Tree: A Life Story by David Suzuki & Wayne Grady

Author:David Suzuki & Wayne Grady [Suzuki, David & Grady, Wayne]
Language: eng
Format: epub
Tags: Non-Fiction, Science, Nature
ISBN: 9781553651260
Publisher: Pgw
Published: 2004-01-01T00:00:00+00:00

A WORLD OF FERNS

The fan of slender sword ferns (Polystichum scopulinum) is still growing at the base of our tree, although the salamander has moved on. There is something elemental about ferns; their beauty is a mathematical beauty, like that of snowflakes or crystals. They look like a plant designed by a computer programmed to illustrate chaos theory. They have the same basic structure as our tree, but in only two dimensions. Whereas the branches of a tree radiate in all directions from the central stem, sword fern fronds are paired and flat, like the shadow of a tree. Like all ferns, the sword fern is a lacy, elegant plant, each leaf in the swirl rising on its vascular tissue to a height of a meter and a half (5 feet), with 30-centimeter-long (12-inch-long) pale green fingers spreading from the axis like knife blades, arranged evenly on either side and tapering toward the top, in the classic pattern. The fern’s base, just above the buried, hiltlike rhizome, is covered with crisp brown scales.

Ferns grow abundantly in almost every habitat on Earth. The sword fern is one of dozens of members of the group, which also includes horsetails and club mosses, associated with the Douglas- fir forest understory, where the presence of ferns and salamanders is a sign of a healthy ecosystem. The deer fern (Blechnum spicant), the only member of its tropical genus found in North America, resembles the sword fern but is shorter, and its fronds are continuous rather than separate, more like a mower blade than a stack of knives; it grows in swampy areas where western redcedars are more at home. The sword and deer ferns are evergreens, but the oak fern (Gymnocarpium dryopteris) drops its triple-headed fronds in the fall; it prefers the acidic soils found on slopes and ledges. The licorice fern (Polypodium glycyrrhiza) is an epiphyte; it grows on the mossy trunks of the bigleaf maples.

Ferns look like primitive trees because that is exactly what they are. When marine plants, the algal seaweeds, moved onto land, they evolved into bryophytes (mosses and liverworts) and then, as the competition for light became fiercer, rose higher from the ground and became pteridophytes (plants with roots, stems, and leaves but no flowers or seeds). Horsetails were the most successful; the several species in our forest include field horsetails, water horsetails, smooth horsetails, and the various scouringrushes, so called because they look like bottle brushes and, in fact, when ground up, were used by Native people for scouring cooking utensils. Their stems contain silica as well as cellulose as a stiffening agent. Horsetail leaves are more like modified bud scales. Their stems are hollow and jointed, not unlike bamboo, and tough as nails; they will push aside concrete slabs and grow through asphalt.

For many millions of years, ferns, horsetails, and club mosses dominated the vegetative world, peaking during the Carboniferous period, when they grew with stems as thick as trees and shaded the swampy landmasses with their huge fronds.

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