Carbon Offsets for Urban Trees Are on the Horizon

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.

Source: Carbon Offsets for Urban Trees Are on the Horizon – Citylab, 2018-08-28

Planting a mix of tree species ‘could double’ forest carbon storage

By Daisy Dunne
Forests containing several tree species could store twice as much carbon as the average monoculture plantation, research finds.

A study looking at the carbon storage of forests in southern China finds that each additional tree species introduced to a plantation could add 6% to its total carbon stocks.

The findings suggest that afforestation programmes – which aim to plant trees to “suck” CO2 out of the atmosphere – should switch from using just one plant species to a more diverse mix, a study author tells Carbon Brief.

Planting a diverse range of trees could also bring many co-benefits, the author adds, including providing habitats for a larger range of animals.

However, the relatively small scale of the experiment may have led researchers to overestimate the relationship between tree species diversity and carbon storage, other scientists tell Carbon Brief.

Source: Planting a mix of tree species ‘could double’ forest carbon storage – Carbon Brief, 2018-08-22

City forests store rainforest-levels of carbon, study finds

By Morgan Erickson-Davis
Nations are hurrying to reduce greenhouse gas emissions and slow global warming, and one way they’re going about this is by encouraging the protection of forests. Trees trap carbon in their biomass and in the soil, and it’s hoped that keeping them in the ground will keep their carbon out of the atmosphere.

Climate-focused forest conservation policies and programs tend to be focused on rainforests. Covering vast areas, rainforests have earned the moniker “lungs of the planet” for their ability to sequester carbon dioxide while producing oxygen.

But pound for pound, other types of forest give rainforests a run for their money. A hectare of mangrove, for instance, can store four times more carbon than can a hectare of rainforest. And now, new research shows that even temperate forests in cities may be able to sequester nearly as much carbon as a similarly sized area of rainforest.

The study was conducted by a team of scientists from University College London, who mapped the carbon stores of areas of tree cover in the London Borough of Camden. Their results were published recently in the journal Carbon Balance and Management.

The team used remotely sensed LiDAR (which stands for “Light Detection and Ranging”) data that provided high-resolution information about tree structure. Armed with specific numbers on the dimensions and extent of Camden’s aboveground biomass (i.e., the parts of trees that aren’t underground), the researchers were able to estimate how much carbon is contained in each pocket of urban forest.

“Urban trees are a vital resource for our cities that people walk past every day,” said lead author Phil Wilkes. “We were able to map the size and shape of every tree in Camden, from forests in large parks to individual trees in back gardens. This not only allows us to measure how much carbon is stored in these trees but also assess other important services they provide such as habitat for birds and insects.”

Their results indicate Camden’s trees contain more carbon than estimated by previous studies. And while, as a whole, the borough’s median carbon density is on the low side when compared to many natural ecosystems – roughly equivalent to subtropical steppe – its urban forests are carbon storage powerhouses. The maximum value they uncovered was in a large, 320-hectare park called Hampstead Heath. There, carbon density approaches that of tropical rainforest.

Source: City forests store rainforest-levels of carbon, study finds – Mongabay, 2018-06-29

To increase forest carbon capture, harvest trees less and less often – but still harvest

“When we shift to forestry practices that less frequently harvest smaller amounts of wood from each acre, this leads to 14 to 33 percent more carbon be stored over the next 100 years. This happens because trees would be allowed to grow older and larger and store more carbon than typically happens under current practices,”

Source: To increase forest carbon capture, harvest trees less and less often – but still harvest – Granite Geek, 2018-05-29

Scientists Boost Biodiversity By Guiding Middle-Aged Forests To Mimic Ancient Ones

By Kathleen Masterson
A new University of Vermont study finds that harvesting trees in a way that mimics old growth forests not only restores critical habitat for animals and plants, but also stores a surprising amount of carbon…

The “old growth” engineering technique succeeded in creating diverse habitats. But the kicker, Keeton says, is that it has also allowed the forest to store a significant amount of carbon, much more than several other conventional tree selection harvesting techniques. That’s key to fighting climate change.

Now, forests that are left alone — with no trees harvested — store the most carbon. But Keeton’s study is finding that it is possible to manage the forest to maximize carbon capture, and still keep it a working forest.

“This greater amount of carbon storage as compared to the conventional treatments was actually a combination of having left more trees behind in the first place, and growth rates that were actually 10 percent higher in this treatment as compared to the conventional harvest,” Keeton says. “And that was really surprising.”

Keeton says after 10 years, the old growth forest management plot stored nearly as much carbon as the unlogged control forest. It came within 16 percent of carbon storage in the unharvested plots.

Source: Vt. Scientists Boost Biodiversity By Guiding Middle-Aged Forests To Mimic Ancient Ones | WBUR News, 2017-04-26