Prune Young Trees in Winter

Bryan Dolney and Angela Masters pruning trees in Mellon Park

It may seem odd to see Pittsburgh Parks Conservancy staff and City DPW crews out in the bitter wind of January, but the winter months are actually the ideal time to give your trees a little attention. In fact, winter pruning ties into our Tree Action Plan as an effective way we can manage the current threats to our urban forest. “In winter the fresh cuts have time to dry out,” says Angela Masters, Parks Conservancy horticulturalist. “When the insects and diseases become active in spring the wood isn’t susceptible to colonization.”

Pruning young trees on your property is beneficial in a variety of ways. Proper pruning helps the tree send its resources to the good strong branches, so that it grows stronger and is less of a liability during a storm or bearing the weight of heavy snow. In addition, “A well maintained tree will serve the community best through storm water management, carbon capture, erosion control, and shade,” says Parks Conservancy Field Ecologist Bryan Dolney.

A branch diseased with fungal spores

Before you pick up the limb loppers, make sure the timing is right. A homeowner should feel comfortable doing developmental pruning, which means that the tree is more than one year old, no more than 20 feet in height, and 3-5 inches in diameter. “Don’t prune your tree in the year immediately following its planting,” advises Phil Gruszka, certified Arborist, and Parks Maintenance and Management Director for the Parks Conservancy,” unless it has one of the four D’s.” Limbs that are dead, dying, diseased, or damaged. This first year is when the tree’s root system is reestablishing itself and unnecessary pruning will disrupt its growth. Equally important is not attempting to prune a tree that is too large because it can become dangerous and should be left to professionals.

While it may be tempting to prune your tree into a pretty sphere, the primary purpose of pruning should be done with the tree’s structure as the paramount concern. Angela also warns to resist the impulse to “limb the tree up,” or cut away at lower branches while neglecting the higher ones. “Try not to remove more than 25 percent of the tree’s live branches while pruning,” she adds. When you’re decided which limbs will stay and which will go, keep your eye out for these primary issues…

Codominant stems with “included crotch”

Codominant stems. Codominance is when two or more stems are competing to become the dominant leader. Codominant stems grow parallel from one another and form a ‘U’ or ‘V’ shaped crotch. 

‘U’ shaped crotches are strong, there are wood cells growing in the bottom of the ‘U’ which connect the limb to the trunk, keep these whenever possible.

‘V’ shaped crotches are not strong because there are no wood cells growing at the point of attachment. ‘V’ type crotches frequently capture outer bark as the tree grows.  This bark, called an “included crotch” becomes included in the growth, preventing wood cells from connecting the limb to the trunk.   If a tree continues to grow in this manner it will eventually split, potentially causing serious damage on your property.

Damage from rubbing branches

Rubbing branches. Think of the way a bow rubs against the strings of a violin. Like water to a stone, the branches rubbing against each other over time will cause damage and eventually, fallen limbs.   

Dead branches. It’s pretty simple, dead branches can fall causing damage to both your property and other branches. They can also potentially be diseased and damage the health of your tree.

Deformed branches. If it doesn’t look right, it probably isn’t.

Angela removing suckers

Suckers. Also called water sprouts, suckers are small limbs that grow vertically in patches either off of a branch or out of the ground surrounding the base of a tree. They are aptly named as their primary dysfunction is that they suck resources away from larger, more vital limbs on the tree. Suckers on your tree are an indication of poor health (often because of improper depth when planted) so you should consider having an arborist take a look at it.

Cut one of the codominant branches as close to the point of the “V” as possible

Now that you know what to prune, how to prune it? “Cut a branch where there is a new shoot or a new branch coming out,” advises Angela. A tree is not a bush, instead of hedging the whole outside of the tree, make decisive reducing cuts to the branches. In the case of a codominant or V shaped stem, select the healthier looking branch to become the new dominant stem and cut the other as close to the point of the V shape as possible.

Ultimately proper care of trees on your property is a benefit to both yourself and the community. Proper pruning at the right time will help slow the spread of disease and insects in Pittsburgh’s urban forest where we currently stand to lose more than 60% of our urban tree population to threats like the Emerald Ash Borer and Oak Wilt disease. Healthy trees also ensure that we receive their maximum benefit to the environment. Finally, taking care of your trees in the first three years of their life will save you expense resulting from property damage and arborist expenses for years to come.  

