I suspect no other relationship is more complex and fraught than that between humans and trees. I’ve been wanting for a long time to write something about it, but every time I try, I get overwhelmed. Where to begin?
For us humans, it indeed goes back to the beginning: Adam and Eve learned of their own humanity from a tree. Or if you prefer more scientific stories, our ancestors took a crucial step in speciating from other apes by descending from the trees. Since then we haven’t gone far from the tree, so to speak. We have eaten from trees, climbed trees, lived in trees, worshipped trees, studied trees, planted trees, bred trees, hugged trees, and saved trees. We have also, at various times, cut trees down for fuel, for lumber, to make paper, to make weapons, to clear farmland, to create subdivisions, because they threatened our infrastructure, because we didn’t like where they were growing, and for no reason whatsoever.
After hundreds of thousands of years of shared history, have we and trees come to understand each other better? Three stories I have come across recently suggest the answer is, it’s still complicated.
Life presents us all with certain problems, one of them being how to move ourselves from place to place. I submit that if you live in a compact, congested city, there’s really only one sane solution: ride a bicycle. Biking is carbon-neutral, it’s efficient, it’s outdoors, it’s exercise, it’s free, it’s fun. It’s a win-win-win-win-win-win.
But as I’m dodging morning traffic on my way to work in Washington, DC, I do find myself wondering, am I just fucking crazy? Could the health benefits from bike commuting possibly outweigh the risk of getting flattened by some latte-swilling, texting SUV driver? And even if I avoid that fate, what about the longer-term effects of the exhaust fumes I’m sucking in with every breath?
Since I am a science writer, I feel compelled to try to answer such questions with data. So it was troubling to find that one of the few sources providing data on the risks of different modes of transport puts biking near the top in deaths per journeys, miles traveled, or time spent in transit (apparently based on a 15-year old British survey). Only motorcycling, which is essentially bicycling at the speed of car traffic, proved more dangerous. U.S. data from a similar time period and cited in this paper tell a similar story.
It’s that magical time of year—after the big harvests and before the hard freezes—when apples at the farmers markets in my area burst with tangy goodness, when the last of the summer tomatoes and peppers mingle with luxurious piles of greens, roots, and winter squash, and when all seems right in the world.
So I admit I found it somewhat hard to believe, while admiring the overflowing stands at my local market last Sunday, that federal bureaucrats would want to make it harder for such enterprises to operate. But that is exactly what some small farmers and advocates are warning. They fear that food safety regulations proposed by the Food and Drug Administration would impose onerous costs on small produce growers, potentially driving many out of business altogether.
The once-mighty monarch butterfly migration—an extraordinary natural phenomenon that passes right through our neighborhoods and fields—has been reduced to a trickle. Where were you all summer, did you notice?
For how things used to be, here is Annie Dillard describing the event in Pilgrim at Tinker Creek, published in 1974:
The monarchs clattered in the air, burnished like throngs of pennies, here’s one, and here’s one, and more, and more. They flapped and floundered; they thrust, splitting the air like the keels of canoes, quickened and fleet. It looked as though the leaves of the autumn forest had taken flight, and were pouring down the valley like a waterfall, like a tidal wave, all the leaves of hardwoods from here to Hudson’s Bay.
Dillard seems to be describing a scene of almost unimaginable natural wealth. The world had such an excess of raw material that it could make monarch butterflies not by the ones and twos, but by the millions. Indeed, estimates of the number of monarchs that used to overwinter in Mexican fir and pine forests range up to a billion. In pictures, the trees seem to be literally dripping with butterflies.
We’ve all heard about the dangers of non-native plants: they outcompete natives; they carpet forest floors and smother roadsides; they cost us billions of dollars a year in control efforts. They’ve colonized huge swaths of the mid-Atlantic, where I live; I’ve written about them on this very blog. But is it possible that some introduced plants could prove beneficial in their new environments?
That’s certainly what Ariel Lugo thinks. Lugo, the director of the US Forest Service’s International Institute of Tropical Forestry, has long promoted a more catholic attitude toward plants of diverse origin. I recently visited him at the University of Puerto Rico’s Agriculture Experimentation Station in San Juan, where his office sits among groves of eucalyptus and bamboo—both of which humans introduced to the island. According to Lugo, the immigrant vegetation reflects the welcoming Puerto Rican spirit. “Here, we don’t persecute trees,” he says. “The federal government is the only one that persecutes trees.”
As far as Lugo is concerned, any species that can help his island recover from past environmental devastation—near complete deforestation, large-scale cultivation of sugarcane and other crops—is welcome. In 1992 he published a paper comparing the understories of pine and mahogany plantations with those in regrowing native forests. Lugo found that similar numbers of species were growing in both places, and that many of the understory plants in the plantations were native. Moreover, he found the older plantations were starting to give way to native overstory trees. “The study challenges the conventional dogma…and underscores the dangers of generalizing about all tropical tree plantations or all natural tropical forests,” he wrote. According to science writer Emma Marris, it took Lugo almost a decade to get his paper accepted.
