Throwing shade: Measuring how much trees, buildings cool cities

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.

Source: Throwing shade: Measuring how much trees, buildings cool cities – Ohio State News, 2021-06-24

Why trees grow at night

By Swiss Federal Institute for Forest, Snow and Landscape Research WSL
Trees form new cells by using the carbohydrates they produce through photosynthesis. However, it is not primarily the availability of carbohydrates that limits growth, but the water tension in the tree, the so-called water potential, as this study recently published in the journal New Phytologist shows.

The international research team led by Roman Zweifel at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL has come to the surprising conclusion that trees grow primarily at night, and that this trend is largely explained by the level of air dryness. In the world’s first comprehensive study of radial stem growth with an hourly data resolution, the scientists analyzed data recorded over up to eight years on 170 trees of seven common species located at 50 sites all over Switzerland (> 60 Mio data points). Researchers from ETH Zurich and other research institutions in Switzerland and Europe were involved in the study. The sites investigated are part of TreeNet, a network in which stem radius changes of trees have been measured continuously using high-precision point dendrometers in parallel with information about the dryness of air (vapor pressure deficit, VPD) and soil (soil water potential) in Swiss forests since 2011.

The data show that the probability of tree growth varies significantly over the 24 hours of a day: stems shrink under the effect of water stress and expand in a range of 1-200 µm per day, and these fluctuations are superimposed on growth rates of 1-5 µm per hour.

Air humidity is key to tree growth

The research team concluded that VPD plays a key role as it allows for growth mainly at nighttime. In their study, during day time, high VPD severely limited radial stem growth and allowed only little growth, except in the early morning. “The biggest surprise to us was that trees grew even under moderately dry soil conditions when the air was humid enough. Conversely, growth remained very low when the soil was moist but the air was dry,” recalls Roman Zweifel, lead author at WSL. The reason for this is the limited water transport capacity of the trees: as soon as the air becomes drier, trees temporarily lose more water through transpiration than they absorb through their roots. The entire tree comes under tension, its water potential decreases, and growth stops regardless of the availability of carbohydrates.

Source: Why trees grow at night – Phys.org, 2021-06-21

Glyphosate pesticides persist for years in wild plants and cause flower infertility

An herbicide widely used in agriculture, forestry and other applications can cause deleterious effects on the reproductive health of a common perennial plant found in forests in British Columbia, Canada. Researchers reported in the journal Frontiers in Plant Science that glyphosate-based herbicides (GBH) deformed various reproductive parts on prickly rose (Rosa acicularis) a year after the chemicals were first applied in both field sites and experimental plots.

The study is one of the first to look at the effects of GBH on the reproductive morphology of a prevalent perennial plant in a commercial forestry operation. The herbicide is commonly used to control plants that could compete with conifers that are grown to be harvested in areas known as ‘cutblocks’. Glyphosate has been used since the 1970s but has come under increased scrutiny in recent years over concerns about carcinogenic effects on human health.

Investigators from the University of Northern British Columbia (UNBC) collected and analyzed samples of prickly rose reproductive parts from three cutblocks, as well as from greenhouse-grown wild plants, and compared them against untreated plants from similar sources.

The results were striking: Pollen viability of plants treated with glyphosate dropped by an average of 66% compared to the controls a year after the initial application. More than 30% of anthers, the part of the stamen that contains the pollen, failed to split open (a process known as dehiscence), condemning these flowers to functional infertility. In addition, researchers found traces of GBH on plant flowers two full years after the herbicide was first sprayed.

Source: Glyphosate pesticides persist for years in wild plants and cause flower infertility – EurekAlert! Science News, 2021-06-16

Forest the size of France regrown worldwide over 20 years, study finds

By Oliver Milman
An area of forest the size of France has regrown around the world over the past 20 years, showing that regeneration in some places is paying off, a new analysis has found.

Nearly 59m hectares of forests have regrown since 2000, the research found, providing the potential to soak up and store 5.9 gigatonnes of carbon dioxide – more than the annual emissions of the entire US.

The two-year study, conducted via satellite imaging data and on-ground surveys across dozens of countries, identified areas of regrowth in the Atlantic forest in Brazil, where an area the size of the Netherlands has rebounded since 2000 due to conservation efforts and altered industry practices.

