What’s This?October 27th, 2017
Look at that pattern! What in nature is making it? And what can this pattern tell us?
Hint: You are looking at the impact of seasons on growth… the tree rings of a Douglas fir!
Tree growth rings are signifiers of many things, but most notably, they signify how a plant reacts to the changing of seasons. Some plants make very distinct rings, such as this Douglas fir tree. That’s because the plant responds to each season very uniquely. The light rings signify spring growth, when rain and snowmelt increases, weather warms, and sunny hours increase. All this equals more rapid and productive growth for the Douglas fir, and is marked in the tree wood as the wider light ring. As summer comes (drier, hotter), growth for the Douglas fir slows down. This is marked in the tree wood as the narrower darker ring. During this season, the cell walls of the tree become thicker, and the cells themselves become denser. The colder fall and winter seasons in our region often mean dormancy in plant growth.
So tree rings can tell us about seasons over time, and are often used to look at how climate changes over long periods of time. But further, they can also tell the story about how different species of plants relate uniquely to the seasons!
Look at this cross-section of a very old English ivy plant. As you can see, that little vine that you’ve likely seen throughout the Park changes as it ages, becoming less pliable and producing wood (this cross-section of wood spans 8.5 cm in diameter!). If you squint, you’ll see the growth rings (no, not those fine lines – the faint “shadows” of rings cross perpendicular to the fine lines in the photo). The question is, why aren’t these rings as noticeable as the Douglas fir’s rings. Any guesses? Well it likely has to do with the behavior of English ivy itself. English ivy is an evergreen plant, meaning it does not lose its leaves in the fall, and further, it is extremely shade tolerant. English ivy can actually continue growing throughout all the seasons, aiding in its very well-known invasive quality. Although it slows in the colder season, like right now, it will continue growing. So the plant’s rings, signifying drastic plant behavior changes with the seasons, just aren’t so drastic with an English ivy plant compared to a Douglas fir.
If you look at this cross section of ivy, you will likely notice some very faint rings. These will signify change in growth by seasons, because just like the other plants, spring is a big growth season for ivy. But the faintness between the darker and lighter rings signifies as very lighter difference in seasonal impact on this plant’s growth.