Want to learn more about how to care for your trees? Join our friends at Tree Pittsburgh and become a tree tender. Also check out the Shade Tree Comission and TreeVitalize.

Ask us your tree questions @pittsburghparks on twitter or on facebook. To help save our urban forest, consider making a donation to our Emergency Tree Fund.

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Tree Spotlight: Pennsylvania’s Birches

On our last Top 15 Trees post, we asked if anyone wanted to learn more about some other trees you might find in Pittsburgh’s parks.  Stephen asked if we might talk a little about birch trees, so Phil and Erin shared some of their knowledge of the three types of birch trees most common to our region.

Photo by Steven Katovich

River birch (Betula nigra) is cinnamon-colored with a very distinctive bark that peels off in curling sheets.  These trees do well as part of landscape plantings (and are very visually interesting), even though their native habitat is more wetland in nature.  This is the type of birch that’s most resistant to boring insects, and it’s the only birch that produces its fruit in spring rather than fall.  You can find river birches planted in Riverview Park along Woods Run Avenue, near the Mairdale parking lot.  They’re native to the northeastern United States, not quite in Pittsburgh’s range, but they do grow well here.

White birch (Betula papyrifera), also known as paper birch because of the consistency of its bark, has a smooth trunk with an often bright-white bark that flakes in small horizontal strips.  It’s another quality landscape tree with many different available cultivars.  However, these trees often don’t live to be very old because they’re susceptible to insects.  They often live around 35 – 40 years in this area.  This is a northern tree that prefers colder climates, although it’s found in some southern states as well.  You can find some in Mellon Park–this photo was taken behind the semi-circle bench that overlooks the Walled Garden.

Photo by Richard Webb

Sweet birch (Betula lenta) is the most common birch in our region and is found within the forests.  Its bark is rough and dark brown to black with cracked plates, and its branches are delicate.  Its name is derived from the sweet aroma of evergreen emitted by crushed leaves or twigs.  There’s a stand of these birches in Frick Park along the Upper Braddock Trail along the drainages. 

The Parks Conservancy includes birch trees in our planting plans.  The three types that we use most commonly are the sweet birch, the yellow birch (Betula alleghaniensis), and the gray birch (Betula populifolia), which is a good early successional tree.

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Goodbye tree friends

After five years of having the privilege of documenting Pittsburgh’s parks and sharing stories about them with all of you, this is my last blog post for the Pittsburgh Parks Conservancy.  I moved back home to Memphis last week (to borrow the politicians’ phrase) to be closer to my family.  Saying goodbye was tough, especially since I was surrounded by such a warm and wonderful community of people who have taught me so much.  But it wasn’t just the people.  I think when you’ve spent so much time in the parks, especially slowing down to really get to know them, you realize you’re going to miss the trees too.  And so it was that I found myself, over the last few weeks, visiting some favorite trees to say a final farewell.  (At least until my next visit…)

Not all these special trees were blooming or leafing out yet (you picked a nice year to delay spring, Pittsburgh!), but there were plenty that were eager to show off.  In a lot of cases, I photographed a tree one day and then came back about a week later to watch it progress from flower to fruit to leaf (not necessarily in that order).  And in a switch this spring, I shot exclusively with a 100mm macro lens to get as much detail as possible.  This stymied Phil when I came back to the office and asked him for ID help; “I’m a silhouette guy!” he would exclaim.  “Come back when you photograph the whole tree.”  So these IDs are good guesses–thanks very much to both Phil and Erin for sharing their expertise.

So enjoy the final batch of tree photos.  I will miss these trees–and interacting with all of you–more than I can say.  Take good care of them for me.

I spent a good deal of time over by Westinghouse Pond, which has a nice assortment of trees that flower and leaf out early. Here’s a sweetgum whose leaves look like tiny stars.

Redbuds near the Frick Environmental Center.

One of the earliest bloomers of spring, the Cornelian cherry dogwood, at Mellon Park.

This one’s pretty but unfortunate: a honeysuckle vine that’s twisted itself around a spicebush in Frick Park.

Now we start with the trees-in-progress shots.  Here is a horsechestnut tree in Highland Park that’s just started to leaf out.

And here’s a horsechestnut the following week.  These were beginning to flower–probably right now the flowers will be standing up in white and pale pink stalks if you pass one of these trees.

Back at Westinghouse Pond, everything was pink.  Here’s a saucer magnolia and some cherry blossoms that haven’t opened yet.

