A Sustainable World...
What does the dogwood tell us?
At first, or even second glance, the massive decline of the dogwood along the Appalachians might seem an isolated event, unhappy for dogwoods and for the other species that depend upon this tree, including those of us whose bond is chiefly aesthetic as we wander these forests in springtime. Scientific study leaves no doubt about the reason for the blight: the culprit is a species of fungus, Discula destructiva, that causes an infection called anthracnose. In a sense, then, when viewed against the long tapestry of evolution, ecological competition and disease what could seem more natural than one infectious agent having its way with one tree species?
More careful examination, however, reveals another force acting behind the scenes. The fungus is especially virulent for dogwood trees weakened by air pollution. Dogwoods that have been showered with acid rain are less able to withstand the fungal attacks. It is not the affect of acid rain directly on the tree that causes the damage. Instead, acid rain reduces the availability of nutrients in the soil. The dogwoods, deprived of crucial nutrients, then lose their disease resistance and succumb to anthracnose.
From whence this acid rain? It comes from distant cities, power plants and automobiles, sources most of which are located west of the Appalachians. This human-made air pollution is transported by atmospheric currents and deposited downwind, smeared as if from a spray can across hundreds of miles of farmland and yards and forests. The effects accumulate over time, and the ultimate impact is determined by a host of local factors including the species composition of the forest, the nature of the soils, the distance from the source, and interaction - as with the dogwood and the fungus - with other organisms.
The interaction of acid rain, dogwoods and anthracnose is but one of the dramas in this theater. In a local cove 18 miles west of Charlottesville, most eastern hemlocks have died within the past 5 years. They were majestic trees, reaching out of the hollow toward the sun, their shadows cooling the trout pools of the north fork of Moormans River. The hemlocks died from infestations of an insect, the woolly adelgid, native to Asia which arrived in the United States perhaps in the 1920s. The adelgid's depredations have reached a scale throughout the east that forest pathologists compare to chestnut blight and Dutch elm disease, two infections that all but eliminated from the wild all stands of two quintessential American trees.
As with the dogwood, at first glance it would seem this tragedy is but another act in a drama of purely biological interactions. But here, too, there is more to the story. Adelgids thrive and hemlocks appear to suffer when nitrogen is abundant¾and nitrogenous depositions from the coal-fired power utilities scattered through the Ohio Valley and American Midwest are one of the downwind consequences of their pollution.
"I thought about all the other species that we knew had begun to die off in these mountains: red mulberry in the early 1960s, chinquapin chestnut; butternut and black oaks in the 1970s; and yellow locust, sassafras, hickories, walnut, the white oaks, beech, yellow buckeye, white basswood, dogwood, hemlock, and sugar maple in the 1980s. Once the previously most disease-resistent species, tulip poplar now appeared to be at risk. … I was reminded in clear images of the healthy old-growth forests [in this region] I had grown up with, and the mortality they began to experience in the 1980s. I was reminded of the soft green and yellow Carolina parakeet, the only parrot to inhabit eastern North America, described by Audubon as once being present in flocks in the upper canopy of these tall, broadleaf forests. Extinct since 1909... Now almost a century later, not only are birds, mammals, and soil insects at risk, even the tree species and ecosystems are at risk. With much more research we might understand the causal agents precisely involved, and based on that, might propose measures to restore integrity and healthy function to the systems at risk. We do have compelling scientific evidence already. … Several generations of experience and research clearly indicate prudence, now." (1)
Dogwood, hemlock, hickory, mulberry, sugar maple… all indicators of something gone awry and portents of larger problems to ensue. Across the landscape, here in the United States and elsewhere around the world, these declining species join a host of other signals that point to problems whose origins are rooted in very human behaviors and whose solutions are essential if we are to find a graceful and equitable resolution to the current global environmental predicament.
The most dramatic of these global signals is the growing indication that human activity is disrupting the Earth's climate by producing greenhouse gases, especially carbon dioxide released by burning fossil fuels. Overall, 1998 was the warmest year since widespread instrument recordings began in the 1800s; last year was the 20th consecutive year with a global mean temperature above the long-term average. Indeed, some scientists estimate that the 20th century is the warmest century in the past 1,200 years. Indications of this warming trend can be found in all corners of the world. Texas suffered from 29 consecutive days of temperatures above 100° F, killing several hundred people. Heat waves in India and the Middle East in summer 1998 killed many people; the temperature in northern India rose to 123° F. Temperatures in the Jordanian capital of Amman averaged 104° F for much of July and August In Bahrain, residents experienced the hottest summer since the beginning of record keeping in 1902.
Climatic disruptions only begin with higher temperatures. Around the globe in 1998, came an unending onslaught of news of droughts and floods and storms. In May, Mexico suffered some 300 new forest fires each day spawned by drought and heat. The smoke from these fires carried northward to Texas, Oklahoma and beyond; subsequent study linked this smoke with unusual amounts of lightning in the US Midwest. Fires fueled by drought and heat also plagued Florida, consuming nearly 190 square miles of the state and wreaking devastation on the corn and peanut crops and forcing many people to abandon their homes. In Asia, a September monsoon barreled into Bangladesh, remained longer than any in recorded history and flooded 20 million people from their homes. Large floods also inundated China and India.
Finally, the most destructive tropical storm of the century, Hurricane Mitch, struck Honduras and Nicaragua in November 1998. Thousands were killed, millions left homeless. The economies of these Central American nations, already impoverished, were left destitute. While, scientists cannot state with certainty that Mitch was caused by climate disruption, computer models have predicted for years that the frequency of intense hurricanes will increase as climate disruption advances.
Biotic systems have already been damaged by these climatic aberrancies. A large swatch of ocean off the California coast stretching from San Diego to Santa Barbara and covering 50,000 square miles has undergone significant warming, which in turn has affected ocean currents and caused an 80% decline in zooplankton, the basic food for many marine species. Scientists report that this region has become a vast, impoverished wasteland with few fish and few birds.
Another study by researchers from the US, Russia, Japan and Canada indicates that changes in the Bering Sea during 1998 - extensive die-offs of seabirds and low salmon runs, both linked to warmer ocean temperatures - may be the first visible signs of climate disruption in the Arctic. And in the Antarctic, the last several years have seen dramatic breakups of coastal icefields. A section broke off in October that was larger than the state of Delaware. Antarctic scientists have also reported plummeting numbers of penguins driven down by declines in krill, their food, linked to rises in temperatures of Antarctic waters.
These are but a few of the many troubling indicators in 1998 to suggest that something is amiss in the global environment, and that the economic development path we follow into the next century must be changed fundamentally to become equitable and sustainable for the long-term. In time, we may discover that not all these indicators of turmoil are the result of human impacts at a global scale. But how much bad news do we need to suggest that this is the moment to take stock? Or to be humbled by the impacts our activity can have on the very ecological systems that make our prosperity and progress possible? And to seek new solutions?
(1)Orie Loucks, "In Changing Forests, a Search for Answers," in An Appalachian Tragedy: Air Pollution and Tree Death in the Eastern Forests of North America, ed. H. Ayers, J. Hager, and C.E. Little (San Francisco: Sierra Club Books, 1998), p 97.