The InterDependent

In 1986, a tiny but hungry new arrival took up residence in Malawi’s conifer trees. The cypress aphid may not have been native to the southern African forests, but once it came, it planned to stay. Unchecked by its natural predators found in its native Northern Hemisphere forests, and now living in warmer weather that allowed it to reproduce nearly year-round, the aphids spread to neighboring Tanzania within the year. Within the decade, they were cropping up as far away as Ethiopia, South Africa and even the island nation of Mauritius.

UN Photo/Eskinder Debebe

The African sun was kind to the cypress aphid, but it hardly returned the favor. As it drained the trees’ sap for nourishment, the 2 to 5 mm-longbugs injected a toxic fluid into the trees. Before long, groves and plantations of cypress and juniper trees in East Africa were dying off. By 1990, $44 million worth of trees had already been lost. And that was just the beginning: The first infestation of the aphids hit Kenya the same year, and within just three months, the bugs were nesting in over 80 percent of that country’s forests. Its main targets were the African pencil cedar, which is the main vegetation cover for the country’s watersheds, and the Mexican cypress, which accounts for 45 percent of its industrial forestry plantations and 80 percent of its industrial wood supply. The outbreak has impacted Kenya’s supply of timber and firewood ever since, resulting in greater risks of fires and soil erosion. A 1995 government report put the potential losses due to aphid damage at $2 billion.

Pernicious as it is, the cypress aphid is just one of the countless invasive species that have pushed and shoved their way into new environments in recent years. “International travel and trade are helping turn local pest problems into global pest problems,” says Beverly Moore, a consultant with the U.N. Food and Agriculture Organization’s Forestry Department. “Climate change appears to be compounding the problem by increasing the probability of new pest establishment as well as providing conditions that allow some species to become more serious pests in their native range.”

The broader costs of forest degradation and destruction in places like East Africa are clear, and they’re not limited to economic—or even the environmental—impact. In addition to their increasingly recognized critical role as carbon sinks, forests are now widely recognized as providing direct sources of food and income for many rural people around the world and as playing key roles in agricultural production such as fixing nitrogen in the soil and preventing soil erosion. Stable forests can play a key role in maintaining political and social stability; deforestation and other environmental crises have been cited as partial causes of conflicts in Darfur, Somalia and elsewhere. Invaders like the cypress aphid have the potential to wipe out all these benefits within decades.

And it’s not just in far-flung forests where invasive species are a problem. Historically, temperate forests like those in North America and Europe have faced the greatest existential threats from invasive pests. A hundred years ago, one of the most infamous invaders, chestnut blight, a fungus native to Asia, arrived in North America through imported timber or trees and in just a few decades brought American chestnut trees, once one of the most prevalent trees in the eastern United States, to near extinction. Dutch elm disease, caused by another Asian fungus, also arrived in Europe near the start of the twentieth century before being accidentally imported to North America as well – with an only slightly less disastrous impact on the continents’ elm trees. U.S. and Canadian forests are still being hit hard today, most notably by the emerald ash borer, a small green Asian beetle which has spread rapidly since its arrival in North America in the 1990s. It has the potential to kill most of the continent's ash trees, destruction on par with that of chestnut blight and Dutch elm disease, and wood-boring insects as a whole cost the U.S. over $3.5 billion annually.

It is hard to compare the number of infestations from a decade or two ago to now, since today's better oversight and communication invariably turns up more and earlier infestations, but what is clear is the harm that these new species are having on their adopted habitats. Nearly one percent of the world's forests can be damaged by outbreaks of forest insects, such as the cypress aphid, annually, according to the UN Food and Agriculture Organization (FAO.) That number—which does not include fungi, nematodes or other major threats to forests—may sound small, but its impact is massive. The livelihoods of 1.6 billion people depend on forests and trade in forest products can exceed 300 billion dollars annually, according to the UN. Most at risk from infestations are the plantations of trees for timber, fruit or oil, where a particularly strong outbreak might rapidly wipe out a family or community's source of income or fuel.

Given the stakes, it’s no wonder that international organizations and governments are raising alarm bells. In order to raise awareness about this critical role of forests, the UN declared 2011 the International Year of Forests.

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In the battle to protect these forests from tiny invaders, a network of largely under-the-radar agencies—almost as easily overlooked as the invasive organisms they monitor—are the first line of defense. From their offices and labs, these scientists, bureaucrats, and researchers have long been working to ensure the export and import of wood products follow careful regulations and that potential invasions can be addressed swiftly.

These backroom fighters are the national agencies, referred to as National Plant Protection Organizations (NPPOs), that turn international standards into local regulations, frequently working with their neighboring county in a regional organization (RPPO). Though the acronyms can result in an arcane alphabet, the result is a network of international collaborators who recognize that the pests which could decimate their forests pay no attention to international borders.