And now a magnolia that’s in full bloom…

…and a cherry blossom.   Some on the tree had petals, others (like this one) didn’t.  I don’t know whether that was because of all the recent wind, or if that just happens sometimes.  Either way, I thought it made for an unusual photo.

Another beautiful kind of magnolia tree grows right around the basin of Westinghouse Pond–the sweetbay magnolia.  Here it is before the flowers have opened.

And a week later, delicate white flowers.

The hawthorn tree is lovely, but you probably shouldn’t play tag anywhere near it.

Here it is beginning to flower (they’ll be pretty and white–check this one out over by the Bartlett Meadow, where the daffodils are blooming):

And now we come to the maples.  Last year, my fascination was with redbuds; this year, it’s been maples.  I was a little disheartened that it seemed like so many of the trees I was asking Erin and Phil about turned out to be invasive Norway maples…but I have to give it up, they are pretty fascinating in the spring.  The trees that look like they’re covered in neon green popcorn balls are Norway maples–probably the first trees you saw flowering this year.  The photo on the left is a native sugar maple, and the one on the right is a Norway maple for comparison.

This one is also a Norway maple, although it sure looks different.  Popcorn of a different variety?

And here’s another Norway maple that’s begun to produce leaves.

This one in the Westinghouse woods in Schenley Park appears to be a sycamore maple–another tree considered by some to be invasive, although it’s not nearly as prevalent as the Norway maple in Pittsburgh’s forests. (Thanks Burlton for the ID!)

Finally, we come to four different red maple trees.  I think these are such beautiful harbingers of spring, especially the big trees that just light up with red flowers.  So I decided I’d track one red maple tree every couple of days for a month to watch its progression.  While it is a pretty tree, I happened to pick one that wasn’t producing seeds, and I had to leave town before the leaf was fully formed.  But here’s the tree (at the corner of Bartlett St. and Panther Hollow Road) on March 22…

…and on April 23.

Since that tree wound up not being particularly showy, I supplemented with some other red maples.  This one was across the street, near the drive up to the Schenley Oval.  It was my original choice to document, but all the branches were too high to get close to.

This one (and many others like it) was putting on quite a show lining the Bob O’Connor Golf Course in Schenley Park.  You can see the winged seeds starting to take shape.

And finally, a closer look at the seeds of another maple along Bartlett Street.

Thanks again for reading and commenting, and for generally sharing the park love over the last few years.  If you want to keep in touch, you can still find me online at www.twitter.com/MelissaPics, where you can bet you’ll see some of the superstar trees of Zone 6.

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Top 15 Trees in the Parks – Part 5

It’s time for the last installment of our Top 15 Trees in the Parks series.  The final four trees include some natives you may not be familiar with, as well as the brightest star in the winter landscape.

12. Eastern hophornbeam (Ostrya virginiana)

Photo by Steven Katovich

This is a small tree in the birch family with an extremely durable wood (which explains another of its common names, “ironwood”).  It grows well in many types of soils and can tolerate living under the shade of taller trees.  When it matures, its bark appears shredded because it forms narrow strips that are loose at the edges.  Leaves are simple, shaped similarly to elms, and doubly toothed at the edges.  The fruit, which resembles hops, is a cluster of papery oval sacs each containing a tiny nut. 

Like the northern pin oak, this tree has both male and female flowers.  Its male flowers are brown “pre-formed” catkins, in clusters of three like birds’ toes, that are visible throughout the winter and open in spring.  Female catkins are light green and only appear in the spring.  This is a good way to distinguish this species from the American hornbeam (Carpinus caroliniana), whose catkins all appear in the spring. 

Phil Says: These trees are often confused with elms because they look very similar with bark characteristics, form, and the nature of the twigs.  But upon close inspection, you’ll see subtle differences in leaf shape and seed set.  Hophornbeam is a great native that is definitely underutilized in both landscape and urban woodlands.  It performs very well as a street tree if planted.

13. Hackberry (Celtis occidentalis)

Photo by Paul Wray

The hackberry tree is a member of the elm family.  It has a distinctive bark—it’s mostly smooth, light brown or gray, but wart-like knobs disrupt the surface.  It’s well-suited to the urban environment, tolerant of air pollution and many different temperatures and soil types.  It can also be planted near waterways to help reduce the risk of flooding. 

