Proof Positive: Fewer Trees Mean Higher Temps

In the back of our rock garden, shaded on three sides by arborvitae and neighboring trees, stands a chest-high, white, capped PVC tube with holes drilled along its sides. Beneath the tube is a wooden stake; attached to the stake are two small climate sensors, one at the top and one at the bottom.

Every day for several months, now, the sensors have been silently recording temperature changes and related data from our garden. Occasionally, a group of graduate and undergraduate students from Clark University’s Geography Department, which owns the equipment, come by to download the data onto a laptop. We chat, they pet our aging golden retriever, who is most curious about any visitors, and then go on their way.

That data, as well as similar information collected from a handful of other sensors placed around Worcester in a variety of spaces with varying tree canopy, have formed the basis of a study this summer about how tree cover affects land surface temperature.

A Ten-degree Drop in Temp Where Trees are Present

The findings, presented on August 1 by undergraduates participating in Clark’s Human-Environment Regional Observatory (HERO) project, are significant: Trees reduce temperature near the ground by between 4 and 10 degrees Fahrenheit.

No surprise for anyone who seeks shelter under a tree on a hot summer’s day. But well worth quantifying and analyzing, given the significant number of trees lost to the Asian Longhorned Beetle infestation here—nearly 32,000 since the eradication effort began in 2008.

About 22,000 trees have been replanted, since, but more trees, still, have been lost to other, human-driven factors. According to a May 21, 2013 op-ed piece by Clark Geography faculty Deborah Martin and John Rogan, between 2008 and 2010, the city lost another 30,000-plus trees to urban development.

Without Tree Cover, Hotter Temps and Higher Energy Bills

To better understand the temperature impact of deforestation and replanting, the HERO student team analyzed satellite images of land surface temperature in Worcester. They compared two periods: 2007-2010, when most of the ALB-infested and at-risk trees were removed, and 2010-2012, when replanting efforts intensified.

The results are striking. In the Burncoat-Greendale neighborhoods that were hardest hit by the beetle, land surface temperatures increased by nearly 2 degrees to a whopping 16 degrees Fahrenheit after trees were removed (1-9 degrees Celcius).

By contrast, during the replanting phase, land surface temperatures began to slip slightly, by nearly a degree Fahrenheit. Given that new plantings are still saplings, it will be decades before neighbors can once again enjoy the cooling comfort of trees on a hot summer’s day.

Hotter temperatures translate into higher energy bills. Researchers from the University of Massachusetts-Amherst found that the presence of trees saved $85 in cooling costs for the average Burncoat resident.

Shared Losses and a Sense of Sacrifice

For now, until the new trees grow taller, higher energy costs will be the norm for neighborhoods stripped of their old, shady tree canopy—just one impact profoundly felt by residents of the affected areas.

Those impacts were the focus of a second team of HERO students, who conducted and analyzed dozens of interviews with residents, government officials and other policy makers to define how tree loss has affected the community’s sense of place.

Even as neighbors grieved the changed landscape, higher energy bills, lowered property values, lack of comforting shade and less attractive views, many of the stakeholders interviewed agreed that the crisis had some unexpected benefits: improved communications between government officials and citizens, increased funding to replant an aging urban forest, and a stronger sense of neighborhood commitment and environmental awareness.

Admirably, residents in the most affected neighborhoods also recognized that their sacrifice of infested trees most likely saved the city, region, and—we hope—the great northern maple forests from ALB devastation.

The HERO students’ presentation concluded a summer of research and the second year of a three-year National Science Foundation grant, headed by Associate Professors Martin and Rogan. The undergraduate teams included students from Clark and around the country.

The students are heading home, now, for a few weeks of well-deserved rest until the fall semester begins. I weeded the back of my rock garden, to make it easier for the next group to download data. Until they return, the sensors continue to silently record temperature changes in my little, tree-shaded corner of the world.

Evelyn Herwitz is the author of  Trees at Risk: Reclaiming an Urban Forest and blogs about ALB prevention and tree stewardship at She predicted the 2008 Asian Longhorned Beetle infestation of Worcester, Mass., in her book, published by Chandler House Press in 2001.

