Textures, Colors, Patterns: Identifying Trees by Their Bark

With most trees stripped bare of leaves, winter is a great time to get a good look at the wonderful variations of pattern, color and texture that form the trunks and branches of local urban trees. With a little practice, you’ll be able to easily identify many local tree species by name just by looking at their bark. Here are a few to get you started:

beech barkBeech

Found in all four of Pittsburgh’s major parks — Schenley, Riverview, Frick and Highland — these trees can live up to 400 years. The beech tree can be recognized by its smooth silvery-gray bark that contrasts with the browns and dark grays of other forest trees.


 

Photo: Selena NBH, Flickr


Lacebark pine

The lacebark pine is an evergreen and keeps its needles year-round. Its bark peels, or “exfoliates,” uncovering patches of white, green and purple underneath, almost like a camouflage jacket. You can find lacebark pines near the tennis courts in Mellon Park and near the Frick Park gatehouse.


 

sassafras barkSassafras

The bark and roots of the sassafras tree have a scent similar to root beer, and its bark was traditionally used to make tea and for medicinal purposes. The grayish-brown trunk of the sassafras tree is ridged and furrowed.

 


 

london plane barkLondon plane

The rows of majestic London plane trees that line the street near the entrance to Carnegie Library of Pittsburgh in Oakland are impossible to miss. These massive trees have gray bark that sheds in flakes almost year-round, revealing smooth, creamy-white bark underneath.


 

dawn redwood barkDawn redwood

The dawn redwood was once thought to be extinct but was found in China in 1948. Seeds and seedlings were brought to North America, where it has survived well. The dawn redwood has needles, but, unlike evergreens, it loses them in the winter. It sheds its dark brown bark in long strands, which squirrels snatch up to use as building material for their nests.


 

What other trees have distinct bark? Share your thoughts in the comment section below!

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A Race with the Red Queen

No disrespect to the ancients, but the best time to plant a tree was not 20 years ago. It might be this spring.

A variety of leaves from trees planted last fall in Highland Park. Photo by Taiji Nelson.

Whether plant, animal, virus, or bacteria, all living organisms are locked in battle with the pathogens, pests and parasites in their surrounding environment, using the tools and tricks nature’s equipped them with to keep them in the game. One of the strongest tools in this arsenal? The ability to adapt, to one-up opponents in a constant arms race.

One huge task that the Parks Conservancy faces is shoring up this arsenal for the trees in our care. The founders of these fine parks left quite the legacy, not only in the consideration that they gave to the design and experience of the parks, but also the impressive diversity of the urban forests.

It’s tough to overstate the importance of biodiversity to healthy parks. Voracious pests and sneaky diseases gain a slight foothold within the bounds of our parklands and spread like wildfire, faster than we can catch and quarantine them — even with sharp eyes out at all times. Our trees need their natural defenses as they stand on the front lines of these attacks, especially since they face added stresses of living in the city: polluted water, poor air quality, micro-climates, and human intervention.

London plane tree in Schenley Plaza.

A general in this battle, the Parks Conservancy’s Director of Park Management and Maintenance Phil Gruszka is a seasoned veteran. Phil has been rocking war paint for years now. Since conducting a study with Dr. Cynthia Morton of the Carnegie Museum of Natural History, he’s realized that our legacy park trees are impressive in their biodiversity… but that we have to really work to keep it that way. Their study found that tree stock from major nurseries across the country have actually been whittling down the tree gene pool.

“When London plane trees were first introduced to the United States, one nursery had a tree that did very well. But they couldn’t get it to reproduce from seed, so they started getting cuttings to grow out. Then they released it to the trade and named that cultivar ‘Bloodgood.'”

Selected for it’s superior resistance to the fungus anthracnose, the cultivar (a plant chosen for its particular genetic makeup) Bloodgood has been spread around now for about 30 years, dominating nursery stock of London planes. Plane trees bought from nurseries have identical genetic material to every other plane tree — they have not been grown from seed from two parent trees. They’re clones.

“Today, if I wanted to replace a London plane, I can only buy the cultivar Bloodgood.”

