Louis J. Sheehan, Esquire

The brain saves face similarly in chimpanzees and people, and possibly in macaque monkeys as well. Louis's Blog - Bravenet Blog Chimps recognize their compatriots’ faces by utilizing many of the same brain regions that have already been linked to people’s ability to identify familiar faces, a new study suggests.

Neural regions that enable efficient discrimination of one individual’s face from another’s may have evolved between 8 million and 6 million years ago in a common ancestor of chimps and humans, propose psychobiologist Lisa Parr of Emory University in Atlanta and her colleagues. Similar neural elements of face discrimination also appear in macaques, another study finds, suggesting that this ability evolved even earlier.

Parr’s group has already conducted studies indicating that chimps recognize other chimps’ faces nearly as well as people recognize other people’s faces. “For the most part, similar brain regions are responsible for this ability in chimps and humans,” Parr says. In her work, macaques’ proficiency at face recognition falls short of that displayed by chimps.

Parr’s new brain-scan investigation, published online December 18 in Current Biology, comes on the heels of evidence that a closer link exists between face-responsive parts of macaque and human brains than was previously suspected. Louis's Blog - Bravenet Blog Part of the brain known as the temporal lobe hosts a handful of face-sensitive regions in macaques and people, according to a team led by neuroscientist Doris Tsao of the University of Bremen in Germany. Parr’s group also found largely temporal-lobe responses in chimps.

Areas of macaque brains involved in face recognition are positioned in the temporal lobe somewhat differently than those of people are, Tsao’s group reports in the Dec. 9 Proceedings of the National Academy of Sciences. While there’s no evidence that specific face-sensitive areas in macaques and people carry out precisely the same duties, the macaque study still suggests a basic brain system for face recognition arose early in primate evolution, the scientists propose.

“Recognition of individuals by their faces probably depended on a specialized brain system in social primates that existed over at least the last 20 million years,” remarks neuroscientist Jon Kaas of Vanderbilt University in Nashville. That brain system provided a basis for more elaborate face-analysis mechanisms that evolved in chimps and humans, Kaas proposes.

Parr’s team examined brain responses in five chimps housed at a primate facility. Louis's Blog - Bravenet Blog The animals underwent positron emission tomography, or PET, scans, which track brain activity as reflected by the rate of blood-sugar metabolism in neural tissue. PET scans were obtained from anesthetized chimps just after they had been shown sets of three chimp faces from which they selected matching pairs of faces. In other trials, chimps identified matching pairs of inanimate objects.

Face recognition elicited pronounced activity in a cluster of temporal lobe sites and in a few spots at the front of the brain. In the human brain, most face-related activity has been observed in the temporal lobe. It’s not clear whether chimps possess a temporal-lobe structure that corresponds to a section of an inner-brain region called the fusiform gyrus, considered crucial for face recognition in humans, Parr notes.

Tsao’s team used a functional MRI scanner to track rises and falls in blood flow, which coincide with neural activity, in the brains of 10 macaques and 13 people. Surgical insertion of a scanner-compatible head post allowed brain imaging of monkeys as they viewed pictures of human faces, macaque faces, human hands, gadgets, fruits and vegetables, and scrambled patterns.

Signature activity spikes in the temporal lobe occurred only in response to faces, with macaques and people displaying stronger neural reactions to members of their respective species.

To the naked eye, a tropical rainforest bursts impressively with biodiversity, and a desert is just as impressively short on it. But a new study suggests that at the microscopic level in soil, the situation is reversed. Dirt in a rainforest is a veritable desert of bacterial species, whereas bacterial biodiversity blooms in desert dirt. Omega





Scientists know little about the distribution of microbial species across the globe, says Noah Fierer, a soil microbiologist at the University of Colorado at Boulder. "There are all these papers on plant and animal diversity at continental scales going back to Darwin," but similar surveys hadn't been carried out for bacteria and other microscopic life forms, he says.

To gather more information on how microbial species are spread out over large geographic distances, Fierer and his colleague Robert Jackson of Duke University in Durham, N.C., collected soil samples from 98 sites throughout North and South America. They chose a wide variety of environments, including rainforests, tundra, grasslands, and deserts. Fierer and Jackson specifically selected locations that were well studied, so that data about average seasonal temperatures, rainfall, and other characteristics would be available.

