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.”
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.
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.
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:
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.
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.
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.
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.
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.”
A recent paper, published in Science Advances, has found that fires in North American boreal forests have the potential to send 3 percent of the remaining carbon budget up in smoke. The study, led by Dr. Carly Phillips, a fellow with the Union of Concerned Scientists (UCS), in collaboration with the Woodwell Climate Research Center, Tufts University, the University of California in Los Angeles, and Hamilton College, found that burned area in U.S. and Canadian boreal forests is expected to increase as much as 169 and 150 percent respectively—releasing the equivalent annual emissions of 2.6 billion cars unless fires can be managed. The study found proper fire management offers a cost-effective option, sometimes cheaper than existing options, for carbon mitigation.
Boreal forests are incredibly carbon rich. They contain roughly two-thirds of global forest carbon and provide insulation that keeps permafrost soils cool. Burned areas are more susceptible to permafrost thaw which could in turn release even more carbon into the atmosphere. Although fires are a natural part of the boreal ecosystem, climate change is increasing the frequency and intensity of them, which threatens to overwhelm the forest’s natural adaptations.
Despite the value of boreal forests for carbon mitigation, the U.S. and Canada spend limited amounts of funding on fire suppression, usually prioritizing fire management only where people and property are at risk. Alaska accounts for one fifth of all burned area in the U.S. annually, but it receives only 4 percent of federal funding for fire management. Limiting fire size and burned area through proper management can be effective at reducing emissions.
To prevent worsening emissions, fire management practices will have to be adjusted to not only protect people and property, but also to address climate change. Fire suppression in boreal forests is an incredibly cost-effective way to reduce emissions. The study found that the average cost of avoiding one ton of carbon emissions from fire was about $12. In Alaska, that means investing an average of just $696 million per year over the next decade to keep the state’s wildfire emissions at historic levels.
Increasing wildfires also pose an outsized threat to Alaska Native and First Nations communities, who may become increasingly isolated, and may lack the resources to evacuate quickly if wildfire encroaches on their lands. Many Alaska Native people already play a crucial role in existing wildfire crews, and investing in more fire suppression could create additional job opportunities for Indigenous communities.
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.
“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”.
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.
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.
“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.”
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.”