By Jeff Grabmeier
When the summer sun blazes on a hot city street, our first reaction is to flee to a shady spot protected by a building or tree.
A new study is the first to calculate exactly how much these shaded areas help lower the temperature and reduce the “urban heat island” effect.
Researchers created an intricate 3D digital model of a section of Columbus and determined what effect the shade of the buildings and trees in the area had on land surface temperatures over the course of one hour on one summer day.
“We can use the information from our model to formulate guidelines for community greening and tree planting efforts, and even where to locate buildings to maximize shading on other buildings and roadways,” said Jean-Michel Guldmann, co-author of the study and professor emeritus of city and regional planning at The Ohio State University.
“This could have significant effects on temperatures at the street and neighborhood level.”
For example, a simulation run by the researchers in one Columbus neighborhood found on a day with a high of 93.33 degrees Fahrenheit, the temperature could have been 4.87 degrees lower if the young trees already in that area were fully grown and 20 more fully grown trees had been planted.
Guldmann conducted the study with Yujin Park, who did the work as a doctoral student at Ohio State and is now an assistant professor of city and regional planning at Chung-Ang University in South Korea, and Desheng Liu, a professor of geography at Ohio State.
Their work was published online recently in the journal Computers, Environment and Urban Systems.
Researchers have long known about the urban heat island effect, in which buildings and roadways absorb more heat from the sun than rural landscapes, releasing it and increasing temperatures in cities.
One recent study found that in 60 U.S. cities, urban summer temperatures were 2.4 degrees F higher than rural temperatures – and Columbus was one of the top 10 cities with the most intense summer urban heat islands.
For this new study, Guldmann and his colleagues selected a nearly 14-square-mile area of northern Columbus that had a wide range of land uses, including single-family homes, apartment buildings, commercial and business complexes, industrial areas, recreational parks and natural areas. More than 25,000 buildings were in the study area.
The researchers created a 3D model of the study area using machine-learning techniques which combined 2D land cover maps of Columbus, as well as LiDAR data collected by the city of Columbus from an airplane. LiDAR is a laser sensor that detects the shape of objects. Combining this data resulted in a 3D model showing the exact heights and widths of buildings and trees.
They then turned to computer software that calculated the shadows cast by each of the buildings and trees in the study area over the course of a one-hour period – 11 a.m. to noon – on Sept. 14, 2015.
In addition, the researchers had data on land surface temperatures in the study area for the same date and time. That data came from a NASA satellite that uses Thermal Infrared Sensors to measure land surface temperatures at a resolution of 30 by 30 meters (about 98 by 98 feet). That resulted in surface temperatures for 39,715 points in the study area.
With that data in hand, the researchers conducted a statistical analysis to determine precisely how the shade cast by buildings and trees affected surface temperatures on that September day.
Results showed that, as expected, buildings turned up the heat in the area, but that the shadows cast by them also had a significant cooling effect on temperatures, particularly if they shaded the rooftops of adjacent buildings.
The statistical model could precisely calculate those effects, both positive and negative. For example, a 1% increase in the area of a building led to surface temperature increases between 2.6% and 3% on average.
But an increase of 1% in the area of a shaded rooftop led to temperature decreases between 0.13% and 0.31% on average.
Shade on roadways and parking lots also significantly decreased temperatures.
“We learned that greater heat-mitigation effects can be obtained by maximizing the shade on building rooftops and roadways,” Guldmann said.
Results also showed the importance of green spaces and water for lowering temperatures. Grassy areas, both shaded and exposed, showed significant heat-reducing effects. However, the impact of shaded grass was stronger than that of grass exposed to direct sunlight.
The volume of tree canopies and the area of water bodies also had significant cooling effects.
In the simulation run in the Columbus neighborhood, the researchers calculated that if the current trees there were fully grown, the temperature on a 93.33-degree F day would be 3.48 degrees lower (89.85 degrees).
