If a Tree Falls: Human Impacts on Forest and Park Trees

Forests are natural, wild places. Trees burn, blow down, mature, and regenerate on their own.

At the same time, forests have fingerprints of Homo sapiens all over them. If you know how to look, a stroll through Frick Park’s shady paths can highlight just how human actions have molded one very visible part of the park forests: the trees.

eastern hemlock magnified

An eastern hemlock attacked by hemlock woolly adelgid.

Dude, where’s my hemlock?

You could scour Frick Park and never come across white pine (Pinus strobus) or our state tree, the eastern hemlock (Tsuga canadensis). Until the 19th century both species were common throughout the state, but as the region industrialized, lumber companies prized these trees for their uses in tanning and construction and they disappeared from much of their former ranges. The result? The number of places in Pennsylvania where massive old-growth stands of white pine persist can be counted on your two hands. Afterwards, when forests began to regenerate, conditions did not always favor the return of these former giants.

If you do see a white pine or eastern hemlock in Frick (and there are a few of each), it was likely planted relatively recently by Parks Conservancy staff and volunteers. Much like logging these species, reforesting requires human labor.

A century later: Cherries

Though white pine and eastern hemlock have fared poorly in our forests over the last 200 years, the forests that regenerated after logging actually benefited other trees. Black cherry (Prunus serotina) is one of these. North of Pittsburgh, in the Allegheny Plateau, it is estimated that black cherry trees made up less than 1% of the pre-logging forest. After extensive clear-cutting in the late 19th century, however, black cherry became a common part of the new forest that regrew there thanks to preference for sunny conditions and fast growth.

The same is true in Frick Park. Easily identifiable by their dark bark that looks like burnt potato chips or corn flakes, black cherries are common these days. You can find a large number of them where there once was a country club (now in the area where Riverview and Bench trails run). After the club’s annexation to Frick in the 1920s, forests regrew on these lands with black cherries. Some of these trees are actually now dying, as the species’ mortality typically increases after 80-100 years.

Tagging Tree 2

Phil Gruszka, Parks Management and Maintenance Director, tagging a dead ash tree.

Invasive species, world travelers

Dead trees can also illustrate how humans have shaped our forests. Since 2007 when it was first detected in Pennsylvania, emerald ash borer (EAB), a tiny green invasive insect, has left a path of destruction across Allegheny County, killing nearly all area ash trees (Fraxinus var.) in just a few years. The evidence is all over Frick Park, with standing and fallen dead ash trees exhibiting the tell-tale scars where EAB larva chewed through the trees’ energy-rich cambium, girdling them.

Globalization not only redistributes products, money, and people around the world, but also non-native plants, animals, and fungi, sometimes in ways that reshape our parks. EAB, for example, likely arrived in the U.S. in a shipping pallet from Asia. This pest, however, is not the first invasive species to change our forests. In the early 20th century, chestnut blight, a fungus accidentally introduced from Asia, killed virtually all American chestnut trees, a species then common throughout the eastern U.S.

Trees on the move (and we’re not talking Ents)

Frick Park’s forests will keep changing as a result of human influence. In addition to the risk of future invasive species, anthropogenic (human-induced) climate change promises big shifts for park trees. Just walk Rollercoaster Trail on the hills between Fern Hollow and Falls Ravine and look out on the sea of young sugar maples (Acer saccharum) that dominate the forest understory.

According to the U.S. Forest Service’s Climate Change Atlas, sugar maples will likely become significantly less important across Pennsylvania as the climate warms and stresses this species, eliminating it from the southerly parts of its range. More heat-tolerant trees may ultimately replace sugar maples in Frick Park and elsewhere in the state.

Learning from the past

Recognizing human fingerprints on our forests gives us opportunity to learn from the mistakes and successes of past generations. How can we leave fingerprints that will improve forest health? Parks are planned spaces, cared for by the people that use them. The team at the Pittsburgh Parks Conservancy is constantly on the watch for invasives like the Asian longhorned beetle and oak wilt and replanting diverse, resilient species of trees to create strong forests that will be around for generations to come.

Kevin C. Brown is an educator with the Parks Conservancy, and a researcher-writer of a National Park Service-funded history of the Devils Hole pupfish, an endangered desert fish that lives in Death Valley National Park. You can read more about his work here.

