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.

mary-on-the-trails

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!

Going to the dredge islands

eagle bones, lichen gardens, and an octopus rescue

On a fine low tide in late April, I headed out to some of the dredge islands in Gastineau channel, along with two friends. Before we even got to the islands, we found several interesting things. In the middle of the dike trail lay the feathers and other remains of a dead bird. Grazing on the innards were at least twenty little brown slugs—officially known as reticulated tail-droppers. We often see them on bear scats filled with digested vegetation, and gardeners make war on them when they attack some treasured plants, but what were they getting from bird guts?

Just as we left the dike trail, our attention was drawn to a pinkish blob lying in sparse grass. A second look told us it was on octopus, stranded by a recent high tide. An octopus has no business being up in the grass, so after determining that it was still alive, we carefully put it in a plastic bag (from which it tried to crawl out, of course) and carried it with us until we reached some permanent salt water, where it was released and slowly crawled away. It may not have been in very good shape by then, and maybe some disability accounted for its being washed up into the grass, but at least it got a second chance.

octopus-escaping-kmh
The octopus tries to escape its rescuers. Photo by  Katherine Hocker

One island of this chain of islands was a real island before the channel silted up; its core is a forested ridge of bedrock, now surrounded by uplifted land that supports a ring of small spruces and elder berry bushes. An exploration of this island turned up two bird skeletons, minus the skulls; a little forensic work later determined that the bones were very likely those of bald eagles. That made us suspect that they had been shot and left to rot. A sorry thing!

Under some of the trees we found burrows that looked like old otter dens, probably made back in the days before post-glacial uplift increased the distance to permanent water. A cast-up pellet of undigested bits, probably from a raven, held—of all things—the better part of the bowl of a plastic spoon. Overhead, a group of eagles and crows circled peaceably.

We flushed several snipe from the sloughs that cross the wetland. A female harrier coursed in and out of the trees on the smaller islands, probably on her way north (although harriers do nest here occasionally). And buttercups were starting to bloom along the edges of the spruce groves.

Best of all were the lichen gardens on the smaller islands, which are made of dredged sediment from the channel. Sometimes called lichen ‘barrens’, these gardens are barren only of trees and shrubs and tall herbs. They can be a wonderfully artistic spread of color and form. The lichens were very happy, owing to recent rains, so we spent some time admiring the natural art show. We also tried very hard to place our feet where they would do the least damage. Each of these gardens of miniatures was surrounded by a ring of young spruces, lending them a feeling of seclusion and privacy.

On the way back to the car, we spotted a little group of five snow geese, busily grazing—the last reward of a profitable excursion.