But that’s not all. The simulation showed that if the neighborhood had 20 more full-grown trees, the temperature would be another 1.39 degrees lower.
New research published by Robert Loeb, a professor in biology and forestry at Penn State DuBois, outlines his efforts to bring the experience of rural forests to those who live in cities, with an eye toward what Loeb calls “environmental justice.” The article appears in the April issue of the publication Urban Forestry and Urban Greening.
Loeb’s article details new research discoveries about urban forests that veer from his typical concentrations. For decades he has studied forests in locations like New York City and Nashville, stewarding forest regeneration by examining the impact that wildlife and humans alike have on the forest and finding ways to curb this impact. This has led to work in a new urban-forest management protocol, “SAFE” — Soils, Aliens, Fire, Exclosure — with the goal of increasing natural regeneration through soil treatments, alien species treatments, fire surveillance, and fencing to eliminate problematic browsers such as deer.
Loeb took a turn toward research in soils when in 2014 he began to study tree regeneration in an urban forest in Philadelphia known as “The Good Woods,” part of the larger Haddington Woods in Cobbs Creek Park.
“The Good Woods is exceptional in having a mature canopy, a normal layer of leaf litter and organic matter, a large number of native tree seedlings, and less herbivory than typically expected,” said Loeb. “During 2015, an exclosure fence for deer was placed around the Good Woods and an act of arson caused a ground fire in approximately half of the forest.”
What sets the Good Woods apart from other similarly situated urban forests is that many native species seedlings and saplings grow naturally below the canopy created by larger trees. Loeb’s goal is to determine why this happened at this particular site, to hopefully replicate the natural tree regeneration in other cities.
Loeb recalled, “Growing up in the Bronx, I was accustomed to seeing urban forests with only tall trees. One summer I was awarded a scholarship from the Student Conservation Association to conduct research in Vermont. What struck me the most was that the forests there had seedlings that are lacking in urban areas. I’ve been trying throughout my career to sort out this lack of natural regeneration so that people in urban settings can enjoy the beauty of rural forests when we visit urban forests.”
The most trusted theory Loeb has on the difference in soil composition impacting the natural regrowth of new trees is one that he believes is rock-solid, so to speak.
“If you have more rocks, you have less soil. So, naturally you have a smaller population of trees,” he said. “I found many of the urban parks to have a great number of stones and even boulders in the soil. One particular area of the Good Woods is almost free of stones, and the soil there supports a greater growth of young trees.”
These findings could go a long way in helping Loeb to recommend soil studies and remediation in other urban forests. “Soils are a critical issue and need to be treated,” he said. “When I was young, horticulturalists taught me that if you spend $100 to plant a tree, you spend $10 on the tree and $90 on the soil. That is a formula that has not always been in use recently, but a historical perspective that maybe we need to revisit now.”
They are iconic to Florida, but palm trees offer little shade to urban heat islands and capture very small amounts of carbon, a greenhouse gas contributing to global warming.
South Florida’s palm trees are postcard promises of sighing sea breezes and sandy beaches, but the icon of the tropics may be an impractical adornment in an era of climate change.
From the regal royal palm to the sometimes shabby cabbage, the perennial symbol of the Sunshine State offers little shade to baking urban heat islands and captures minimal amounts of carbon — a greenhouse gas contributing to global warming.
As city officials look for more ways to cool concrete jungles and balance carbon emissions, the priority for new plantings is often broadleaf hardwood trees, not the idyllic palm.
Live oaks can absorb and store 92 pounds of carbon a year with a mature tree’s canopy spanning more than 100 feet. That’s compared to less than one pound of carbon for a royal palm and its compact crown of 15 to 20 fronds.
“People coming from up north or other parts of the country are expecting to see palm trees, so I don’t see them disappearing entirely from the landscape,” said Charles Marcus, a certified arborist who wrote an urban tree management plan for West Palm Beach. “But it would benefit most communities if they increased the percentage of hardwoods and I think it’s something cities will have to consider.”
