Today we round out the top five in our series of the 15 most common trees found in Pittsburgh’s regional parks. Two of these trees are valuable natives, and the other is an ornamental street and garden tree that has become a woodland menace over the years.
#3: Black Cherry (Prunus serotina)
This native tree has a significant population in all four regional parks, although its largest concentration is in Schenley Park. It is easily distinguished by its broken-looking bark, which is dark gray to black. Unlike other types of cherry trees, black cherries generally flower well after their leaves have developed, usually in mid-May.
The cherries are drupes (fruits derived from flowers where the flesh surrounds a pit, which contains a seed). Straight off the tree, they may taste bitter to us, but birds and other animals love them. The fruits can be used to flavor wine and jelly.
Phil Says: The black cherry is an early successional species, so its role is to take disturbed sites and colonize them, making them ready for other native species like oaks and sugar maples to grow there someday. Genetically, it is capable of germinating and growing in a lawn area or a disturbed area, such as a place where invasive plants (like vines) are choking out other plants. Black cherry has the ability to establish there and work its way into the canopy, eventually shading out the lawn or the invasive plants. This tree is on our planting list for the oak wilt site in Highland Park; it’s a great candidate to begin regenerating the forest.
#4: Sugar Maple (Acer saccharum)
This native alternative to the Norway maple makes up about 9% of the park tree inventory, or just about half the population of the Norway maples. Although these two trees are not closely related genetically, they are often mistaken for one another. Among other differences, sugar maples have more interesting fall color, showing a range from bright yellow through red-orange, often on the same tree at the same time. The largest concentration of sugar maples in our parks occurs in Frick Park, where there are more than 20,000 of these trees.
The sugar maple is one of the most shade-tolerant trees in this region, so it can serve as a good understory plant. When a canopy gap opens and more sunlight comes through, its growth rapidly accelerates. It has been outcompeted by the Norway maple partially because it is less tolerant of urban conditions, such as pollution, acid soil, and road salt.
Phil Says: Our beloved sugar maple is a strong native. It’s been embraced by horticulture and bred and selected for form, size, and fall color. Someday it will be a true disaster if the Asian long-horned beetle makes it here, that the sugar maples too will be gone.
#5: Tree of Heaven (Ailanthus altissima)
If you’ve ever heard us say “fuzzy is a friend” on a walk through the park, we’re making reference to the strong resemblance between the invasive tree of heaven and the native staghorn sumac tree. From a distance, the leaves look very similar. However, the sumacs have “fuzzy” stems covered in tiny rust-colored hairs, while the tree of heaven has a smoother bark. The tree of heaven is also distinguished by a rancid odor that is released when the leaves are crushed or rubbed. (In the tree’s native China, its name is chouchun, or “malodorous tree.”)
Tree of heaven is one of the fastest-growing trees in North America, shooting up between 3 and 7 feet per year for the first four years of its life. Introduced to the United States in the 1700s as an ornamental, it was heavily planted as a street tree because it can grow in harsh conditions. It has escaped cultivation and moved heavily into natural areas, where it has been extremely destructive to native plants. The tree thrives in full sun and disturbed areas, so it’s quick to populate a canopy gap, where (like the Norway maple) it adds to its destructive effect by releasing toxins into the soil that inhibit the growth of other plants.
Phil Says: This tree is affectionately known as the Pittsburgh palm. We embraced this as a horticultural plant during the Industrial Revolution era, because we were devastating our environment and very few species really thrived. When we found the Pittsburgh palm, the tree just loved it here. And even though our air is much cleaner now, our soils are recovering, and our water quality is improving, the Pittsburgh palm still loves it here. It, along with its buddy the Norway maple, exudes herbicides from its roots and excludes our native trees, shrubs, and flowers from growing. So there’s a need to control the beloved Pittsburgh palm—not on all sites, but where we still have good native plant communities that can grow, that’s where we implement control measures.