Canopy Trees
A tree canopy is the layer of branches and leaves that “cover the ground when viewed from above.” Tree canopies have many measurable benefits, for example reducing stormwater runoff and both gaseous and particulate pollution.
Tree canopies also cool the areas beneath and around them. Areas under dense tree canopy can be as much as 45℉ cooler than areas covered with pavement. The key word there is “dense.” A recent study by University of Wisconsin researchers found that the cooling effect of urban trees was noticeable only when canopy coverage – the fraction of the surface covered by tree canopy – was above 40%.
The 2022 assessment of the tree canopy in Charlottesville determined that overall tree canopy coverage in the city was 40%, down from 45% in 2014. However, the 2022 assessment found that coverage was uneven, ranging from 14% to 58% amongst the city’s neighborhoods. Not surprisingly, Charlottesville’s 2021 Urban Heat Island Mapping Campaign showed that areas with little tree canopy were much hotter than areas with dense canopy.
Charlottesville’s tree canopy decreased twice as much on privately-owned land than on city-owned property between 2014 and 2022. Moreover, private land contains 75% of the potential tree canopy within city limits. Clearly, landowners can play a big role in increasing the tree canopy in Charlottesville, and probably in other locales.
This article starts with suggestions for canopy trees that should thrive in central Virginia, explains how to choose sites for canopy trees, then briefly describes when and how to plant trees, with links to in-depth instructions. Finally, the article discusses how to care for trees to give them the best chance of forming a canopy.
Suggested canopy trees
The following are native canopy trees recommended for Charlottesville and Albemarle County. It’s important to plant native trees because they’re adapted to regional soils and climate. Native trees also provide habitat and food for local animals, in particular birds and insects. The Virginia Native Plant Society and Doug Tallamy’s Homegrown National Park initiative are great sources for more information about the benefits of native plants.
American beech summer foliage. Photo: Tim Ross, public domain image
American beech winter foliage. Photo: Gorillo.chimpo, CC BY-SA 4.0
• American Beech (Fagus grandifolia)
Mature height: 60 – 120’; usually shorter with a wider trunk when open-grown
Spread: 50’
Form: single trunk, branches extend straight out
Drought tolerance: moderate
Light requirement: shade, partial sun, full sun; best development in moderate shade
Bark: light gray and smooth, even in maturity
Autumn/winter appearance: very beautiful; bright yellow-brown leaves stay on the tree all winter
Further reading: https://edis.ifas.ufl.edu/st243
American elm, showing its graceful, upwardly-arching branches. Photo: Marty Aligata, CC BY-SA 4.0
• Jefferson American Elm (Ulmus americana ‘Jefferson’) – a Dutch elm disease-resistant variety!
Mature height: 70 – 90’
Spread: 50 – 70’
Form: trunk divides 10 – 20’ up, especially in bright sun. Branches arch upwards
Drought tolerance: moderately tolerant of short, but not long, droughts
Light requirement: full sun, partial shade
Bark: gray; overlapping scales, narrow fissures
Autumn/winter appearance: brilliant yellow foliage
Further reading: https://edis.ifas.ufl.edu/st649
The straight, unbranched trunk of a tulip poplar. Photo: Chris Stroupe, CC BY-NC 4.0
• Tulip poplar (Liriodendron tulipifera)
Mature height: 100 – 150’; can reach 200’ in ideal conditions
Spread: 30 – 50’
Form: very straight, single trunk; high canopy
Drought tolerance: moderate
Light requirement: full sun
Bark: brown; intersecting ridges form diamond-shaped patterns
Autumn/winter appearance: bright yellow foliage
Further reading: https://edis.ifas.ufl.edu/st363
Sweetgum’s spectacular autumn foliage. Photo: Ontologicalpuppy, CC BY-SA 4.0
• Sweetgum (Liquidambar styraciflua)
Mature height: 60 – 75’
Spread: 35 – 50’
Form: single trunk with a conical canopy, more oval in maturity
Drought tolerance: moderate
Light requirement: full sun, partial shade
Bark: gray-brown blocks, deep furrows
Autumn/winter appearance: excellent autumn color – yellow, orange, red, burgundy
Further reading: https://edis.ifas.ufl.edu/st358
Note: Spiky spherical seedpods are messy. There is a fruitless variety, “Rotundiloba”.