The hackberry is a fantastic tree for wildlife, hosting bees, birds, and butterflies.  The birds love its sweet fruit, and butterflies (like the hackberry emperor) drink its sap.  Humans can eat the berries too, and although they’re fairly thin and dry, they have a taste similar to dates.  Another good quality for wildlife is that the hackberry has fairly weak wood, so late in its lifespan it begins to split and form cavities that provide shelter. 

Phil Says: Another great native.  Definitely underutilized in our landscape and streetscape.  They are beneficial in both those settings, and it’s a great woodland tree as well.  It has an interesting bark that grows in bumpy ridges.  I liken it to the Velcro tree—if you were to run and jump and grab onto it, it would be difficult to slide down the tree because the ridges are so rough they’d hold you there. 

14. Yellow buckeye (Aesculus flava)

Photo by William Ciesla

The yellow buckeye is a close relative of the Ohio buckeye (Aesculus glabra), but can be distinguished by its flowers.  In the yellow buckeye, the stamens are shorter than the petals, and in Ohio buckeye they are longer.  Both trees have an unpleasant odor, but the Ohio buckeye’s is much stronger, which has led to the yellow buckeye sometimes being termed “sweet buckeye.”  The yellow buckeye is also a larger tree. 

Its leaf is distinctive, usually having five leaflets.  It’s similar to the horse chestnut, which is in the same family of trees.   (The leaf buds of the horse chestnut are very sticky, which is a helpful way to distinguish them.)  The yellow buckeye’s flowers are yellow and form upright clusters.  The fruit, a smooth nut enclosed in a thick husk, is poisonous to humans but beloved by squirrels. 

Phil Says: There are native and non-native buckeyes here; there are probably a half-dozen non-natives that have been hybridized in horticulture and brought to this area.  They do grow in the parks as well.  I don’t plant them in the landscape because there’s a pretty common leaf blight that affects them, so often they get pretty brown by July.  But they’re part of the ecosystem, so they’re appropriate for growing in the woods. 

15. Witch hazel (Hamamelis virginiana)
Unlike most other trees, the witch hazel is easiest to identify in the winter months.  It begins showing its small, thread-like yellow flowers in late fall and retains them throughout the winter.  In very cold weather the petals might curl up close, but they usually last until spring, when everything else begins to bloom.  Then the small buttons that contain the seed pods burst and shoot out the seeds that have been ripening over the past year.  

The witch hazel is a small, shrubby tree, well-suited to the understory.  Its scientific name Hamamelis means “together with fruit,” which refers to the fact that its fruit, flowers, and leaf buds all appear at the same time (making it unique among trees native to North America).  

Phil Says: That is a great native plant that blooms during the winter when nothing else blooms.  It does best in wet, riparian areas, but it is adaptable.  It’s a smaller tree, usually multi-stemmed.

We hope you enjoyed this peek into the composition of our forests.  Any other trees you’d like to see spotlighted here on the blog?

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Top 15 Trees in the Parks – Part 4

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

9. Hawthorn (Crataegus pennsylvanica)

Photo by David Hawgood

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)
(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. 

Photo by Paul Bolstad

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.  

Photo by Paul Wray

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!

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Top 15 Trees in the Parks – Part 3

Time for the next few trees in our Top 15 Trees in the Parks series: 

6. Elm (Ulmus americana)

Elm stand at the Schenley Park Overlook

Despite the high mortality caused by Dutch elm disease, Pittsburgh’s parks still feature a significant population of elm trees, although many of them are smaller than the elm’s traditional soaring height (often around 100 feet tall).  Because of its strong wood and tolerance of many stress factors like pollution and poor soil quality, the elm is a high-quality tree for an urban park. 

Prior to Dutch elm disease’s reign in the 1950s – 1970s, the elm was the most popular street tree in the country thanks to its elegant Y shape, sturdy build, and ample shade.  Over 100 million elms were felled by the disease, changing the character of cities, from neighborhoods to forests.  But the elm is working its way back into the landscape: to combat the disease, a breeding program has sought to hybridize American elms with Asian elms, which are highly resistant to the disease. 

In Pittsburgh, we’re working to become part of the solution.  In 2005, Norway maples were removed from the border of the Schenley Park overlook and replaced with 30 elms from six different cultivars: Accolade, Allee, Frontier, Pioneer, Prospector, and Triumph.  Students from the Penn State Cooperative Extension are studying the trees to observe their development and keep a careful eye on whether the elms exhibit invasive tendencies in the adjacent natural areas (so far, so good!).

