Forests are under attack from invasive species

Over a hundred years ago, a tiny worm called the pinewood nematode landed in Japan, hitching a ride on wood products imported from North America. In the United States, native pines are relatively unaffected by the worm. But in Japan, it spread from tree to tree on native beetles, and the forests began wilting and dying.

In the 1980s, the worm spread again, to China and the Korean Peninsula, and in later decades to Portugal and more recently to Spain. Today, countries in Europe are preparing for an onslaught.

The nematode’s damage has been massive. To kill the pests, Japan, China and South Korea routinely bombard forests with harsh insecticides, which can also kill pollinators like bees. Even with that, South Korea is losing heritage forests with sacred cultural value. Japan now has to import its prized mushroom, the matsutake, because it requires pine trees to grow.

This isn’t an isolated story. The impacts of forest pests are dramatic. In the early 2000s, myrtle rust was introduced to Oceania after being spotted on shipments of eucalyptus from South America; 75 percent of the forested land of Australia is now at risk. A root pathogen that spreads on hikers’ boots and dogs’ paws is bringing down thousand-year-old kauri trees sacred to the Māori in New Zealand. A wilt disease threatens the sacred 'Ōhi'a lehua flowers in Hawaii. Invasive pathogens are particularly problematic in the low-diversity, intensively cultivated landscapes prevalent in the Southern Hemisphere and Europe.

More than 500 species of plant pathogens and insect herbivores have been brought to North American forests, decimating ash, elm, chestnut, pine, tanoak, hemlock and more, and releasing as much carbon annually as wildfires. The annual cost of invasive species (of all kinds, including plants and animals) in the United States has risen from $2 billion in the 1960s to more than $20 billion in the 2010s. A 2023 international report implicated invasive species in 60 percent of all species extinctions.

Covid-19 alerted everyone to the risks and impacts of animal disease pandemics. Plant diseases may yet prove more nefarious in their cascading consequences for the economy and for human and animal health, particularly in a warming climate. We are in the midst of an epic global forest health crisis that demands a global response. Accordingly, the United Nations Convention on Biological Diversity acknowledges the importance of invasive species as drivers of biodiversity loss and lays out recommendations to build capacity and share information to reduce impacts.

Fungi and insects are by their nature small and can easily adapt to new hosts and environments. So forest pest invasions often go undetected until late in the game. When they are detected early, action is often slow because economic incentives are not readily apparent. Consider laurel wilt, which ravaged Florida’s forests for years before it struck avocados and policymakers started to pay more attention. Today, Florida’s avocado industry has lost more than 300,000 trees to this pest alone.

When pests cross international borders, the short-term economic benefits of trade often outweigh concerns over longer-term ecological costs. World trade conventions require strong evidence about the threat of specific pests to justify trade restrictions. Such information is seldom available until the problem is out of control. As a result, the world finds itself in a perpetual defensive state against the next big threat.

What can be done? Science can help. For example, researchers have had luck making white pines more resistant to blister rust and chestnuts resistant to chestnut blight, and they are selecting ash trees that are less affected by the emerald ash borer. Yet despite rapid advances in biological technologies, the invasion of forest pests and their impacts continues to accelerate.

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Limiting trade to regional partners would greatly reduce both the introduction of invasive pests and fossil fuel emissions, which accelerate the problem through climate change and amplified stress to trees. The pandemic, recent wars and other economic factors have led to a slowdown in global trade. But deglobalization is likely an impractical long-term solution.

No single, quick economic or policy fix can solve the problem. What we need instead is proactive, collective action. The list of what we need to do is long, and often asks nations to set aside specific economic incentives for the greater good. Big changes come through incremental progress.

One of my coauthors of a 2023 article in the Annual Review of Phytopathology, the late Gary Lovett, created and dedicated himself to advocacy for Tree-SMART Trade, a policy framework that proposes practical solutions. These include switching to non-wood packaging material in international shipments; expanding monitoring of pests and responses to them; augmenting biosecurity measures in trade agreements; restricting the import of live relatives of native plants, which might carry pests that transfer easily to these new hosts; and tightening penalties for importers who violate rules. This is a great start.

Finances must be pooled to strengthen pest management, biosecurity and conservation in resource-poor countries, and to adapt those efforts across different cultural and political systems. More work can be done to track where destructive pests originate and how to hold people accountable. Citizen scientists can help by monitoring local trees to spot hints of emerging threats. Most of all, forests should be managed for resilience rather than for timber yield or carbon credits.

In the long term, success requires equal representation that leaves no one behind. “International” scientific meetings, literature and research on forest invasive pests are today dominated by representatives from institutions in Europe, North America and English-speaking nations of the Southern Hemisphere (Australia, New Zealand, South Africa) — rather than their Indigenous populations or the rest of the world where English may represent a barrier — resulting in blind spots in scientific knowledge of invasive pests and ideas about their management.

It is time for a serious, proactive international response to the forest health crisis. If we continue to just react to threats as they pop up, biodiversity will continue to suffer.