Another regrowth area is found in the boreal forests of Mongolia, where 1.2m hectares of forest have regenerated in two decades due to the work of conservationists and the Mongolian government. Forests also made a comeback in parts of central Africa and Canada.

However, the world is still experiencing an overall loss of forests “at a terrifying rate”, the researchers warned, with deforestation occurring much faster than restoration schemes.

Over a similar period outlined in the regrowth study, which was led by WWF as part of the Trillion Trees project, 386m hectares of tree cover were lost worldwide, around seven times the area of regenerated forest.

Source: Forest the size of France regrown worldwide over 20 years, study finds – The Guardian, 2021-05-11

Auburn University Researcher Demonstrates NASA Satellite’s Ability To Observe Forest Health

By Teri Greene
The study, “Using ICESat-2 to Estimate and Map Forest Aboveground Biomass: A First Example” in the journal Remote Sensing, shows how NASA’s Ice, Cloud and land Elevation Satellite-2, or ICESat-2, can be used to estimate aboveground biomass, or AGB, of forests and map its distribution.

Narine said limited information on the three-dimensional structure of forests has contributed to uncertainties in determining carbon budgets. However, ICESat-2 can capture this information using a laser-based lidar (light detection and ranging) instrument.

Lidar facilitates direct three-dimensional structural measurements, and using this technology from a space-based platform translates to exciting possibilities for assessing forest resources up to global scales, Narine said.

Knowing the capabilities of ICESat-2 allows for a better understanding of the satellite’s capabilities and limitations for characterizing vegetation.

“With ICESat-2 providing elevation measurements globally, a plethora of indicators of ecosystem health and function — including a key surrogate measure of forest AGB — can be potentially estimated to support sustainable management of forests,” Narine said.

The ICESat-2 mission was primarily designed to capture ice measurements, but its capture of data over vegetated areas offers investigators broader insights into ecosystem structure and the potential to contribute to the sustainable management of forest ecosystems.

Source: Auburn University Researcher Demonstrates NASA Satellite’s Ability To Observe Forest Health – SatNews, 2021-04-11

Citizen scientists can help study, halt die‑off of Pacific Northwest’s redcedars

by Seth Truscott
Washington State University scientists seek help from residents of the Pacific Northwest in tracing the worrying die-off of an iconic forest tree, the western redcedar.
A distinctive, useful, and beautiful giant, the western redcedar has historically provided Native American tribes with much of the materials for practical objects and culture. Valued for its natural beauty and soft, red timber, which resists decay and repels insects, redcedars can reach nearly 200 feet in height and live for more than a thousand years.
Western redcedars are found throughout the Northwest due to their tolerance for shade, flooding, and poor soils, thriving where other trees cannot.
Over the last few years, however, scientists have observed an increasing number of dead and dying trees. Mortality begins with dieback, in which the tops and branches die from the tips. Some specimens survive, but the condition can also kill.
Joseph Hulbert, postdoctoral fellow in WSU’s Department of Plant Pathology, founded the Forest Health Watch program to enlist citizen scientists in understanding and preventing dieback.
Researchers believe the problem is spurred by longer, hotter droughts in the region. But it’s unclear if precipitation, temperature, consecutive dry days, or other environmental factors are the main factor.
Launched in 2020, Forest Health Watch seeks answers. Citizens help by logging and photographing sites where trees are healthy, dead or dying back. People can also identify sites and conditions where trees may be vulnerable, and watch for signs of disease or pests.
“Anyone can be a community scientist,” Hulbert said. “All you really need is a camera for this project.”
Hulbert launched the Western Redcedar Dieback Map on the iNaturalist citizen science website to allow citizens to easily log their sightings.
“Once we have a strong understanding of the areas where trees are vulnerable, we can begin to explore options for keeping trees healthy in those areas,” he said.

Source: Citizen scientists can help study, halt die‑off of Pacific Northwest’s redcedars – WSU Insider, 2021-03-19

Penn State DuBois professor has the ‘dirt’ on sustainable urban forests

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.”

Source: Penn State DuBois professor has the ‘dirt’ on sustainable urban forests – Penn State University, 2021-02-11

Transparent Wood Could Be the Window of the Future

By Amy Androff
Could looking through trees be the view to a greener future? Trees replacing the clear pane glass in your windows is not a work of science fiction. It’s happening now.

