Portland on Tuesday began a five-year-long project to take inventory of the number of trees, tree survival and mortality rates, green space and ground cover on public and private lands in Maine’s largest city.

The urban forest inventory will be conducted by city workers in cooperation with the U.S. Forest Service, the city said in a statement.

“More than 80 percent of the nation’s population lives in urban areas where urban forests are helping clean the air, reduce energy costs, and give people a vital connection to nature,” Tony Ferguson, director of the Northern Research Station and the Forest Products Laboratory, said in a statement.

The survey will initially focus on municipally-owned parcels before it looks at private land. Participation is voluntary.

Survey teams visited the Eastern Promenade, Evergreen Cemetery and Baxter Woods on Tuesday. Portland is only the third city in New England selected to participate in the USDA’s Forest Service Forest Inventory and Analysis Program.