We Need Our Tropical Forests More Than Ever

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The rapid worldwide spread of coronavirus is proving to be a massive shock to everything we know, from our daily lives to the global economy. There is no doubt that the most pressing need now is to do everything possible to prevent the spread and lend urgent support to the people and the communities most susceptible. At the same time, the drastic change of pace may afford us a moment to reflect on the conditions that lead to the outbreak — and to widen the frame to see glimmers of the world we hope to see once this pandemic subsides.

A spate of recent articles and a growing body of scientific literature has illuminated the ways in which novel infectious diseases like coronavirus are often rooted in the destruction of forests and biodiversity. In the case of COVID-19, the scientific community has not established this link with absolute certainty, but the origin of the disease in humans appears to track to “wet markets” in Wuhan, China — urban marketplaces where wild animals are sold for food and medicine and trade.

In early February, the New York Times suggested that the origin of the novel coronavirus might be linked to the trade in pangolins — the world’s most trafficked animal. Shortly after, the scientific journal Nature noted that pangolins, which were being sold for their medicinal value in the markets in Wuhan, China, carry a virus with a 99 percent similarity to coronavirus, prompting a hypothesis that coronavirus did in fact mutate its way from pangolins into human hosts.

Zoonotic diseases — those that are passed between animals and humans — are clearly on the rise, with Lyme disease, Ebola, West Nile virus, Zika, and now Coronavirus, being among the most well-known. Each of these diseases is, in its way, linked to the destructive approach humans as a species have taken to our natural world — and many of them are specifically linked to the loss of primary forests.

It may not be intuitive to understand how cutting down rainforests can unleash infectious diseases. So, what’s the connection? In A Community Guide to Environmental Health, a widely translated book I co-authored back in 2008 called, we said it as plainly as possible:

“In a forest, it is easy to see the web of life because a healthy forest contains many different kinds of plants and animals. This diversity of life protects people’s health in many ways…. When human settlements are built in or close to degraded forests, the number and variety of animals are reduced because their sources of shelter and food become less plentiful and less diverse. Also, the animals that remain are forced to live in closer contact with people. This leads to a greater possibility that animal diseases will be passed to people. By maintaining enough forest to support a variety of plants and animals, we protect human health.”

David Quammen, author of Spillover: Animal Infections and the Next Pandemic, said it with more force in The New York Times: “We invade tropical forests and other wild landscapes, which harbor so many species of animals and plants — and within those creatures, so many unknown viruses. We cut the trees; we kill the animals or cage them and send them to markets. We disrupt ecosystems, and we shake viruses loose from their natural hosts. When that happens, they need a new host. Often, we are it.”

Any ecosystem can act as a “disease reservoir” — a habitat where microbes potentially harmful to humans naturally live and grow — and when the number of natural hosts is reduced, these organisms jump the species boundary and enter human hosts as disease. Entering a population with no evolved immunity allows the disease to spread; distressed public health systems aid the spread. The UN Environment Programme notes that up to 75 percent of emerging infectious diseases are zoonotic, almost universally emerging as a result of ecological disruptions.

Dr. Cindy Parker, a scientist at the Bloomberg Johns Hopkins School of Public Health, cites Lyme Disease as “a primary example of how decisions about land use affect our personal health.” The bacteria that transmits Lyme disease is transferred to humans through the bite of infected blacklegged ticks, commonly known as deer ticks. In an intact forest ecosystem, the “disease reservoir” for this bacteria consists of a wide range of species including raccoons, possums, chipmunks, squirrels, birds and mice, keeping transmission to humans in check. But when the habitat is fragmented by suburban sprawl, as it has been in the U.S. Northeast, one species — the white-footed mouse — comes to dominate. The deer tick population thrives on the white-footed mouse, and from there makes its way to the human host, spreading a disease which, prior to 1975, had never been detected in people.

The spread of malaria can follow a similar pattern. National Geographic reports on a study from the Amazon where a 10 percent yearly increase in forest loss between 2003 and 2015 led to a 3 percent rise in malaria cases. In one year of the study, a newly clear-cut patch of forest the size of 300,000 football fields was linked to 10,000 new cases of malaria. The article notes that “the effect was most pronounced in the interior of the forest, where some patches of forest are still intact, providing the moist edge habitat that the mosquitoes like.”

Ecologically speaking, it’s precisely these “edge habitats” where diseases mutate and spread into humans, often due to poor environmental practices. Forest boundaries are a clear example of an “edge habitat.” In a manner of speaking urban markets are another, and in the same sense, so are international airports, cruise ships and other areas of our built environment where people from vastly different places are thrown together and then spread back out across the world.

Global bodies like the World Health Organization have made it clear that climate change itself has also altered and accelerated transmission patterns of infectious diseases. As the UN Environment Program points out, combatting zoonotic diseases like coronavirus requires addressing “the multiple and often interacting threats to ecosystems and wildlife, including habitat loss, illegal trade, pollution, invasive species and, increasingly, climate change.”

The world’s primary forests contain more carbon dioxide than all of the world’s oil reserves combined. They also make rain, provide medicine, and act as a buffer between humans and an unknown world of lethal and potentially lethal viruses. Instead of seeing these forests as the temples of life that they are, we’ve been cutting them down for palm oil, paper and soybeans — which is to say, for cookies, hamburgers and toilet tissue.

Our violent disregard for biodiversity and our own part in the web of life has generated a perfect storm of global proportions. When the world returns to normal — if the world returns to normal — let’s use this time to think about which parts of normal we want to return to.