Wired: “American trees are in trouble. Based on recent estimates, up to one in every six native species in the continental US is in danger of going extinct, due to mounting threats such as invasive species, diseases, climate change, logging, and wildfires. Metropolitan areas, meanwhile, are losing an astounding 36 million trees every year, according to a 2018 study from the US Department of Agriculture’s Forest Service. This loss of urban trees is a particular problem. They’re a critical part of the green infrastructure of US cities. Without the cooling effect of foliage, a city’s sprawling concrete and asphalt can turn into an urban island of deadly high heat—made even worse by global warming—which then forces buildings to use more energy to stay cool. Trees also lower air pollution and sequester carbon. The Forest Service estimates the annual cost of urban tree loss at $96 million. But there’s a way to attack this problem on multiple fronts, using undervalued waste—from trees and people—that would otherwise be sent to landfill. A new analysis from Yale University suggests that the dry waste from urban trees in the US—leaves, cuttings, and so on—could be diverted from landfills or incinerators, where much of it still ends up, and instead be reused to grow new trees, reduce logging, and lower carbon emissions. It’s a potentially huge resource: US cities generate more than 45 million tons of tree waste every year.

The Yale researchers, led by Yuan Yao at the university’s Center for Industrial Ecology, calculated that converting leaves into compost, wood into chips and lumber, and the remaining tree residues into a charcoal-like substance called biochar, can be environmentally beneficial on several levels. “These products can be substitutes for virgin materials such as fertilizers, and thus reduce associated environmental impacts,” the authors write. Recycling cut-down tree wood for lumber can also store carbon for the long term and reduce logging. Biochar, meanwhile, can be used to improve aeration, water storage, and nutrient retention in soils…”