Artist: Nathan Borson

In the trackless wilds of Glacier Bay, every serious hiker eventually tangles with an equally serious alder thicket. Cyanobacteria inhabit nodules they create in the roots of Sitka alder. They remove nitrogen from the air and “fix” it in a form usable by plants, a great advantage where topsoil has been scraped away by glaciers. Dense stands of the tangled shrub often spring up within 25 years after the glaciers retreat and now dominate large parts of upper Glacier Bay. Eventually Sitka spruces take root in alder-fertilized soil and shade out their short deciduous benefactors, replacing that hiker’s bane with other vegetative obstacles such as devil’s club.