Rising temperatures are causing Earth’s coldest forests to shift northward, raising our concerns about biodiversity loss, an increased risk of wildfires and the mounting impacts of climate change on the people who live in the region.
But it’s not only the planet’s forests that are marching northward. Researchers, using 50 years of data on bird distributions, have recently concluded that whole ecosystems (biological communities of interacting organisms and their physical environments) have shifted north by hundreds of miles.
When these forests, ecosystems, and their animals and plants move to new places, will they be welcomed by those already there?
Forests are shifting
The boreal forest is a belt of cold-tolerant conifer trees that stretches nearly 9,000 miles across Eurasia and northern North America. It accounts for almost a quarter of the Earth’s forested area and is the coldest—though mostly rapidly warming—forest biome.
And now, it’s shifting north.
According to research published in the journal Global Change Biology in February 2022, there is emerging evidence that climate change is causing boreal shrubs and trees to expand into Arctic and alpine tundras, while at the same time causing them to become more stressed and to die along the warm, southern margins of the boreal forest. These dynamics will lead to a gradual northward shift in the geographic extent of the boreal forest biome, but how much this has already happened was not yet known.
For the Global Change Biology study, researchers, funded by NASA’s Arctic–Boreal Vulnerability Experiment (ABoVE), used 40 years of moderately fine-resolution satellite observations and various geospatial, climate-related datasets of the boreal forest and determined where and why vegetation greened and browned during recent decades. “Greening” indicated higher rates of vegetation growth, which can happen when climate warming promotes growth of trees and shrubs, as was observed near the Arctic and alpine tree lines. “Browning” marked lower rates of vegetation growth and vegetation death, such as what occurs under drier and hotter conditions.
What they found wasn’t exactly a surprise. Vegetation became greener across much of the cold, northern margins of the boreal forest; warmer conditions led to increased vegetation growth and enabled shrubs and trees to expand into Arctic and alpine tundras. Conversely, vegetation became browner along parts of the warm, southern margins of this biome because of the drier, hotter conditions increasing tree stress and death. Intriguingly, vegetation was more likely to become greener in areas that had a high level of soil nitrogen, indicating that soil nutrient availability is an important constraint on the response of boreal vegetation to climate change.
So, forests are getting more productive in the cooler northern and higher-elevation areas, and they’re getting less productive due to drying and hot air masses in the warmer and more southerly areas. It’s expected that this will continue and probably intensify in the years to come.
These changes in vegetation could affect both plant and animal biodiversity, especially species such as caribou and moose, which have specific foraging preferences (deciduous shrubs and trees). These wildlife species are critical sources of food for subsistence communities in the boreal–tundra ecotone. Changes in vegetation along both the northern and southern margins of the boreal forest will also impact wildfire regimes, likely increasing the risk of more fires and more severe ones. Too, changes in vegetation disturb the stability of carbon-rich permafrost soils and the absorption of solar energy by the land surface in ways that could accelerate climate warming. Moreover, increasing tree mortality could have widespread implications for forest products.
U.S. ecosystems are moving
These future effects are not just limited to the geographical area around the boreal forest.
In fact, whole ecosystems are shifting dramatically northward in the Great Plains, according to new, University of Nebraska–Lincoln research that analyzed nearly 50 years’ worth of data on bird distributions.
The Nebraska U scientists analyzed 46 years’ worth of avian data collected for the North American Breeding Bird Survey, a U.S. Geological Survey program designed to track bird populations. That survey included more than 400 bird species found within a 250-mile-wide transect stretching from Texas to North Dakota.
The team then separated bird species into groups based on their body masses and searched for gaps in the distribution of the groups. There were a lot of animals that fell within the small-body-size category; then, a gap with nothing in the middle-body-size group; then, another group and another gap. Those gaps act like the DNA signature of an ecosystem, allowing the scientists to identify where one ecosystem ends and another begins. The researchers identified three distinct ecosystem boundaries, with a fourth—and thus a fourth ecosystem—appearing in the final decade.