Tackling Oak Wilt in Schenley Park

On this blog and through a variety of media, The Pittsburgh Parks Conservancy has had an open discourse about the health of our parks and the battles to keep threats such as Emerald Ash Borer and oak wilt at bay. Earlier this year, these conversations with the community really paid off for our parks. Thanks to an observant park visitor, we were able to act quickly to curb the damaging effects of what we were holding our breaths not to discover: oak wilt in Schenley Park.

Infected oaks at the Bartlett-Greenfield and Panther Hollow-Hobart intersection

After oak wilt was discovered in Pittsburgh city parks in 2009, it didn’t take long for it to make its way to three of the four major parks: Frick, Riverview, and Highland. Now, only four years later, we are seeing that this devastating fungus has finally put down roots in Schenley Park.

The oak wilt site in Schenley Park was called in this summer by a park visitor who became suspicious of five or six oaks that seemed to be losing their leaves and generally looking unhealthy. Parks Conservancy staff immediately visited the site, where five to seven oak trees were showing signs of active oak wilt infection. Added to the toll were 25 nearby oaks that had already succumbed to oak wilt and died.  In all, we believe 50-55 red oaks will be affected on this site, covering an area of about 1.5 acres. City of Pittsburgh and Parks Conservancy staff have since been fighting to arrest the spread of oak wilt on this site.

Oak trees killed by oak wilt

As in the other major parks, the fungus will force the removal of infected trees in Schenley Park. The loss of so many trees is unfortunate and will be a noticeable change to the landscape. But there is good news; oak wilt can be managed and stopped (unlike the Emerald Ash Borer). There are also positive outcomes, such as the restoration of a more bio-diverse tree canopy. The site at Schenley was dominated by just two types of trees: Norway maple and red oak.  Plans are already being made to replant the site with an enhanced, diverse assemblage of native tree species. These new species will not only be visually appealing, but will also provide renewed habitat for wildlife, help capture storm water, and reduce erosion potential.

Oak wilt will continue to be found from time to time throughout our city parks. But with careful management and mitigation the City of Pittsburgh and the Pittsburgh Parks Conservancy will minimize the impact it has on our parks and, when possible, make our parks even stronger.

You can help prevent oak wilt in your own trees by avoiding trimming between April and October. Wounding trees during the growing season makes it easier for the fungus to spread.  If you have any questions about oak wilt, call us at 412-682-7275 or the City Forester at 412-422-6655.

Bryan Dolney, Parks Conservancy Field Ecologist

Notes about Oak Wilt

Oak wilt disease is a fungal vascular disease. Aided by its biology, it readily spreads; once infected, oak trees will begin to lose leaves in just a few weeks. Some trees can be killed within a month of first infection. Oak wilt is so rapid because of how efficiently the fungus fills the water conducting vessels (xylem) of the tree. This not only spreads the fungus, but also blocks the tree from attaining water. 

Oak wilt spreads underground by root grafts, which is noticeable while viewing stands of oak trees growing in groups close together. Red oaks in particular form these root grafts, making them the primary target for oak wilt. Roots of adjacent trees grow together as they share nutrients, water, and sometimes oak wilt. When one tree becomes infected and spreads, infecting adjacent oaks, we call this an infection center. This is how oak wilt is spread from one tree to the next, eventually infecting the entire stand. 

Infected oaks are most easily spotted in July

Infection centers can move long distances via picnic beetles from mats of fungus called pressure pads.  Once a tree has been killed by oak wilt, these pressure pads form under the bark and crack open.  This often happens the spring after a tree has been killed by oak wilt (about 9-10 months after the tree has died).   These pressure pads produce a sweet odor that attracts picnic beetles and sap feeding beetles that feed on it. Once the beetles crawl on these pressure pads they pick up the oak wilt fungal spores and carry it to healthy oak trees.

Signs of infection are often noted in July. A tree infected with oak wilt is characterized by:

  • Leaves at top of tree wilt and turn brown along tips and margins. 
  • Leaves begin to fall while they are still green. This can be rather conspicuous in the summer when tree should have full canopy of leaves, not a Fall canopy.
  • On the forest floor one can see a mixture of brown, green, and partially green leaves amassed at base of tree.

