The end of autumn

It’s early December, and in Cambridge, MA, most of the trees have shed all their leaves by now. There are exceptions: some of the red oaks are still holding on to a few crispy-dry, brown leaves (the same is true for American beech), and some shrubs – like Euonymus, also known as burning bush – continue to display vibrant autumn colors. And then there’s witchhazel, which has actually started to flower (totally normal; this species always puts out its slender and fragrant, bright yellow, flowers in late autumn).

As much as I love the first green leaves of spring, and the riot of colors in autumn, I also find the leafless winter period to be beautiful as well. When trees are without leaves, you can see the tree’s woody skeleton so much more clearly. And when you look closely, you’ll be amazed how much variation there is among species in the form of this skeleton, and how much else there really is to see! If you live in an environment where trees drop their leaves in autumn, here are some things to look for:

  1. What is the branching pattern – opposite (e.g. maple) or alternate (e.g. oak)? Do you see how this branching pattern is repeated throughout the crown, and gives the tree a distinct canopy architecture?
  2. Can you see next year’s leaf and flower buds, which are already formed, and are just waiting for spring to come?
  3. Do you see any evidence of other organisms living in the canopy? Nests of squirrels or birds, for example?
  4. Does the tree have many fine branches (e.g. birch) or few (e.g. ash)? Birch is susceptible to heavy loading during ice storms because of all its fine branches. But, the finest branches an ash ever puts out are about the diameter of a pencil – because ash has compound leaves, with many “leaflets” attached to a “rachis”, it doesn’t need fine branches – the rachis is basically a disposable fine branch.
  5. Do you see any evidence of the tree’s efforts at reproduction? Trees have a variety of different methods for seed dispersal, and this is reflected in how they carry their seeds. Locusts have long pods that look like beans; cherries and hackberries have fruits that are called drupes; beech nuts are contained within a prickly bur; sweet gum fruits look like spiky balls that are actually clusters of small capsules.

Here are some photos I took last week as I walked into work, which show off the stark beauty of leafless trees.

canopy3canopy4canopy5canopy2

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About Andrew Richardson

I am an Associate Professor in the Department of Organismic and Evolutionary Biology at Harvard University
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