Palms aren’t even an option at City of West Palm Beach community tree giveaways, and a 2018 city ordinance puts an emphasis on using more shade trees in new construction, especially parking lots where 75 percent of the required trees must now be shade trees.
“We’re not trying to seek out and replace palm trees with canopy trees, but we are looking at if we have to do a replacement, would a canopy tree fit,” said Penni Redford, resilience and climate change manager for West Palm Beach.
Three years of studies in cities including Baltimore, Richmond, Va., and Washington by the National Oceanic and Atmospheric Administration found that areas covered in concrete with few trees could be 17 degrees warmer than shaded areas.
The same study conducted in West Palm Beach this past August found a heat-index temperature of 122 degrees near downtown, compared to 92 degrees taken during the same time period near the wetlands area of Grassy Waters Preserve.
“These are samples taken in one time period and one day out of the year, but given the conditions, the difference is staggering,” said Michael Rittehouse, sustainability project coordinator for West Palm Beach.
By Will Brendza
Jeremy Altdorfer’s day of delivery was hectic, but successful. All day on Saturday, Oct. 5 he was zipping around Boulder in his car, which was loaded to the brim with white pine saplings; making one delivery after the next, dropping off the baby trees wherever they’d been requested. Meanwhile, his brother and other partners from Experience Dental, opening Oct. 30, were doling out more trees at several different locations throughout the county.
Their goal: to plant 1,000 trees in Boulder County in a day. Or, at least, to give out 1,000 ready-to-plant trees to individuals, businesses and schools that wanted and needed them. In part, Altdorfer wants to reduce his own business’ carbon footprint, and in part, he wants to help save Boulder’s threatened canopy of trees.
“I thought we were crazy, trying to do 1,000 in a single day,” Altdorfer says. But by the end of the day, they’d met their goal — all 1,000 trees had been distributed.
Altdorfer’s 1,000 white pines are going to help offset what the City of Boulder is calling the “Tree Crisis of 2019.” Boulder’s trees are currently under threat, and while the City’s forestry department plants about 500 new ash trees a year, Altdorfer’s contribution of 1,000 white pines in a single day is a welcome offering and a much-needed addition.
“Planting new trees is crucial to maintaining our urban tree canopy,” says Kathleen Alexander, a forestry worker with the City of Boulder’s forestry department.
According to Alexander, Boulder is projected to lose some 70,000 ash trees to the emerald ash tree borer (EAB), an invasive insect from Asia, over the next 10 years. By 2035, she says, the EAB could destroy 25 percent of Boulder’s urban tree canopy.
It’s why the City is urging residents and the community to take action and plant trees to replace those being killed, and to protect existing trees. It’s why the City has planted more than 2,500 trees on public property since 2013, and why it’s provided more than 3,900 trees to residents for planting on private property.
Having an assorted mix of tree species around the City and throughout Boulder County means the urban canopy is less vulnerable to any one stressor.
“A diversity of tree species is going to help make the urban forest more resilient long-term,” Alexander says.
White pines are good options because they grow fast, they grow large (so they sequester a lot of carbon) and they aren’t at risk from EAB.
By Mary Frost
“Today is a great day for our urban forest.”
The insect that threatened to wipe out tens of thousands of the city’s trees has been squashed.
State, city and federal agencies announced on Thursday that the Asian longhorned beetle has finally been eradicated in Brooklyn and Queens, the last two holdouts in the city.
At a celebration in McCarren Park in Williamsburg, cupcakes decorated with pictures of the distinctive black insect were served to jubilant parkgoers and agriculture and horticulture experts.
“Today is a great day for our urban forest as we announce the eradication of the Asian longhorned beetle,” announced Liam Kavanagh, first deputy commissioner of the city’s Parks Department. “It was a bleak day for forestry in New York City when this pest was discovered. Half of the hardwood trees in New York State are susceptible.”