As my devoted readers no doubt realize by now, I’m on a bit of a Rachel Carson kick. I wrote a blog post and produced a radio show about her last fall, and I’m working on an article about her for Johns Hopkins magazine (Carson got her master’s degree at Hopkins). Why this slight Carson obsession? It started with the 50th anniversary of Silent Spring, which got me wondering, as a science writer, how someone armed only with scientific knowledge and words could have such influence. I believe we science writers sometimes sell ourselves short in terms of what we can accomplish, especially in this age of disposable Web writing. Carson can remind us of the potential of writing for impact, not just for mouse clicks.
In 1953, Rachel Carson spoke at a symposium at the American Association for the Advancement of Science’s annual meeting. The topic was the sea frontier. Unlike the other eight panel members with whom she shared a stage, Carson was not a research scientist; she had until recently worked as a staff writer for the US Fish and Wildlife Service. (She was also the only woman on the panel).
At the conference she talked about the book she was writing, The Edge of the Sea, which would be based mainly on her observations, and less on the work of other scientists, as her previous books had been. Carson had scientific training, but it was her writing that earned her the speaking slot: her 1951 book The Sea Around Us had made her the nation’s most famous writer about the oceans and perhaps about all of science.
Although Rachel Carson spent almost her entire career writing about the sea, she is remembered today for her one book about things that happen on land. That book, Silent Spring, awoke the American public to the dangers of many common pesticides, and launched the environmental movement. But while the birth of environmentalism would not have happened exactly when it did and how it did without Carson’s advocacy, it would have happened: Americans would not have tolerated smoggy cities, burning rivers, and toxic chemical clouds for much longer. “I suspect that the audience [of Silent Spring] was close to an environmental awakening,” said Jane Lubchenco, a marine biologist and past head of the US National Oceanic and Atmospheric Administration, at a symposium dedicated to Carson at this year’s AAAS meeting. “No doubt [Carson] catalyzed it, but the ground was fertile.”
If you’re a writer looking for a good symbol, consider the tree. The author of Genesis did, twice: he placed the tree of life and the tree of knowledge front and center in the Garden of Eden. Homer did, too: When his hero Odysseus returned home after twenty years of war and travel, needing to prove his identity to his skeptical wife, Penelope, he used a tree. “Move our bed into the hallway,” Penelope told her servant, laying a trap. (I’m paraphrasing here.) “It can’t be done,” Odysseus protested. “I carved a post of that bed from a living olive tree.” Only then did Penelope believe the strange man was really her husband, as steady as that post.
Trees have long impressed us with their steadfastness; in fact, some trees from Biblical times are still with us today. But a new story I read recently casts trees in a different role. I first came across a version of this story in a paper published in the journal BioScience in 2007. The authors looked at where trees live using a tool known as a “climate envelope,” which is a line drawn on a map around the entire range where a given species is able to survive. The scientists compared climate envelopes for 130 trees under 2007 conditions to those predicted for the end of the century, using the same computer models that the UN’s Intergovernmental Panel on Climate Change bases its forecasts on. On average, they found that trees’ envelopes moved 700 kilometers north, nearly the distance from Memphis to Chicago.
So does that mean our trees will be moving north as things get warmer? Traveling trees can make great stories: Shakespeare’s Macbeth was vanquished when Birnam Wood moved a few miles to his fortress at Dunsinane Hill. And it would be dramatic indeed if future northern woodsmen and women hunt deer among sprawling live oaks and big-leaf magnolias instead of spruce and pine trees. But the scientists who wrote the BioScience paper noted that actual trees are unlikely to track their climate envelopes’ northward migration in the coming years, at least if unassisted by humans. Trees can “move” up to a few miles in a generation, by setting their seeds aloft in the wind or encasing them in a shell so they can survive a trip in the gut of an animal. But tree generations are long, and most seeds land close to home. Sugar maples, for example, lead a chaste adolescence, and don’t start making seeds until the age of 22 or so. They then send out seeds attached to little helicopters, which spin and float at most the length of a football field before touching down. Scientists estimate trees’ maximum migration rate to be around 50 kilometers per century, with many traveling far slower—a tortoise’s pace in this race.
An Ecologist’s Battle
Invasive plants are the ones that don’t play well with others. They steal their neighbors’ food and water, and they refuse to share. And you’ll see them all around the Baltimore area: vines smothering stream banks and blanketing entire trees; the brambles tangling and choking the understory; the annuals carpeting the forest floor. They’re the botanical version of an alien invasion.
