small but carbon-rich ecosystems are “too dense to fell”

Southeast Asia map of soil organic carbon (SOC)

Ecosystems like mangroves or peatlands offer opportunities to make big emissions reductions over relatively small areas. Mangrove forests store vastly more carbon per hectare than most terrestrial forests—primarily due to large soil carbon stores—and only occupy thin strips of coastline across much of the tropics.

Carbon mitigation potential chart: protection and restoration are best

Their outsize carbon sequestration and storage potential means that restoring them offers a much greater return on investment than other ecosystems, and failing to protect them could place climate goals in serious jeopardy. Though employing all land-based mitigation strategies at our disposal is crucial, targeting the most carbon-rich forests could be a quicker, easier, more cost-effective first step.

Black spruce are losing their legacy to fire

Although evolved to thrive in fire-disturbed environments, a recent study shows more frequent fires are threatening black spruce resilience

burnt black spruce forest with young poplar understory, photo by Jill Johnstone
For the past five to ten thousand years, black spruce have been as constant on the boreal landscape as the mountains themselves. But that constancy is changing as the climate warms.

A recent study published in the Proceedings of the National Academy of Sciences, led by Dr. Jennifer Baltzer, Canada Research Chair in Forests and Global Change at Wilfrid Laurier University, found that shifts in wildfire regimes are pushing black spruce forests to a tipping point, beyond which the iconic species may lose its place of dominance in boreal North America.

Synthesizing data from over 1500 fire-disturbed sites, the study showed black spruce’s ability to regenerate after fire dropped at 38% of sites and failed completely 18% of the time—numbers never before seen in a species evolved to thrive after fire.
healthy black spruce forest

The Stabilizing Feedback of Black Spruce

“They almost look like a Dr. Seuss tree.” says Dr. Brendan Rogers, an Associate Scientist at Woodwell and co-author on the PNAS study. He’s referring to the way black spruce are shaped—short branches that droop out of spindly trunks. Clusters of small dark purple cones cling to the very tops of the trees. Black spruce forests tend to be cool and shaded by the dense branches, and the forest floor is soft and springy.

“The experience of walking through these forests is very different from what most people are accustomed to. The forest floor is spongy, like a pillow or waterbed,” Dr. Rogers says. “It’s often very damp, too, because black spruce forests facilitate the growth of moss and lichen that retain moisture.”

However, these ground covers can also dry out quickly. Spruce have evolved alongside that moss and lichen to create a fire-prone environment. It only takes a few days or even hours of hot and dry weather for the porous mosses to lose their moisture, and the spruce are full of flammable branches and resin that fuel flames up into the tree’s crown.

Black spruce need these fires to regenerate. Their cones open up in the heat and drop seeds onto the charred organic soil, which favors black spruce seedlings over other species. The organic soil layers built up by the moss are thick enough to present a challenge for most seedlings trying to put down roots, but black spruce seeds are uniquely designed to succeed.

Dr. Jill Johnstone, Affiliate Research Scientist at the University of Alaska Fairbanks, who also contributed to the PNAS study, compares it to a lottery system that black spruce have rigged for millennia.

“After fire, anything can happen,” says Johnstone. “But one way to make sure you win the lottery is to buy a lot of tickets. Black spruce has the most tickets. It has the most number of seeds that are the right size to get roots down into mineral soil, and so it tends to regenerate after fire.”

Potential competitors like white spruce, Dr. Johnstone says, don’t disperse very far from standing trees so they only get a few lottery tickets. Deciduous species like aspen or birch have seeds that are too small to work through the thick organic layers—their tickets are faulty. So the fire lottery tends to perpetuate black spruce’s dominance in what’s known as a “stabilizing feedback loop”.

intact spruce forest, photo by Brendan Rogers

Hotter, Dryer Conditions are Inhibiting Black Spruce Regeneration

That stable loop has begun to break down, however. Black spruce just aren’t re-establishing themselves as frequently after fire. The study examined the characteristics of different sites to better understand what might be hampering regeneration success.

recently burned black spruce trunks, photo by Brendan Rogers
Sites that failed to regenerate with black spruce were typically drier than normal. They also tended to have shorter intervals between successive fires. Black spruce stands have historically experienced the kinds of intense, stand-replacing fires that burn through everything only once per century. This long interval allows the trees to build up a healthy bank of cones to release seeds the next time they burn. More frequent, returning fires short-circuit the regeneration process.

Increased burning also strips away more of that thick organic soil layer that favors black spruce, revealing mineral soils underneath that level the playing field for other tree species. The more completely combusted those organic layers are, the more likely spruce are to have competition from jack pine, aspen, or birch. Loss of black spruce resilience was more common in Western North America, which aligns with the fact that drier sites are more likely to lose their black spruce.

burnt boreal forest, photo by Brendan Rogers
“Basically, the drier the system is, the more vulnerable it is to fire,” Dr. Baltzer says. “And these are the parts of the landscape that are also more likely to change in terms of forest composition, or shift to a non-forested state after fire. If climate change is pushing these systems to an ever drier state, these tipping points are more likely to be reached.”

For Dr. Rogers, it also highlights the real possibility of losing black spruce across much of boreal North America as the region warms.

“This is evidence that black spruce is losing its dominant grip on boreal North America,” Rogers says. “It’s happening now and it’s probably going to get worse.”

Losing Black Spruce Could Accelerate Permafrost Thaw

Landscape-wide ecological shifts from black spruce to other species will have complicated, rippling impacts on the region.

Of most concern is the impact on permafrost. In many parts of the boreal, those mossy soil layers that promote black spruce also insulate permafrost, which stores large amounts of ancient carbon. Replacing the dark, shaded understory of a black spruce forest with a more open deciduous habitat that lacks mossy insulation could accelerate thaw. Thawing permafrost and associated emissions would accelerate a warming feedback loop that could push black spruce to its tipping point.

Widespread loss of black spruce also has implications for biodiversity, particularly caribou species that overwinter in the forest and feed on lichen. Both barren-ground and boreal caribou, important cultural species for northern communities, are already in decline across the continent and would suffer more losses if the ecosystem shifts away from the black spruce-lichen forests that provide food and refuge.

Dr. Johnstone did point out some potential for black spruce to recover, even if initial regeneration post-fire is dominated by other species. Slower growing, but longer lived, conifers can often grow in the shade of pioneer deciduous species and take over when they begin to die off—but this requires longer intervals between fires for the spruce to reach maturity. There is also the possibility that more deciduous trees, which are naturally less flammable than conifers, could help plateau increasing fires on the landscape.

But both these hopes, Dr. Baltzer says, are dependent on getting warming into check, because deciduous or conifer, “if it’s hot enough, and the fuel is dry enough, it will burn.”