Natural processes deposit nitrogen from the air onto land and water at the rate of about 0.45 pounds per acre per year. But add in human sources from burning fossil fuels, agricultural practices and energy production, and the average deposition rate jumps to 8.9 pounds per acre per year. By 2050, these rates could double as the global population rises.
“We have more people on the planet, and when you have more people, you have more cars, more industries, more buildings, more stores, and all of that leads to more pollution,” says Woods. At a certain point, too much nitrogen can harm ecosystems, often by changing the chemical makeup of the soil; the threat varies greatly depending on the habitat, and researchers are still trying to understand where those thresholds are, she adds.
But how do you study the impacts of future pollution? Cardelùs devised an unusual experiment that, in effect, brings the future to the present. For the past five years, Cardelùs and Woods have added pollution to a handful of trees in the rainforest surrounding the La Selva station. Just like you’d first test a new stain remover on an inconspicuous part of your favorite jacket, the researchers want to test how an influx of nutrients will affect epiphytes, effects that Cardelùs predicts will preface changes throughout the rest of the forest.
A Lab in the Canopy
Cardelùs remembers the first time she climbed a tree and realized the vastness of the epiphyte community. “I looked at a branch, and I had an entire other forest,” she says, “and I thought, ‘Holy cow, how does this function?’ ” Since 1997, she’s climbed hundreds of trees in Central and North America as well as Ethiopia. Woods is equally obsessed. From another branch, she gestures toward a toucan. “When you’re up here, you’re living the rainforest life,” Woods says. “Nothing is better.”