Or, they can make nice additions to our gardens. Vanessa Beauchamp, an invasive plant ecologist, tells me about a hiker who came upon her research team in a park outside Baltimore. “She asked us what we’re doing, and we explained we’re studying this invasive grass that we think is a really big problem, and we’re trying to understand more about its ecology. And she says, ‘Oh my gosh that stuff is so pretty, I dug up a bunch and planted it in my yard.’”
The plant was wavyleaf basketgrass, a native of Europe and Asia. It sounds innocent enough, like a prairie grass that might rustle softly in a summer breeze. And it’s pretty enough, too, with intensely green leaves that unfurl on either side of a central shoot, and a head of spiky seeds that sticks up a foot or so above the ground. The seeds are the problem, though—they hitch rides on pant legs, animals, basically anything that comes by—and disperse to new locations that way. The plant can grow just fine even in the deep shade of a mature forest. In Patapsco Valley State Park, where it was discovered in the mid-1990s, it now carpets acres of forest floor. The Maryland Department of Natural Resources launched a war on it but lost, due to lack of funding. Now the plant has spread to other parks in the area, and experts like Beauchamp fear there may be no containing it.
But if it’s green and pretty, what’s the worry? Beauchamp says it’s all about the community of life in the forest. Exotic plants like basketgrass are newcomers to this community, so nothing has evolved to eat them—a lesson Beauchamp has learned firsthand. “When we worked on wavyleaf basketgrass, we literally spent the summer crawling around on the forest floor. I figured we would just be tick city,” she says. Instead, of the half dozen people on her crew, “We got one tick between all of us. I mean, that’s insane.”
Few of us would be sad to see the ticks disappear. But without the thousands of insects, worms, mites, and spiders that make their living in the forest understory, the woods would be a vastly different—and less lively—place. “Nobody’s looked at how insects are able to use this grass…We see very little insect damage on the grass at all. We see no deer damage,” says Beauchamp. “If there’s no insects eating them, there’s no birds eating those insects, and up and up and up.”
A wavyleaf basketgrass army
Beauchamp moved to Towson University in Baltimore from Arizona five years ago. For an invasive species expert, the move meant more than packing and unpacking boxes—it meant abandoning one biome and learning a new one. Luckily for Beauchamp, Maryland has no shortage of invasive plants, and it didn’t take her long to find one she could claim as her own. “I came across this wavyleaf basketgrass that nobody knew anything about, and I said ‘All right. That’s mine.’”
One of the questions Beauchamp is asking is how aggressive the grass actually is. Many writers on the Web claim it crowds out other plant species, but Beauchamp wonders whether it might just take advantage of openings on the forest floor, especially those created by Maryland’s massive plant-munching deer population. To test how competitive wavyleaf basketgrass is, her research team is growing the grass in a greenhouse alongside other native and invasive grasses, and seeing which puts on the most weight. They hope to have results soon.
Beauchamp is also trying to figure out how the seeds disperse. And she thinks she’s found a suspect: pet dogs. When hikers let their dogs run through a basketgrass patch, they “come out looking like a chia pet,” says Beauchamp. Fore more precision, she had her students count the number of seeds sticking to a dog. “We found that a single dog going through this grass for 30 seconds can get over 2000 seeds on it,” she says.
Dogs may not be the only culprit, though; Beauchamp also has her eye on deer. She and her team tested this hypothesis in a rather macabre way: they got severed deer legs from a meat processor, and “walked” the legs through a basketgrass patch. Again, the legs came out covered in seeds.
But Beauchamp admits she can’t answer the most important questions: how much wavyleaf basketgrass is there, and where? “I have absolutely no number to tell you in terms of how many acres this grass covers in Maryland,” she say. “None.” Unfortunately, when she wrote a grant to fund a project that would get at such a number, she got caught in a chicken-and-egg situation: the review panel rejected the proposal, saying Beauchamp and colleagues hadn’t demonstrated how much of a threat the grass poses. “But if I don’t have any money to study it, how can I demonstrate that?” she asks.
So like any good scientist, she’s gotten creative. She mustered a “wavyleaf basketgrass army” of undergraduates and high school teachers to go out and count plants in different locations. She’s also teaming with a Catonsville Community College professor who’s developing a smartphone app that will allow anybody to report a basketgrass sighting, along with GPS coordinates. Beauchamp is hoping the data her team and concerned citizens collect will convince funders and policymakers that the grass is worth studying on a larger scale.
Beauchamp vs. basketgrass
Beauchamp versus basketgrass is the latest chapter in a long saga of human battles against invasive plants. And so far the invaders have scored most of the victories. Here in Maryland, English ivy, Japanese stilt-grass, mile-a-minute weed (an Asian species known as “kudzu of the north”), and other exotics have become far more familiar sights in our parks and forests than most of our native plants. Will wavyleaf basketgrass join this list of dubious characters, or could this be the time we outsmart the weed?
