The answers might surprise you. Think of those patches of green, gray or sometimes bright orange lichens on tree trunks and branches. These epiphytic lichens have no connection the soil. Instead, they absorb all their nutrients and water from rain and mist. And that makes them more vulnerable to air pollution than rooted plants.
Collections of botanical specimens held in musty museum cabinets rarely make headlines. But recently, a set of lichen specimens collected in 1866 were rediscovered at the Brooklyn Botanical Garden. From that collection, we’ve learned that 130 lichen species thrived in Manhattan during pre-industrial times. Today, only 18 of those species occur in New York City.
Such dynamics may also be happening in the West. Paul Rogers, a professor at Utah State University, studies epiphytic lichens in northern Utah. Using historical climate data, fire records and ammonia sensors, he documented profound changes in the health of aspen trees and in the composition of their epiphytic lichen communities over the past 150 years.
His conclusions? The diversity of aspen-dependent lichen species is declining, and local air pollutants are a contributing factor.
Trees provide us with many ways to chart their present and past environments, and help us to better understand our role in our changing landscapes.
