How Ice Storms May Shape the Future of Forests

In order to study the effects of an ice storm on tree growth, susceptibility to pests and pathogens, changes in habitat for wildlife, a team of researchers created an ice storm at Hubbard Brook Experimental Forest in New Hampshire.

By the Cary Institute of Ecosystem Studies

A team of scientists in New Hampshire recently succeeded in capturing one of nature's most destructive forces - ice - and corralling it in two large research plots on the Hubbard Brook Experimental Forest.
 
Scientists from the USDA Forest Service, Syracuse University, the Cary Institute of Ecosystem Studies, Cornell University, University of Vermont, and the Hubbard Brook Research Foundation created an experimental ice storm that will improve understanding of short- and long-term effects of ice on northern forests.

Ice storms are a big deal in a changing world. Ice storms are expected to become more frequent and severe in the northeastern United States and eastern Canada as long term climate continues to warm while short term weather patterns still bring blasts of arctic air into the region.

Large Ice storms disrupt lives and damage infrastructure in towns and cities in northern New England, resulting in billions of dollars in damage. Ice storms also literally reshape forests. Heavy ice loads break branches and topple whole trees, resulting in reduced tree growth in ensuing years, increased susceptibility to pests and pathogens, changes in habitat for wildlife, and alterations in how nutrients like carbon and nitrogen cycle in the forest.

"Science is critical to our understanding of how climate change may shape forests in the future," said Tony Ferguson, acting director of the Northern Research Station and the Forest Products Laboratory. "Creating an ice storm is a very unique experiment that would not be possible without all of our partners and funding from the National Science Foundation."

While ice storms are a powerful force in forests, they are also inherently difficult to study because scientists, like citizens, have little lead time on when and where these storms are going to occur. Scientists at the Hubbard Brook Experimental Forest are changing that equation, and instead of waiting for the next big storm to hit, they are creating their own artificial ice storms using high-pressure firefighting pumps and hoses to spray water high up into the forest canopy during a cold snap. They are measuring the obvious and immediate downing of limbs and trees, as well as subtler longer term growth responses, interactions with invasive species, and impacts on forest nutrient cycling.

"This research will provide the scientific community, land managers and the concerned public greater insight on the impacts of these powerful, frightening, and curiously aesthetic extreme winter weather events on ecosystem dynamics in northern hardwood forests," said Lindsey Rustad, team leader at Hubbard Brook Experimental Forest and an investigator on the ice storm experiment.

"Ice storms are a great example of extreme weather events with complex outcomes. The experimental ice storm is part of a comprehensive study of ice storms and their effects at Hubbard Brook, which also includes examining forest recovery from a severe ice storm in 1998, developing and applying models to depict the climate conditions that result in ice storms and forest ecosystem effects, and associated outreach and education," said Charles Driscoll, a professor at Syracuse University and investigator for the Hubbard Brook ice storm experiment.

In addition to Rustad and Driscoll, investigators in the experiment include John Campbell and Paul Schaberg of the USDA Forest Service; Katharine Hayhoe of Texas Tech University, and Sarah Garlick of the Hubbard Brook Research Foundation. Partners include Peter Groffman of the Cary Institute of Ecosystem Studies, Timothy Fahey of Cornell University, and Robert Sanford and Joe Staples of the University of Southern Maine.

The Hubbard Brook Ice Storm Experiment is funded by a grant from the National Science Foundation (DEB-1457675 - Collaborative Research: Understanding the Impacts of Ice Storms on Forest Ecosystems of the Northeastern United States).

The mission of the Forest Service's Northern Research Station is to improve people's lives and help sustain the natural resources in the Northeast and Midwest through leading-edge science and effective information delivery.

The mission of the Forest Service, part of the U.S. Department of Agriculture, is to sustain the health, diversity, and productivity of the Nation's forests and grasslands to meet the needs of present and future generations. The agency manages 193 million acres of public land, provides assistance to state and private landowners, and maintains the largest forestry research organization in the world.

