10 “Climate-Smart” Trees that Can Take Our Future Heat

April 27th, 2021

   Our climate isn’t like it was just a generation ago, and our plants are showing it – especially trees.

White oak is a species tolerant of our future heat.

   Many of Pennsylvania’s recent tree demises – from diseases on spruce and firs to branch diebacks on Japanese maples to “mysterious” deaths of sugar maples – are directly or indirectly related to climate changes.

   The U.S. Department of Agriculture’s Climate Change Resource Center says we’re on a road toward wetter, warmer, and less snowy winters; earlier springs; hotter, drier summers; more extreme fluctuations between heavy downpours and “flash droughts;” more erratic temperature swings; longer, drier autumns, and new bugs, diseases, and weeds that didn’t use to withstand our colder winters.

   All of that is taking a toll on trees – particularly those that don’t adapt well to change and that don’t do well in hotter weather.

   Gardeners, urban foresters, and public gardens such as Longwood Gardens and the Chicago Botanic Garden have been documenting that some species are struggling more than others.

   Of 50 trees the Chicago Botanic Garden studied, for example, 10 were identified as ones that won’t fare well 30 years from now – American and Greenspire lindens, shagbark hickory, Black Hills spruce, American hop hornbeam, katsura, Norway spruce, Sargent cherry, amur maackia, and Serbian spruce.

   The U.S. Forest Service also identified beech, sugar maple, gray birch, eastern white pine, and black cherry as others “vulnerable” in the climate that’s unfolding.

   Knowing which species are best equipped to adapt to the future climate is good to know because trees are such long-term investments.

   As Penn State Extension urban forester Vincent Cotrone wrote in a post on tree selection, “We need to take into account whether (a tree) can handle conditions in 20 to 30 years. If we decide to plant 50 new street trees of a given species, and they begin to decline and die off in 10 years, we have just wasted time and lost 10 years of establishment.”

   If you’re planning a new tree or three, it makes sense to take into account the likely future conditions as well as “conventional” selection factors such as light, soil moisture, available space, and whether the species is a prime target for those deer that are lurking nearby.

   Based on studies by the Chicago Botanic Garden and the U.S. Forest Service’s Northern Institute of Applied Climate Science, below are 10 of my all-around-best tree choices that also are equipped to handle future heat. Let’s start big and work small…

1.) Autumn Blaze Freeman maple

Autumn Blaze in fall.

   This tough shade tree is a hybrid that combines the showiness of red maple with the durability of silver maple.

   Autumn Blaze is very tolerant of heat, wind, and wet soil, and it’s adaptable to most soils (except salty) as well as urban air pollution. It’s also strong-limbed and produces very few of those “helicopter” maple seeds that some people don’t like.

   It’s a fast grower to 50-60 feet tall and 30-40 feet wide in 25 years, ideally in full sun.

2.) Red maple

   Arguably Pennsylvania’s best native shade tree, red maple is a fast-grower and is a good choice for occasionally wet sites since its roots can tolerate poor drainage and wet soil better than most species.

   The leaves have three main lobes and emerge reddish. But the real show is fall when the leaves of the best varieties turn brilliant red. Three of the best for fall color are Redpointe, Red Sunset and October Glory.

   Figure on a size of 50-60 feet tall and 30-35 feet wide in 25 years, ideally in full sun. Avoid salty sites.

3.) White oak

   You won’t find any bigger, stronger, or more majestic American hardwood than this Pennsylvania-native oak.

   White oak gets its name from its flaky, light gray bark (almost white). The leaves are sharply lobed and go from glossy green to russet-red in fall.

   White oak also is a heavy acorn producer, which makes it one of the best choices if you’re trying to be kind to native mammals (but not such a good choice if you’re looking for a tree for next to the patio).

   Its growth rate is slow to moderate, but it can eventually work its way up to 80 feet tall and wide – or more. Full sun.

The bark of a triple-trunk river birch.

4.) River birch

   Another Pennsylvania native species, river birch is best known for its peeling cinnamon-colored bark and yellow-gold fall foliage. It’s a more durable choice than the bug- and disease-prone white birch.

   This species prefers damp, acidy soil, so you’ll do it a favor by occasionally deep-watering in hot, dry weather.

   River birch is useful to native birds and butterflies, but it can be “messy” with dropping racemes, petals, and leaves if you’re looking for something near a patio.

   Don’t under-estimate how big this species can get, as many people do who plant one four feet off a house corner. River birch grows fairly fast to 40 or more feet tall with a spread of 25 to 30 feet in sun to light shade.

   Dura Heat is a good variety for heat tolerance, and the 15-foot Fox Valley (‘Little King’) is a good choice if you don’t have the space for a full-sized birch.

Fall foliage of ginkgo.

5.) Ginkgo

   This species has been around since dinosaur times, so it has a proven durability record of dealing with climate changes.

   Ginkgo trees have distinctive fan-shaped leaves that turn brilliant gold in fall. They grow fairly fast to about 50 feet tall and 30 feet wide.

   ‘Autumn Gold’ is particularly showy and grows about 45 feet tall and 30 feet wide. If you need something narrower, look to ‘Princeton Sentry’ or Golden Colonnade.

   Avoid female types (rarely sold anyway) that produce very stinky fruits. Males don’t fruit. Full sun.

6.) American hornbeam

   This durable 25- to 30-footer is a mid-sized native tree with orange-red fall foliage and a smooth, gray trunk that earns it the nickname “musclewood.”

   American hornbeam is slow-growing, a favorite nesting tree of hummingbirds, and its fall winged nutlets feed wildlife.

   ‘Fastigiata’ is a narrow form for tighter areas. Full sun to light shade.

The bark and fall foliage of Persian parrotia.

7.) Persian parrotia

   Nicknamed Persian ironwood, this is another 25- to 30-footer that’s tough, slow-growing, and offers some of the most brilliant golden fall foliage of any species.

   The bark also flakes with age, giving a Dalmatian-like appearance. And it’s a tree that can be grown as a single-trunk specimen or a multi-stemmed one. Full sun to part shade.

8.) American smoketree

   Gardeners are far more familiar with purple-leafed smoketrees than this native, green-leafed species that also gets the puffy, white, rounded late-spring flower heads.

   Besides being a native tree, American smoketree produces glorious golden-orange fall foliage in a small, trouble-free package. Figure on 20 to 25 feet tall and wide in 25 years in full sun to light shade.

Sweetbay magnolia flower and leaves.

9.) Sweetbay magnolia

   This small, native magnolia is both cold- and heat-tolerant in our climate and is versatile in both sun to part shade. It prefers damp soil, though.

   Another plus is its fragrant white flowers in May. Sweetbay magnolia makes an excellent patio tree and grows to about 20 feet tall and almost as wide in 25 years.

10.) Serviceberry

   One of the best small flowering trees, this native species has multi-season interest with its springtime white flowers, then blue June berries (that taste like blueberries and that birds love), and finally a blend of blazing fall foliage.

   Serviceberries grow in sun to part shade and reach about 18 to 20 feet tall and almost as wide in 25 years.