Black gum, or black tupelo. Rumored to be Van Morrison’s favorite tree. Photo: Jean-Pol Grandmont, CC BY-SA 3.0
• Black gum, aka Black tupelo (Nyssa sylvatica)
Mature height: 65 – 75’
Spread: 25 – 35’
Form: straight, single trunk with horizontal branches
Drought tolerance: moderate
Light requirement: full sun, partial shade
Bark: dark gray, shallow furrows
Autumn/winter appearance: excellent autumn color – orange, red, deep purple
Further reading: https://edis.ifas.ufl.edu/st422
Maples look great in the summer too! Photo: Bruce Marlin, CC BY-SA 2.5
• Sugar maple (Acer saccharum)
Mature height: 60 – 80’
Spread: 35 – 50’
Drought tolerance: moderate
Light requirement: full sun, partial shade, full shade
Bark: gray-brown; smooth in younger trees, furrowed when older
Autumn/winter appearance: classic fall color – red, orange, yellow
Further reading: https://edis.ifas.ufl.edu/st051
Note: Also consider red maple (Acer rubrum), described in this article by Piedmont Master Gardener Sue Martin.
White oaks can become truly enormous, after a few hundred years. Photo: msact, CC BY-SA 3.0
• Oaks (genus Quercus):
Fourteen oak species are native to Virginia. Six are recommended as canopy trees:
White oak (Q. alba): http://edis.ifas.ufl.edu/st541, and this article by Piedmont Master Gardener Pat Chadwick.
Swamp white oak (Q. bicolor): https://edis.ifas.ufl.edu/st543
Scarlet oak (Q. coccinea): http://edis.ifas.ufl.edu/st545
Southern red oak (Q. falcata): https://edis.ifas.ufl.edu/st546
Pin oak (Q. palustris): http://edis.ifas.ufl.edu/st555
Willow oak (Q. phellos): https://edis.ifas.ufl.edu/st556
Mature height: 50 – 100’, depending on species
Spread: 35 – 80’, depending on species
Drought tolerance: moderate to high, depending on species
Light requirement: full sun; white and swamp white tolerate partial shade
Bark: depending on species, from dark brown to gray, and deeply furrowed to scaly or flaky
Autumn/winter appearance: All have showy red foliage, except for willow, which is yellow, and Southern red, which is brown. All oaks hold their leaves over winter.
Notes: Acorns make a mess, especially in “mast years”, but wildlife love them. Humans can eat acorns too, after processing to remove tannic acid. Also, Piedmont Master Gardener Ralph Morini’s article on oak decline describes how to care for oaks to ensure a long lifespan.
Willow oak autumn foliage. Photo: Famartin, CC BY-SA 4.0
Plant large canopy trees well away from power lines. Photo: Chris Stroupe, CC BY-NA 4.0
Location
Plan ahead. Consider whether a mature tree will impinge on power lines. Plant at least 35’ away from houses. Keep trees away from sidewalks (minimum 8 – 10’) and septic drain fields (a distance equal to the height of the tree). Minimize the impact of soil compaction by planting where there won’t be much foot or car traffic. For the best cooling effect from shade, plant on the southern and western sides of houses.
Timing
Plant deciduous trees in late fall, winter, or early spring, while the tree is dormant. This will let their root systems develop before summer. Oaks and black gum should be planted in early spring; their roots grow slowly and might be damaged by winter temperatures.
How to Plant
The following is only an overview of tree planting. These links offer detailed descriptions and videos:
• University of Maryland Extension
• Charlottesville Area Tree Stewards
• Charlottesville Area Tree Stewards (video)
• Virginia Cooperative Extension (video)
The Charlottesville Area Tree Stewards offer free classes on tree planting and many other topics.
