Canada’s eastern boreal forest could become a climate change refuge


 Canada’s eastern boreal forest could become a climate change refuge

16 September 2016

published by https://news.mongabay.com


Canada / Global—   With climate change driving species in the Northern Hemisphere ever further up the latitudinal ladder, a recent study released in the journal Science finds that Canada’s eastern boreal forests may act as crucial ecological reservoirs, islands of cooler habitat for the dominant tree species, black spruce (Picea mariana), and the panoply of plant and animal life that depend on it.

Stretching around the northern third of the planet from Siberia to the Yukon, Finland to Alaska, global boreal ecosystems – also referred to as “taiga” – comprise 1.9 billion hectares – 14 percent of the world’s land and 33 percent of its remaining forests. These hardy evergreen forests still contain “a large fraction of the planet’s remaining unmanaged forests,” according the Science study, “responsible for ~20% of the total carbon sequestrated annually by forest ecosystems.”

Boreal forests are home to iconic wildlife like grey wolves, brown bears, snowshoe hare, moose, and lynx. They also have their fair share of endangered species such as woodland caribou and whooping cranes, found in the boreal regions of North America, and Siberian tigers and Blakiston’s fish owl in Russia.

But while the boreal is vast, human activities are putting parts of it at risk. The forest monitoring platform Global Forest Watch shows intact boreal forest has declined and is particularly patchy in Eurasia. In the Canadian province of Alberta, the thirst for oil has led to the razing of more than a quarter-million hectares of forest as companies seek to exploit the tar sands that lie beneath. Another recent scientific report from Cornell spells out the hazards of industrialization in grim detail, with three billion birds – Canada warblers and evening grosbeaks particularly – at risk of population collapse across North America’s 1.5 billion acres of boreal forest.
The Canadian government is recognizing the economic and ecological cruciality of its boreal habitats by entering into the Canadian Boreal Forest Agreement. Billed by signatory The Nature Conservancy as “the largest agreement of its kind anywhere in the world,” the Agreement seeks to sustainably balance forestry and conservation across 178 million acres—an area twice the size of Germany.

But as promising as reduced or confined logging might be to the long-term health of Canada’s boreal refuge, the real threat, as is increasingly the case globally, is climate change.

Big changes around the bend

“During this century, the north woods will experience some of Earth’s largest increases in temperature,” according Loïc D’Orangeville, a postdoctoral researcher at Université du Québec à Montréal and Indiana University. He led the team of researchers that authored the Science study.

For their work, the team used tree-ring samples studied 26,000 black spruce across an area the size of Spain in southern Quebec. They found that more than two-thirds of their sample areas north of the 49th parallel “should still be showing a positive response” to climate change. In other words, northern spruce forests will actually benefit from a warming world.

Only the boreal forest of northeastern North America is home to the black spruce and its attendant ecosystem. Globally, boreal forests are tough customers, distinguished by an ability to thrive in freezing temperatures six to eight months annually, with about a third of their coverage area underlain by permafrost. This necessitates shallow roots and a short growing season; global warming might bring about earlier and longer growing seasons, allowing for denser growth and the expansion northward of black spruce forests in the study area.

“The typical black spruce boreal forest, studied here, reaches out to the 52nd parallel,” D’Orangeville told Mongabay. “North of that, it is the same black spruce tree that dominates, but because of the colder climate and shorter growing season, mosses are replaced by lichens and trees become more sparse in the landscape. The soils are also younger and less fertile, but a recent study at 54N has reported that the tiny black spruces there are already showing increasing vertical growth. So we think there is plenty of space for black spruce to migrate.”

However, the future may not be entirely rosy for black spruce and other boreal denizens. North of the 49th parallel, the temperature and precipitation threshold that D’Orangeville’s study is the first to pinpoint, amplified snowmelt could lead to a three-week expansion of the black spruce growing season. South of that crucial line, however, “warming and the lengthened growing season are more likely to cause drought stress that could overwhelm black spruce.” In addition, the researchers warn that unpredictable disasters like the huge, uncontrollable wildfires that recently raged in Alberta could be become more common in the future. While boreal forests do burn naturally, climate changed-fueled droughts could make the situation unnaturally worse and add to further habitat loss.

Aside from outright destruction through overharvesting and tar sands oil extraction, other risks lie in wait for the black spruce, making climate change a mixed blessing for the species. According to D’Orangeville, among these are “water desiccation injuries” which occur when a tree’s natural uptake of water to fuel photosynthesis is reduced by declining precipitation over time, diminishing the tree’s capacity to efficiently pump water through its system.

