Prove your humanity

The nonprofit Tree Pittsburgh released some disturbing data about Allegheny County’s tree canopy earlier this year. The canopy includes the leaves, branches, and trunk. It’s all of the area taken up by trees above the ground. From 2010 to 2015, 11,044 acres were lost. Matt Erb is the director of urban forestry for the organization. He says that the data were collected with Lidar technology, which uses a laser from an airplane to gather a detailed look at the tree canopy below.

Kara Holsopple talked with Erb at their nursery along the shores of the Allegheny River recently to learn more about what’s going on.

Kara Holsopple: Is it specific types of trees? How do you drill down into the data?

Matt Erb: We’ve been really looking at the data as many ways as we possibly can. We’re looking at it by land use, we’re looking at it by ownership. But we’re also looking at Google Earth and Google Street View which both have great archive sections with older imagery. We can look at specific streets that have lost a lot of tree canopy. And through that Google street view, we can see that in 2012 the tree was alive and green, and in 2015 the tree was removed.

By looking at those images, we can also see the species. So we do know in some cases ash trees, which were impacted by Emerald Ash Borer during that time frame, have nearly been wiped out from our landscape. But we’re also seeing just general development: land clearing for development, infrastructure improvements, the widening of the Pennsylvania Turnpike. And those larger infrastructure projects have a bigger impact on forest canopy, not necessarily specific species.

LISTEN: “Where are the Trees Going in Allegheny County?”

KH: Are you concerned about these numbers?

ME: Yes. If you think of the Allegheny County Park System — so that’s North Park, South Park Roundhill Park, Harrison Hills — the park system is about 12,000 acres. Looking at the county, we lost about 11,044 so that’s pretty close to the entire county parks system disappearing in a five year time frame.

And the amount of benefits that those trees provide — they’re providing a lot of ecosystem services, managing stormwater, reducing air pollution, providing oxygen. Not to mention a lot of human health benefits. That’s a significant quantity of tree benefits that are being lost. And these trees take decades to regrow. It’s not something that we can say, ‘Alright, in five years we want to regrow 10,000 acres of canopy,’ because it’s going to take at least 100 years to grow those trees to that size, and really fill that part of our canopy.

Matt Erb, director of urban forestry for Tree Pittsburgh, at the organization’s nursery in Pittsburgh’s Lawrenceville neighborhood. Photo: Kara Holsopple

KH: You mentioned developers like new housing, commercial development. Is there a push to make sure that trees are part of that equation?

ME: The Pittsburgh Shade Tree Commission has been working for the last few years to change the tree protection and development codes for the city of Pittsburgh with the end goal of helping to protect more trees during development, as well as to have more trees planted at the end of development.

More recently Tree Pittsburgh has received a grant from the Pittsburgh Foundation to take this work to municipalities throughout the county and help them rewrite their tree protection ordinances and zoning codes to help protect forest patches to help replant trees at the end of developments and ensure that these parcels are staying green.

KH: And when you say tree protection ordinances, what do those cover?

ME: It’s kind of broad, but generally to protect trees during development or just protect trees at all times. People that don’t know about trees may take them for granted. They may not know that stapling no parking signs or yard sale signs all over trees is not good for the tree.

Tree protection codes most basically protect trees from being pruned by unauthorized people — to keep people from hammering signs or even billboards to trees; from pouring herbicides or other liquids in the ground that may be harmful to the trees; excavations around the base of the tree should be thoughtful and not overly damaging.

They can also outlined different fines that may pertain to damage or destruction of public trees. To plant a new street tree in the city of Pittsburgh costs almost 800 dollars. If that tree is vandalized or removed, recouping that money is can be a good thing to help replant that tree there. And that’s for a young tree. A fully mature oak tree that’s been there for 100 years, depending on its condition and other things, could be appraised at tens of thousands of dollars. These trees have a lot of value, and protecting them is definitely worthwhile.

KH: So what’s it going to take to turn this around?

ME: Tree Pittsburgh was founded in 2006. And ever since our founding, we’ve been working with a number of partners throughout the region to plant and maintain trees. Our work with our partners has probably planted over 50,000 trees in Allegheny County in 10 plus years. That’s a big, significant step into helping reverse this trend.

A lot of the tree loss is in people’s backyards. People are removing trees, whether it’s due to old age or they’re just tired of raking leaves. We want to help reverse that trend. Get people educated. Those trees are actually providing them with a lot of benefits and a lot of benefits to the community as well.


If you want to add a tree to Allegheny County’s canopy, there’s a good opportunity this weekend. Tree Pittsburgh’s Heritage Nursery will be at Phipp’s May Market (and they usually don’t sell to the public). You can find out more here.