Herbert River Trail is study in effects of retreating ice

First several miles of trail have been rebuilt and partially rerouted

Posted: Sunday, April 09, 2006

The Herbert River Trail begins in nice spruce forest on the floodplain between Herbert and Eagle Rivers. The trees are large, with a good accumulation of moss on large branches and sometimes on the bases of the trunks.

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Surprisingly, moss wads on branches 30-40 feet up are occasionally used by birds such as juncos, which normally nest on the ground. Cavity-nesting winter wrens commonly use the moss clumps for nesting, although they also use holes in logs, stumps, and earthen banks.

Winter wrens are one of the few forest songbirds known to be regularly polygynous (more than one female per male). In some sites in our area, bigamy is quite common, and trigamy has been reported occasionally, but in the Herbert River forest, most males were socially monogamous. I said "socially monogamous," meaning that there is a pair bond between one territorial male and one female, but if these wrens are like most other songbirds, there is usually some hanky-panky going on between neighbors, and not all the chicks in a nest may have the same father.

In the muddy riverbank near the first part of the trail, you may be able to see some buried tree stumps and trunks that have been exposed as the river erodes the banks. These were apparently buried by sediment as the Little Ice Age glacier melted and the outwash was deposited in the floodplain. Close to the present terminus of the glacier, there are recently exposed tree stumps that are what's left of a forest that developed around 8,000 years ago, after the big Pleistocene ice age. The trees were snapped off and buried when they were overrun by the advancing ice.

The first several miles of trail have recently been rebuilt and partially rerouted. Instead of the old series of mud holes and tree roots, there is now a wide, gravel walkway that is much easier on the feet. It is great for cross-country skiing too, when there is enough fresh snow. Too much foot-trampling, however, can spoil the skiing by creating lumps and pits that harden into ice. The trail goes past a pond where, on a good day, the reflection of a rock on the far side is so perfect that it looks like the rock is floating on the surface. Some rolling terrain is created by a series of low moraines, ever younger as the trail goes toward the glacier, were left by the glacier during the Little Ice Age, which ended in the 1700s, approximately

As of last fall, the improved trail stops at a rock outcrop, but there is an expectation that the outcrop will be blasted into conformity in summer, allowing the improved trail to continue into the early-successional alder thickets more recently exposed by the retreating ice. In the meantime, the old trail negotiates the outcrop, wriggles through the alders, and emerges on a broad, flat expanse of sediment often used for camping. If the water levels are not too high, it is easy to walk out in the braided channels toward the glacier.

The main river comes directly out of the face of the glacier, but a smaller stream enters the rivers from the north. A rough, unofficial route goes up the ridge above this stream and descends into a valley carved by ice and meltwater. The stream was larger in the recent past, when more melting ice fed this channel. In this valley, you can walk right up to an arm of the glacier, look at ice caves, and contemplate the power of moving ice.

• Mary F. Willson is a retired ecology professor and a Trail Mix board member.

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