Tree Stewards Do i-Tree Canopy Measurement from their Desks

By Nora Palmatier, President

Ever since Tree Stewards’ first tree census project at Ft. Myers Joint Base in 2008, members have completed similar tasks for the Tree Canopy Fund, and in neighborhood parks, schools, churches, and condos. Each project, we kept our feet on the ground, looking up into the trees’ canopy, and recording information with pencil and paper.

This summer, our tree measuring projects were literally turned upside down and we looked down on the tree leaves using Google Earth imagery through i-Tree Canopy. This is a free software tool from the United States Forestry Service that can be used on personal computers to easily and accurately estimate tree and other cover classes (e.g., grass, building, roads, etc.) within a set area. Urban Forest Manager Vincent Verweij used his GIS skills to set up our citizen science project using the boundaries of Arlington County, Virginia (including National Airport and all Department of Defense properties, which affects comparison with past canopy studies). The program is used to estimate results of tree canopy coverage – i.e., how much tree shade is there. Suddenly, we were measuring trees by looking down on the canopy instead of upwards!

Seven Tree Stewards worked on the project, and all together we looked at 6,399 views covering  Arlington County. i-Tree Canopy randomly generates sample point views and places a crosshairs marker in the middle of the view. After looking where the crosshairs fell in each scene presented, we clicked on whether it landed on: a) Tree Canopy, b) Pervious grass and vegetation, c) Impervious building rooftop or pavement of roads, sidewalks, parking lot, e) bare soil, or f) water. Each of us did close to 1,000 views.

Above is an example of what we Citizen Scientists saw, minus the crosshairs indicator.  The program provided a screen shot with the target point shown, and we clicked on whether the area beneath it is impermeable (red dots on roof and parking lots in lower left corner), tree canopy (green dots along Four Mile Run), or water (blue dot in middle of stream – on larger view water is obvious).

Among my 1,000 views where the crosshairs landed were: on top of an airplane on a runway, the roofs of houses, offices, and apartment buildings, trees, golf courses, and cemeteries (which had many gorgeous trees but a lot more herbaceous cover between graves, so where specifically the crosshairs fell determined the cover I listed). All science projects tell us to beware of operator bias, so I tried very hard to distinguish between tops of trees and shade on ground and not let my bias overcome the purpose – but it was so difficult when I identified Lacey Woods Picnic pavilion rooftop under the crosshairs so had to mark it Impermeable even though it was surrounded by a forest!

Above is the image of all 6,399 points throughout the county. Even when enlarged, it won’t clearly show the lowest canopy areas along major transportation lines as the 2016 aerial study does. 

The program report gives us much to consider. Our study estimated that the dollar value of carbon sequestered in county trees is $1,292,714, and that reduced air pollution benefit is $1,798,460 – all this besides providing beauty and shade on hot days. Statistically, having 6,399 points analyzed for a county land mass of 27 square miles is very solid, but it was sampling rather than review of the entire county land.

Comparing the results from our i-Tree Canopy points with previous studies is the proverbial apples and oranges, while comparing studies that exclude DOD and airport is like comparing apples, oranges and puppy dogs. They are all wonderful but not interchangeable. The 2022 i-Tree Canopy reported Tree Canopy at 35% compared to the 2016 aerial study of 38%. Impervious surface in 2022 was 40% and in 2016 was 38%. There was no difference between the two reports in grass and vegetation at 23% and bare soil at 1%. (Numbers for both reports are rounded and do not include sampling error estimates.)  The 2016 aerial estimate of 41% canopy coverage did not include the Pentagon parking lot or airport runways while 2022 does, so they shouldn’t be compared.

The 2022 study is county wide and doesn’t provide guidance on where tree canopy has been lost since 2016. It doesn’t provide data to determine: How much tree canopy decrease occurred on DOD land such as the National Cemetery when 700 trees were replaced with columbariums for cremated remains? How much decrease of tree canopy is due to lot clearance on private property when small houses are replaced with large ones? Was percent of increase in impervious surfaces due to new pavement or landing strips as compared to housing? Is there room in parks to plant more trees? We await the next aerial canopy study to be able to see where loss is happening and how best to manage our urban forest. Arlington County is funded to perform another study after the adoption of the Forestry and Natural Resources Plan.