The successful eradication was the result of a decadeslong collaborative effort by multiple city, state and federal agencies, non-governmental organizations and private landowners, officials said.
These include the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, the state’s Department of Agriculture and Markets and Department of Environmental Conservation, and the city’s Department of Parks.
“It’s been a long, hard road,” USDA’s Samantha Simon said. “We knew that if it became established, the Asian longhorned beetle would threaten billions of dollars’ worth of timber [and] the maple syrup industry.”
The insect attacks maple, elm, willow, horse-chestnut, mulberry, birch, green ash, sycamore and London planetrees.
It’s been 23 years since the invasive beetle (technically not a bug) was first detected in Brooklyn. Experts believe it entered the country on wooden pallets shipped to Greenpoint.
The USDA calculated the speckled insect, about the size of a waterbug with antennae as long as its body, has wiped out more than 24,000 New York trees, and 180,000 nationwide. Thursday’s announcement marks the end of a six-year quarantine in northern Brooklyn and Queens.
To eliminate the beetle, APHIS regulated the movement of trees, firewood and woody debris and carried out surveys to find and remove infested trees. In total, APHIS removed 5,208 infested trees and treated 67,609 at-risk trees.
By Sam Lounsberry, Boulder Daily Camera
Even as Boulder County foresters press on in their fight against the invasive emerald ash borer harming the local tree population, officials acknowledge it is a losing battle.
But it is one lovers of ash trees don’t have to walk away from empty-handed, even as sickened trees are in line for removal or have already been sawed to stave off the infestation.
Woodworkers like Evan Kinsley, who started the Boulder-based business Sustainable Arbor Works several years ago, have turned to ash trees to supply their furniture and art crafting practices as a way to maintain the local benefit provided by the species slated for a countywide death at the hands of the insect. Emerald ash borer has already dramatically altered the composition of forests across the middle and eastern regions of the country.
“It’s a privilege to be able to work with a local hardwood like ash,” Kinsely said.
When he first learned of the 2013 detection of emerald ash borer in Boulder — it has since spread to Longmont, Lafayette, Lyons and Superior, but until last month, when it was first detected in Broomfield, Boulder County remained the only area in the Mountain West with a confirmed presence — Kinsley and his now-business partner Aaron Taddiken looked at each other and said, “We have to do something.”
The solution was to build a wood kiln to speed up the drying process for felled trees, and now Kinsely focuses on harvesting trees removed from the urban landscape, a large proportion of which are ash due to the pesky beetle’s invasion, and reusing them for wholesale lumber slabs and designing and building custom furniture.
“It used to be most of this time, that a lot of woodworkers got their wood from big wood suppliers. That would come from all over the country, all over the world,” Kinsley said. “It’s not a new thing to use local lumber. But it was a new idea for smaller woodworkers, smaller lumber mills to start working with tree (removal) companies.”
Supporting Kinsley’s living is not the life cycle he prefers for the trees, but he feels he is making the best out of a bad situation…
While the city and Boulder County continue treating public ash trees to keep them alive as long as possible using pesticide applications, tree adoption programs and biological weapons, enforcement against declining ash trees on private property continues to ramp up.
In 2018, Read said the city sent 182 letters to private property owners asking them to address declining ash trees posing safety hazard; in 2017 the number was 118, in 2016 it was 82. This year he expects to send a significantly larger number of such letters. The growing number of letters aligns with the advance of the beetle infestation. Tree owners who receive such a letter will have to show the city a good-faith effort is being made to remove trees considered dangerous.
But work to preserve ash trees still free of the emerald ash borer goes on, even as replanting species that won’t be affected by the invasive bug remains the focus of foresters for the future of Boulder’s canopy. The city’s Tree-Imagine campaign launched this spring is pushing city residents to collectively plant 25,000 new trees by 2025.