Elm leaf photo by Paul Wray

Phil Says: Even though Dutch elm disease swept through Pittsburgh decades ago, elm is such a strong native tree genetically.  It’s very well adapted to growing here, and so as these mature trees were sickened, they produced tens of millions of seeds that were dispersed throughout the urban forest.  Many of those seedlings grew up, and Dutch elm disease did not find them until they became larger trees.  So we still have lots of American elms left—they’re known as climatic escapees.  It’s a regenerative population that has survived because the disease is not at the level it once was and the insects that spread it aren’t nearly as abundant.  For the most part these newer trees will never attain the height and girth of the elms we were used to seeing in Pittsburgh.  To have thousands of large trees is probably not going to happen.

7. Northern Red Oak (Quercus rubra)
(We’re focusing on the Quercus rubra species here, but this section includes all oaks in the red oak family.  In this family, the lobes at the ends of the leaves are pointed and acorns ripen over two seasons.  The “red” refers to the wood inside the tree, although many of them also have red leaves in fall.) 

Red oaks are a fast-growing, fairly tall tree with a mature diameter of 2-3 feet.  They are good urban trees because they tolerate pollution and compacted soils.  The red oak is a dominant forest tree throughout the state of Pennsylvania. 

The leaves contain tannin, which makes them leathery and resistant to decomposition.  They are simple, with between 7 and 11 toothed lobes on each leaf.  They are dull green throughout the summer and turn a brick red color in fall. 

Phil Says: When we mention “red oak,” that refers to a group of oak trees.  The trees in the red oak group that are most common in Pittsburgh are red oak, black oak, and pin oak.  Oak wilt disease has directly impacted the red oak group, having claimed several hundred trees last year alone in Riverview, Highland, and Frick Parks.  

8. Black Locust (Robinia pseudoacacia)
The dark, deeply furrowed bark of this tree and the twisty character of its upper branches make the black locust easy to distinguish.  They also have paired thorns that can grow to half an inch long.  It has an especially striking winter silhouette.  They are usually medium-sized trees but can grow to 100 feet tall.  

Black locusts are similar to cottonwood trees, but in summer can be easily distinguished by their compound leaves (cottonwoods have simple leaves).  There are between 7 and 19 leaflets on one stem, and all of them are paired except for the leaflet on the end.  They are smooth and oval-shaped, and droop at night.  Locust fruits are dark brown pods up to four inches long.

Black locusts are the host plants for clouded sulphur butterflies and silver-spotted skippers.  They are considered invasive in some parts of the United States, particularly where they have begun to colonize dry prairies and savannas.

Phil Says: Like black cherry, this is an early successional species, so wherever it’s growing, it’s making that site more suitable for other dominant trees—oaks, maples—to move in.  It’s a site colonizer.  Black locust trees have thorns, even though most people never see them.  The thorns occur on new growth, and they are there to protect the tree from being browsed by deer.

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Top 15 Trees in the Parks – Part 2

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)

Photo by Dan Mullen

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)

Sugar maple leaves, flowers, and fruit

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 seeds

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.

The stems of a tree of heaven (left) and a staghorn sumac

Look out for the next few trees on the list in the next few days!

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Top 15 Trees in the Parks – Part 1

We’d like to introduce you to our trees.

In 2010, the City of Pittsburgh completed a Natural Areas Study of Frick, Highland, Riverview, and Schenley Parks.  The study included a tree inventory that tallied about 373,000 trees on 900 acres of forested park land.  That’s a whole lotta shade–and habitat, and air cooling, and soil stabilization, and many other good things. 

But we were interested in how the trees broke down by the numbers.  We took a look at the tree inventory and decided to introduce you to the top 15 species (by density) that you’ll find in the parks.  (We’re leaving out the sixth item on the list–which was just a catch-all line for dead trees that came in at around 23,000.  We’re sure those trees are making lots of birds and squirrels happy, but we don’t have much else to say about them!) 

Along with a general introduction to each tree, I asked our resident Tree Guy, Phil Gruszka, to pass on a few words about each species.  We’ll bring these to you a few at a time over the next week or so.  Enjoy!