Land Cover classification2022 iTree points by Tree Steward volunteers2016 study including DOD and Airport
Tree Canopy35%38%
Impervious surface (building & pavement)40%38%
Pervious grass & vegetation23%23%
Bare soil1%1%

What our i-Tree Canopy study seems to say is that Arlington County tree canopy is definitely not increasing, and it’s most likely decreasing. Our Tree Steward mission to educate the public on the importance and care of trees is even more vital as we know it is on private property that trees can be preserved and more plantings occur. We are already working to decrease canopy loss through planting efforts with the Tree Canopy Fund, tree distributions, and plantings on park land. And we provide public encouragement to plant more trees on private property as well as how to maintain mature trees. We Tree Stewards do a lot, yet this study is a call to increase our efforts; fortunately, we know that is a labor of love.

Additional information you might wish to review

TS work at Ft Myers:

TS census of Tree Canopy Fund:

About Arlington’s tree canopy

Tree removal National Cemetery

Tree Canopy Fund will plant trees for homeowners:

Free Tree Distribution:

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2022 Trainee Graduation and Membership Meeting

On April 2, TSAA celebrated the graduation of our 2022 class of Trainees! These new “Interns” have to report 30 volunteer hours in their first year to become full Tree Stewards and earn our signature green polo shirts and nametags.

Over 55 Tree Stewards and Trainees were present at this event in Lacey Woods Park.

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Tree Stewards Prune Trees in Mosaic Park, Arlington

On Monday, February 21, 2022, Tree Stewards of Arlington and Alexandria spent time pruning trees in Arlington’s Mosaic Park. By correcting structural defects in young trees, Tree Stewards expect the trees to grow up strong and healthy to shade Mosaic Park in Ballston.

Along Quincy Street in Ballston
Tree Stewards Marilyn Stone, Hugh Robinson and Dean Amel work on a willow oak.
Tree Stewards use a pole pruner on a tree near Mosaic Park’s climbing wall.

Photos by Tree Steward Jo Allen.

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TSAA Training Class Field Hike along Taylor Run

Taylor Run sees daylight at the concrete culvert east of Chinquapin Rec Center along Rte. 7 in Alexandria. Photo by Tree Steward trainee Victor Lopez

Tree Steward Bill Gillespie describes how citizens sampled water in Taylor Run to demonstrate that City of Alexandria staff, using data collected in Pennsylvania, had overestimated by five times the amount of phosphorus in Taylor Run. Photo by Tree Steward Jo Allen

Tree Steward Russ Bailey explains Alexandria’s — now halted — plan to bulldoze trees and other native plants and creatures to widen Taylor Run to slow its flow during storms. Photo by Tree Steward Jo Allen

Stormwater from nearby neighborhood roofs, streets, sidewalks, driveways, and parking lots all feed into Taylor Run, raising the water level many feet within 10 minutes of the onset of rain, according to Tree Steward Russ Bailey. Ten minutes after rain stops, the creek’s water level returns to normal. Photo by Tree Steward Jo Allen

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Tree Stewards Activities from Fall 2021

Tree Stewards volunteered for numerous planting, pruning, invasive plants removal, and tree distributions/native plant sales this fall. Here are a few photos of TS at work in the community.

TS Bonnie Petry secured a grant from TD Bank and the Arbor Day Foundation for a tree planting at Ben Brenman Park in Alexandria. On October 16, TS and community volunteers planted 35 native trees, which will provide food and habitat for birds and other wildlife, absorb storm-water run off, sequester carbon, shade paths to make the park more usable for humans in the summer months, mitigate the heat island effect, and make the park more visually interesting.
Bonnie writes: “The most meaningful parts of the project were teaching a lot of new people how to plant a tree, educating the folks on the value of native trees, and seeing people’s pride in and excitement about being a part of a truly meaningful, high value, long term value activity.  It was also meaningful to me that people will have accomplished something real and tangible that took hard work, and they will be able to go back and see the trees they planted!”
On November 13, TS restarted the natural plantings of Brandymore Castle in Arlington. Twelve TS and Master Naturalists turned out to provide supervision of fifteen volunteers from community and five of the new TS training class which doesn’t start till February 2022.