Public lands the Forest Service manages contribute more than $13 billion to the economy each year through visitor spending alone. Those same lands provide 20 percent of the nation's clean water supply, a value estimated at $7.2 billion per year. The agency has either a direct or indirect role in stewardship of about 80 percent of the 850 million forested acres within the U.S., of which 100 million acres are urban forests where most Americans live.

How Ice Storms May Shape the Future of Forests

Hypoallergenic Parks: Coming soon?

Garcia Lorca Park, one of the urban green spaces studied by Cariñanos Gonzalez and her team. Credit: Manuel Casares-Porcel.

Ah-choo! If you suffer from seasonal allergies, you're probably sick of this refrain. And you're not alone. Millions of Americans suffer from seasonal allergies. Moreover, there are allergy sufferers around the world echoing this allergy anthem.

Among the ranks is Paloma Carinanos, a professor of Botany at the University of Granada, in Spain. Rather than sitting back with a box of tissue, Dr. Carinanos has taken a more proactive approach to fighting her seasonal allergies. She studies how the trees in urban green spaces contribute to and even cause allergies.

Carinanos' interest in studying allergies started early. She and her seven brothers and sisters all suffer from seasonal allergies, a trait they inherited from their father. "Since I was young, I became an expert in everything associated with this disease, its symptoms, how to prevent it, avoid it, or treat it." Carinanos said. Despite this early interest in plants and allergies, she originally planned to attend veterinary school. But she says, "I think that my destiny was written, and I was admitted to the Faculty of Biology of the University of Cordoba."

Now she is an expert in the conservation and management of plants and wildlife. With her team, she studies how the plants in urban green spaces affect the air quality of that area. Then they look at how the air quality affects human health. Her team specifically studies the city of Granada, Spain. This city's climate and layout is like that of many cities in the Mediterranean area, which has the highest occurrence of pollen allergies in the world. The researchers hope their efforts will lead to fantastic urban green spaces that don't cause allergic reactions for 30% of the city's population.

Cypresses in the historical neighborhood Albayzin, in Granada. You can see how symbolic (and common) these trees are to the region. Credit: Paloma Cariñanos Gonzalez.

To start, Carinanos and her team began by classifying the trees in Granada's ten largest green spaces. They grouped the trees into three categories. Then they recorded the type of pollination, the length of the pollination period, and the potential for causing allergies for each tree. The researchers used all of this information to calculate if the green space was negatively affecting air quality and causing allergies.To start, Carinanos and her team began by classifying the trees in Granada's ten largest green spaces. They grouped the trees into three categories. Then they recorded the type of pollination, the length of the pollination period, and the potential for causing allergies for each tree. The researchers used all of this information to calculate if the green space was negatively affecting air quality and causing allergies.

 What the researchers found was surprising. Many of the most common trees in Granada were among the trees causing unhealthy or hazardous air quality. Carinanos also found it surprising that the design of these green spaces thought about landscaping, climate, and fashion criteria, but didn't think about pollen problems.

From their findings, the researchers have made suggestions for planning future green spaces. Their recommendations are to make sure that all citizens can enjoy the great outdoors with clear eyes and dry noses. Carinanos says that in the future, urban green spaces "will become 'comfort islands' inside 'urban heat islands.'" She wants to make sure these comfort islands are "for all citizens without exception."

This research may be just what allergy sufferers have been waiting for, and it's good news for others, too. Carefully selecting trees for green spaces may help combat climate change. Increasing the variety of trees in green spaces can both decrease allergies and increase the urban vegetation's ability to clean pollutants out of the air.

Carinanos and her team stress that their research is a tool for planning and prevention. They hope that other cities will be able to use their methods to prevent high allergen levels. Doing so may help growing city populations live more comfortably and with fewer health issues. The researchers ultimately want to ensure that urban green spaces play a role in keeping both the climate and people healthy.

http://phys.org/news/2015-08-hypoallergenic.html

Urban Trees Save Lives

A recent study by urban forestry guru David Nowak and other researchers at U.S. Forest Service and The Davey Institute found that urban trees save at least one life per year in most cities and up to 8 people per year in large metropolises like New York City.

