We are all dismayed to see so many trees removed when an old house is torn down and a new one built. Arlington County follows The Chesapeake Bay Preservation Ordinance which requires a Landscape Conservation Plan for any site disturbance greater than 2,500 sq. ft. Department of Parks and Recreation forestry staff reviews and enforces the requirements of the Landscape Conservation Plan. Residential properties must demonstrate how the site will have 20% forest canopy in twenty years. This can be achieved by using existing trees or trees proposed for planting.
In 2018, 320 private properties were developed in Arlington County. For each of the 320 properties, a site plan was required by the County which showed 1) the trees to be removed due to construction, 2) the trees to remain after construction (conserved trees), and 3) any trees that need to be planted to provide the 20% canopy density after twenty years (planted trees)if the credit for conserving existing trees is not sufficient. Note that this requirement only applies to the development of the property, and legal restrictions to removal of trees after the completion of the development may be limited. In summer 2024, ten Tree Stewards conducted a survey of 90 such sites under the direction of Urban Forester Vincent Verweij to determine the answer to this question. We based the survey methodology on a smaller pilot project of 32 properties done the year before.
Spoiler alert: An aerial survey using 2023 data did show these plots had 23.9% average tree canopy for these lots. This would imply that on average, the lots are meeting the goals of the Chesapeake Bay Preservation Ordinance, but do not yet meet our County goal of 40%. Please continue reading for detailed analysis of how the survey was conducted and number of trees found.
This time we notified homeowners before we knocked on their door. Each of the homeowners selected was sent a letter describing the reason for the survey and asking for Tree Steward Volunteers to be permitted to enter the property. We decided to have the letter printed on Tree Steward letterhead with the signature of the TS coordinating the project and the county forester, believing that a citizen science study can be welcome whereas a government study may not. With this method, we gained access to 84 of the 90 properties, with the few not surveyed because we couldn’t reach the homeowners after two visits; only 1 asked not to be in the survey.
The volunteer work was fun and instructive. First, we learned how to read the intricate site plans required at each development so we could tell how many trees should have been conserved, and how many new plantings should have been installed on what spot in the property. (See example below) Then in pairs we went to that address, knocked on the door, and asked if we could count their trees. Usually the homeowner welcomed us, proudly showing off their beautiful trees conserved, planted during development and those they’ve added over the five years! Only a few were skeptical and refused admittance to the property, and several were not home leaving us to determine how many trees existed on the property from public sidewalks. We must have looked strange to neighbors, wearing our yellow TS vests, standing on tip toe to see over fences, and making notes on clipboard!
The best part of the volunteer work was the interaction with the homeowners with whom we discussed tree maintenance. I fondly recall showing one person the best way to remove ivy from a tree and the value of mulching instead of turf grass. We carried educational material with us and provided on line resources to many.
The data we collected indicate that homeowners change their landscaping after they move in. Yes, the developer probably planted the required trees but the homeowner does not have to adhere to the plan. The great news is that we counted an additional 503 trees than the plans required! All of the property plans required 612 trees be present after development and we counted 927 trees. In hindsight, we wish that each tree counted had been designated either a canopy tree (oak, maple, river birch, etc) or an understory (serviceberry, crepe myrtle, etc.) as that has a significant impact on canopy coverage. Still it is reassuring to know that homeowners value trees and plant more after they move in.
The news was not great concerning mature trees conserved thru tree protection fencing during the development. Of the 292 trees that were required to be conserved, only 215 were on the site five years later, or 74% survival. We have no way of determining if the missing ones were removed due to construction damages or simply from homeowners’ preference. Given that conserving trees is more ecologically beneficial than planting new ones, this was disappointing.
Of the 320 trees the plans required be planted in a specific location and of a specific species, we could only locate 209 or 65%. We Tree Stewards were strictly following what was on the plan so if a river birch was shown to be in the right front yard, and we didn’t see one, we marked “Not planted”, but if a maple not shown on the plan was present, it was counted under “Additional” rather than “Planted”. Back in 2018 the landscape plans were not updated when changes were approved, so it could be that a County Forester approved moving the location of a tree or changing the species due to soil issues. These probably account for some of the missing Planted trees or it may be that homeowners removed or changed out the trees. Given the large number of Additional Trees, some of this may have occurred.
As a double check, County Forestry reviewed the 2023 aerial canopy study for only these plots and it was 23.9%, which reflects our on the ground counting. This would imply that on average, the lots are meeting the goals of the Chesapeake Bay Preservation Ordinance, but do not yet meet our County goal of 40%
Below is an example of the landscape plans used.
Photos for this blog post were provided by Steve Geiger and Nora Palmatier