Kissing Trees

Fused ash trees (photo from Wikimedia Commons)

28 November 2023

If you’ve spent a lot of time in the woods chance are you’ve see trees kissing. The fusion of their trunks in what looks like a kiss is called inosculation from the Latin word for kiss.

University of New Hampshire explains how it occurs:

Inosculation happens when the friction between two trees causes the outer bark of each tree to scrape off at the point of contact. The trees respond by producing callus tissue that grows outward, thereby increasing the pressure between the two trees. This pressure, along with the adhesive nature of sap or pitch that exudes from the wounds, reduces the amount of movement at the point of contact. The cambia layers from the two trees come in contact and the vascular tissues become connected, allowing for the exchange of nutrients and water.

— UNH: Inosculation: Making Connections in the Woods

Though I’ve seen fused trees several times, I have only one photo of a pair “kissing,” fused twice at Raccoon Creek State Park in February 2015. The date is notable because that hike is also the last time I saw a long-eared owl.

Two trees “kissing” twice, Raccoon Creek State Park, 8 Feb 2015 (photo by Kate St. John)

An extreme case tweeted by Science girl @gunsnrosesgirl3 reminded me of the phenomenon. The smaller tree on the left does not touch the ground and is completely sustained by the larger one that’s holding it up. The embedded tweet below does not show that the smaller tree is cut off so click here to see a larger photo.

Some species are more likely to “fuse “kiss” because their bark is thin. Check out this list of likely suspects at Wikipedia.

(credits are in the captions)

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