By analyzing the geographic movements of the distinct body-mass signatures over the 46-year period, the researchers managed to measure how much and how fast each ecosystem had shifted north. The northernmost ecosystem boundary moved more than 365 miles north, with the southernmost boundary moving about 160 miles from the 1970 baseline. Because the northernmost boundary shifted more than its southernmost counterpart, it reflects a well-documented phenomenon known as “Arctic amplification,” suggesting that climate change is at play. The movement also aligns with other global-change drivers, including agricultural land conversion; energy development; the invasion of woody plants, such as eastern red cedar trees; urbanization and wildfire trends.
This study, published in the journal Nature Climate Change, quantified this spatial component of change for the first time. Ecologists have long thought that ecosystems respond to external pressures—such as climate change and invasive species—in idiosyncratic, largely unpredictable ways. This study suggests that ecological responses are much more ordered and predictable than previously thought. That’s good news, because it could lead to the development of an “early-warning system” (the siren song for extreme weather events, such as tornadoes) that would give land managers decades to prepare for an ecosystem shift or collapse, allowing them to accommodate or foster the change rather than simply reacting to it after it happens.
For example, grasslands are the most endangered ecosystem in the world, partially due to woody-plant encroachment. If a grassland is coming to the edge of its resilience and about to collapse, conservationists and managers can act preemptively and work to control that intrusion by increasing burning and tree removal and decreasing planting.
Early warning is an emerging goal in ecology. Not only does it save money and time, but it may lessen the need to worry about specific endangered species because we will be protecting the systems that they require.
The U.K. is inviting
As species worldwide are traveling along with their ecosystems—leaving areas that are becoming too warm and moving into areas that were previously too cold—they are encountering new neighbors. Luckily, some are welcoming them.
Wildlife-watchers in the United Kingdom are a case in point.
Recently, researchers at the University of Exeter in England asked volunteers who contribute to wildlife recording projects about their attitudes regarding various bird and insect species that have newly arrived in the UK under their own steam (not species introduced by people). The examples included birds, such as the little bittern and Eurasian spoonbill; and insects, such as the small red-eyed damselfly and the mottled shield bug.
According to findings published in the journal People and Nature, the wildlife recorders viewed range-shifters more as vulnerable “ecological refugees” than as threatening “climate opportunists.” They mostly welcomed the new arrivals, although this welcome was cooler in the case of insects and species that the survey participants weren’t familiar with. And, while the respondents were strongly opposed to controlling or eradicating new range-shifters, they also did not want to see conservationists trying to boost their numbers. They were less positive to newly arrived species if they harmed native animals.
Scientific evidence was a key factor in the respondents’ answers, but many also spoke of the “wow factor” that some of these species had for them. The researchers hope that this could be an opportunity to engage more people in the excitement of biodiversity conservation.
We are soul-searching
It’s now a well-established fact that greenhouse gas emissions from human activities are causing Earth’s climate to warm, which in turn is leading biomes, such as the boreal forest, to shift northward. Other ecosystems across the planet are being impacted, as well.
It’s also clear that to minimize the adverse impacts of climate change, efforts are needed to dramatically reduce greenhouse gas emissions, especially related to deforestation and fossil-fuel consumption. Furthermore, Northern communities need to plan for potential changes in vegetation that could decrease the availability of resources—such as timber and wildlife—and increase wildfire risk.
Large-scale ecosystem transitions should not be underestimated. Restoring what has been lost has proven to be extraordinarily difficult when the challenge spans large geographic regions. It’s far better to know ahead of time what’s coming and try to mitigate the worst possible scenarios.
That leads to the increasingly urgent, complex questions of how and when to manage new arrivals. Public opinion—especially among volunteers engaged in conservation—will play an important role in how we treat species arriving in our own homelands.
But I think it’s time that we all start asking ourselves: will we be welcoming or not?
Here’s to finding your true places and natural habitats,