Published today in Nature Ecology & Evolution, the study projects that if global greenhouse gas emissions continue on their current trajectory, rising temperatures and shifting rainfall patterns could amplify tree pest and disease pressure across more than 80 percent of North American forests by mid-century. The implications stretch far beyond the timber industry: these forests serve as some of the planet’s most important carbon sinks, filter the air billions of people breathe, and anchor entire regional economies. Their transformation, the researchers warn, is not a distant possibility but a process already underway.

“The forests that exist today aren’t going to be ones existing in 2040,” said Dr. Jonathan Davies, professor in the departments of forest and conservation sciences and botany at the University of British Columbia and senior author of the study. “The process is happening already. I think we’ve got to put everything on the table because the status quo is no longer tenable.”

To arrive at these projections, the research team assembled an extraordinarily rich dataset: observations from more than one million individual trees across the United States and parts of Canada, combined with both current and historical climate records. By analyzing where tree damage from insects and pathogens has occurred and how those occurrences correlate with climatic variables, the team built statistical models capable of forecasting where future risks are most likely to emerge under continued warming. The result is a set of continent-scale risk maps that reveal, in unprecedented detail, which forests face the greatest threats and from which agents.

The findings paint a picture that is anything but uniform. Climate change, Dr. Davies explains, is creating a complex mosaic of winners and losers rather than affecting every forest in the same way. Perhaps counterintuitively, the forests most likely to suffer are those that have historically been coolest. As temperatures rise, previously cold-limited insect populations and pathogens are expanding their ranges into ecosystems that never evolved defenses against them. In some historically warmer regions, the effects may be smaller—or even reversed—as conditions become less favorable for certain pests and pathogens already at the thermal limits of their tolerance.

Among the species facing the steepest projected increases in pressure are northern and mountain-dwelling trees: gray willow, Rocky Mountain fir, and—perhaps most iconically—black spruce, the slow-growing conifer that dominates vast stretches of the boreal forest and stores enormous quantities of carbon in its soils. The prospect of losing these trees carries global significance. Boreal forests are among the largest terrestrial carbon reservoirs on Earth, and their degradation would not merely eliminate a carbon sink; it could actively convert these ecosystems into carbon sources, creating a feedback loop that accelerates the very warming driving the problem.

The insects themselves tell a compelling story about what warming makes possible. More than 60 percent of the areas examined are projected to experience 30 percent more insect pressure by mid-century, with insects posing the more immediate threat compared with pathogens. Among the most notorious beneficiaries of a warming climate is the spongy moth, an invasive defoliator already wreaking havoc in Canadian forests, which is projected to expand significantly across eastern North America. Another is the hemlock woolly adelgid, a tiny sap-sucking insect that has already devastated hemlock forests throughout parts of eastern North America, killing mature trees and transforming the composition of entire forest stands. As winters warm, cold snaps that once killed off overwintering pests fail to arrive, and insect generations that once required two years to complete their life cycles now manage it in one, allowing populations to explode.

For Canada specifically, the projections reveal a fascinating east-west divide. In western British Columbia, the models indicate elevated insect pressure but potentially fewer pathogens, while the pattern reverses in parts of eastern British Columbia—a reflection of the profound differences in climate and forest composition between the two regions. Species of particular ecological concern include limber pine and whitebark pine, keystone trees of the province’s mountain ecosystems that may be especially vulnerable to the combined effects of a changing climate and shifting pest pressure. These five-needle pines already face existential threats from white pine blister rust and mountain pine beetle; the addition of climate-driven stress could push them past a threshold from which recovery becomes nearly impossible.

Yet the study’s authors are careful to acknowledge the limits of their models. Because the underlying damage data is drawn primarily from the United States, projections become less certain further north, where forest conditions diverge from those represented in the training data. “With more local forest health monitoring data, it might be possible for future work to refine these projections for B.C. forests,” said Dr. Zihui Wang, a postdoctoral researcher in UBC’s department of botany and lead author of the study. This data gap represents a genuine vulnerability for a country whose forests cover nearly nine million square kilometers—more than a third of its landmass—and whose forest products sector supports hundreds of communities.