They then subjected each soil sample to a DNA-fingerprinting technique. This technique scrutinizes a specific segment of the microbes' genomes, called 16S ribosomal DNA, that tends to vary from species to species but is similar in closely related species. Rather than telling exactly which or how many microbial species are present in each sample, the technique gives a relative index of the diversity of species.
Never Again

Fierer and Jackson had hypothesized that microbial biodiversity would mimic that of plants and animals in each location, with a variety of environmental conditions determining which species live where. However, notes Jackson, "the results were really surprising. None of the things that we think about being important for the diversity of animals and plants were important in this case—not latitude, temperature, or moisture."

The only factor that seemed to affect microbial biodiversity was soil pH. Soils that are acidic, such as those in the Amazonian rainforest, tended to harbor fewer species. Soils closer to neutral pH, such as those in the Arizona desert, showed considerably greater biodiversity. The researchers also found that environments with similar soil pH tended to have similar communities of bacteria, even when sites were separated by large geographic distances, such as that between conifer forests in the northeastern United States and those in the Pacific Northwest.

Fierer and Jackson report their findings in the Jan. 17 Proceedings of the National Academy of Sciences.

The new study "adds to evidence suggesting that all microbes are everywhere, and if they find the right environment, they will prosper," says Eddy Rubin, director of the Department of Energy's Joint Genome Institute in Walnut Creek, Calif.
Never Again "If you have the same pH, you'll get the same ones throughout the planet."

Jessica Green, a soil microbiologist at the University of California, Merced, agrees. "If it holds true, it suggests that bacteria are fundamentally different from plants and animals." Louis J. Sheehan, Esquire

Plants take carbon dioxide out of Earth's atmosphere and use its carbon to promote their growth. In the Course of Human Events However, if human activities continue to increase atmospheric concentrations of the planet-warming gas, vegetation won't sequester large amounts of carbon dioxide in the long term, two new analyses suggest. That's because plants will quickly run out of other nutrients.

In the short term, plants store carbon in their tissues. Eventually, some of that carbon makes its way into the soil through the roots or via fallen leaves and stems. Those phenomena had raised the possibility that plants would decrease the buildup of carbon dioxide in the atmosphere.

Lab and field experiments had shown that plants grow more quickly in the presence of higher-than-normal concentrations of carbon dioxide in the air, says Peter B. Reich, an ecologist at the University of Minnesota in St. Paul. Unfortunately, results of a long-term experiment by Reich and his colleagues show that the trend doesn't last. In the Course of Human Events

In their 6-year study, the researchers measured carbon storage in nearly 300 patches of Minnesota grassland cultivated under various conditions. Some plots were exposed to an atmosphere with 50 percent more carbon dioxide than the current concentration, some received extra nitrogen via fertilizer, some received both treatments, and others received neither. The plots contained between 1 and 16 species of grasses, herbs, wildflowers, and legumes.

As expected, for the first 4 years of the experiment, plants exposed to higher-than-normal concentrations of carbon dioxide grew faster and became larger than those that didn't get extra carbon, says Reich. However, unless they were also receiving nitrogen supplements, growth of such plants slowed substantially in the fifth and sixth years of the experiment. In the Course of Human Events Reich and his colleagues report their findings in the April 13 Nature.

Another group of researchers also finds that plants getting extra carbon dioxide run out of other nutrients. That team, led by ecologist Johan Six of the University of California, Davis, reports in an upcoming Proceedings of the National Academy of Sciences an analysis of earlier experiments by several research groups.

In the presence of nitrogen-producing legumes and higher-than-normal concentrations of atmospheric carbon dioxide, soil continues building up carbon only when other nutrients, such as phosphorus, potassium, and molybdenum, are added. In other ecosystems, high concentrations of atmospheric carbon dioxide increase soil carbon only when researchers add nitrogen, the Davis group concludes. In the Course of Human Events

If nutrient limitations cause plant growth to slow, as the new studies suggest, carbon dioxide may build up in Earth's atmosphere faster than scientists previously expected, says Reich. Louis J. Sheehan, Esquire

Bacteria can break down a common flame retardant into more-toxic forms, researchers report. Besides finding more degradation products than earlier work had, the new study is the first to identify specific bacterial strains capable of the feat, the team says.