“Trees growing in cities help clean the air of fine particulate air pollution — soot, smoke, dust, dirt — that can lodge in human lungs and cause health problems,” Grist explains. As an example, “trees clear 71 tons” of air particulate matter 2.5 micrometers in diameter (PM2.5) from Atlanta’s air each year.

Urban particulate air pollution kills as many as 2.5 million people each year. PM 2.5 has a drastic effect on human health, including premature mortality. Researchers noted that larger particles between particulates 2.5 to 10 micrometers in diameter—also called coarse dust particles or PM10—are removed by trees at a substantially higher rate. However, the health benefits of PM2.5 removal is 30 to 350 times more valuable.

What happens to our health when those trees die from natural causes en masse? Apparently, as another recent study claims, people die, too. This study showed that the “loss of trees to the emerald ash borer increased mortality related to cardiovascular and lower-respiratory-tract illness. This finding adds to the growing evidence that the natural environment provides major public health benefits.” Untrammeled development would then also have the same negative health impacts at the ash borer.

Of course, the health benefits are not restricted to our lungs and heart, but also our minds. As can be seen in a new UK-wide study, parks, gardens, and even street trees in urban areas improve the mood and mental well-being of the surrounding residents.

The value of trees goes well beyond their immediate air quality-reducing properties, too. According to one recent U.S. Forest Service study, “urban forests are responsible for storing 708 million tons of carbon—a service valued at $50 billion.”

Not to ignore the financial side of better health, the Nowak study also claims that “the average health benefits value per hectare of tree cover was about $1,600, but varied [from city to city].”
The study concludes that “trees can produce substantial health improvements and values in cities.” Although more research is needed to improve these estimates, this study also leaves room for new research that explores the local effects of tree-filled landscapes in cities.

http://dirt.asla.org/2013/08/06/urban-trees-save-lives/

Reconsidering the Underworld of Urban Soils

by Laura Solano

Look down. If you are in a city or large town, below you is a vast network of hidden systems that support your life: pipes that carry natural gas, potable water, stormwater, sewage, and communications wires. These pipes rarely come to mind, but we agree that their operation is for the common good, that survival is not possible without them, and that armies of workers should keep them running. Surrounding those pipes are soils that are equally critical to our existence but to which we give much less attention. If we truly understood the delicacy of soil as a dynamic living system integral to the health of our towns and cities, our neighborhoods and families, we would be more cautious about how it is perceived, treated, and protected. Healthy soil performs important functions such as sequestering CO₂, mitigating stormwater runoff, supporting plant life, and sustaining the microbial populations that form the basis for all living things. So essential and complex are the conditions for soils in more developed areas that a new branch of science has arisen and is now being intensively pursued: the science of urban soils.

The Challenges of Urban Soils

Urban soils are are naturally-occurring soils that have been disturbed by development in a way that affects their functioning and properties. Urban soils are distinguished by a number of similar features: Their horizons (the natural vertical order of soils) have become jumbled by excavation. This makes urban soil horizons confoundingly diverse; one layer may be hospitable, but adjacent layers may not be, creating abrupt changes that can cause impermeable interfaces. Soil structure (the balance of solids and pores) has been crushed out of existence by mechanical compaction that chokes off water and air exchange. Organic matter (the source of plant nutrients) is low or missing from lack of replenishment, and this imbalances the soil biological community (bacteria, fungi, nematodes, arthropods, earthworms, insects, and more). Soil volumes that are important for plant health decrease because of interruptions from urban debris such as construction waste and rocks. Finally, the predominance of pavement separates soils from natural inputs such as nutrient-rich leaf litter, and this separation causes the nutrient cycling system to slow or shut down.

In the urban environment, soils are likely to be sealed off from the agents that build healthy soil—including wind, precipitation, ice, temperature, gravity, and mineralization—which frequently have been replaced by anthropogenic processes detrimental to soil functioning. Urban soils often become defined by human activities and land use histories at a particular location rather than by the continuum of geologic processes. This disrupted order makes urban soils particularly challenging to analyze, manage, and construct.

