Over the last few years, Arlington has compiled resources and gathered input from experts and the public on what trees work best in Arlington to provide our community with the greatest benefit now and for the future. Urban foresters have put together several lists of recommended trees for different situations. These lists can be found here, and this article will speak to some of the aspects we look for in trees to plant in our community. All issues are weighed when selecting species for these lists, and no tree is perfect. A tree that may work in one place may not work somewhere else, so always do your research before choosing a tree that may be with you for decades.

Utility lines and cars damaged by silver maple Picture:: Montreal CTV
Structural stability and health issues
Because of our urban nature, we have to be very aware of the impact trees can have on surrounding structures, roads, utilities, and of course people. Historically, many trees were picked to plant because of their fast growth (such as Silver maples or Bradford pears), but these trees were not always the most structurally sound trees. While some of the less structurally-sound native species still have a place in less damage-prone areas such as natural areas or floodplain restorations, these species are generally kept off the lists.
Another issue to consider when picking a species is susceptibility to pathogens like insects, fungus, bacteria, or fungi. Foresters have learned hard lessons over time, seeing entire streets planted with American Elms or Green Ash die from their respective pathogens, Dutch Elm Disease, and the Emerald Ash Borer. We take this into account when recommending trees, and recommend resistant varieties (as with the Elm), or restrict planting of certain species (as with the Ash).
Aesthetics and form

Sumac in bloom
A tree’s appearance is often one of the first things taken into account when selecting species. Trees are still primarily seen as a landscape feature, even with growing appreciation of their other essential values. This is why certain species that may have low environmental value, but high cultural value, such as ornamental cherries and European hornbeams remain on our recommended tree lists. They are non-invasive, attractive trees, that add to our community with their color and beauty. Luckily, we also have many trees that are both beautiful and have a high value. Almost nothing beats a mature oak in its majesty, while also providing some of the greatest wildlife value. We seek to keep this balance equal, and there is a place for every tree on our lists.

Utility line clearing can alter the form of a tree drastically, such as with this Sugar Maple
Form and size is part of the aesthetic of a tree, but often is looked at to fit the space in which the trees are grown. Some trees are selected to be particularly narrow, short, broad, vase-shaped, pyramidal, the list goes on. This is often related to how people want their site to look, but can also be done to reduce interference with utility lines, provide sight lines for signs and roads, or overhead clearance for paths underneath.
Resistance to urban conditions
In an urban environment, we also have to worry about the stresses that come with roads, an increased pollution load. Some pollutants are obvious, such as exhaust and road salt, but other pollutants may

Narrow Ginkgo next to a building.
be less clear, such as pet waste, lead from lead paint, or pH-altering chemicals from surrounding concrete. Trees have to be able to adapt to these stressors, and not all trees can handle this. Unfortunately, many trees that adapt readily to short-term stress are opportunistic, invasive species, and the damage caused by these species to our natural areas is too great to risk additional invasion. However, there remain species native and non-invasive on our list, that have adapted to urban environments, or naturally occur in environments of high stress, such as floodplains or mountainous environments.
Oaks and maples, London planetrees, tupelo, and other species on our lists are noted for their pollution tolerance, and are prioritized for street tree planting. It does give us a much more restrictive list to pick from, so ultimately, much of our tree canopy’s diversity will have to come from trees in natural areas, or more protected landscaped areas on private and public land.
Benefit to our environment and natural landscape
One of the major aspects of supporting trees in our county is for the environmental and natural benefit trees provide to our community and the Chesapeake Bay. Many of our regulations and tree canopy requirements were originally created for the benefit to stormwater runoff reduction and pollution reduction. Large canopy trees provide the most interception of stormwater, capture the most carbon, and, in the right place, live the longest. The Urban Forest Masterplan outlines many of the benefits we seek from planting and maintaining trees in the county.

Tuckahoe park has some great examples of our native trees.
A high premium is also placed on trees native to our region, as native trees fare better in the long term, and provide the greatest benefit to our community. The Natural Resource Management plan lays
out how we coordinate with all agencies and the public to promote native species, and these species are prioritized when planting trees. There exist occasions where native trees may not be appropriate, due to space, cultural or aesthetic restrictions, which is why non-invasive non-native trees are still on our lists, but we work to find and foster the right places for our highest value native trees.

Willow oaks planted along Fairfax Drive.
All of these considerations have to be balanced with a need for diversity. Having learned over time that monocultures, or large groves of the same species, can lead to serious issues, Arlington county tries to balance the species planted, so we have as diverse palette of trees as we can. This sometimes conflicts with a desire for uniformity, and compromises can be difficult to be reached. Willow oaks and red maples, for example, are great urban trees, but are widely overplanted throughout the county. Where possible, we restrict the use of these trees, but there remains a high demand for them from developers, as they tend to be very reliable.
Tree selection
Every tree reacts differently to a site, and care should be taken when picking your species. There is no tree that meets all of the restrictions discussed in this article, and there is no “golden bullet” tree. Consulting with arborists, our extension service, and landscape architects, along with digging around the internet for research are all tools to find the tree that fits your site best. Days of research went into compiling the lists on our website, and they are still evolving, as we learn more about each tree, and get input from the community. Never hesitate to reach out to staff with suggestions or new information, as these recommendations are part of a living document, and mature with the trees we plant.
Resources