Plant trees in wide, shallow holes with sloping sides. Image: Chris Stroupe, CC BY-NC 4.0
Plant trees in wide, shallow holes with sloping sides. The hole should be as deep as the root ball and 2 – 3 times as wide. Tamp the bottom of the hole and pile a little dirt in the center, where the root ball will rest. The “root collar” – the ring where the trunk meets the root zone – should be 2 inches above ground level. Finding the root collar can be tricky; this document has good pictures showing how to do it.
If a tree is in potting mix in a container, gently remove as much mix as possible from around the roots before planting. (The potting mix will deplete the surrounding area of oxygen as it decays.) A flat-blade screwdriver is a great tool for this. Moistening the potting material with a gentle stream of water also helps. Don’t put the potting mix in the hole with the tree; save it for mulch instead. If a tree is wrapped in burlap and/or wire, remove the wrapping from at least the top 12 inches, or top ⅔, of the root ball, whichever is greater. Free up any tangled roots so they point outwards and downwards.
Put the root ball in the hole and re-check the height of the root collar. Backfill the hole with the soil from the hole, filling a little past half-way. Don’t add grass, leaves, mulch, or any other amendments to the fill. Add water to make a thick slurry and work this slurry in amongst the roots. Fill the rest of the hole with the soil from the hole, again without amendments. Add more water, so the soil is moist but not sodden. Cover the backfilled area with 2 inches of compost; it will work its way into the soil and keep it loose for optimal root growth.
Finally, spread 3 inches of mulch in a 3-foot diameter circle around the trunk. To keep the bark from rotting, push the mulch 3 inches away from the base of the trunk. Consider staking and fencing.
Maintenance
Keep newly-planted trees well-watered. A rule of thumb is that they need 1 inch of water per week. This works out to a little less than a 5-gallon bucket of water in a 3-foot diameter circle. However, avoid over-watering, which can damage the roots. Do not amend the soil.
Keep the area around the trunk well-mulched, roughly 3 inches deep. This helps the soil retain moisture and reduces soil compaction around the roots. Ideally, mulch should extend out to the drip line, i.e. the maximum extent of the tree’s canopy.
After the first year or two, prune the tree to correct any problems. It’s important to prune early on because it’s challenging – and expensive – to prune a tall tree. Look for multiple central leaders (main trunks) and weak structures, like branches making a small angle (close to parallel) with the trunk. These links include details about pruning:
• Virginia Cooperative Extension
• University of Maryland Extension
In the decades to come, your tree might need professional care. Hire a Certified Arborist.
Closing thoughts
I hope this article will encourage us to do what we can to increase the tree canopy in our communities. Natural beauty, the environment, and human health will benefit. The descriptions of the trees and methods in this article are extremely brief, so I encourage readers to learn more from the references provided here – then dig in!
References and further reading
Featured image: Andrew Preble, CC0 1.0
Charlottesville Master Tree List (PDF) – also contains great descriptions of planting and maintaining trees
Find an arborist International Society of Arboriculture
Follow proper pruning techniques Texas A&M Extension
How to plant a tree (video) Virginia Cooperative Extension
Planting a bare root tree (video) Charlottesville Area Tree Stewards
Planting a tree or shrub University of Maryland Extension
Pruning deciduous trees (PDF) Virginia Cooperative Extension publication SPES-403
Pruning trees in the home landscape University of Maryland Extension
Red maple earns its popularity Sue Martin, Piedmont Master Gardeners
Select, plant, and care for your tree (PDF) Tim Maywalt, Charlottesville Area Tree Stewards
Study suggests trees are crucial to the future of our cities University of Wisconsin
Urban Tree Canopy Assessment (PDF) City of Charlottesville, VA
Urban Heat Island Mapping Campaign City of Charlottesville, VA
Using trees and vegetation to reduce heat islands Environmental Protection Agency
Virginia Tech Dendrology Factsheets
What’s killing our oak trees? Ralph Morini, Piedmont Master Gardeners
White oak – a majestic native species Pat Chadwick, Piedmont Master Gardeners