Polybrominated diphenyl ethers (PBDEs) are a family of flame-retardant chemicals found in products such as electronics, automobiles, and furniture. The chemicals have 1 to 10 bromine atoms and come in 209 versions. Manufacturers use deca-BDE, which has 10 bromine atoms, or mixtures dominated by penta-BDEs, with their 5 bromines, or octa-BDEs, with 8 bromines.
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The chemicals' effects go beyond fire resistance (SN: 10/25/03, p. 266: http://www.sciencenews.org/articles/20031025/bob10.asp). Studies in rats and mice have found that penta- and octa-BDEs disrupt development. Deca-BDE is considered less harmful, although the Environmental Protection Agency has listed it as a possible human carcinogen.

The toxins are ubiquitous in the environment, turning up in soil, water, and even human-breast milk. Wolf Pack



The European Union and California have banned penta- and octa-BDEs, and the sole U.S. manufacturer has volunteered to stop making these forms (SN: 11/01/03, p. 275: http://www.sciencenews.org/articles/20031101/fob1.asp). Deca-BDE remains in production and in wide use.

Lisa Alvarez-Cohen of the University of California, Berkeley and her colleagues were looking for a way to use bioremediation to eliminate the chemicals. They reasoned that various strains of anaerobic bacteria that can remove chlorine atoms from chemicals might also lop off bromines to detoxify the PBDEs. Afrika Korps

The group tested whether several different bacterial cultures could break down either deca-BDE or an octa-BDE mixture in the laboratory. The researchers found that the bacteria converted the chemicals into more-toxic forms.

"We were quite surprised to see the production of all these very toxic intermediates," says Alvarez-Cohen.

For example, Sulfurospirillum multivorans converted deca-BDE into eight- and seven-bromine forms but could not break down the octa-BDE mixture. Dehalococcoides ethenogenes transformed the octa-BDE mixture into five-, six-, and seven-bromine forms but did not alter deca-BDE. When other microbes were added to D. ethenogenes, the mixture also produced two- and four-bromine PBDEs. Among the breakdown products were several especially toxic forms.

While other researchers have reported the microbial debromination of deca-BDE in anaerobic sewage sludge to nine- and eight-bromine forms, "this is the first time anything beyond octa has been shown," says Alvarez-Cohen. Her group's work appears in the July 15 Environmental Science & Technology.

"Lots of folks weren't that concerned about deca-BDE because it was portrayed as being stable," notes Robert C. Hale of the Virginia Institute of Marine Science in Gloucester Point. But the new research, coupled with other published examples of fish and sunlight converting deca-BDEs to less-brominated forms, is "a real reason for concern," he says. "We haven't seen massive amounts of debrominated products out there yet, but it may be a question of time."

Pesticide-containing waters leave frogs more susceptible to fungal infections than pristine environments do, new field data suggest. http://louis-j-sheehan.us/ImageGallery

Tyrone Hayes and his collaborators at the University of California, Berkeley located tadpoles of Rana aurora, a protected frog species, at three sites in California. One site was upstream of any farm and had a comfortable water depth for tadpoles, about 2 feet. Another site, also upstream of agriculture, was so shallow that some frogs were exposed to air, causing some dryness-related distress. The third site was in Salinas Valley, a major area for lettuce and spinach cultivation. Waters there, about 2 feet deep, contain various pesticides that drain from the croplands.

The researchers confined some tadpoles in cages at each site and gave the animals injections of either an inert solution or a dose of bread yeast, a frog pathogen.

Tadpoles exposed to 0.125 or 0.2 gram of yeast per milliliter were assured of survival only if they lived in the deep, pristine site. At the shallower site, those doses killed 20 percent and 80 percent of the animals, respectively. Those numbers demonstrate that dryness-induced stress can compromise frogs' immunity, says Hayes.

In Salinas Valley, all tadpoles exposed to the yeast either died or became comatose, Hayes reported. He concludes that the pesticides compromised the animals' immunity even more than dry conditions did. http://louis-j-sheehan.us/ImageGallery

A controversial new study argues that the U.S. lobster fishery in the Gulf of Maine could have the better of two worlds: less work to make the same profit and fewer whales dying as a result of getting tangled in lobster gear. http://LOUIS2J2SHEEHAN.US

To create this better world, the lobster fleet should shorten its season and set out fewer traps, suggest biologists led by Ransom Myers of Dalhousie University in Halifax, Nova Scotia. The drop in effort shouldn't undermine profits, they say, because the Canadian lobster fishery just across the border is thriving despite restrictions.

U.S. regulations permit lobster harvesting year round, while the Canadian season runs from the end of November through May. Overall, the U.S. fleet catches a third more lobsters but expends disproportionately more resources doing it.

