Rate of Tree Carbon Accumulation Increases Continuously with Tree Size

Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations1. Our ability to understand and predict changes in the forest carbon cycle—particularly net primary productivity and carbon storage—increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age.

A global analysis of 403 tropical and temperate tree species, shows that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-leve productivity can be explained, respectively, by increases in a tree’s total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density.

Results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12914.html

Prairies Vanish in the US Push for Green Energy

 

1.2 million acres of prairies vanish, undermining Obama's green energy goal

ROSCOE, S.D. (AP) — Robert Malsam nearly went broke in the 1980s when corn was cheap. So now that prices are high and he can finally make a profit, he's not about to apologize for ripping up prairieland to plant corn.

Across the Dakotas and Nebraska, more than 1 million acres of the Great Plains are giving way to cornfields as farmers transform the wild expanse that once served as the backdrop for American pioneers.

This expansion of the Corn Belt is fueled in part by America's green energy policy, which requires oil companies to blend billions of gallons of corn ethanol into their gasoline. In 2010, fuel became the No. 1 use for corn in America, a title it held in 2011 and 2012 and narrowly lost this year. That helps keep prices high.

"It's not hard to do the math there as to what's profitable to have," Malsam said. "I think an ethanol plant is a farmer's friend." What the green-energy program has made profitable, however, is far from green. A policy intended to reduce global warming is encouraging a farming practice that actually could worsen it.

That's because plowing into untouched grassland releases carbon dioxide that has been naturally locked in the soil. It also increases erosion and requires farmers to use fertilizers and other industrial chemicals. In turn, that destroys native plants and wipes out wildlife habitats. It appeared so damaging that scientists warned that America's corn-for-ethanol policy would fail as an anti-global warming strategy if too many farmers plowed over virgin land. The Obama administration argued that would not happen. But the administration didn't set up a way to monitor whether it actually happened.

It did.
More than 1.2 million acres of grassland have been lost since the federal government required that gasoline be blended with increasing amounts of ethanol, an Associated Press analysis of satellite data found. Plots that were wild grass or pastureland seven years ago are now corn and soybean fields. That's in addition to the 5 million acres of farmland that had been aside for conservation — more than Yellowstone, Everglades and Yosemite National Parks combined — that have vanished since Obama took office.

In South Dakota, more than 370,000 acres of grassland have been uprooted and farmed from since 2006. In Edmunds County, a rural community about two hours north of the capital, Pierre, at least 42,000 acres of grassland have become cropland — one of the largest turnovers in the region. Malsam runs a 13-square-mile family farm there. He grows corn, soybeans and wheat, then rents out his grassland for grazing. Each year, the family converts another 160 acres from grass to cropland.
Chemicals kill the grass. Machines remove the rocks. Then tractors plow it three times to break up the sod and prepare it for planting.

Scattered among fields of 7-foot tall corn and thigh-high soybeans, some stretches of grassland still exist. Cattle munch on some grass. And "prairie potholes" — natural ponds ranging from small pools to larger lakes — support a smattering of ducks, geese, pelicans and herons. Yet within a mile of Malsam's farm, federal satellite data show, more than 300 acres of grassland have been converted to soybeans and corn since 2006.

Nebraska has lost at least 830,000 acres of grassland, a total larger than New York City, Los Angeles and Dallas combined. "It's great to see farmers making money. It hasn't always been that way," said Craig Cox of the Environmental Working Group. He advocates for clean energy but opposes the ethanol mandate. "If we're going to push the land this hard, we really need to intensify conservation in lockstep with production, and that's just not happening," he said.

Jeff Lautt, CEO of Poet, which operates ethanol refineries across the country, including in South Dakota, said it's up to farmers how to use their land. "The last I checked, it is still an open market. And farmers that own land are free to farm their land to the extent they think they can make money on it or whatever purpose they need," he said. Yet Chris Wright, a professor at South Dakota State University who has studied land conversion, said: "The conversation about land preservation should start now before it becomes a serious problem." Wright reviewed the AP's methodology for determining land conversion.

