Hey! I know I’m a little late (what else is new). I’ll be on a 4-week holiday that begins in one week, so you may or may not see a January newsletter. I will be working on other projects that I’ll release on the Tree First Instagram, YouTube, or in the Articles section during that time though.

What should we talk about this time? How about dormancy? Yeah, let’s do that since I’ll be dormant soon too.

Not Dying; Dormant

Leaves fall off in autumn and the tree goes to sleep until environmental conditions improve in spring. That’s pretty much it, right? Sorta of.

What the tree is actually doing is much more complex than just shutting off. It is a multitude of processes that can take months to complete, and months to start up again.

I think I could write a feature-length article on dormancy. That might be easier than writing the cliff notes! Maybe I will do that actually.

Rather than go through each phase and each process, I’ll just talk about some particularly cool ones.

I love talking about leaf abscission, or leaf drop. Leaf drop is an active process that requires energy, the leaves aren’t simply ‘falling off’.

Behind each leaf of our deciduous trees, a zone called the abscission zone forms. Its function is for this exact purpose. It is a zone where a temporary attachment point forms between the twig and the leaf, with enzymes and pre-programmed cell death within this zone in order to facilitate leaf drop when the time comes.

The leaf scars you see on twigs are one side of this abscission zone that sort of functions as a “cap” on the twig to prevent things from entering the twig after the leaf falls off. The ones pictured above look like lil faces, they belong to either black walnut or white walnut. I can’t remember, I took the photo in 2018.

While the leaves are changing colors, they are resorbing some of the pigments to use for other physiological functions within the tree. Moving around those chemicals inside. Once that process is complete (or nearly complete), the abscission zone executes its function and separates the leaf from the twig.

Another cool thing that affects leaf abscission is day length, or photoperiod. It is an easy thing to find in urban spaces; trees near street lights. Check this out:

Might be kind of hard to see, it is a night photo after all. Leaves closer to street lights tend to delay their abscission. I’m not totally sure if this has meaningful negative impacts on them, but I sort of doubt that it does. Just a neat thing you can find in your neighborhood.

Last thing I’ll talk about is at the other end of dormancy—when things ‘wake up’. The dormancy processes taking months to run their course is partially explained by tree size. Larger organisms are more complex and chemicals take longer to move around within them.

Smaller woody plants tend to exit dormancy before their larger friends. Spend some time in early spring forests, and you’ll undoubtedly notice this too:

Leafing out before your larger neighbors has another benefit too: getting available sunlight before the taller trees hog it all up. This early burst of photosynthesis is undoubtedly important for smaller woody plants in forests.

That’s all for now. Stay warm and cozy and tell your trees I said to have a good dormancy.

OK bye bye see ya next year

TF