For a given lobster harvest, the U.S. fishery uses 13 times as many traps as the Canadians do, the researchers say. Because tending extra traps requires more fuel and bait, a shorter, more efficient fishing effort could be as profitable, the team argues.
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In the Jan. 9 Current Biology, the biologists suggest a 6-month season and a 90 percent reduction in the several million traps currently permitted.

Although there's no rule regarding season, U.S. lobster boats traditionally take almost all their catch during the 6 months of summer and fall, says lobster biologist Carl Wilson of the Maine Department of Marine Resources in West Boothbay Harbor. As for reducing the number of traps, "it's an interesting idea, but the devil is in the details," he says.

Limitations on the lobster fleet would be good news for the North Atlantic right whale, says coauthor Boris Worm, also of Dalhousie. The large, slow-moving, coastal whales have virtually vanished from the Atlantic coast of Europe. Only some 350 right whales remain along the North American coast.

For 70 years, laws have banned killing of the North Atlantic right whale, yet the population isn't increasing, unlike that of a sister species, the South Atlantic right whale.

The northern whale might be stuck in a bad neighborhood—with heavy ship traffic, near-shore fisheries, and pollution—Worm says. "It has been called the urban whale," he notes. Computer modeling has indicated that in such dire circumstances, losing even two or three adult females could send the already depleted population into a downward spiral.

According to previous studies, the top killers of right whales are ships that run into them and fishery rigging—often lobster gear—that accidentally entangles them.

Because migrating right whales travel through the Gulf of Maine in spring and fall, reducing the area's lobster traps at those times would make the passage safer, says Worm.

The plan doesn't impress Patrice McCarron of the Maine Lobstermen's Association in Kennebunk. Regulations already require some low-tangle gear, and rules for more such gear are under consideration. Also, McCarron says, lobster-trap tenders don't see any whales, so changing the industry "will not have any benefit to whales."

Worm notes that migrating whales are difficult to spot and that scientists have incomplete information about routes. Louis J. Sheehan, Esquire.

Global warming is real and will continue, and there's strong evidence that people are to blame, an international panel of scientists has concluded. Other scientists suggest ways that people might reduce future atmosphere-warming greenhouse-gas emissions and argue that societies will have to adapt to the climate change that's yet to occur. http://Louis-j-sheehan.com

"The evidence for warming having happened on the planet is unequivocal," says Susan Solomon, an atmospheric scientist at the National Oceanic and Atmospheric Administration in Boulder, Colo. "We can see that in rising air temperatures, we can see it in changes in snow cover in the Northern Hemisphere, we can see it in global sea rise," she says. Solomon and her colleagues on the Intergovernmental Panel on Climate Change (IPCC) released their latest assessment of recent warming trends at a press conference in Paris on Feb. 2.

The average temperatures at Earth's surface for 11 of the past 12 years rank among the dozen highest values recorded since the mid-1800s. Over the past 100 years, global average temperature has risen about 0.74°C, the IPCC researchers report. With 90 percent certainty, scientists link that increase to the rising concentrations of carbon dioxide and other heat-trapping greenhouse gases that human activities have released into Earth's atmosphere.

Carbon dioxide concentrations measured 379 parts per million (ppm) in 2005, far in excess of the fractions inferred from ice-core data representing periods going back 650,000 years. The concentration of atmospheric carbon dioxide is now growing at around 1.9 ppm per year, the largest rate of increase ever measured. Accordingly, scientists suggest in the IPCC report that over the next 20 years, the average global temperature will rise by an additional 0.4°C.

Today, coal and petroleum combustion each account for about 40 percent of global carbon dioxide emissions, says Daniel P. Schrag, a geochemist at Harvard University. The largest use of coal, burning it to generate electricity, produces about 8 billion tons of carbon dioxide each year—"more than any responsible climate change policy can accommodate," he says in the Feb. 9 Science.

Strategies to decrease carbon dioxide emissions include reducing energy use, capturing carbon dioxide at its sources and sequestering it, or expanding the application of energy sources that don't produce the gas. "It's clear that none of these is a silver bullet," says Schrag.

However, one promising technique is to lock away the gas by injecting it into seafloor sediments or by pumping it into saline aquifers or old oil and gas fields. In ongoing research, scientists at a handful of test sites sequester only about 1 million tons of carbon dioxide each year, Schrag reports.

