FOREST SERVICE STUDY FINDS TREE COVER DECREASING IN US CITIES

摘要

For US Forest Service scientists David Nowak and Eric Greenfield, it all started with a simple question: How is tree cover changing within US cities? "We wanted to address the question of how tree cover in our cities is changing in the United States.We know that as cities expand, regional tree cover changes and that change depends on where you are in the United States," said Nowak, Forest Service project leader and research forester at the Northern Research Station. "Within cities, we weren't sure whether tree cover has recently gone up or down because, on one hand, there are million-tree campaigns, people planting trees, and natural regeneration, and on the other hand we are losing trees to development and natural mortality. So, we wanted to findout what the net change in canopy cover is within cities across the United States."