Urban Soils in the Service of Stormwater Management

Urban soils have the potential to be an important partner in stormwater management, use, and protection. The Natural Resources Conservation Service has recognized that soils with good infiltration and permeability can significantly reduce stormwater runoff rates and volumes that might otherwise overwhelm and impair the performance of the chain of water bodies that sustain our water supplies and the ecosystems that are necessary for healthy living [1]. Good infiltration reduces runoff by letting water soak into soils before it builds up to damaging volumes and velocities that would erode topsoil and carry both silts and pollutants to waterways. Permeability influences how quickly absorbed water drains through soil to useful depths for plants and recharge. Water that reaches root zones reduces irrigation needs. Some soil can filter toxic compounds or excess nutrients by holding them, degrading them, or otherwise making them unavailable. All of these benefits are feasible when soil has adequate pore space, which is only possible when soil’s natural physical texture and structure have been preserved or created.

Over-compaction of soils is one of the greatest deterrents to implementing best practices for stormwater management, because crushed particles minimize pore space and prevent water and air from moving through. In a study by the University of Florida, soil compaction from construction vehicles reduced infiltration by 70 to 90% [2].  This is perilously close to impermeable pavement.While people recognize that reducing pavement is the primary way to improve stormwater management, few see the same connection with soil. It is not enough to substitute pavement with plant beds if nothing has been done to prevent construction compaction. Without a soil management plan that includes practices for dealing with compaction before, during, and after development, urban soils will continue to become, plot by plot, a decommissioned resource in stormwater management.

 A Partnership between Urban Soils and Vegetation

The greatest positive effect of healthy urban soil is most evident in plants, the workhorses of the environment that clean the air, absorb CO₂, abate high temperatures, support wildlife, slow stormwater runoff, and keep erosion in check. In recent years, there has been resurgence in support for increasing the vegetation and tree cover in American cities. We are well aware of the positive ecological, social,[3]  and economic value of plants for individual properties, community open space, and urban regions [4]. Ecologically, a single large tree in the city is said to be ten to twenty times more beneficial to the environment than a single tree in the forest [5]. Yet the health of urban trees is declining at a rapid rate. A recent study by the U.S. Forest Service looked at twenty cities and found that they are losing tree canopy cover on average by 3% per year [6]. While this loss may seem small, over time the cumulative effects are severe. For example, Washington, D.C. lost 64% of its acreage-coverage from 1973 to 1999 at an average annual rate of 2.5% [7]. Still we continue to ignore the most basic need of trees: healthy soils. On most urban sites, fertile topsoil is absent, plant roots are restricted, air and water movement is suppressed, and nutrients cannot be exchanged. All this puts plants at an extreme disadvantage. The evidence of poor soil is all around, telegraphed by unhealthy plants. So if trees are to become “beautiful utilities” as urban tree expert Henry Arnold [8] suggests, then soil must also be treated in projects as an essential utility: analyzed, engineered, budgeted, scrutinized, and maintained.

Advocating for Soil

There are sound economic reasons to invest in good soil. As one of the core infrastructural materials in every urban landscape project, soil needs only to be tended more carefully to make it a viable component of stormwater management. Using soils to store and retain water as part of the stormwater management system can reduce costs for piping, drainage structures, runoff storage tanks, irrigation systems, and infrastructure maintenance and can provide more flexibility in design, since hard systems can add horizontal and vertical complexity that limits design options. Plants (especially street trees) with well-functioning soil are more able to start and sustain the nutrient cycling system without big infusions of maintenance after establishment and in maturity. When they do get maintenance, they are more likely to respond. Healthy soils beget trees that live longer and grow bigger, enabling them to cast more shade, and absorb more CO₂, and runoff. Even asphalt benefits from healthy trees, since shade improves its performance and durability [8]. Last, trees in good quality soil are far less prone to infection and pests, virtually eliminating the need for chemical treatments [9]. Investing in soil is critical for the long-term health of urban trees and by extension for the success of sustainable landscape projects and green infrastructure programs.