TS Jo Allen has been leading the effort to remove invasive plants from all trees and groundcover and trying to keep bike riders from damaging more of the fragile environment for years, so it’s great to see the progress made.  Arlington Urban Forester Melissa Gildea worked with Earth Sangha in choosing 80 trees and shrubs to block off the bike paths and 50 Virginia Creeper to stop one bank’s erosion. We got these small plants in during the morning and in the afternoon did the hardware part, along with ground ivy removal.
TS Doug Dickman went with Melissa to pick up plastic tree tubes, short and large wooden stakes, bundles of wire, plastic deer guards, etc. from the Trades Center and County Nursery. You can see Doug securing a plastic tube with a large stake.  There will also be a large enclosure of chicken wire surrounding the steep bank where TS struggled to get in the 50 Virginia Creeper. It will be a learning experience over the next year to see which protective device is most effective at deterring deer and bikers.  
TS Marilyn Stone and Hugh Robinson collect debris after Tree Stewards pruned trees on November 14 at Arlington Traditional School on North McKinley Road. Photo: Tree Steward Eden Brown
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Application Now Open for January 2022 Training Class

**UPDATE: The 2022 training class is now full, so we are no longer taking applications. Thank you for your interest!**

Tree Stewards of Arlington & Alexandria will begin a new membership class in late January 2022, and applications are being accepted via this Google Form now through December 31, 2021.

This will be a hybrid training of weekly Zoom presentations (both live and pre-recorded) and assigned readings you do at your own home. In person weekend sessions with experienced Tree Stewards will provide discussions of that week’s Zoom and readings, hold tree walks, practice pruning and planting, and teach the correct way to identify and remove invasive plants.

The schedule of classes will be announced in November 2021 — although we’ve all learned to be flexible this past year!

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Check for Spotted Lanternfly Spread

This is a great time of year to go out and check your neighborhood for spotted lanternflies. The best place to scout for them is near tree of heaven  where the adults congregate from September to first frost. If you see them please report them to your local authorities immediately. Contact information and other information are provided in the spotted lanternfly Alert document at

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Arlington County Free Trees Spring 2021 – Sign up now open

Arlington County knows the importance of its trees. Through the Tree Canopy FundEcoAction Arlington offers twice-yearly grants to plant or maintain trees on private property. View the list of available trees and apply online by Fri., Jan. 8. Applicants will be notified in advance; trees will be planted by a contractor in spring 2021. Learn more about the Tree Canopy Fund Grant Program.

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Remembering Tom Schelstrate

I am bereft to learn of the passing of Tom Schelstrate, an educator who never stopped learning and who helped everyone in the room, woods or park more deeply understand trees, even when they seemed confusing.

As a student who helped to inaugurate our new training modules in 2018-2019, he asked what may have seemed to be impertinent questions, but no one ever interrupted him—or the answer. His queries were insightful, even when he seemed most flummoxed.

Professor Schelstrate endeavored to learn tree identification from their leaves and collected a notebook full of them that he carried to each tree walk. His prize may have been the leaf of an American chestnut tree that instructor Emily Ferguson noticed during a walk in Glencarlyn Park. Emily handed the cherished leaf to Tom, knowing he would treasure it even if he never saw another living American chestnut.

In the classroom, Emily mentioned that one tree has three different leaves, and Tom was aghast. “How will I ever learn this if one tree has three leaves?” he exclaimed, declaring what every other Tree Steward student present was thinking.

Tom, your questions made every tree encounter better for your having asked. I wish you peace in repose among chestnuts and sassafras, mighty oaks and elms, maples and sycamores, every tree you learned and have yet to know. When we join you, we expect a lesson.

Jo Allen
Training Committee, 2018-2019
Tree Stewards of Arlington and Alexandria

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Decision Making for Tree Lovers: Assets and Liabilities

By Nora Palmatier

Oaks in my backyard
Oaks in my backyard

Tree Stewards have heard me brag about the huge oaks in my backyard, especially since the Quercus falcata became not only the Arlington County Champion but also a Specimen Tree, entered on the property deed and needing County permission to remove.  It has a Diameter at Breast Height (DBH) of 60 inches, which means I can stretch out on the ground beside it with toes touching a buttress root while hands over my head can barely touch the opposite side buttress root.  The fact that a Quercus alba (DBH 30 inches) shares the same mound and stretches almost as tall is another bragging right. 

This year, the white oak is gorgeous and full. The southern red oak is, well, even a tree lover would call it scraggly, and quite a few large limbs show no greenery on the tips (Qf to the left in the photo above, Qa to the right).  I think everyone on the Tree Steward list serve has read about the high incidence of oak decline and most likely guesses what the arborist from Bartlett Trees said. He commiserated with me and gave two choices:

  1. Remove the dead limbs (sheds, fences, play areas, and a house could all be considered “targets”), and treat the borers. No promise that one would not need to prune more limbs each year or how long tree would not be considered a risk. Given the height of tree and safety for climber, this would cost about the equivalent of a nice vacation for us. 
  1. Remove the tree now at a cost of three times the one-year pruning and borer treatment. 

