By Sonja Dümpelmann
Many cities, in recent years, have initiated tree planting campaigns to offset carbon dioxide emissions and improve urban microclimates. In 2007, New York City launched MillionTrees NYC, a program designed to plant 1 million new trees along streets, in parks and on private and public properties by 2017. They hit their goal two years ahead of time.
These programs are popular for a reason: Not only do trees improve the city’s appearance, but they also mitigate the urban heat island effect – the tendency for dense cities to be hotter than surrounding areas. Studies have shown that trees reduce pollutants in the air, and even the mere sight of trees and the availability of green spaces in cities can decrease stress.
But as I show in my new book, “Seeing Trees: A History of Street Trees in New York City and Berlin,” trees weren’t always a part of the urban landscape. It took a systematic, coordinated effort to get the first ones planted.
By Maria Dolan
Austin, Texas, and King County, Washington, are testing carbon credits for planting and protecting urban trees.
The evidence is in: Urban trees improve air and water quality, reduce energy costs, and improve human health, even as they offer the benefit of storing carbon. And in cities across the country, they are disappearing.
A recent paper by two U.S. Forest Service scientists reported that metropolitan areas in the U.S. are losing about 36 million trees each year. The paper, by David Nowak and Eric Greenfield, was an expansion of the same researchers’ 2012 study that found significant tree loss in 17 out of the 20 U.S. cities studied.
This arboreal decline is happening even in some areas that promote “million-tree” campaigns, Arbor Day plantings, and street-tree giveaways. Cash-strapped municipalities just can’t find enough green to maintain the green. Additionally, many cities are adjusting to population booms, and to temperature increases and drought due to climate change—both conditions that can be hard on trees (while increasing their value as sources of cooling and cleaner air). There’s also a growing recognition of the inequity of tree-canopy distribution in many cities, with lush cover in wealthy neighborhoods and far fewer trees in disadvantaged areas.
To find more funding for urban trees, some local governments, including Austin, Texas and King County, Washington (where Seattle is located), are running pilot projects with a Seattle-based nonprofit called City Forest Credits (CFC). The nonprofit is developing a new approach: generating funding for city tree canopies from private companies (and individuals) that wish to offset their carbon emissions by buying credits for tree planting or preservation.
The vast majority of forest carbon credits worldwide have been issued for trees in tropical rainforests and other forests far from urban areas. A study released last year of the forest offsets in California’s cap-and-trade program found that they are effective at reducing emissions.
By Erik Lief
In evaluating the health of living things – whether they be humans, plants or animals – when advanced age or decay sets in we can observe the physical changes as they happen with our own eyes.
The same, however, cannot be said when studying trees. That’s because when they’re stricken by old age or disease, they rot, invisibly, from the inside out. And not knowing their true health misleads foresters and scientists around the globe who track climatic shifts and other natural occurrences.
As a result, foresters, arborists and researchers obtain their tree health data employing an alternative method: sound waves. However, while that method – called sonic tomography – is fascinating and revealing, it has its limitations since previously it could only be deployed on trees with cylindrical trunks.
But a new study, just published in Applications in Plant Sciences, claims to have taken sonic tomography to the next level, where now irregular-shaped trunks, which are predominately found in tropical climates, can be analyzed as well. And according to the research team headed by Greg Gilbert, lead author of the study and Professor and Chair of the Department of Environmental Studies at the University of California, Santa Cruz, evaluating tree decay “is of special concern in the tropics because tropical forests are estimated to harbor 96% of the world’s tree diversity and about 25% of terrestrial carbon, compared to the roughly 10% of carbon held in temperate forests.”