Why then do urban soils get so little attention when they are such a critical part of our environmental infrastructure and, ultimately, of human well-being? Some of the unawareness stems from societal and governmental ignorance. While keeping water and air usable is an unquestioned necessity, few people have the same association with city soils. For the most part, urban soil is considered mysterious, complex, and costly. Design professionals have an important role to play in dispelling unwarranted concerns and helping solve tangible problems: They should lead the way, project by project, educating their clients, agencies, and others about the need for healthy soil. Before that happens, designers must step up their own soil education. My interactions with colleagues suggest a dearth of understanding of basic soil science and the need for soil management in landscape projects. Often other landscape architects reach out for soil advice only when something has gone wrong. Designers do however have a thirst for this information as is shown by the increasing number of packed sessions in soil education at the annual meeting of the American Society of Landscape Architects (ASLA), the professions’ largest organization. Perhaps the neglect is also due to the fact that soil is not yet a hip topic; it has no visual presence. For many, design attention is reserved for visual effects; the hidden, infrastructural elements of landscape have long been considered the domain of engineers and scientists.

In my work as a landscape architect at Michael Van Valkenburgh Associates, soil discussions begin early, sometimes in the concept phase and always by schematic design. Soil is always an item on the design checklist. Just as all practitioners request surveys to locate utility lines, we request USDA soil tests to understand what we have to work with. Partnering with soil scientists, we have learned to interpret laboratory tests so we can ask the right questions and frame discussions. We keep up with developments in soil science (biology is the big topic now), often consult allied professionals, incorporate quality control practices into our specifications, and closely monitor sourcing, blending, and installing of soils during construction. We consider soil rigorously, as we do any other product or system in our projects.
I don’t mean to imply that assuring good soil is obvious or easy; it is neither, even for a firm that has been attempting it for twenty years. Every project brings unique soil challenges and clients with different agendas. The client may be unfamiliar with non-traditional stormwater approaches and therefore reluctant to consider soil-dependent systems. Brownfield properties often have contaminated soil or no useful soil at all. In other kinds of properties, existing soils could be reused if amended, but space may be too limited to manage soil-blending operations. Sometimes soil chemistry is limiting. For example: elevated pH from concrete or limestone rubble can interrupt nutrient exchange and narrow plant selection; high salinity in soil near tidal waters wreaks havoc on water uptake and cellular structure in plants. Local contractors often have no experience with installing designed soils. In my experience, construction managers show little tolerance for any aspect of landscape construction that is dynamic, an inherent characteristic of soil in particular and landscapes in general. Unless we have a repeat client, the process of educating, convincing, and making monetary tradeoffs to get good soil starts anew on every project. Sometimes we battle the sins of others’ projects in which someone tried but failed to improve soils. Projects with unsuccessful or difficult soil processes often produce rumors that the landscape architect specified unrealistic soils that cost too much and slowed the schedule, even if the problem was caused by the laxity of a member outside the design team.

Repositioning Soil as Infrastructure

How can we begin a campaign for good urban soil? We can start by talking with city hall, one of the biggest makers of landscapes and planters of trees, about the importance of soil. How many of the thousands of landscapes planted every year include soil improvement? Atlanta, Detroit, Denver, Los Angeles, and many other cities have tree-planting programs. Ambitious past and current mayors like Richard Daley and Michael Bloomberg launched campaigns to plant a million trees. Despite current commitments to increasing urban vegetation through tree planting, under current practices the mortality rate for young street trees is shockingly high: Some studies have found that over twenty-five percent of newly planted trees die within two years of installation [10,11], wasting already strained public funds and leaving behind a depressing reminder of failed nature. Wouldn’t it be more strategic to forgo planning one million trees in poor soil and instead plant 500,000 trees in good soil? [12]

