The Emergence of the North Woods

Abstract

In May or June, trees dust the landscape with a thin film of pollen. Smear a thin layer of Vaseline on some glass slides and leave them overnight under pine, spruce, birch, or maple trees whose flowers are shedding pollen. The next day, with a binocular microscope under 400 power (10 × eyepiece and 40 × objective), you can see the intricately sculpted shapes of pollen characteristic of each genus of trees. Pollen grains of pine, spruce, and fir look like squashed footballs with two conspicuous air-filled bladders attached to them; the bladders often have a network pattern in their surfaces that aids in identifying them to the species level. These bladders help keep the grains aloft in the breeze, enabling them to disperse widely. In contrast, pollen grains of deciduous hardwood species are more rounded grains with surface patterns. Birch pollen is somewhat flattened, with three evenly spaced conspicuous pores that give the grain a triangular appearance. Maples are slightly fattened spheres, with three shallow furrows evenly spaced around the equator that meet at the “poles” of the grain. With care and with more sophisticated microscopes, it is possible to distinguish the pollen from different species in the same genus.

The North Woods did not exist intact south of the ice sheet waiting to move north but was assembled bit by bit as the ranges of plant species shifted northward and distributed themselves along the gradients of soil moisture in the landscape left by the ice sheet.