Why are Douglas-fir cones falling when they're still green?

At the house of my good friends Stuart and Ruth Rosen, there’s a drumbeat of green Douglas-fir cones raining down. Then the cones magically get piled up into mounds. What’s causing this?

Inside Douglas-fir cones are winged seeds — two seeds tucked under each scale. In the fall, the cones dry out and the scales open. Out come the winged seeds, high up in the tree for the wind to disperse.

Right now, it’s a bit early for Douglas-fir cones to open. The cones are still “green,” meaning that they are green(ish) in color, the scales are mostly closed, and the seeds inside are not quite mature.

A Douglas-fir tree reaps no benefit from dropping its unripe cones straight down.

  • First, the seeds are not yet ripe and are unlikely to germinate (especially trapped inside the cones).

  • Second, if the seeds were to germinate, the seedlings would grow right next to the parent tree, shaded by it and perhaps someday competing with it.

This would not be a good way for the tree to spread its DNA.

Then why are the cones falling? And what is piling them up into mounds?

Here’s the rascal! This is a Douglas squirrel, wearing its summer coat of orange on its underside. It’s sitting on a fence post, dismembering Douglas-fir cones.

These small squirrels live from northern California to southern British Columbia, generally on the west side. They are scarcely larger than a chipmunk.

In my friends’ yard, it appeared to me that one or more Douglas squirrels were snipping off green Douglas-fir cones from the treetops. On the ground, I saw a Douglas squirrel piling the green cones by the dozens into a mound shown in the first photo above. A squirrel was also burying some cones.

Evidently the Douglas squirrel(s) hoped that the green cones would make a nice winter snack. My friends kept cleaning up the mound, but within a day there was a new mound, bigger than before.

Why do squirrels eat douglas-fir seeds?

Many small mammals and birds eat seeds from the cones of various trees including Douglas-firs. Why?

Inside the kernel of each seed is an embryo that, under the right conditions, can grow into a new tree. With the embryo is a tiny bit of carbohydrates, fats, and water. That sounds as tasty as a french fry! The seed provides “getting-started money” for a new seedling and is a perfect snack for a squirrel.

This green Douglas-fir cone and many detached scales are at the foot of a Douglas-fir tree. Scales are thick on the ground within a few feet of the trunk. Farther away, scales are scarce.

Two points jump out at me:

  • One, it looks like a squirrel snipped off this cone to retrieve later. There’s no reason an unopened cone should have fallen off by itself.

  • Two, it looks like a squirrel has eaten almost all of the seeds. Each scale has an imprint like a fossil where two winged seeds were growing. Few of the seeds remain.

It is difficult for me to tell whether the guilty party dismembered the cones up in the tree or on the ground. Either is possible, though up in the tree would provide more safety for a busy squirrel.

Here’s a close-up of the dismembered cone scales on the ground.

I see a bit of green color on one of the “mousetail” bracts. This indicates to me that the scales are from this year — 2018 — and not some previous year.

Also, it is easy to see the fossil-like imprints where the winged seeds were growing. The seeds are gone now, no doubt eaten or cached. Interesting!

For more pictures of Douglas-fir seeds and cones, click here.

What’s going on in your yard this week?

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