The county this summer introduced a swarm of a non-stinging, parasitic member of the wasp family on the Mayhoffer open space property in Superior, and also has enlisted 159 participants in its adopt-a-tree program for ashes slated for removal from public places. Program participants can choose to commit to pay for treatment to keep the trees alive.
“A lot of these ash trees are old and they’ve been with the community a long time,” Kinsley said. “Trying to protect them in every way is a valiant effort.”
By Meg Anderson and Sean McMinn
Annie Haigler steps out of her home in Louisville, Ky., pulling a handkerchief out of her pocket to dab sweat off her forehead. She enjoys sitting on her porch, especially to watch the sunrise. She has always been a morning person.
But as the day progresses, the heat can be unbearable for her. On summer days like this, when highs reach into the 90s, the lack of trees in her neighborhood is hard for Haigler to ignore.
“That’s what I’m accustomed to trees doing: They bring comfort. You don’t notice it, you don’t think about it. But they bring comfort to you,” she says.
The tree cover in her neighborhood, Park DuValle, is about half the city average. As one of the lower-income areas of Louisville, it’s in line with a citywide trend: Wealthier areas of the city have up to twice as many trees as do poorer areas.
Trees can play a huge role in the health of people living in cities, but across the country, cities are losing millions of trees year after year. And many poor urban neighborhoods — often home to a city’s most vulnerable — are starting at a disadvantage.
“If we show you a map of tree canopy in virtually any city in America, we’re also showing you a map of income,” says Jad Daley, president and CEO of the nonprofit American Forests. “And in many cases we’re showing you a map of race and ethnicity.”
That lack of tree cover can make a neighborhood hotter, and a joint investigation by NPR and the University of Maryland’s Howard Center for Investigative Journalism found just that: Low-income areas in dozens of major U.S. cities are more likely to be hotter than their wealthier counterparts, and those areas are disproportionately communities of color.
“If you live in an area in cities that is seeing more extreme heat days, but you don’t have tree cover to cool down your neighborhood, that can literally be a life or death issue,” says Daley. “The folks who are least likely to have air conditioning to weather heat waves, the folks who are most likely to have preexisting health conditions that put them at greater risk from those heat waves, aren’t getting the benefits of trees.”
A study by the Georgia Institute of Technology found Louisville to be getting hotter faster than any of the other 50 largest U.S. metropolitan areas, compared with the rural areas around them. One reason cities tend to be hotter? Fewer trees.
By Georgina Wilson-Powell
FOR FOREST-The Unending Attraction of Nature brings trees to the terraces this autumn.
Artist Klaus Littmann is creating a central European forest of 300 trees within the Wörthersee football stadium in Klagenfurt into Austria as an enormous public art installation.
The work puts trees and our view of nature firmly in the spotlight instead of soccer stars and people will be able to view the forest during the day and night and watch the turning of the autumn leaves, as if it was a sporting fixture.
It’s based on a drawing from 1937, The Unending Attraction of Nature, by Austrian artist and architect Max Peintner, that Littmann discovered almost thirty years ago.
According to Littmann, FOR FOREST, also provokes the feeling of a future memorial for nature and the fact we so often take it for granted. One day, he points out, we might be reduced to viewing ‘nature’ in this way, in designated urban spaces, much like animals in a zoo.
16 varieties of trees will be used in the forest, which were selected from tree nurseries in Italy, Germany and beyond. They were transported to Austria on lorries already on existing routes and have been cared for locally for the last six months.
The trees were selected by renowned landscape architect Enzo Enea, and have been chosen to recreate the mixed forest that once thrived in Austria before industrialisation. One of the issues explored by the project is how what we consider to be nature is not actually natural, but monoculture cultivated for profit by industry.
Once this incredible art installation is finished, the trees will be replanted locally as a permanent feature near the stadium.
By Susan Perry
“Our findings suggest that urban greening strategies with a remit for supporting community mental health should prioritize the protection and restoration of urban tree canopy,” the researchers concluded.