Urban EcoStewards Celebrate a New Year – A Winter Gathering

You know what’s better than a Winter Gathering to kick-off the 2013 Urban EcoSteward training year? A snow-covered Winter Gathering complete with a one-mile hike in Schenley Park! Around 35 dedicated park stewards signed up for the event on Saturday, January 26. The Urban EcoStewards represented a variety of organizations including the Pittsburgh Parks Conservancy, Mount Washington Community Development Corporation, Frick Environmental Center, Allegheny Cleanways, Allegheny Land Trust, and Nine Mile Run Watershed.

Wintry Schenley Park

Tufa Bridge in Schenley Park

The day started with lunch at the Schenley Park Café and Visitor Center which was restored by the Parks Conservancy in 2002. Rumor has it, Patty’s Smoked Mac and Cheese was the big hit of the day! After a brief overview of the participating organizations, the day continued with a celebration of 2012 successes and what the EcoStewards have to look forward to in 2013.

Urban EcoSteward celebration at the Schenley Park Cafe and Visitor Center

The group then bundled up and strapped on their snow boots for a one-mile hike around the Lower and Upper Panther Hollow Trails.

Headed down for a snowy hike through Schenley Park

Looking up at Panther Hollow Bridge from the Hollow

Led by Pittsburgh Parks Conservancy Education Program Coordinator, Taiji Nelson, the group discussed winter tree identification, soil erosion, and emerald ash borer along the way.

Pittsburgh Parks Conservancy Education Program Coordinator, Taiji Nelson, explaining soil erosion to the EcoStewards

Lesson in destructive tree identification

The day ended with an overview of Phipps Run and Panther Hollow Watershed’s and restoration efforts being implemented in the area.

Hiking along Upper Panther Hollow Trail

Urban EcoStewards give back to their communities by adopting a specific section of park land that they agree to maintain. Stewards receive training from Parks Conservancy staff and other program partners and visit their site throughout the year to remove invasive species, plant native flora, slow erosion, and clean up trash. EcoStewards report to a coordinator, who will accompany them on at least one site visit per year to determine maintenance needs.

If you’re ready to take on your own little piece of the park, sign-up for our next training date on our Urban EcoSteward webpage. For more information, please contact our education department at 412-682-7275 ext. 232 or volunteer@pittsburghparks.org.

[Presentation]: Emerald Ash Borer / Native Wildflowers

David SchmitPennsylvania’s resident emerald ash borer expert, David Schmit, is a Forest Health Specialist with the PA Department of Conservation and Natural Resources.  He can spot an EAB-infested ash tree from a mile away thanks to his familiarity with how their bark looks after woodpeckers have discovered the larvae.  In today’s presentation from “Preserving Pittsburgh’s Trees: Action and Recovery,” he shows you all the life stages of emerald ash borer and explains why it’s a much bigger threat than, say, the forest tent caterpillars that periodically defoliate our trees.

He also picks up on a theme from Dr. Carson’s presentation yesterday about deer, and that’s the idea that “deer are the deciders” when it comes to what wildflowers you’re going to see in the parks.  He paints a picture of what the forest would look like if we could isolate an area from deer and begin reintroducing the plants that grew there before their populations were decimated by the overabundance of deer. 

Given our distaste here at the Parks Conservancy for garlic mustard, it’s interesting to think of this plant in terms of deer.  Basically, if the deer liked to eat it, it wouldn’t be invasive–in fact, you’d hardly ever see it.  The main key to being invasive is having no natural predators in a particular location.  It makes sense that native deer love to eat native plants–it’s just unfortunate that the deer population has climbed so high that they’re the ONLY ones who get to enjoy those plants.

Without further ado, check out some of these lovely and little-seen wildflowers (as well as the lifespan of the emerald ash borer) below, or download the slides here.

[Presentation]: Urban Parks Woodlands

Phil GruszkaIf you weren’t one of the 100+ attendees of last Thursday’s event, “Preserving Pittsburgh’s Trees: Action and Recovery,” that doesn’t mean you have to miss all the great information provided!  Each day this week, we’ll be posting one of the presentations from the evening, six in all.  These are the full slideshows along with the audio from Thursday. 

We’ll start with the evening’s introductory presentation from our own Phil Gruszka, Director of Park Management and Maintenance at the Pittsburgh Parks Conservancy.  Phil gives an overview of the threats facing our park trees and a rundown of some of the adaptive management practices in which we’re already engaged.

To watch the presentation, click on the video below.  Or if you’d prefer just to see the slides, you can download those here.