#1: Norway Maple (Acer platanoides)

Norway maple leaves

The runaway winner in the Pittsburgh parks tree sweepstakes is unfortunately the invasive Norway maple, covering almost 18% of the regional parks’ wooded areas.  It achieves dominance over native plants through its abundant production of seedlings, the deep shade produced by its canopy, and the release of phytotoxic chemicals that inhibit the growth of other plants.  By contributing to the lack of understory plants, Norway maples also help cause erosion and compacted soil.  In our restoration work with the City, we’ve tried to turn that on its head by using cut or fallen Norway maples to stabilize hillsides. 

Norway maple can be distinguished from native maples by the white, milky sap in its leaves and twigs (the natives have clear sap).  It’s also one of the last trees to lose its color in the fall, remaining green into November and then turning bright yellow.

After most other trees have lost their leaves in the fall, the Norway maple remains yellow.

To indicate how invasive Norway maple is, Phil says it’s a good rule of thumb that an ideal, balanced forest would contain no more than 10% of any one genus.  So all the maples put together should total less than 10%.  Instead, this one species alone makes up 18%.  And, in fact, the Norway maple accounts for more than half the trees in Highland Park, which means that replacing this species with more appropriate trees will be a long-term effort.

Phil Says: For the past 13 years, the City of Pittsburgh’s Department of Public Works and the Pittsburgh Parks Conservancy have been working towards removing this non-native, environmentally invasive tree from the park woodlands.  However, with the advent of EAB and oak wilt disease and other destructive insects and diseases that are making their way to Pittsburgh, we need to be careful about how we approach the Norway maple.  Most recently, when oak wilt struck a stand of native red oaks in Highland Park, the understory was made up of Norway maple.  There, we ended up leaving the Norway maple tree because it was better to have that tree than no tree at all, because the steep slope needed to have trees on it to prevent soil from running off.  The Norway maples will remain until native trees have replenished that site, at which point they will be removed.

#2: White Ash (Fraxinus americana)
Today, the most prevalent native species in the parks is white ash, at about 50,000 trees.  It is most prominent in Schenley Park, where it makes up 26% of the forest.  Its impending, almost total loss to the emerald ash borer beetle will dramatically change the composition of the canopy, especially in Schenley Park. 

Before the introduction of EAB, white ash was an excellent tree to plant in the parks because of its size, ease of transplantation, and attractiveness as wildlife habitat.  It grows relatively rapidly and has fall colors ranging from yellow to orange to maroon.

Phil Says: In sections of park woodlands where we have removed Norway maple, the very first native species to naturally repopulate those sites have been white and green ash.  Genetically, this is a strong plant with so many great qualities. It’s truly unfortunate that such a great native tree species is being destroyed because of emerald ash borer.

Stay tuned as we continue to reveal more about our parks’ most prominent trees!

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[Presentation]: TreeVitalize Pittsburgh

Today we’re posting the last of our six presentations from “Preserving Pittsburgh’s Trees: Action and Recovery.”  We’re very much aware that the picture painted by the previous speakers is grim, but we’ve felt it’s crucial to make the public aware of the problems so that we can try to address them before it’s too late.  As we put the finishing touches on the Tree Action Plan, we’ll be able to give you more actionable items for how YOU can help save trees, including lists of currently-unthreatened native species to plant on your own property.

And speaking of planting, now’s the perfect time to introduce you to Lisa Ceoffe, the City of Pittsburgh’s urban forester and coordinator of the TreeVitalize program.  She tells the other side of the story, the side where volunteers from across the city mobilize to plant trees in their neighborhoods and then to take care of them.  And she offers many suggestions for how you can bring all the advantages of the TreeVitalize program to your own community.

Watch her presentation below, or download the slides here.

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[Presentation]: Responding to Threats in Pittsburgh’s Urban Forest

“This may be one of those bellwether times in our society and in our region, where what we plan to do now will greatly impact not just us but our children and our children’s children.  We’re going to look back someday and say did we do the right thing or did we not do enough?”

City Forester David Jahn is responsible for looking after Pittsburgh’s tree population, and for mobilizing a response to things that threaten it.  He’s constantly on the lookout for things such as potential landslide conditions or dying trees that may pose a hazard to their surroundings.  As he points out in his presentation from “Preserving Pittsburgh’s Trees: Action and Recovery,” he needs the eyes of the community to make sure all issues with trees are addressed.  If you see a tree that looks like it may pose a hazard, or that exhibits symptoms of one of the diseases or pests we’ve been discussing, calling 311 will alert David and his team to look into the situation.

Watch David’s presentation below, or download the slides here.

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