Not every forecast is grim. In a twist that underscores the complexity of ecological responses to climate change, some tree species may actually benefit. Tulip trees and American sycamores in the southeastern United States could see reduced pest and disease pressure as warming conditions become less favorable for the agents that currently attack them. These relative “winners” may expand their dominance in forests that are simultaneously losing other species, reshaping the structure and function of eastern woodlands in ways that are difficult to fully anticipate. But even for these apparent beneficiaries, the long-term picture remains uncertain, as ecological communities reorganize under conditions without historical precedent.

What distinguishes this study from previous work on forest pests is its predictive utility. Rather than documenting damage after the fact, the risk maps produced by Wang, Davies, and colleagues give forest managers a genuine window into the future—and, critically, time to act. “Our maps can help forest managers to identify where additional monitoring and prevention efforts should be focussed,” said Dr. Wang. “We can also project which tree species may be particularly vulnerable and which pests and pathogens could pose the biggest threat, giving us a window into the future and hopefully, a headstart on protecting our future forests.”

The practical interventions that follow from such foresight are diverse. Governments and forest managers can prioritize planting hardier tree species in vulnerable regions. They can create physical barriers to pest or pathogen spread by strategically removing specific trees or entire forest sections, disrupting the continuity that allows outbreaks to sweep unimpeded across the landscape. And they can maintain and enhance tree diversity—a form of ecological insurance, since forests composed of many species are far less likely to be completely destroyed by any single pest or pathogen than monoculture stands. Assisted migration, in which foresters deliberately plant species better suited to future conditions, represents a more controversial option that some researchers argue deserves serious consideration.

Underlying all of these strategies, however, is a more fundamental point that Dr. Davies is eager to emphasize: the findings are a reminder that climate change is not merely a story about weather. Its effects cascade through biological systems in ways that reshape entire ecosystems, and pest dynamics are one of the most potent and least visible vectors of that transformation. “Forests are a fundamental part of our lives, but climate change is reshaping these ecosystems,” he said. “This research is another early warning sign of how we’re altering the climate system and the impact it’s going to have.”

The research was partly funded by the Natural Sciences and Engineering Research Council of Canada. As emissions trajectories continue to point toward a warmer world, the study’s message is unambiguous: the forests that define North America’s landscapes, economies, and carbon balance are being rewritten in real time. Whether the continent’s forests of 2050 resemble those of today depends, in large measure, on decisions made in the next few years—about emissions, about monitoring, and about how boldly forest management adapts to a future that is no longer hypothetical.

Professor Jens-Arne Subke and colleagues, in collaboration with Dr. Thomas Parker of the James Hutton Institute, published a critical commentary in the journal Global Change Biology, dissecting evidence from a recent European study that assessed carbon stocks in beech forests across Central Europe. Their analysis elucidates that ignoring deep soil carbon measurements artificially inflates the perceived carbon sequestration benefits of forests. The commentary underscores a ubiquitous challenge in forest carbon accounting: below-ground carbon pools, especially those deeper within mineral soils, may exhibit significant carbon losses even as trees mature and accumulate biomass above ground.

This discovery is not isolated to deciduous beech ecosystems but echoes previous work by Subke’s team on non-native pine plantations in Scotland. Soil sampling from 16 sites where pines had been planted decades ago on land formerly under long-term grassland revealed a startling trend: soil carbon content diminished progressively with forest age. Critically, the carbon lost from forest soils accounted for roughly a third of the atmospheric carbon captured by tree biomass. This net carbon loss occurs despite forest growth, suggesting a decoupling between above-ground gains and below-ground carbon depletion, which complicates the narrative that tree planting unequivocally results in a net negative carbon balance in the atmosphere.

The implications of these findings extend to global afforestation campaigns, many of which incentivize landowners and policymakers to prioritize tree planting as a climate mitigation strategy. While trees undeniably provide myriad ecosystem services beyond carbon storage—such as biodiversity support, water regulation, and soil protection—the assumption that forest soils invariably act as enduring carbon reservoirs must be revisited. Subke’s research indicates that soil carbon stability diminishes beneath forests compared to prior grasslands, where carbon is more securely stored. This instability implies that soil organic matter may decompose and emit greenhouse gases over time, offsetting carbon sequestration achieved via photosynthesis.