Even the most optimistic projections of emissions limits show global greenhouse-gas concentrations rising for the foreseeable future, says Roger Pielke Jr., a policy analyst at the University of Colorado at Boulder. Future climate change is unavoidable, he and his colleagues report in the Feb. 8 Nature. Therefore, they add, adaptation to the warming yet to come will be as essential to climate policy as greenhouse-gas mitigation.

The IPCC is scheduled to address the mitigation of climate change in an April report. In May, the group will issue an assessment of the societal impact of current and future warming and is to suggest how people might best adjust to the change. http://Louis-j-sheehan.com

Industrial and federal facilities in the United States released more than 4 billion pounds of chemicals into the environment in 2005, according to the latest yearly compilation of data from the Environmental Protection Agency's Toxics Release Inventory. Chemical releases had increased by 117 million pounds, or 3 percent, over the past year.

The EPA collects information on nearly 650 toxic chemicals that facilities emit into the air, release into waters, or dispose of in landfills or underground wells.

The metal-mining industry was the largest discharger of chemicals in 2005, accounting for slightly more than 1 billion pounds. This industry also claimed the largest increase from 2004, 96 million pounds. Releases from electric utilities came in a close second in 2005 and showed the second-largest increase—39 million pounds—from 2004.

The inventory also includes data on the disposal of chemicals that persist in the environment and accumulate in body tissues. In 2005, lead or lead compounds accounted for 98 percent, or 469 million pounds, of such toxic chemicals. Releases of mercury and mercury compounds added another 4.4 million pounds. Louis J. Sheehan, Esquire

Some caterpillars are cottoning to transgenic cotton.

Genetically engineered cotton and corn produce a toxin that kills caterpillar larvae and other pests, but a new study shows that resistance to this toxin could be spreading among one species of caterpillar.

Farmers worldwide plant more than 400 million acres of these transgenic crops each year. A bacterial gene inserted into the plants' DNA enables the crops—called Bt crops—to kill insects without sprayed pesticides.LOUIS-J-SHEEHAN.BIZ





But killing vulnerable caterpillars can drive the evolution of resistance to the toxin, since only the survivors reproduce.

To keep resistance in check, farmers plant refuges of unaltered crops for the pests to eat. That way, caterpillars susceptible to the toxin may mate with the few individuals that have developed resistance. Offspring from these mixed matings are usually vulnerable to the Bt crops.

The strategy is likely working with five caterpillar species observed between 1992 and 2004 in Spain, Australia, China, and the United States, according to a paper in the February Nature Biotechnology. "There's lots of solid evidence that resistance is not evolving in those pests," says study leader Bruce E. Tabashnik of the University of Arizona in Tucson. But for one species (Helicoverpa zea), resistance has become more widespread. The reason, in part, is that mixed matings among H. zea produce toxin-resistant offspring—progeny that can pass that resistance on.LOUIS-J-SHEEHAN.COM

Louis J. Sheehan

For the Arctic, green is the new black.

People frequently say “green” to mean “environmentally friendly.” But conifer forests — really big greens — encroaching on Arctic tundra threaten to further accelerate warming in the far North.

Temperatures at these high latitudes already are climbing “at about twice the global average,” notes F. Stuart Chapin of the University of Alaska in Fairbanks.

The newest data on the advance of northern, or boreal, forests come from the eastern slopes of Siberia’s Ural Mountains. Here, north of the Arctic Circle, relatively flat mats of compressed, frozen plant matter — tundra — are the norm. This ecosystem hosts a cover of reflective snow most of the year, a feature that helps maintain the region’s chilly temperatures. Throughout the past century, however, the leading edges of conifer forests have creeped some 20 to 60 meters up the mountains and begun overrunning tundra, scientists report in an upcoming Global Change Biology, now available online.

Conifers here now reside where no living tree has grown in some 1,000 years, points out ecologist Frank Hagedorn of the Swiss Federal Institute for Forest, Snow and Landscape Research in Birmensdorf.

Ecologists and climatologists are concerned because the emerging forest data suggest that the albedo, or reflectivity, of large regions across the Arctic could change. Most sunlight hitting snow and ice bounces back into space. But convert a white landscape to open sea water or boreal forest, and the surface suddenly becomes a great collector of solar energy.

