Dredge islands

…there’s so much to be learned!

Gastineau Channel rounds the north end of Douglas Island with a short stretch that is roughly east-west. On the north side of this part of the channel lie islands mostly made of the material dredged from the channel in the 1950s; actually, they are islands only at high tides. One island is apparently a rocky outcrop that may have been a real island. Post-glacial uplift has raised the islands well above the reach of the tides, so that they now support a diversified community of plants. Most of them are now capped with stands of vigorously growing spruces and cottonwoods.

After careful consultation of the tide tables, we set out to explore the eastern series of islands, on a nice low tide. Although I’d previously visited the westernmost islands, this was new terrain for me. We waded through wide expanses of tall grass and crossed several tidal sloughs where dowitchers and yellowlegs foraged and mallards loafed on the banks.

A characteristic of most of the islands we visited was what might be called a lichen barrens—a habitat quite reminiscent of recently deglaciated lands. Not really barren at all, they are wonderfully rich in lichens, mosses, and a few small flowering plants. They are generally surrounded by a ring of trees, lending them a feeling of seclusion. As we reveled in their diversity and beauty, we also wondered why they are there—why didn’t the trees grow there too?

We were pleased to find abundant meadow rue on some islands but much less happy to find a big stand of hemp-nettle. This prickly plant is an invasive weed from Eurasia. There was evidence of the passage of some large creature through the grasses and herbs, and eventually we found several scat piles that told us the creature was a deer.


Perhaps the most intriguing observations came from fireweed. The flowering stage was different on every island: flowers just opening on this island but nearly finished on another, with intermediate stages on still other islands. One bumblebee was flying busily, but two very wet bees rested, each nestled in an open flower. Bumblebee workers often sleep outside the nest, wherever they happen to be. These bees were so wet that we wondered if they had died as they slept, but we did not disturb them to find out.

On one island we noted some swollen buds on several fireweed stems. These flowers had not opened and all the sexual parts were present; no pollinator could have visited. Nevertheless, the fruits (or pods) below the flowers were well developed. The pods contained lots of the white fluff that we see on each seed when the pod opens and the seeds become airborne, but no seeds were visible. Why did the pod develop if no pollination had occurred?

The swollen buds frequently contained tiny insect larvae about one millimeter long. If no larva was detectable, then the female parts of the flower were often mutilated and deformed. Do these larvae somehow prevent the flower from opening and cause the pod to develop anyhow? There is much to be learned here!

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