Central to this emerging understanding is the concept of “carbon capital”—the aggregate amount of carbon stored in soils and ecosystems over extended periods. Although forests accumulate substantial carbon in living biomass, this does not guarantee a net positive carbon outcome if soils concurrently lose more carbon than is being sequestered above ground. The dynamic equilibrium between microbial decomposition, root turnover, soil chemistry, and environmental conditions determines whether soil carbon pools are replenished, stabilized, or lost. Factors such as soil texture, mineralogy, moisture regimes, and previous land use history critically influence these processes, yet remain insufficiently integrated into existing carbon accounting frameworks.

In their comprehensive soil assessments, the researchers employed advanced molecular and chemical analyses to quantify both carbon concentration and its molecular stability. Stability metrics provide insight into how resistant soil organic matter is to microbial breakdown, thereby predicting the longevity of carbon storage. The team’s findings were unequivocal: forest soils harbored carbon compounds more susceptible to degradation, signaling a potential temporal release of stored carbon that could exacerbate atmospheric CO2 concentrations. This refines our understanding of soil carbon beyond quantity towards quality—acknowledging that not all carbon is equally sequestered or permanent.

The geographic scope of this research, spanning Scottish Lowlands and Central European forests, highlights the pervasiveness of these processes across temperate regions. Yet, much remains to be elucidated concerning how these mechanisms operate in other biomes. The diversity of tree species, climatic conditions, and soil types interact in complex ways to mediate carbon dynamics. For example, root exudates from certain species may stimulate microbial activity leading to carbon mineralization, while others may promote humification and carbon stabilization. Therefore, nuanced, site-specific investigations are critical to inform effective land management and policy decisions.

Financial and regulatory incentives, including programs such as the Woodland Carbon Code, currently support forest planting as a climate mitigation measure. The new evidence presented by Subke and colleagues signals the urgent need for these schemes to incorporate potential soil carbon losses into their carbon budget models. Without accounting for below-ground carbon fluxes, carbon credits risk being overstated, undermining climate targets and potentially misguiding investment. Integrating soil carbon dynamics into forest carbon inventories demands refined methodologies, increased soil monitoring efforts, and perhaps reforms in the verification processes used to certify carbon offsets.

The complexity of forest-soil carbon relationships also presents a cautionary tale about the risks of treating forests as a simple panacea for climate change. Dr. Thomas Parker emphasizes that while forests remain indispensable for ecological and societal well-being, their capacity to sequester carbon long-term is neither linear nor guaranteed. Recognition of trade-offs, including possible unintended consequences such as soil carbon depletion, is vital to developing holistic strategies that maximize climate mitigation while preserving ecosystem health.

Experts advocating for continued research stress the importance of dissecting the myriad variables influencing soil carbon storage. Dr. Mike Perks of Forest Research highlights the necessity of understanding soil depth profiles, variations in soil texture, species-specific productivity, and root dynamics. Clarifying the ultimate fate of sequestered carbon—whether it remains in stable pools or returns to the atmosphere—is paramount to refining global carbon budget models. Multidisciplinary collaborations leveraging soil science, ecology, and climate modeling will be essential to unravel these complexities.

In conclusion, the narrative of forests as unequivocal carbon sinks demands revision in light of accumulating evidence demonstrating soil carbon vulnerability following afforestation. This evolving scientific knowledge calls for a paradigm shift in how climate mitigation policies and land use practices incorporate below-ground carbon dynamics. Tree planting remains a valuable tool in the climate response arsenal, but it must be complemented by a deep understanding of ecosystem carbon fluxes to ensure genuine net atmospheric carbon reductions over relevant timescales. Continued investigation will illuminate pathways to optimize forest management, ensuring that the carbon capital we invest in ecosystems indeed translates into enduring climate dividends.

Article Title: Uptake and Release—What Is Driving Change in the Net Carbon Budget in Forest Soils?

News Publication Date: 30-Jan-2026

Web References:

• Global Change Biology Commentary
• Study on Temperate Grassland Conversion

References:

• Commentary by Professor Jens-Arne Subke and Dr. Thomas Parker, Global Change Biology, 2026.

Image Credits: University of Stirling

Keywords: Climate change, Earth sciences, Climate change adaptation, Climate change mitigation, Soil chemistry, Soil carbon