North Douglas Rainforest Trail

mostly musings on tree bark

I have walked the rainforest trail on North Douglas I-don’t-know-how-many times, but every time there is something worth noticing—including some things that I’ve missed or just didn’t think about on past walks there. In mid January a friend and I strolled that trail again, just to see what we could see. It was a productive stroll! Here are some of the things of interest.

The hemlocks in that area commonly have ‘fluted’ trunks, with pronounced, rounded ridges running up from the base. This ropy-looking growth feature (no relation to the musical instruments!) is common in Southeast Alaska but less common farther south, for reasons unknown. The fluting apparently results when lateral transfer of nutrients is restricted, so some parts of the trunk get more nourishment than others and therefore grow better. Several factors, such as root or branch damage, have been shown to have temporary effects on lateral transfer of nutrients, but damaged trees can overcome the effects as they continue to grow. One study reported that trees exposed to mechanical bending by the wind are more likely to develop flutes than trees not subject to much bending; thus, trees on windy coasts or unstable substrates are more likely to develop flutes than inland trees. An experiment that stabilized the trunks of young hemlocks by running guy lines out to nearby trees showed that stabilization reduced flute development (as judged by growth rings) only in some years. So other, still unknown, factors must be involved as well.

The red alder trunks near the trail often bear belts of dark, rough bark with short vertical fissures. Some belts are only a few inches wide but others may be a foot or more in width. According to the forest pathologists (Paul Hennon and Robin Mulvey) at the Forestry Sciences Lab, these areas have been infected by the so-called rough-bark fungus that does not damage the wood but rather affects only the bark layers. Young alders are particularly susceptible to infection, but the rough bark remains as the tree ages. Scanning several trunks, I thought I could detect newer infections, just beginning to develop, that had bands of small vertical fissures round the trunk, without the dark color. Although this fungus seems to be common along this trail, a search for it in the Amalga Harbor area failed to find it, so the distribution appears to be localized.

We noticed that some of the rough-bark belts had several old, oval divots in the bark, above or below the belt. The divots bear a resemblance to the sap wells made by sapsuckers and we wondered if the birds had sampled these trees in the earlier stages of the infection. Or could the birds have helped to disperse the fungus by drilling wells, some of which are now covered by the rough bark?

Many of the hemlocks out here have rows of deep conical pits around the trunk (not at all like sapsucker wells). In addition, lots of the trunks have had the outermost layer of bark flaked off, exposing paler bark layers below. All of this is evidence of woodpecker activity—in search of bugs living in the bark crevices or burrowing under the thick bark. Some of the activity was quite recent, because flakes of outer bark lay on top of the snow. Who dunnit?? Not sapsuckers, because they are gone for the winter. Maybe three-toed or black-backed woodpeckers. Neither is common in our region—in fact, except for sapsuckers, woodpeckers are strangely uncommon in our forests. But why? One speculation is that local predators such as goshawks keep woodpecker populations down.

We found at least two vertical scars on older trees; the scars had been made a long time ago, because the trees had grown healing tissues over the edges, reducing the openings to narrow slits. Both scars were about four feet long and very similar to each other, located about eye level. Inside the slit we could see the flat, gray wood. We wondered if these scars could have had an anthropogenic origin and, if so, then what was the reason for people to make them. Or perhaps an adjacent tree had fallen along the trunk, stripping off the bark—a fairly common occurrence, but these scars were so similar to each other that this seemed unlikely. There’s more to be learned…

This walk was not just about trees, however. Large flocks of pine siskins swooped over the canopy. A mixed flock of golden-crowned kinglets and chickadees foraged on the beach fringe, talking all the while. A lone horned grebe in winter plumage dove in the bay, ignoring the mallards that nibbled at the water’s edge and the goldeneyes loafing near the point. Most interesting to me was a chance observation: I happened to turn around in a lucky spot and something caught my eye. A tuft of moss and grass stuck out of a niche in a tree trunk, so I went over to check it out. ‘Twas a bird nest—but maybe not just one! There were three layers piled one atop the other, as if three nests had been built here (I did not tear the structure apart to be sure). Perhaps some small bird had really liked this spot. Birds don’t usually renest in a site where their previous nest failed, so (if this was the same individual), she had been successful here before. Who was it? Possibly a junco…