U.S. urban forests are in a crisis.
Cities in half the states in the country lost a significant amount of tree cover over a five year period, according to a new study. In some cases, the changes were drastic, amounting to almost half a percent of a city’s tree cover every year. Without programs to counter the trend, those fractions of a percent add up to significant, noticeable losses over just a few years.
David Nowak and Eric Greenfield, two U.S. Forest Service scientists who have been following urban forests for years, wrote the new report. While they’re hesitant to call it a trend, the new research builds on their previous work, which found similar results. That suggests the loss of urban forests across the country may be ongoing and not just a hiccup in the data.
Here’s Richard Conniff, reporting for Scientific American:
The biggest losses on a percentage basis were in Rhode Island, Georgia, Alabama and Nebraska, together with the District of Columbia. Only three states—Mississippi, Montana and New Mexico—saw increased metropolitan tree cover, all by “nonsignificant” amounts. (State-by-state figures are available here.) The research team used Google Earth imagery to examine 1,000 randomly chosen points in each state for a before-and-after comparison over a five-year period, generally ending in 2014 or 2015.
There are plenty of reasons for the downward trend, from insect infestations to storms, population growth, and old age, all of which have been claiming large numbers of trees. Tree planting programs haven’t kept up with the attrition, either. They’re often trotted out with much fanfare, but follow-through has apparently been lacking. Conniff points out that one “million tree” program ended with less than 53,000 saplings planted.
Now and Greenfield conservatively estimate that we’ve lost $96 million in benefits from the lost trees over the period of the study. They arrived at that number by calculating a narrow set of benefits for urban trees, including air pollution removal, energy conservation, carbon sequestration and avoided emissions (for example, due to lowering the heat island effect).
Their $96 million estimate, though, isn’t just conservative, but likely significantly understates the losses. Trees also add thousands of dollars to home values, help lower crime rates, and reduce stress. They are even correlated with students performing better in school—a tree outside a classroom or cafeteria is associated with better test scores, higher graduation rates, better behavior, and higher likelihood of attending a four-year school. Together, these effects could greatly alter a city’s prospects.