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The way your coffee is grown can affect important tropical plants that provide food and shelter to birds and other wildlife. In research recently presented at an Ecological Society of America meeting, doctoral student Ricardo Carvajal has documented a decline in the abundance of plants called epiphytes (also known as “air plants”), on coffee farms that use intensive agricultural practices.
In traditional coffee farming, coffee bushes are grown in natural forests, under a canopy of trees. But due in part to the burgeoning demand for coffee worldwide, many traditional plantations have been altered to produce higher yields. In the most extreme cases, forests have been cleared, and sun-tolerant varieties of coffee now are grown on virtually treeless slopes. Other growers take a less drastic approach, planting various combinations of trees to shade the coffee bushes, but pruning the trees to let in the proper amount of light.
Carvajal wanted to find out how the various methods of coffee production affect the abundance of epiphytes, a category of plants that includes many orchids, ferns and members of the pineapple (bromeliad) family. Rather than sending roots into the soil as most plants do, epiphytes grow only on other plants, drinking in dew, rainwater and moisture in the air and absorbing nutrients from dust and plant debris that collect in crooks of their home plant.
These diverse plants—which range from thumb-sized specimens to leviathans with six-foot-long leaves—provide nectar, fruit and nesting materials to resident and migratory birds. They also harbor insects, another important food source for birds and other wildlife. Concerned about dwindling numbers of migratory birds and aware of ephiphytes’ important role, the influential Smithsonian Migratory Bird Center has recommended that the growth of epiphytic plants be encouraged in coffee growing areas.
Carvajal, whose research is part of a larger project headed by John Vandermeer, professor of biology, and Ivette Perfecto, associate professor of natural resources and environment, surveyed epiphytes on a large coffee farm in Mexico that uses three different production methods. In a “restoration area” established about a decade ago, coffee bushes grow under planted trees of various species and heights. A second area has a less diverse assortment of planted trees, but still more than the most intensive cultivation area, where 80 percent of the trees belong to a single species. There is also an adjacent area of natural, undisturbed forest—the only area that has a true canopy of treetops shading the understory.
In comparing the areas, Carvajal found an “enormous difference” in epiphyte abundance between undisturbed forest and intensive coffee production areas, even those with a fair amount of shade. “There’s no question that once you eliminate the whole canopy structure of the forest, you’ve done a tremendous amount of damage,” he says. “And it’s not that easy to restore; even if you rebuild the forest with a high density of trees, there’s still an enormous difference.” Severe tree pruning and the coffee harvesters’ habit of scraping epiphytes off the trees where they do manage to take hold also enters in.
But Carvajal was encouraged to find that even the most intensive plots had “reservoirs” where epiphytes flourished. They thrive, for example, on yucca-like plants that often are used to mark the corners of coffee plots tended by an individual harvester. “Those plants are like signposts, and since they’re not part of the active production system, harvesters tend to leave them alone,” says Carvajal. As a result, “they’re like little islands of epiphytes—they’re absolutely covered with orchids and bromeliads.” Planting a few more of the “signpost” plants might help protect the epiphyte population—and the associated wildlife—without interfering with coffee production, he suggests.
Carvajal and other U-M researchers now want to look more closely at the tree-epiphyte-bird connection to figure out which specific growing practices are best for both coffee production and wildlife conservation. They want to learn, for example, how tree size, species composition and density affect epiphyte abundance and diversity and to better understand the finer points of birds’ reliance on epiphytes.
“Ultimately,” says Carvajal, “what this is about is making sure that if particular practices are recommended, the recommendations will be based on a thorough understanding of the biology.”