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Dear Susan,
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<div>I have botanized in the US for thirty years and I have often marveled at how Poison Ivy will climb a tree, spread its long, but limited lateral branches, but not kill the tree.</div>
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<div>Yes, it can be aggressive and form large stands, but these almost always form after significant disturbance by humans or the rare natural disturbance like fire, landslide, flood or blowdown. Yes it can climb a tree and appear to “smother” it. What it
does is climb weakened trees with already reduced canopies. It does not climb from tree to tree in the canopy and break down a forest limb by limb until there is no forest left. That is what Kudzu, Porcelainberry, Bittersweet, Japanese Honeysuckle and other
invasive vines do. Vines that were brought here by humans and that have no natural checks and no value for wildlife. </div>
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<div>Poison Ivy is native to North America. Numerous birds and mammals evolved over millennia to depend on its abundant crop of fruit high in fat and other nutrients needed for migration and winter survival. </div>
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<div>Yes, Poison Ivy causes contact dermatitis in humans. People should learn to stay away from it. </div>
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<div>Haven’t we humans already destroyed enough of the planet? Must we destroy a species of plant just because we can’t figure out how to avoid it and in the process imperil countless insects, birds and other wildlife? </div>
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<div>Best wishes,</div>
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<div>Daniel Atha</div>
<div>Botanist</div>
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<div dir="ltr" id="AppleMailSignature">Sent from mobile device</div>
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On Apr 6, 2020, at 9:36 AM, Susan Gitlin <<a href="mailto:susan.mclaughlin@alumni.stanford.edu">susan.mclaughlin@alumni.stanford.edu</a>> wrote:<br>
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<p style="text-align: center;"> </p>
<p style="text-align: center;">[<strong><span style="color: #ff0000;">External E-Mail</span></strong>: Verify source before clicking on any links or opening any attachments.]</p>
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<div dir="ltr">Hello, folks.
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<div>I know that poison ivy is a noxious weed, but I believed that was because of harm to human health. I was not aware that it behaved as an invasive vine, smothering trees a la English ivy. That would not make sense to me, except in rare cases, because
in that case our local ecosystems would have far fewer trees. </div>
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<div>However, someone today told me that poison ivy smothers and kills trees. Has this always been the case, or is it now happening due to increased carbon dioxide in the air? If the latter, is climate change converting our native plants into plants that
cause ecological harm?</div>
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<div>If you could share your knowledge on this, I'd appreciate it.</div>
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<div>Thank you!</div>
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<div>--Susan</div>
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