But trees from Schenley Plaza and around the park surprised them. “The Schenley Plaza trees were all genetically different, very diverse.” The park trees, planted before Bloodgood started to gain popularity, were much more diverse than the current nursery stock. The surviving 100, of the 200 that were planted years ago, were of a strong and diverse population, toughened from years of fighting off pests and disease.

Then, they widened their net. Was this true only for London planes? How much more diverse are our park trees than trees sold around the country? After polling nurseries from various parts of the country, they found that ten common trees used all over the U.S. were clones — their genetic diversity was actually getting less and less diverse.

Red oaks with oak wilt in Schenley Park, soon to be cleared.

Why has this study been so important? As the Parks Conservancy has taken on ecological restoration projects in the parks over the years and established the Park Tree Action Plan with the City of Pittsburgh, TreeVitalize, and Tree Pittsburgh, we’ve actively worked to increase biodiversity in the parks. Taking cuttings of our own heterogeneous tree stock, we’ve started growing new trees around the park and city in our own sort of diversity study, learning as we go about resistant new cuttings that withstand biological threats. This knowledge gives us only a peek at the immeasurable value of Pittsburgh’s parks; less mature forests and parks elsewhere are markedly more homogeneous, posing a threat to themselves and surrounding forests against the pests and diseases that have shown an uptick in recent years. Our trees are better equipped to keep our parks healthy and beautiful.

This week, a large stand of red oaks — about 50 trees in total — will be cleared from Prospect Drive in Schenley Park. Oak wilt, discovered earlier this year by an observant park user, got a stranglehold on the interlocking root system of the trees, infecting an entire grouping of trees. Left there, the trees are a risk to the health of other park trees. It’s terrible to have to take down so many trees, but it’s something that needs done for the overall well being of the park. And when these trees are replanted in the spring, a variety of new and diverse tree stock will be added to the expanding biodiversity and health of the park.

Wondering about the title of this post? Read more about the Red Queen Effect here.

Nature by design

This is an article I originally drafted for Sylvan Communities magazine, but I thought I’d share it here as well.

It’s easy to forget when taking a walk through the lush woodlands in our regional parks that these natural wonders are actually designed landscapes.  When Frick, Highland, Riverview, and Schenley Parks were being developed from the late 19th to mid-20th centuries, teams of landscape architects worked to shape park users’ experience of nature.  Working largely in a traditional romantic picturesque style, they laid out parks with open meadows surrounded by woodlands that emphasized a rustic view of nature.  While there was certainly some vegetation in place when the parks opened, the selection of trees, shrubs, and herbaceous plants for the park was an important component of these designers’ work.

We can still see the efforts of these original craftsmen in places such as the Reynolds Street entrance to Frick Park, which contains open fields and planting beds leading into a series of forested trails.  Preserving these historic designs–and balancing them with the needs of today’s users–is a guiding principle of the Pittsburgh Parks Conservancy’s work with the City of Pittsburgh.  But along with history and modern use comes a third, and equally important element–ecology.

Stands of Japanese knotweed like this one in Highland Park grow quickly and are difficult to eradicate.

Stands of Japanese knotweed like this one in Highland Park grow quickly and are difficult to eradicate.

Today we have much more information about the ecological impact of the plants that are selected for the parks than the original designers had available to them.  The parks are collections of native and non-native species, many of which were imported from other areas of the world for their aesthetic beauty or their ability to grow well in this climate.  Over the years it became apparent that some of these non-native species were also environmentally invasive, and they began to have a devastating impact on the parks’ natural areas.  Trees such as Norway maple, Siberian elm, and tree of heaven, shrubs such as jetbead and privet, and herbs such as garlic mustard and Japanese knotweed have overtaken entire sections of parkland, killing or crowding out native species and vastly reducing the amount of biodiversity in the area.

The Parks Conservancy leads numerous volunteer projects aimed at educating the community about invasive species control.  Managing invasives is a major task of the Urban EcoStewards, volunteers who provide long-term care to designated areas of parkland.  Corporate and community volunteer days provide hands-on training to Pittsburghers of all ages, while putting thousands of hours annually into park maintenance.