The AP's analysis used government satellite data to count how much grassland existed in 2006 in each county, then compare each plot of land to corresponding satellite data from 2012. The data from the U.S. Geological Survey and the Department of Agriculture identify corn and soybean fields. That allowed the AP to see which plots of grassland became cropland.

To reach its conservative estimate of 1.2 million acres lost, the AP excluded grassland that had been set aside under the government's Conservation Reserve Program, in which old farmland is allowed to return to a near-natural state. The AP used half-acre sections of earth and excluded tiny tracts that became corn, which experts said were most likely outliers. Corn prices more than doubled in the years after Congress passed the ethanol mandate in 2007. Now, Malsam said, farmers can make about $500 an acre planting corn. His farm has just become profitable in the past five years, allowing him and his wife, Theresa, to build a new house on the farmstead.

Four miles south, signs at each end of the town of Roscoe announce a population of only 324. But the town, which relies in part on incomes like Malsam's, supports a school, a restaurant, a bank, a grocery store and a large farm machinery store. The manager of the equipment dealership, Kaleb Rodgers, said the booming farm economy has helped the town and the dealership prosper. The business with 28 employees last year sold a dozen combines at about $300,000 apiece, plus more than 60 tractors worth between $100,000 and $300,000, he said.

"If we didn't have any farmers we wouldn't have a community here. We wouldn't have a business. I wouldn't be sitting here. I wouldn't be able to feed my family," Rodgers said. "I think ethanol is a very good thing." Jim Faulstich, president of the South Dakota Grasslands Coalition, said the nation's ethanol and crop insurance policies have encouraged the transformation of the land. Faulstich, who farms and ranches in central South Dakota near Highmore, said much of the land being converted is not suited to crop production, and South Dakota's strong winds and rains will erode the topsoil.

"I guess a good motto would be to farm the best and leave the rest," he said.

Gillum reported from Washington. Associated Press writers Dina Cappiello and Matt Apuzzo contributed to this report from Washington.


http://www.newsdaily.com/article/15847e18e6398470fc3bf01220241814/prairies-vanish-in-the-us-push-for-green-energy

577 Trees Saves 77,000 kWh in Energy in Ten Years

Planting a tree will significantly reduce summer energy bills and improve environment, study finds.

Now that spring is in full swing, many people are sprucing up their yards with perennials, annuals and shrubs. However a new study led by Ryerson University may convince residents to plant a tree close to their home, not only because trees can lead to reducing utility bills, but they have environmental benefits as well.

"Our urban environment has many structures made of concrete and asphalt, which absorb a great deal of the sun's energy, creating a 'heat-island' effect," says Andrew Millward, co-author of the study and a geography professor at Ryerson University. "To mitigate the rise in city temperatures during the summer, we need to protect and expand urban vegetation cover, such as large trees, which provides shade and cooling in the areas that we live and work."

Millward and his research team used an online tool to measure the energy savings generated by 577 trees planted by Torontonians on their property between 1997 and 2000. The study found that these trees saved homeowners 77,000 kWh in energy over a 10-year period. On a per-tree basis, these savings are equivalent to the amount of electricity needed to run an average Canadian home for about a week (assuming household use is approximately 25 kWh per day).

As trees grow larger, their energy conservation benefits increase significantly; after 25 years, Millward estimates each tree will save between 435 and 483 kWh per household—equal to running a dishwasher once every day for an entire year. This can translate into a saving of upwards of $40 annually.

The researchers also found that in Toronto's densely built urban neighbourhoods, more than half of the energy conserved was from shading provided by trees planted in neighbouring lots. Trees also provide environmental benefits such as reducing air pollution, providing a natural habitat for wildlife, sequestering carbon dioxide from the air and mitigating storm water runoff. Toronto's urban forest covers 20 per cent of the land, with 60 per cent of trees located on homeowners' property.

Thinking about where to plant a tree? Professor Millward says residents who don't have any trees on their property should plant a native tree species either west or south-west of their home. This provides the most shade during the afternoon, typically the hottest time of day. For those with existing trees, he suggests they find a place for a new tree that will give it enough space to grow.