I immediately swung into the denial part of the grief cycle and contacted experts who have taught us Tree Stewards.  Eric Wiseman, Ph.D. Associate Professor of Urban Forestry, Virginia Tech, is director of the Big Trees Virginia program that keeps track of state champions. I emailed him asking if there was research proving that the largest champion trees took much longer to decay (and thus were safer) since they had such huge trunks. Nope. 

I do not have any specific research that I can direct you to on this topic. Although I don’t follow the literature on this topic real closely, I feel confident in stating that controlled studies of oak decline in urban settings is scarce, particularly when it comes to evaluating treatment response and recovery rates. Oak decline has been studied quite a bit in natural forest settings, but those studies mostly revolve around examining the causes of decline and describing its epidemiology, and don’t get into treatment because it is rarely feasible to treat ailing oaks in natural forests. And obviously the environmental context is completely different, so it’s hard to extrapolate to urban areas.   When trees lose vitality, they lose their defenses against borers. It’s analogous to an elderly person becoming more susceptible to secondary infections when in poor health. Just like with the human, you have to control that secondary infection (the borers), but also treat the primary sources of poor health, which in this case may be soil and root health.”

He did suggest contacting Arborist Guy Meilleur with Historic Tree Care in Apex, NC, and the website filled me with hope! The Case Studies of Historic Tree Care had photos of trees bigger than my oak that were carefully preserved for decades. Guy Meilleur is also a great writer, so I spent hours perusing the site.  Like most tree lovers, he knew how much my oak meant to me and provided information on rejuvenating the soil. He would not be up in Northern Virginia for several months, and he did refer to significant loss of red oaks and asked about “targets” around my oak, which made me rethink my optimism. 

Extension Agent Kirsten Conrad also responded to my plea for assistance, but she offered no magic cure: “I’m happy to come by, but here’s my two cents and I doubt that it would change on site.  As you know we saw crazy numbers of oaks fail last year of oak decline.  The stresses on the trees lowered the trees’ ability to defend itself, and borers were found in large numbers in many of them. Yet the borers are not the cause of death or even of the tree’s decline. So, there is no question that they do actually cause some harm and primarily as the holes become entry sites for wood decay organisms. Also, if i thought that pruning would somehow invigorate the tree then yes, I would prefer that option, but I don’t think that pruning will do more than just extend the eventual removal of the whole tree.  So ask about leaving a 15-18′ snag for wildlife and what would that cost.”  

Photo of the borer holes

Virginia Department of Forestry Arborist Jim McGlone called after getting my anguished email.  His response was the 60 inch DBH Quercus falcata was declining because it was 60 inches, meaning it had matured to its fullest after a long life. He referred to the session he does on tree physiology, which discusses the impact of stressors such as drought, flooding, crazy weather impacts the xylem, phloem, leaves’ stomata. and roots. It’s a complex system. This was a learning I did not want to hear, but it does bring us back to the basics: trees are living beings, and they do die.

I needed closure, so I did what we Tree Stewards recommend and contacted an expert arborist not connected with a tree service.  Consulting Arborist Ed Milhous came out and did a high tech assessment  — he tapped a rubber mallet all over the red oak’s trunk which resulted in a hollow, drum sound. Then, he tapped the white oak which gave a firm, solid thunk. The red oak was full of decay and rotten inside while the white was in good shape.  He then stood back and examined the canopy, pointing out where dead branches started and those nearby with sparse leaves. Together we reviewed the surrounding neighbors’ yards with sheds, playground, fence, and patio all under large limbs. Should the entire tree fail, it had four houses it could impact, including a direct hit on our bedroom! The conversation turned to ways to minimize tree removal cost with options to leave a 20 foot snag, placing large limbs at the back of the property instead of hauling away, checking ability to salvage for local wood workers in such a tight space, and waiting till winter to minimize impact on the white oak and landscape.

Arborist Ed Milhous assessing tree

I did not truly learn anything new, and the first arborist’s suggestion to remove is what we will do. I clearly went through the rage, denial, and bargaining to end at grudging acceptance. My new goal is to research and interview companies to ensure that the Quercus alba is not damaged during the removal of its long-time partner. I will keep you updated on the process.

Oh, and I still believe mature trees are a valuable asset to one’s landscape in most situations. But I have a greater appreciation for their becoming liabilities!

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