Arbor Day Reminder: Protect Our Urban Forests

spring_trees_cropIt’s been one long, cold spring so far here in Worcester, but the trees are finally in bloom. The Norway and sugar maples that line so many miles of our city’s streets are bursting with pale green flowers. Cylindrical Callery pears shyly show their snowy petals. A few magnolias offer cream and purple blooms to the sky.

It’s an appropriate welcome for Arbor Day, marked in Massachusetts and in most states on the last Friday of April.

Proposed in 1872 by Nebraska newspaper journalist and editor J. Sterling Morton as a way to promote tree planting to create wind breaks, shade, fuel and building materials for the vast Nebraska Territory, Arbor Day soon caught on across the U.S. By 1885, it had become a legal holiday in Nebraska—the same year that Massachusetts first observed the tree planting celebration.

Worcester’s First Arbor Day Shadowed by Deforestation

Worcester marked the Commonwealth’s first Arbor Day on April 30, 1885, by planting nearly 500 trees, thanks largely to the efforts of the Worcester Grange: 413 shade trees (mostly maples), and 80 fruit trees and ornamentals, to be precise.

Standing on a stage bedecked with flowers and potted plants in Horticultural Hall, before a canvas inscribed “Our first Arbor Day—may it take as firm and lasting a hold on the hearts of the people as the trees take root in the soil,” State Grange Master James Draper urged an enthusiastic audience to plant trees. Draper’s concerns about dwindling timber resources and deforestation around Worcester were echoed by Stephen Salisbury III, a member of the city’s Parks Commission.

“It is a matter of common knowledge . . . that the timberlands of the country were disappearing,” reported the next day’s Worcester Daily Spy. “Something more than Arbor Day was needed to prevent utter desolation in New England. Those who participated in its observance, however, would always be honored and their service would be appreciated.”

19th Century Forests Depleted by Centuries of Waste

Deforestation in Massachusetts—the result of centuries of wasteful timber harvesting for fuel, potash and building materials, as well as clear cutting for farmland—had become a serious problem by the mid-19th century. Writing in 1846, botanist George B. Emerson warned that the Commonwealth’s wood-based industries, such as ship building and furniture manufacturing, had so depleted native forests that the state was rapidly becoming depending on timber imported from Maine and New York.

In Massachusetts, deforestation peaked about 1860, when roughly two-thirds of the state was open land, compared to one-tenth in 1800; many Central Massachusetts hill towns had cleared more than 75 percent of upland area by midcentury.

Arbor Day was one step in a long process of reversing that trend. Today, Massachusetts in one of the most forested states in the U.S., with nearly 71 percent tree cover, compared to a national average of 34 percent. According to David Nowak of the U.S. Forest Service, there are about 273 million trees in Massachusetts, moderating climate, stabilizing soil, controlling storm run-off, improving air quality, sheltering animals and beautifying our world.

Urban Tree Canopy Threatened by Development

But that green canopy is once again in jeopardy. Here as throughout the country, development is chipping away at urban forests, replacing trees with buildings and impervious surfaces, such as roads and parking lots.

Nationally, according to Nowak, 17 out of 20 major cities have experienced a significant decline in tree cover during the first decade of the new millennium. On average, we’re losing 4 million trees annually.

It’s a trend we ignore at our peril. Just as deforestation surrounding Worcester in the mid-19th century caused observable changes in climate and growing conditions, so a loss of trees as we continue to expand cities and suburbs will degrade our natural environment.

This past year, Worcester intensified planting to help offset the many trees lost to the Asian Longhorned Beetle infestation. Our streets are lined with young saplings, still taking root after the cold, harsh winter. It will be decades before they shade streets like their aging sylvan neighbors. On this Arbor Day, our 128th, their future, and our city’s, is in our hands.

Evelyn Herwitz is the author of  Trees at Risk: Reclaiming an Urban Forest and blogs about ALB prevention and tree stewardship at She predicted the 2008 Asian Longhorned Beetle infestation of Worcester, Mass., in her book, published by Chandler House Press in 2001.