(All photos courtesy of Vanessa Beauchamp)
The 2010 US census workers had a tough job, but at least they were on land, counting residents with home addresses. 2010 was also the year a group of marine biologists completed a much tougher assignment: a global canvass of ocean residents who don’t fill out forms, live in some of the most remote places on the planet, and often move thousands of miles in a single year. The first study of its scope, the Census of Marine Life has added thousands of new species to the books, and has shown, in the words of project director Jesse Ausubel, that “the ocean’s even richer in diversity than anybody had known.”
Census scientists collected over 6,000 new species, and have already described 1,200 of them in detail. They discovered deep-sea jellyfish, 500-year-old tubeworms, bejeweled copepods and isopods, and a hairy white crab that lives near sulfurous vents on the ocean floor. They found a mat of filamentous bacteria the size of Greece off the coast of Chile, and located a squid previously believed to have gone extinct in the Jurassic. The Census uncovered new life forms even in some of the world’s most studied and heavily trafficked ocean regions, said Ausubel, Census co-founder and program director at the Alfred P. Sloan Foundation, who described the results in a talk in Washington, DC last Thursday.
Each newly discovered species now has its own web page in the online Encyclopedia of Life, which will eventually catalog every known life form on Earth. Pages in the encyclopedia include physical descriptions of the species, scientific information like where the creature is found and how common it is, and, of course, color photos. “It’s like facebook,” Ausubel said. In addition, scientists gathered DNA from every creature found, new or not, for a project called the International Barcode of Life. The iBOL is a reference library made of segments of specific genes that are shared among many forms of life, but whose precise sequence varies in an identifiable way from species to species.
Scientists also learned that many familiar marine animals make long-distance trips across the ocean, “commuting like jetset businessmen” in Ausubel’s words. Census researchers attached acoustic tags to various creatures and released them; the tags then emitted sounds that were picked up by receivers on the ocean floor as the animals passed by. Scientists watched bluefin tuna swim from Mexico to Japan and back in a year, and tracked seals fishing from underwater mountains off the Antarctic coast. They monitored salmon swimming up the west coast of Canada, and learned that many of them don’t make it back to rivers to spawn the next year. And they used the tags to collect data beyond just the animals’ locations; for example, they enlisted leatherback turtles to collect ocean temperature readings during their journeys around the South Pacific. “Animals connect the ocean in incredible ways,” said Ausubel.
Surveying the astounding diversity of marine habitats—coastlines, continental shelves, deep-sea trenches and mountain ranges, the vast open ocean—required a correspondingly varied array of exploratory techniques: “a concerto of technologies,” said Ausubel. To explore the ocean surface and shallow waters, scientists worked from submarines, airplanes, and massive research vessels. For probing the deep ocean, they turned to robotic and remotely controlled vehicles that could operate at depth without risk to human life. In total, the project cost $650 million spread over a decade, and involved almost 3,000 scientists. “Marine biology hasn’t had a tradition of big science” like physics has, said Ausubel, but with the Census of Marine Life, that may be starting to change.
Although Ausubel noted that “extinction is rare in the ocean,” scientists found ample evidence of humans’ effects on life in the sea, few of them good. Overharvesting has depleted the populations of various fish, mammals, and reptiles since the time of the Romans, and in recent times has led to explosions of less desirable creatures, like jellyfish. Modern scourges like the huge floating garbage patches in the Atlantic and Pacific are also harming aquatic life, particularly island-nesting birds that are often found dead with plastic in their stomachs. But the greatest impacts may be yet to come, as humans increase shipping, oil drilling, and underwater communication, and as rising greenhouse gas emissions continue to warm the ocean and make it more acidic. The Census has given scientists a valuable baseline against which to measure future changes to the abundance and distribution of ocean dwellers.
Despite their impressive findings, marine biologists have just begun the hard part of counting every creature in the sea. They believe the ocean could contain a million or more undiscovered species, most of which are likely to be small, rare, and hard to find. And those are just the relatively well-studied multi-cellular ocean dwellers; the number of microbial species in the ocean is far larger, perhaps as many as a billion. Ausubel also noted that few people study most marine life forms, besides the well-known ones like fish and mammals (a hint to any young scientists out there searching for a specialty.)
The seas have long fascinated and mystified us. Over 60 years ago, Rachel Carson’s best-selling book The Sea Around Us told the public about the stunning discoveries in marine biology made possible by World War 2-era innovations in sonar and submarine technology. Since then we have learned much about what lives in the deep sea, and we now know the ocean floor is not barren but in fact teems with strange and wonderful life. But the Census of Marine Life also reaffirms the lure of the unknown that Carson described in her 1951 masterpiece: “We can only sense that in the deep and turbulent recesses of the sea are hidden mysteries far greater than any we have solved.”