![Untitled-2.png](https://files.peakd.com/file/peakd-hive/cliffagreen/23zS3TYUiuGNeuGjkbKaHUD8ZNBhkFovaxWdAPBdU3rWnN4pzZNpBJApYUCCxFAGPJeed.jpg) **Alien World** *** No, we aren't looking at the top of a volcano on some alien world. It's the trunk of a birch tree where a branch as broken off, but in my imagination the ridged bark looks like cooled magma, and the lichen looks like forests ringing the mountain. I also see the empty eye socket of an elephant, though I don't know what the lichen would be equivalent to in that scenario. Setting the imaginary aside, I wondered if the ridges in the bark and the raised area in the trunk around the missing branch were a result of the branch breaking off, if it was the tree trying to 'close the hole'. An article from Purdue University suggests otherwise: > A swollen area or collar develops at the junction of branch and stem because of their differential growth rates and by the intermingling of vascular tissues from both the branch and the stem or trunk.^{([source](https://www.purduelandscapereport.org/article/branch-component-identification-for-better-pruning-cuts/))} So, it seems the raised area is normal, and I would guess the ridges in the bark are part of the differing growth rates as well. A healthy tree will try to 'close the hole'. In my browsing, I learned that the term for this is 'occlusion'.^{([2](https://gabrielhemery.com/tree-wound-occlusion/)/[3](https://treeterms.co.uk/files/definitions/occlusion/))} The tree will grow special 'wound wood'^{([4](https://treeterms.co.uk/files/definitions/wound-wood/))} to occlude the wound; in our photo you can perhaps see this wood; I think it is the light red-colored lip around the edge of the hole. You can read a little more about tree wound occlusion in [this article,](https://www.purdue.edu/fnr/extension/tree-wounds-and-healing/) also from Purdue University. If we read the adjective 'alien' in my photo title in Merriam-Webster's second sense ("differing in nature or character to the point of incompatibility"),^{([6](https://www.merriam-webster.com/dictionary/alien?utm_campaign=sd&utm_medium=serp&utm_source=jsonld))} then we really are looking at an alien world here. If you look closely at the bottom center of the photo, you can see a tiny slug traversing the foothills of our birch tree mountain.