The network is housed under the umbrella of the International Plant Protection Convention (IPCC), an international treaty organization formed in 1952 whose secretariat is hosted by the FAO and requires its 177 signatories to work to prevent pests from spreading. "Collaboration and information sharing between people working in forestry and plant-health regulators are helping prevent, detect and eradicate new pest outbreaks," says Moore.

Back in the national offices, the toolbox to keep out pests is wide-ranging. Agencies inspect plants and plant products for signs of invasive species. They set guidelines for how best to select healthy, resistant species for export and import; they recommend precise strategies for when and how to harvest timber so that the likelihood of infested products is lowest. Inspectors use technologies such as pheromone traps and "sentinel plants" to detect a pest's presence in points of entry before it becomes established. In the European Union, regulators rely on “plant passports” to manage shipments of high-risk nurseries.

Such mechanisms for prevention are fascinating in their minutiae. Wood packaging materials such as palettes or crates, for example must be heat-treated to a minimum of 56 degrees Celsius (132 F) for 30 minutes or fumigated with methyl bromide at equally specific concentrations, timings and procedures. The wood must be debarked before fumigation; “long thin” pieces of bark can remain only if they are no wider than 3cm or short enough that they do not have a surface area exceeding 50 square cm. The procedures must be repeated if more than one-third of the packaging is replaced.

The specificity of measures like these might be an indication of the significance of the risks posed by invasive pests. And amid the plethora of strategies, national agencies rely on the FAO to stay up to date. Earlier this month, the UN agency issued a Guide to Implementation of Phytosanitary Standards in Forestry in hopes to help industry and governments comply with the latest interventions and international standards. "FAO assists, advises and supports countries and national institutes and agencies in their efforts to protect forests from pests and other disturbances…and on recommended actions to minimize risks of transboundary transfer of pests," explains Moore.

International collaboration is key, notes Gregg DeNitto, who leads the U.S. Forest Service's Wood Import and Pest Risk Assessment and Mitigation Evaluation Team. Together with his colleagues, DeNitto evaluates the risks from exotic pests associated with potential imports of forest-related products. In response to a request from a U.S. company or overseas supplier to import a product into the U.S., his small team performs a risk analysis of which a key component is collaborating with their counterparts in the country of origin since, as DeNitto says, "they are the ones who know the pests and the hosts best and have first-hand knowledge of the risks.”

Relying on this risk analysis and the IPPC standards, the U.S.'s Animal and Plant Health Inspection Service then makes recommendations for the type and degree of prevention measures needed—whether fumigation time or temperatures should be increased for a certain product from a certain country, for instance.
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Twenty years ago in East Africa, this international network of agencies and regulations began to churn in response to the cypress aphid’s spread.

“We were not able to contain the spread of the pest from the Tanzanian border, and the pest continued to spread fast—not just in Kenya but to Uganda and other neighboring countries,” explains Eston Mututi, an entomologist who worked on the effort to develop a method of control the aphid’s spread.

Eventually, an idea was broached to approach the issue regionally with the cooperation of countries in east, southern and central Africa. A conference was held in Nairobi in 1991, where the country representatives agreed on a common approach built around the method of “classical biological control” in which a pest’s natural enemies are introduced or pushed to establish themselves where they do not naturally thrive.

Researchers in Kenya eventually identified a parasitoid that might work. In 1995, they brought some of the parasitoids to Kenya from the cypress aphid’s native habitat, released them and tried to get them established. Success finally came in 1999.

“Since that time, the population of the aphid has gone down every year,” says Mututi, who was an assistant project manager on the regional initiative and helped identify and rear the parasitoid.

The Kenyan team then distributed the parasitoid to nearby countries. “Today, the parasitoid is actually in all areas where we have cypress aphid and suppresses the aphid very, very well. Kenya, Uganda and Tanzania do not have cypress aphids as a pest of economic importance.”

With the collapse of aphid populations, it is hoped that the affected plantations and forests will eventually fully recover and reprise their critical economic and ecological roles.

Mututi cites the “very key role of coordination by the affected countries, as well as international funding and key role of national institutions” in enabling the small teams of researchers to face down a once daunting threat. He is now working with South African collaborators on protecting eucalyptus plantations from recent invasions by the eucalyptus gall wasp and other threats.

New threats are constantly emerging and new strategies for preventing them are constantly being developed. But in a world of globalized trade and rapidly changing climates, where the imported timber for your new fence just might contain the start of a devastating invasion, it appears clear that combating these emerging environmental threats will take a cooperative effort that is just as international as the marketplace through which cypress aphids and others are invading new forests.