The online tool used in the study to measure the energy conservation benefits of trees was created by Millward for Local Enhancement and Appreciation of Forests (LEAF), a Toronto-based non-profit organization. Using the Ontario Residential Tree Benefits Estimator, homeowners can select their city, tree species and location to plant. The tool then provides an estimate of the energy savings, reduction in air pollution and other conservation benefits.

"I would strongly encourage homeowners to explore all of the benefits that trees can provide, not just the energy cost-saving measures," says Millward. "This really is a win-win for not only residents, but for our environment because we are helping to mitigate rise in urban temperatures and buffer the impacts of global warming."

The study's research team comprises Ryerson graduate student Michelle Sawka, lead author of the study, Environmental Applied Science and Management, Ryerson University; Janet Mckay, LEAF; and Misha Sarkovich, Sacramento Municipal Utility District. Programming of the online tree benefits estimator was done by student Nikesh Bhagat of Ryerson's spatial analysis graduate program . The study, "Growing Summer Energy Conservation through Residential Tree Planting," was published in the May issue of the journal Landscape and Urban Planning.

http://phys.org/news/2013-05-tree-significantly-summer-energy-bills.html

U.S. Urban Trees Store Carbon, Provide Billions in Economic Value

From New York City's Central Park to Golden Gate Park in San Francisco, America's urban forests store an estimated 708 million tons of carbon, an environmental service with an estimated value of $50 billion, according to a recent U.S. Forest Service study.

 

Annual net carbon uptake by these trees is estimated at 21 million tons and $1.5 billion in economic benefit.
In the study published recently in the journal Environmental Pollution, Dave Nowak, a research forester with the U.S. Forest Service's Northern Research Station, and his colleagues used urban tree field data from 28 cities and six states and national tree cover data to estimate total carbon storage in the nation's urban areas.
"With expanding urbanization, city trees and forests are becoming increasingly important to sustain the health and well-being of our environment and our communities," said U.S. Forest Service Chief Tom Tidwell.

"Carbon storage is just one of the many benefits provided by the hardest working trees in America. I hope this study will encourage people to look at their neighborhood trees a little differently, and start thinking about ways they can help care for their own urban forests."

Tens of thousands of people volunteered to plant and care for trees for Earth Day and Arbor Day this year, but there are opportunities all year long. To learn about volunteer opportunities near your home, visit the Arbor Day Foundation. The Forest Service partners with organizations like the Arbor Day Foundation and participates in programs like Tree City USA to recognize and inspire cities in their efforts to improve their urban forests. Additionally the Forest Service is active in more than 7,000 communities across the U.S., helping them to better plan and manage their urban forests.

Nationally, carbon storage by trees in forestlands was estimated at 22.3 billion tons in a 2008 Forest Service study; additional carbon storage by urban trees bumps that to an estimated 22.7 billion tons. Carbon storage and sequestration rates vary among states based on the amount of urban tree cover and growing conditions. States in forested regions typically have the highest percentage of urban tree cover. States with the greatest amount of carbon stored by trees in urban areas are Texas (49.8 million tons), Florida (47.3 million tons), Georgia (42.4 million tons), Massachusetts (39.6 million tons) and North Carolina (37.5 million tons).

The total amount of carbon stored and sequestered in urban areas could increase in the future as urban land expands. Urban areas in the continental U.S. increased from 2.5 percent of land area in 1990 to 3.1 percent in 2000, an increase equivalent to the area of Vermont and New Hampshire combined. If that growth pattern continues, U.S. urban land could expand by an area greater than the state of Montana by 2050.
The study is not the first to estimate carbon storage and sequestration by U.S. urban forests, however it provides more refined statistical analyses for national carbon estimates that can be used to assess the actual and potential role of urban forests in reducing atmospheric carbon dioxide.

More urbanization does not necessarily translate to more urban trees. Last year, Nowak and Eric Greenfield, a forester with the Northern Research Station and another study co-author, found that urban tree cover is declining nationwide at a rate of about 20,000 acres per year, or 4 million trees per year.

http://www.sciencedaily.com/releases/2013/05/130507195815.htm