When yard waste ends up in the landfill, it can have serious environmental impacts, with landfills responsible for the third-highest human-caused methane emissions in the United States. In light of this, a new study investigated other ways for cities to tackle their tree waste outside of the landfill.
Researchers from the Yale Center for Industrial Ecology have conducted a lifecycle assessment to determine the environmental benefits of different ways to use urban tree waste. The team says this is important, as more than 45 million dry metric tons of such waste are generated in the United States each year.
Yuan Yao, study co-author and assistant professor of industrial ecology and sustainable systems at Yale, says, “Cities have lots of trees and they will not live forever. You also have leaves and other tree waste. We wanted to investigate different ways we could use this waste, the potential pathways and benefits, to create something of value.”
Their findings, published in the journal One Earth, show that beneficial options apart from the landfill include composting leaves and repurposing trunks into wood chips or lumber for wood products. However, the team says that using fallen trees as lumber for wood products reduces emissions further than just making them into wood chips. Another one of the best ways to utilize tree waste was biochar, which is black carbon produced from plant matter and stored in the soil that helps remove carbon dioxide from the atmosphere through plant uptake. Yao says it can be used in agriculture, energy, and wastewater treatment, as well.
The team categorized these options as low to optimal utilization, finding that even fair utilization like incineration could reduce carbon emissions by about 115 megatons. Meanwhile, full utilization of tree waste with lumber, wood chips, and composting could offset between 127.4 and 251.8 megatons of carbon dioxide annually.
The team wrote, “We find that converting urban tree waste to compost, lumber, chips, and biochar substantially reduces national environmental emissions compared with landfilling waste. Such benefits vary by location within the US, and the most environmentally beneficial combination is using merchantable logs for lumber and residues for biochar.”
The team says that though the best methods will differ from city to city and state to state, they hope their findings show that there are beneficial ways for all localities to handle tree waste.Whizzco