A potential scourge of budworms

Another potential problem, a gray lining to the silver cloud of projected sustainability north of the 49th parallel, comes in the form of insects that can damage spruce forests. The biome of the study area notably provides habitat for the spruce budworm, of which there are around 40 species in the genus Choristoneura. According to Dan Kneeshaw, a forest ecologist also with the Université du Québec à Montréal and a co-author of D’Orangeville’s study, climate change may shift the interaction between spruce budworms and the trees they colonize and consume.

“Every insect forest system will be different,” he told Mongabay. “There will also be interactions between species….the thermal range for a species may shift but if its food resource reacts in a different way then there could be an uncoupling or alternatively a positive feedback.”

The northward migration of black spruce forests due to climate change, in other words, might reduce the parasitism of spruce budworms north of the magic 49th parallel. South of that line, however, trouble awaits.

“That is what we seem to be observing in the spruce budworm system where larval emergence and bud burst (i.e., food resource) seem to be better synchronized with warmer temperatures. This may in fact open up a new food resource for the insect as one potential host was traditionally only lightly affected due to a….mismatch between budburst and larval emergence.” Heightened synchrony through global warming could thus open up the black spruce forest ecosystem below the 49th parallel to greater plundering by the budworm.

If northeastern North America above the study’s critical 49th parallel retains its current and projected levels of snow and rainfall, Kneeshaw says that budworm outbreaks may still happen, but not to the extent of further south. But if climate patterns shift past expectations, these northern forests could be severely threatened.

“The (budworm) outbreaks will still occur but they may not be like what we’re used to in the fir zone. It’ll still be a pain for foresters but not like further south. Damage and mortality would be less,” Kneeshaw told Mongabay. “However, if warming improves synchrony then we’re in trouble since the black spruce zone covers a lot of Canada and the US and since black spruce is a much more desired commodity due to its better quality wood fibers.”

Still, aggressive and damaging as it can be, the spruce budworm is native to North America – thus, trees have developed methods over evolutionary time to counter the extent of their damage.

“The black spruce ecosystem should be fine,” Kneeshaw “Trees and insects have coevolved and so levels of wood production will fluctuate, but from a conservation point of view the refugium will be there” in the more northeastern areas of the continent.

This reassurance may not hold true for the drier areas to the west, however, especially at lower latitudes. “In the west more fires could limit the spread of the spruce budworm,” Kneeshaw said. However, budworms “will still occur since fires—at least in the next century—should not burn everything. Spruce budworm could perhaps even increase fire risk after killing or defoliating trees. Potentially then people will in some transition zones get hammered by losing wood to fires, budworm and drought. This is the doomsday scenario.”

“In sum there will be winners and losers,” Kneeshaw concludes. “The unpredictability of saying exactly where and when is probably what scares people most. There will be people in Alberta who will get hit hard and neighbors 200km away who will live without a problem in their lifetime. Same thing here in Quebec. What we can probably say is that in northeast Quebec there will be greater odds of getting through unscathed—but don’t count your chickens until they’ve hatched.”

Changing fire regimes

Fires are a natural occurrence in much of the boreal region, with multitudes of fires arising in a given season — such as the mammoth conflagration that consumed nearly 1.5 million acres around Fort McMurray, Alberta earlier this year. The fire created a crisis that led to the forced evacuation of 88,000 people and shut down tar sands oil production north of the city. Western and central Canada (save for the rainy west coast) receive considerably less precipitation than does the East due to the fluctuation of the polar jet stream, churning up intensified humidity, rain and snow.

Yet climate change may shift fire patterns in the coming years – even in the chilly eastern area of the Science study. Yves Bergeron is another forest ecologist with the Université du Québec but was not part of the D’Orangeville study. He told Mongabay that a warming planet could potentially cause four times the wildfire outbreaks north of the 49th parallel than today, and that “most boreal fires in North America (unlike Eurasia) are stand-replacing,” that is, lethal to the trees. That said, some form of fire regime is necessary for the black spruce to survive, as the species is at least partially dependent on fires to trigger the opening of their cones and the dispersal of their seeds. However, an overly hot or recurrent fire regime will simply wipe out the trees, cones and all.

Despite the Northeast’s projected high levels of future precipitation, says Bergeron, “the problem arises when the increase in precipitation does not compensate for increase in evaporation due to (rising) temperature. Of course increase in drought might cause increase in fires.”

But despite likely shifts in the face of a warming planet – and the fact that there are a multitude of unknown factors – the study’s findings indicate that North America’s northeastern forests may have a good chance of persevering in a changing world.

“In a world where many ecological forecasts appear dire for plants, animals, and people,” said Neil Pederson, coauthor of the Science study and a senior ecologist at Harvard, “identifying areas that could serve as potential havens for biodiversity during potentially tumultuous times is good news.”


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