Many studies have found that living near a green space — land that is partly or completely covered with natural vegetation — is associated with health benefits, including lower blood pressure, reduced levels of stress and anxiety, and an increased sense of general wellbeing.
Research has even linked green space with lower Medicare expenditures.
What hasn’t been clear from these studies, however, is whether all types of green space confer the same benefits. Or are some green spaces potentially more healthful than others?
A new study from Australia, published recently in JAMA Network Open, offers an answer. It found that although residents of neighborhoods with plenty of leafy trees tend to have higher levels of psychological health and well-being, the same isn’t true for people living in neighborhoods where the green space consists primarily of open areas of grass.
In fact, people living in areas with higher percentages of bare grass tend to have higher levels of psychological stress, the study found. They also report being in poorer health.
“Our results suggest the type of green space does matter,” write the study’s authors, Thomas Astell-Burt and Xiaoqi Feng, in an online article for The Conversation. The two researchers are founding co-directors of the Population Wellbeing and Environment Research Lab at the University of Wollongong.
This finding doesn’t mean, however, that existing grassy areas should be removed or plans for new ones should be scrapped, they stress.
“Large open areas of grass can be awesome for physical activity and sport,” they write, “but let’s make sure there is also plenty of tree canopy too, while also thinking about ways to get more people outdoors in green spaces.”
Astell-Burt and Feng offer several possible explanations for their study’s findings. One has to do with the shade offered by trees:
Studies are linking high temperatures with heat exhaustion and mental health impacts. Research has suggested trees, rather than other forms of green space, may be best at reducing temperatures in cities. It may also simply be more comfortable to walk outside in cooler temperatures — not to mention going for a run or bike ride, both of which are good for mental health.
The biodiversity that trees offer may also be beneficial:
Research suggests tree canopy tends to be more biodiverse than low-lying vegetation. Increased biodiversity may support better mental health by enhancing the restorative experience and also via the immunoregulatory benefits of microbial “Old Friends” — microorganisms that helped shape our immune systems but which have been largely eliminated from our urban environments.
Open areas of grass, on the other hand, are not as inviting and therefore may impede rather than enhance health:
[L]arge areas of bare grass in cities can make built environments more spread-out and less dense. Without tree canopy to shield from the midday sun, this may increase the likelihood of people using cars for short trips instead of walking through a park or along a footpath. The result is missed opportunities for physical activity, mental restoration, and impromptu chats with neighbours. Previous work in the United States suggests this might be why higher death rates were found in greener American cities.
By Dean Mosiman
Threatened by infestations, climate change and competing demands for space, Madison’s tree canopy will shrink with “potentially disastrous results” unless the city invests more in its trees, a new report says.
After nearly two years of study, the city’s Urban Forestry Task Force is making a series of recommendations — some with potentially significant price tags — to nurture and dramatically increase the area covered by trees from 23% to 40% of Madison’s 80 square miles.
Already, the city has had to deal with infestation by the emerald ash borer that’s forcing the removal of thousands of trees, as well as disease, climate change, loss of mature trees to development, road salt, and cramped space for planting and growth in the public right of way.
On private property, where most of the trees in the city are located, uneven care is also affecting the urban canopy, the report said.
The task force, created by the City Council on Aug. 1, 2017, has offered a 25-page report and recommendations aimed at elevating the importance of trees in the city’s planning, investments and operations and creating a new city role in expanding the canopy on private property.
“We have a quality urban forest in the city,” parks superintendent Eric Knepp said. “However, there are many opportunities to improve it.”
The 46 recommendations call for a preservation ordinance to protect mature trees; a yet-to-be defined grant program for planting trees on private property; focusing attention on neighborhoods that need trees; written standards for how to care for trees; hiring a forestry outreach and education specialist; revisiting old sites that don’t require much landscaping, such as parking lots at big shopping malls, and bringing them up to current standards; and planting more trees in parks than needed to replace those that are lost.