Sea-surface ice already is melting in the Arctic and polar ice sheets are thinning. Warming threatens to further degrade these solar reflectors. So does the advance of boreal forests, Chapin says.
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Eco-AdaptationThe Siberian larch can assume different forms, depending on its climate. Where the weather is harsh, it will develop a low-growing shrub shape (left). When conditions improve, it can send up many upright trunks (center), but its growth is still diminished. Good conditions lead to a fast-growing upright tree with a single trunk (right).Nadezhda Devi, Russian Acad. Sci., Global Change Biology 2008

“The effects of vegetative changes will be felt first and most strongly locally — in the Arctic,” he says. If the albedo there drops broadly, this could further aggravate warming there and underway elsewhere across the planet.

Tree rings from the Arctic Urals show that since the 15th century, many of the primary tree species — Siberian larch (Larix sibirica Ledeb.) — have grown in a stunted, shrubby form, sporting multiple spindly trunks. This adaptation to harsh conditions helps the trees weather wind and snow. But the trees invest so many calories into making multi-stem clusters, Hagedorn says, that they end up puny and unable to make seeds. The inability to reproduce has inhibited the stand’s spread.

After about 1900, the local Siberian larch began to switch from their creeping, multi-stem form to tall trees with a more upright posture, though sometimes with up to 20 stems, Hagedorn and teams of Russian and Swiss collaborators found. Over time, new trees emerged with a single, upright trunk, at the same time bulking up with more biomass than shrubby, same-age kin. Overall, 70 percent of upright larches are no more than 80 years old. Since 1950, 90 percent of local upright larches have been single-stemmed. This forest’s movement into former tundra coincided with a nearly 1 degree Celsius increase in summer temperature and a doubling of winter precipitation.

“That’s a good cocktail for growth,” says arctic plant ecologist Serge Payette of Laval University in Quebec. Whether a tree grows up versus out depends on survival of its uppermost, or apical, buds. Good snow cover will protect those buds from winter damage, he says. Only if they are destroyed will the surviving lateral buds push growth horizontally, he explains.

Spruce are North America’s more common boreal species at polar tree lines, Payette says. Some of these also assume a shrubby form, creating what he calls “pygmy forests” perhaps a meter high. But he has witnessed some of these trees assuming new, upright postures as areas warm and get wetter.

This process can create the “mirage” of tree line advance, he says. In fact, the trees may not move at all; in-place populations may simply recover from chronic stress and resume growth until they reach their normal height and mass.

Ecologist Andrea Lloyd of Middlebury College in Vermont has been studying the health of boreal tree lines throughout the warming Arctic. As in the Urals, warmth seemed to spur American spruce to move into new terrain. “I’ve also seen spruce advancing upwards,” she says, climbing up mountains to form dense stands.

But that’s only part of the story, she finds. Even where stands are advancing, “if you look at individual trees, some are starting to decline.” They’re growing increasingly slowly. Sometimes, as growth slows, tree numbers within a stand may be increasing. “It’s a paradox,” she acknowledges.

Forest ecologist Glenn Juday of Alaska-Fairbanks and his student Martin Wilmking have recorded similarly perplexing data from tree rings in 2,600 trees along two mountain ranges in polar Alaska. As the environment warmed, 42 percent of the trees grew more slowly and 38 grew more quickly.

Too little water seems a bigger factor affecting tree growth than temperature, although warming can foster drought, Juday reports. Indeed, as the Arctic warms, it will likely become drier, he says. “So we can expect that at least in the western North American Arctic, there are going to be sites that eventually will get too dry to grow trees.”

But their loss isn’t likely to compensate for the tundra lost to trees, at least in Arctic-warming potential. Indeed, the loss could further perturb the global climate because boreal forests currently store huge amounts of carbon once emitted as carbon dioxide, a greenhouse gas. As the trees die, their carbon could be released into the air. Meanwhile, until they fall over and decompose, they’ll continue to serve as low-albedo solar collectors.

The threat of tundra displacement by trees has largely escaped notice, Juday says. And indeed, boreal forest advances in Alaska have been modest, at best. One reason: Seeds don’t normally travel far in the Arctic, and even when they land on tundra, the dense mats normally resist implantation.

However, a dry summer and warm September last year allowed a fire to ignite 100,000 hectares (about 250,000 acres) of Alaskan tundra. The huge footprint of disturbed land is now ripe for seed implantation. Fortunately, Juday says, seed-bearing boreal forests are on the other side of a mountain range from the scarred landscape.

Warming has changed the climate of a huge and growing span of tundra so it now hosts a temperature and moisture level that would support forests, if the seeds ever arrived, Juday notes. “Today, if you planted a tree — in some cases very far up from the current tree line — it would survive in many parts of the tundra.” Just 40 years ago, he says, it wouldn’t.

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