Top 15 Trees in the Parks - Part 4

April 18, 2011 by Melissa McMasters

Time to spotlight a few more commonly found trees in our parks:

9. Hawthorn (Crataegus pennsylvanica)

Hawthorn flowers

Sometimes called thornapples, hawthorns are small trees with 1-3cm thorns growing from their branches or trunks. The leaves are variable in shape, but usually have serrated margins. Their small berry-like fruits are beloved of birds and mammals, and the nectar from their flowers is a food source for insects. Cedar waxwings are especially fond of these trees.

The tree is distinctive in three seasons—with beautiful clusters of white flowers in the spring, red fruit in late summer, and attractive fall color.

Phil Says: We frequently don’t put a lot of value on trees which do not attain great height or girth, but our native hawthorn occupies a niche in the overall ecology of Pittsburgh. In its native state, it is a floodplain and wet areas tree. And those are frequently areas that are difficult to have large canopy trees succeed, even though boxelder and poplar and sycamores will grow there. But it is rare to see hawthorn trees fail in flooded conditions, where larger canopy trees are subject to failure. They are a great habitat tree with a dense branch structure. The seed set is prized by wildlife—birds, squirrels, deer, raccoons, and opossum all utilize it.

10. White Oak (Quercus alba)
White oak(We’re focusing on the Quercus alba species here, but this section includes all oaks in the white oak family. White oaks are generally defined by having leaf lobes whose tips are not bristled, and by acorns that ripen within one season.)

White oaks, despite not being extraordinarily tall, often project a massive appearance thanks to low branches that reach out parallel to the ground. White oaks can grow as wide as they are tall, giving them a distinctive silhouette. They have a light gray bark that peels slightly, and glossy green leaves that are lobed and oval in shape. In the spring, leaves are downy and silvery pink.

White oak leaf

The white oak is an excellent shade tree because of its wide branching and its tendency not to drop its limbs. It grows well in almost all soils except those that are particularly dry and shallow. They are fairly slow-growing compared to other oaks, but they tend to have long life spans.

Phil Says: White oaks are somewhat resistant to oak wilt disease. They will contract the disease but they generally do not have fatal symptoms, unlike the red oak group. Like red oaks, white oaks are also a group—white oak, swamp white oak, and bur oak are the most common. To date, wherever oak wilt has been controlled in the parks, we have removed the white oaks as well as the red oaks, knowing that the white oak could be a host for future infections of red oaks.

11. Northern Pin Oak (Quercus ellipsoidalis)
Also called Hill’s Oak, this member of the red oak family is often found in dry, sandy soils. Despite its ability to tolerate poor soil conditions, it is extremely intolerant to shade and so is usually succeeded by other oaks that need less light.

Northern pin oak

Its name suggests that it’s closely related to the pin oak (Quercus palustris), but its nearest relative actually seems to be the black oak (Quercus velutina). Northern pin oak gets its scientific name from the ellipse shape of its acorns. The tree is medium-sized and has a bright red color in the fall, making it a good choice for ornamental plantings.

Northern pin oak has male and female flowers appearing on the same tree, with male flowers taking the form of catkins and females as small hanging flowers either alone or in groups of two or three. Its leaves can be distinguished from those of the red oak (Quercus rubra) by their shiny surfaces and deep sinuses (the indentations between lobes).

Check back soon for the final installment in this series!

Trees and Forestry