In addition to combating invasive species, the Parks Conservancy is working to improve the long-term outlook for native plants.  The American chestnut tree made up almost 25% of Pennsylvania’s forests before the fungus that causes chestnut blight was imported in the late 1800s.  By 1950, the tree had been almost completely eradicated.  An extremely valuable source of food, habitat, and timber, the loss of the American chestnut was economically and ecologically devastating.  But foresters have hope that through backcross breeding techniques, new cultivars can be created from surviving American chestnut trees and the more blight-resistant Chinese chestnuts.  Pittsburgh’s Highland Park is home to an experimental orchard that is growing these hybrid trees.

Phil harvests chestnuts at the Highland Park orchard.

Phil harvests chestnut seeds at the Highland Park orchard.

The Highland Park orchard was planted in 1996 when the City of Pittsburgh, led by the support of then-City Forester Dale Vezzetti and then-City Councilman Dan Onorato, joined The American Chestnut Foundation‘s breeding program.  Blight-resistant Chinese chestnuts are pollinated with some of Pennsylvania’s surviving American chestnuts, with the ultimate goal of creating a tree with the characteristics of the American chestnut but the genes to resist blight.  Each year hundreds of seeds are generated, and these hybrid trees have been planted throughout the city parks, including test sites in Frick and Riverview Parks and in the Highland Park orchard.  The trees are studied over the years to determine how well the breeding process has worked, with a goal of using a new hybrid chestnut as a restoration planting when invasive trees are removed from a site.  The Parks Conservancy has been testing chestnut seeds in areas heavily populated by Norway maples to determine whether chestnuts can grow in soil that has been altered by the Norway maple.  The chestnut is an ideal restoration tree because it grows rapidly and can quickly re-establish a canopy, which in turn discourages the growth of sun-loving invasive species on the forest floor.

Another important park tree that fell victim to disease is the American elm, and the Conservancy is also part of efforts to reintroduce a hybrid elm that will be resistant to disease.  The Schenley Park Overlook is ringed by six hybrid elm varieties which are being studied by the Conservancy and the Penn State Cooperative Extension to determine their viability as landscape trees.  A crucial aspect of the study is whether these trees, which are bred partially from the invasive Siberian, Chinese, and other elm varieties, will become invasive in the surrounding woodlands.  The mulch beds around the trees are carefully observed for seedlings, and the forests (which contain no other elms) are watched to determine whether new trees are becoming aggressive and require action.  So far, the trees are not exhibiting aggressive tendencies and are functioning as positive replacements to the Norway maples that used to occupy the site.

Despite the many benefits of genetically diverse tree populations, modern horticulture is actually trending toward less genetic diversity in tree propagation.  New tree stock is often replicated from tissue culturing and cuttings, which can result in thousands of trees with the exact genetic makeup of a single parent tree.  Hybridization and sexual reproduction, by contrast, produce trees with diverse genetic makeup, reducing a tree population’s susceptibility to catastrophic loss.

The London Plane trees at Schenley Plaza have defined the space for almost a century.

The London Plane trees at Schenley Plaza have defined the space for almost a century.

In 2004, the Conservancy’s Director of Parks Management and Maintenance, Phil Gruszka, began working with Dr. Cynthia Morton of the Carnegie Museum of Natural History to study the genetic makeup of 81-year-old London Plane trees at Schenley Plaza.  Almost half of the original London Plane population at the Plaza had been lost to disease, and the Conservancy wanted to replant a new, genetically diverse group of London Planes as part of the Plaza’s 2006 restoration.  The study revealed that the remaining trees were very genetically diverse, providing an excellent alternative to the “Bloodgood” cultivar (which was originally taken from a single-parent cutting) that is most often raised and sold by nurseries.  Local nurseries began propagating new trees from the diverse population at Schenley Plaza, reducing the possibility that these new trees could infect each other should some of them contract a disease.  Schenley Plaza’s London Plane trees now represent a genetically diverse, historically inspired population.

The people of Pittsburgh owe a great debt to the original park designers, whose vision of beautiful natural retreats still enriches our lives today.  But the parks are more than attractive places to enjoy a stroll–they are ecological treasure troves, and maintaining them requires extensive knowledge and effort.  The Pittsburgh Parks Conservancy is proud to carry on the parks’ legacy and continue improving their ecological health for future generations of park users.