Global Map Reveals Where Forest Pests Threaten Timber, Carbon and Biodiversity

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The scale of the new analysis is what sets it apart from earlier attempts to map forest-pest danger. By assembling more than seven million occurrence records covering 1,875 pest species, the researchers were able to move beyond the single-pathogen or single-insect case studies that have historically dominated the literature, such as well-known invaders like the emerald ash borer or the mountain pine beetle. A dataset of this breadth makes it possible to ask a genuinely global question: where do the largest numbers of pest species coincide with the forests that matter most for timber supply, carbon storage, and tree diversity? The answer, according to the study, is that pest richness is heavily concentrated in two broad regions, northwestern Europe and eastern North America, and that this concentration is dominated by insects rather than by fungal or bacterial pathogens.

The dominance of insects in these epicenters is worth pausing on. Insect herbivores differ from many pathogens in how they disperse, how quickly they can adapt to new hosts, and how strongly their populations respond to climate. Many forest insects are capable of long-distance flight or hitchhiking in timber, packaging materials, and live plant trade, which helps explain why temperate trade hubs with dense shipping networks accumulate so many established species. Warmer winters in temperate zones have also progressively removed a historical barrier: cold temperatures that once killed off overwintering larvae or eggs. As minimum temperatures rise, species that were previously limited by frost can survive and complete their life cycles further poleward, a mechanism that is consistent with the study’s finding that regions with stable temperatures and adequate precipitation support elevated pest richness.

The study’s central risk accounting distinguishes between forests that sit inside the native range of a given pest and forests that lie outside it. This distinction matters because the ecological consequences of pest attack are usually far more severe when a pest encounters host trees that share no evolutionary history with it. Native pests and hosts have typically co-evolved some degree of tolerance or resistance, whereas novel host-pest pairings can produce explosive mortality. The classic example is Dutch elm disease, a fungal pathogen vectored by bark beetles, which devastated elms across Europe and North America after being moved outside the region where tree and pathogen had coexisted. By quantifying both within-range and out-of-range exposure, the new work captures this asymmetry: potential risk zones where timber production, carbon-rich forests, or diverse tree communities overlap with high pest richness cover about 3.5 percent of global forest area when hosts are within a pest’s native range, and about 1.6 percent when they are outside it.

Those percentages may sound modest, but they translate into enormous absolute areas given that forests cover roughly four billion hectares of the planet. Even the smaller out-of-range figure corresponds to tens of millions of hectares of forest that harbor high-value ecosystem services while facing pest communities with which they have never contended. Moreover, the exposure metric is a potential-risk measure, not a prediction of inevitable damage. Actual outcomes depend on pest establishment success, host susceptibility, management responses, and chance events, all of which can amplify or dampen the underlying exposure. What the metric does provide is a prioritization tool: it identifies where surveillance budgets, quarantine inspections, and breeding programs for resistant planting stock would deliver the greatest expected benefit per unit of investment.

The linkage the authors draw between timber imports and pest richness deserves particular attention from a policy standpoint. Global trade in logs, lumber, pulpwood, and wood packaging has long been recognized as the dominant pathway for forest pest introductions, a conclusion formalized in international phytosanitary standards such as the International Plant Protection Convention’s measures on wood packaging material. The new analysis adds a macroecological dimension to this understanding by showing that forests embedded in regions with high timber import volumes are precisely the forests that support high pest richness alongside high ecosystem-service value. In other words, the same connectivity that makes an economy efficient at sourcing wood also makes its forests efficient at accumulating pests. This creates an inherent tension for wood-security policy: restricting trade outright is neither feasible nor necessarily desirable, but the study’s spatial blueprint suggests that import-driven risk is spatially predictable and can therefore be targeted.

Fragmentation emerges from the analysis as a second, more controllable driver of vulnerability. The finding that forest fragmentation amplifies pest impacts aligns with a substantial body of ecological theory and evidence. Fragmented forests have proportionally more edge habitat, where microclimates are warmer, drier, and more variable than in forest interiors, conditions that often favor herbivorous insects. Edges also concentrate some pest natural enemies less effectively and can disrupt the population dynamics of the birds and parasitoid wasps that suppress outbreak insects. Fragmentation additionally impedes the dispersal of the predators and parasitoids that would otherwise track pest populations, while simultaneously making it easier for human-assisted pest movement to reach isolated forest patches via nearby roads and settlements. From a management perspective, this is arguably the most actionable result in the paper, because connectivity and patch size are directly influenced by land-use planning, whereas climate and trade volumes are not.