Forest Products Laboratory (FPL) researcher Junyong Zhu in co-collaboration with colleagues from the University of Maryland and University of Colorado, have developed a transparent wood material that may be the window of tomorrow. Researchers found that transparent wood has the potential to outperform glass currently used in construction in nearly every way.

Their findings were published in the Journal of Advanced Functional Materials in their paper, “A Clear, Strong, and Thermally Insulated Transparent Wood for Energy Efficient Windows.”

While glass is the most common material used in window construction it comes with a costly economic and ecological price.

Heat easily transfers through glass, especially single pane, and amounts to higher energy bills when it escapes during cold weather and pours in when it’s warm. Glass production in construction also comes with a heavy carbon footprint. Manufacturing emissions are approximately 25,000 metric tons per year.

Now, transparent wood is emerging as one of the most promising materials of the future.

Transparent wood is created when wood from the fast-growing, low-density balsa tree is treated to a room temperature, oxidizing bath that bleaches it of nearly all visibility. The wood is then penetrated with a synthetic polymer called polyvinyl alcohol (PVA), creating a product that is virtually transparent.

Source: Transparent Wood Could Be the Window of the Future – USDA, 2021-01-05

Research looks into 400 years of Pennsylvania’s forests, which have been ‘completely transformed’

By Marcus Schneck
Researchers at Penn State and other universities investigate historic influences on modern forests.

While forests of the northeastern U.S., from Pennsylvania north to Maine, may hold mostly the same tree species as they did 400 years ago, significant differences emerge under closer inspection.

“If you only looked at a tree species list, you’d have the impression that Northeast forests haven’t changed,” explained Jonathan Thompson, research associate at the Smithsonian Conservation Biology Institute. “But once you start mapping the trees, and counting them up, a different picture emerges. In some ways the forest is completely transformed.”

While forests of the northeastern U.S., from Pennsylvania north to Maine, may hold mostly the same tree species as they did 400 years ago, significant differences emerge under closer inspection.

“If you only looked at a tree species list, you’d have the impression that Northeast forests haven’t changed,” explained Jonathan Thompson, research associate at the Smithsonian Conservation Biology Institute. “But once you start mapping the trees, and counting them up, a different picture emerges. In some ways the forest is completely transformed.”

The researchers found that farming was the most significant factor in today’s composition of the forest. If more than half of a town was farmed, the local forests likely have changed considerably from their colonial-era selves.

But, even as the composition of the forests changes, the forest as a landscape type is resilient across the region and, short of significant human development, will return to that state, explained David Foster, director of the Harvard Forest.

Source: Research looks into 400 years of Pennsylvania’s forests, which have been ‘completely transformed’ – pennlive.com, 2019-11-21

The Survivors: Sugar Pine Trees and the Future Forest

By Kat Kerlin
CCalifornia’s drought and bark-beetle infestation killed more than 129 million trees between 2012 and 2016 in the Sierra Nevada. But amid the devastation stood some survivors.

At the time, UC Davis biologist Patricia Maloney and a team of researchers entered the forest to collect seeds from 100 surviving sugar pine trees. Alongside other parched sugar pines etched with the tell-tale tunnel marks of bark beetles, were green, healthy trees. The researchers spent the past two years raising 10,000 seedlings from 100 surviving mother trees around the Lake Tahoe Basin. They were first cultivated at the USDA Forest Service’s Placerville Nursery and then moved to the UC Davis Tahoe City Field Station.

This week, between 4,000 and 5,000 of the seedlings are being planted around Lake Tahoe’s North Shore as part of a restoration project funded by the Tahoe Fund and the California Tahoe Conservancy. About 1,500 will be used to study and identify important adaptive traits, and the remainder will be given to private landowners to plant.

f the seedlings turn out to be as genetically resilient as Maloney thinks and hopes they will be, these trees could represent the future forest, one better able to withstand the threats of climate change, including more droughts and bark beetle outbreaks.

“These survivors matter,” said Maloney, a scientist in the UC Davis Department of Plant Pathology and Tahoe Environmental Research Center. “Essentially, these are the offspring of drought survivors. This is hopefully the genetic stock of the future.”

Source: The Survivors: Sugar Pine Trees and the Future Forest – UC Davis, 2019-11-07