To be stewards of urban soils, we need to ask pointed questions early in and throughout projects and insist on satisfactory answers that ensure positive long-term results for stormwater and planting. When zoning requires developers to add or replace trees, we need to ask for more than in-kind caliper inches and to require a soil management plan. When contractors install soil, they need to treat it like the valuable commodity it is or bear the cost of remediation. State and municipal specifications (which are used by contractors defensively instead of proactively) already define which dirt is suitable for backfill—why not extend this thinking to include requirements for the type, procurement, handling, and installation of planting soil? Landscape architects and anyone else who works with the landscape need to heed these too. Such guidelines should not be overly technical or onerous. Plant species should be matched to soil conditions, especially its pH and water supply. Trees should be planted at the right elevation to expose the root flare so soil doesn’t suffocate the tree. Adequate soil volume (800 to 1400 cubic feet per tree) and shared root space to encourage root spread should be provided [13]. Soils should be arranged to mimic the horizons in nature in which the top is rich in nutrients, the middle has the correct structure to encourage root growth, and the bottom is drainable. To resist compaction and maintain water and air exchange, soils higher in medium-to-coarse sands (rather than easily compactable fine sands and loam) should be used, and limits on density should then be set. Wet or frozen soils should not be moved or installed. To promote water and air exchange, rootball zones in tree pits should be exposed and at least half of the surface area of a plant bed should be left open, or a simple aeration system should be installed. Well-aged compost should be used to to provide 5% to 10% organics to the top layer of soils. And last, utilities should be placed at least three feet from trees.

There are more technical elements and specifications to consider, especially for sites with no soils, but as Stuart Shillaber the superintendent of horticulture at Boston’s Rose Fitzgerald Kennedy Greenway Conservancy advised me recently about introducing organic maintenance, “be happy when someone can implement 60% of the program. The rest will come when clients see results.”

The installation and upkeep of our existing “hard” utility systems requires substantial public and private investment. Creating well-functioning soils would not require large funds from the public since this work can be achieved project by project.  Upkeep of hard utilities is costly and disruptive; not so for soils that can be tended several times a year with substantially less trouble. The ASLA estimates that every year nearly 4.6 million acres are affected by public and private landscape projects [14]. Making headway on a quarter to third of that amount would start a revolution.

The Future of Urban Soils

From my vantage point, prospects for improving urban soils are good. In my thirty-year career as a landscape architect, there has never been a time of greater interest, research, and resources for managing urban soils and as many successfully constructed projects using urban soils. Advocacy for higher quality soil is rising nearly forty years after Dr. Phil Craul (professor emeritus at SUNY) and his colleagues started the field studies on urban soils that led to his 1992 publishing of the seminal Urban Soil in Landscape Design. Today, the USDA’s National Resources Conservation Service has substantial mapping, literature, and research on urban soils [15]. Ted Hartsig, a division chair of the Soil Science Society of America, tells me that the organization recently formed an urban soils division and committee whose focus is issues of urban soils including morphology and classification, the relationship of chemicals and nutrient quality, physics, biology, and structure, as well as the restoration and management of these soils. Urban soils studies are proliferating at public and private universities like Johns Hopkins and Kansas State.

Most critically, the public is starting to understand at the personal level of their gardens that the old adage “better to put a $5 tree in a $50 hole than to put a $50 tree in a $5 hole” is correct. Remember that until professionals and individuals teamed together to demand action, climate change was downplayed. Landscape architects and other professionals must play a part, whether through projects, lobbying our government, writing articles, lecturing, self-education, or speaking up in any propitious situation. We can be plausible leaders in the discussion to invest in another underworld utility, the first that is purely for the public good.

References

[1]  Soil Quality Information Sheet. Soil Quality Indicators: Infiltration”, Natural Resources Conservation Service, USDA, January 1998 http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_019144.pdf

[2]  J.H. Gregory, M.D. Dukes, P.H. Jones, and G.L. Miller, “Effects of urban soil compaction on infiltration rate,” Journal of Soil and Water Conservation, Volume 61, Number 3. http://abe.ufl.edu/mdukes/pdf/stormwater/Gregor-et-%20al-JSWC-compaction-article.pdf

