[MAIPC] Philly Street Trees

Beth Burnam bburnam at brandywine.org
Tue Feb 7 10:53:58 PST 2017

The brief conversations I’ve had with Philly Rain Check about these non-natives yielded the explanation that these trees have been proven to survive and grow in an entirely unnatural environment and therefore are important from an ecosystem functioning perspective, regardless of their native/non-native status. This is not an apology for the list, which surprised me too when I first saw it.
I have a hard time imagining that a yellowwood or Carolina Silverbell would thrive in harsh urban heat islands, at least as youngsters—they never have for me. But maybe there’s a secret. It’s an interesting question.

Beth Burnam, RLA


From: MAIPC [mailto:maipc-bounces at lists.maipc.org] On Behalf Of Nathan Hartshorne
Sent: Tuesday, February 07, 2017 9:09 AM
To: Muth, Norris (MUTH); MAIPC Listserve (maipc at lists.maipc.org)
Subject: Re: [MAIPC] Philly Street Trees

So with some spare time due to rain, I googled up quite a few of the species on the list (but certainly not all).  For the most part, it was difficult to find information since they are not as distributed or studied as plants like Norway Maple.  Many appeared in Invasives.org or Invasiveplantatlas, but didn't say much.  Many of the cultivars are harder to learn about.  Acer x freemanii is a cross between Red and Silver maples, so I am not sure what to even think about that, but it does easily grow in a forest setting.  Some species, like Carolina Silverbell and American Yellowwood are regionally non-native.

It is good to note that generally it seemed that species not known for invasions were chosen.  However, the four main caveats there are:
1)  Maybe it can hybridize with natives or other introduced species
2)  Callery Pear was infertile until people imported more trees and they could then cross.
3)  Many species do not appear invasive, such as Autumn olive until one day suddenly, they are.
4)  Accidental introduction of pathogen that kills natives.  Hopefully this is more unlikely today, but who knows.
Here is some information I found:
Aesculus hippocastanum https://www.na.fs.fed.us/fhp/invasive_plants/weeds/horse_chestnut.pdf

Styrax japonicas  http://www.njisst.org/files/plantidfactsheets.pdf  - Listed as "moderate" as a threat code by the NJ Invasive Species Strike Team.

Acer Campestre http://www.mortonarb.org/trees-plants/tree-plant-descriptions/hedge-maple-not-recommended
Other sources have said this has become invasive in some areas.

Cornus Mas  http://hvp.osu.edu/pocketgardener/source/description/co_mas.html
This source does call it invasive, but I didn't see much else.  It does produce fruit that birds would love to distribute.

Crataegus laevigata - Was listed as invasive in Canada, though I realize this cultivar may be less fertile (or more fertile).
I will write Lori Hayes and start a conversation.  Let me know if you want to be individually added to it.

On Fri, Feb 3, 2017 at 9:25 AM, Muth, Norris (MUTH) <MUTH at juniata.edu<mailto:MUTH at juniata.edu>> wrote:
I’m glad you picked up on this. Perhaps someone on the listserve has a contact with Philadelphia Parks and Rec.

My personal view is that we might want to try to move towards something of a white-list type of advice where MAIPC or others could work towards getting these lists moved more and more towards native species and non-invasives (dare I say, that have gone through “extreme vetting?” I dare). If we could get some evidence-based information on where these non-natives have been used and for how long, it might be reasonable to give them a different designation than less well studied non-natives. I see this approach as entirely a pragmatic one (I’d prefer that nurseries produced far more diversity and abundance of native species so that they would be easier to recommend or mandate) - but at least this approach could make some inroads towards these types of plantings doing less damage and it might be more successful than a full frontal assault that could be more easily ignored and would be difficult to implement at best.


Norris Z. Muth, Associate Professor of Biology
muth at juniata.edu<mailto:muth at juniata.edu><mailto:muth at juniata.edu<mailto:muth at juniata.edu>>

office: 1054 VonLiebig Center for Science
Office Hours Spring 2017
M&F 11-noon,  T 2-2:30, Th 1-2:30, or by appointment

Juniata College
1700 Moore St.
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tel: 814-641-3632<tel:814-641-3632>

From: Nathan Hartshorne <nshartshorne at gmail.com<mailto:nshartshorne at gmail.com><mailto:nshartshorne at gmail.com<mailto:nshartshorne at gmail.com>>>
Date: Thursday, February 2, 2017 at 5:05 PM
To: "MAIPC Listserve (maipc at lists.maipc.org<mailto:maipc at lists.maipc.org><mailto:maipc at lists.maipc.org<mailto:maipc at lists.maipc.org>>)" <maipc at lists.maipc.org<mailto:maipc at lists.maipc.org><mailto:maipc at lists.maipc.org<mailto:maipc at lists.maipc.org>>>
Subject: [MAIPC] Philly Street Trees

Hi all,

My roommate was applying for an internship with them and came across the list of approved Philly street trees.  Recently Philly has made a push for more planting similar to NYC's.  Well, she knows a lot about invasives due to her proximity to me talking about them.  We were very disappointed to find a number of non-natives (regionally non-native as well).  Other than crabapples (which I can't tell what species they are since they are all cultivars), I didn't immediately recognize any as commonly naturalizing, but as we all know that doesn't mean much for the future, and doesn't do as much for the environment anyways.

So I was wondering what we could do as an organization (aside from me writing a letter to them since I live here).  An impact here could make a huge difference given the geographical size of the city.  Perhaps any contacts with NYC million trees program could be useful.  Here is the list:


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