The carbon dimension of the study connects forest health to climate policy in a way that is increasingly hard to ignore. Forests currently remove a substantial fraction of anthropogenic carbon dioxide emissions from the atmosphere each year, and standing forest biomass represents one of the largest terrestrial carbon pools. When pest outbreaks kill trees, that stored carbon can be released through decomposition or, worse, through salvage logging and burning, while the affected area temporarily shifts from a carbon sink to a carbon source. Large-scale episodes illustrate the magnitude: bark beetle outbreaks in North American and European conifer forests have converted millions of hectares from net sinks to net sources for periods of years to decades. The study’s identification of carbon-rich forests within high-pest-richness zones therefore quantifies a financial as well as an ecological exposure, since carbon credits, national greenhouse-gas inventories, and offset schemes all implicitly assume that forest carbon will remain standing.

Biodiversity exposure adds a third layer of concern. The finding that diverse tree communities can coincide with high pest richness cuts against a widely held expectation that diversity buffers against damage. That expectation, often summarized as the diversity-disease hypothesis, holds that mixed forests dilute the impact of host-specific pests because specialized herbivores and pathogens encounter susceptible individuals less frequently. The new results do not necessarily contradict that mechanism at the stand scale; rather, they show that at the global scale, the same climatic and trade conditions that support many tree species also support many pest species. Regions that are favorable for plant growth are favorable for the insects and pathogens that feed on plants, so high-diversity forests can simultaneously enjoy the dilution effect locally and face high pest pressure regionally. Reconciling these two patterns is an important task for follow-up research, and it suggests that diversity-based planting strategies should be designed with the regional pest pool in mind rather than assumed to be protective by default.

Methodologically, the study reflects a broader shift in macroecology toward synthesizing massive occurrence databases, such as digitized museum records and citizen-science observations, into risk frameworks. This approach brings real power but also real caveats. Occurrence records are spatially biased toward wealthy regions with active sampling, toward roads and research institutions, and toward species that are conspicuous or economically important. The authors’ finding that northwestern Europe and eastern North America emerge as epicenters may partly reflect this sampling intensity, although both regions also genuinely host enormous non-native pest loads accumulated over two centuries of intensive trade. Readers should therefore interpret the mapped epicenters as a combination of true biological pattern and observation effort, and treat under-sampled tropical regions with appropriate caution, since the tropics host the majority of tree species and may harbor substantial undocumented pest diversity.

For forest managers and policymakers, several practical implications follow from the work. First, surveillance should be spatially targeted: the 3.5 percent and 1.6 percent risk zones provide a defensible starting point for allocating inspection capacity at ports, detection surveys in vulnerable forests, and pre-emptive breeding of resistant stock. Second, biosecurity investment at the point of entry remains the most cost-effective intervention, because preventing a pest establishment is orders of magnitude cheaper than managing an outbreak, as the cumulative costs of invasive forest insects, estimated in the hundreds of billions of dollars globally over recent decades, attest. Third, the fragmentation result argues for maintaining and restoring interior forest conditions, consolidating reserves, and reducing edge density in managed landscapes, measures that build general resilience regardless of which specific pest arrives next. Fourth, the climate signal implies that adaptation planning should anticipate expanding pest ranges rather than assume historical boundaries, meaning that planting choices made today for timber or restoration should consider the pest communities trees are likely to face over their lifetimes.

The study also highlights a gap in how forest ecosystem services are typically valued. Timber yield models, carbon accounting frameworks, and biodiversity assessments are usually conducted in isolation from one another, yet the new analysis shows that all three are exposed to the same underlying threat gradient. Integrating pest exposure into each of these accounting systems would give governments and companies a more honest picture of the risks embedded in supply chains, offset portfolios, and conservation commitments. Certification schemes for sustainable forestry, for example, could incorporate pest-risk zoning, and national forest inventories could track pest-related mortality as a standard variable rather than an afterthought following major outbreaks.

Finally, the work underscores that forest health is a genuinely global commons problem. A pest introduced through one country’s ports can devastate forests across a continent, as history with chestnut blight, Dutch elm disease, and emerald ash borer demonstrates, yet biosecurity budgets remain nationally fragmented and often small relative to the value at stake. The spatial blueprint offered by this analysis gives the international community a common map on which to coordinate: shared risk zones, shared trade pathways, and shared climate drivers all point toward the value of collective action, from harmonized wood-treatment standards to joint early-warning networks. As global trade continues to move living material faster and farther than ever, and as warming continues to relax the climatic constraints on pest survival, the window for cost-effective prevention narrows. The study’s message is ultimately one of timing: the exposure is mapped, the drivers are identified, and the remaining question is whether management and policy will act on that knowledge before the risk zones convert into realized losses.

Subject of Research: …

Article Title: Potential exposure risk of global timber production, carbon stocking, and biodiversity to forest pests

Article References: Potential exposure risk of global timber production, carbon stocking, and biodiversity to forest pests. (n.d.). https://doi.org/10.1038/s41467-026-78728-x

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78728-x

Keywords: forest pests, biodiversity, timber production, carbon storage, Nature Communications, forest health, invasive species, Potential, exposure, risk, global, timber