[3]  Geoffrey H. Donovan, David T. Butry, Yvonne L. Michael, ScD, Jeffrey P. Prestemon, Andrew M. Liebhold, Demetrios Gatziolis, Megan Y. Mao, American Journal of Preventive Medicine, “The Relationship Between Trees and Human Health: Evidence from the Spread of the Emerald Ash Borer,” Volume 44, Issue 2, pp. 139–45, http://www.ajpmonline.org/webfiles/images/journals/amepre/AMEPRE_3662-stamped_Jan_8.pdf

[4]  “Statistics on the Economic Value of Trees,” Conservation Montgomery, http://conservationmontgomery.org/resources2.html

[5]  “Study: Nations urban forests losing ground; New Orleans, Albuquerque, Houston losing Trees.” News Release, USDA Forest Service, February 23, 2012, http://www.fs.fed.us/news/2012/releases/02/urban-forests.shtml

[6]  Stephen C. Fehr, “Mayor Working To Keep It Green; Williams Pleads For More Trees,” Washington Post, November 17, 1999, http://caseytrees.org/wp-content/uploads/2012/02/02.01.1999-original-article-washingtonpost.pdf

[7]  Henry Arnold, “Sustainable Trees for Sustainable Cities,” Arnoldia, Volume 53, Number 3, 1993, http://arnoldia.arboretum.harvard.edu/pdf/articles/1993-53-3-sustainable-trees-for-sustainable-cities.pdf

[8]  E. Gregory McPherson and Jules Muchnick, “Effects of Street Tree Shade on Asphalt Concrete Pavement Performance,” Journal of Arboriculture, Volume 31, Number 6, November 2005, 303, http://www.fs.fed.us/psw/publications/mcpherson/psw_2005_mcpherson001_joa_1105.pdf

[9]  “Basics of Organic Maintenance”, UMass Extension, Center for Agriculture, http://www.extension.org/pages/62978/basics-of-organic-landscape-maintenance

[10]  “New Research Survey Suggests Urban Trees are On the Decline,” Public Radio International, March 16, 2012, http://www.pri.org/stories/science/environment/new-research-survey-suggests-urban-trees-are-on-the-decline-8967.html

[11]  Jacqueline W.T. Lu, Erika S. Svendsen,
Lindsay K. Campbell, Jennifer Greenfeld, Jessie Braden, Kristen L. King, and Nancy Falxa-Raymond, “Biological, Social, and Urban Design Factors Affecting Young Street Tree Mortality in New York City,” City and the Environment, Volume 3, Issue 1, 2010, http://digitalcommons.lmu.edu/cgi/viewcontent.cgi?article=1069&context=cate

[12]  “As City Plants Trees, Some Say a Million Are Too Many,” The New York Times, October 18, 2011, http://www.nytimes.com/2011/10/19/nyregion/new-york-planting-a-million-treestoo-many-some-say.html?pagewanted=all

[13]  James Urban, Up by Roots: Healthy Soils and Trees in the Built Environment, International Society of Arboriculture, 2008

[14]  “What is Landscape Architecture?” American Society for Landscape Architects, http://www.asla.org/nonmembers/LicPac99.htm

[15]  Soil Quality Information Sheets, Soil Quality Institute in cooperation with the National Soil Survey Center, NRCS, USDA; and the National Soil Tilth Laboratory, Agricultural Research Service, USDA, http://soils.usda.gov/sqi/publications/publications.html#utn

Suggested Reading

Timothy A. and Philip J. Craul, Soil Design Protocols for Landscape Architects and Contractors, Jon Wiley & Sons, 2006.

James Urban, Up by Roots: Healthy Soils and Trees in the Built Environment, International Society of Arboriculture, 2008

“Standards for Organic Land Care, Practices for the Design and Maintenance of Ecological Landscapes”, NOFA Organic Land Care Program publication, Northeast Organic Farmer’s Association, 2011. http://www.organiclandcare.net/sites/default/files/upload/standards2011.pdf

“Landscape Performance Series: Benefits Toolkit, Fast Facts Library, Scholarly Works”, Landscape Architecture Foundation, http://lafoundation.org/research/landscape-performance-series

http://landscapeurbanism.com/article/reconsidering-the-underworld-of-urban-soils/

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