Page 328 - Environment: The Science Behind the Stories

FIGURE 12.2 Forests cover 31% of
Earth’s land surface Most wide-
spread are boreal forests in the north
and tropical forests near the equator.
Areas classified as “wooded land”
support trees at sparser densities. Data
from Food and Agriculture Organization of the
United Nations, 2010. Global forest resources
assessment 2010.

Forest
Other
wooded
land

forest intermixes with forests of aspen, birch, maple, and beech, by an extensive array of fungi and microbes, in both parasitic
and areas of white, red, and jack pine. and mutualistic relationships (pp. 97–98).
Altogether, forests currently cover 31% of Earth’s land In a forest’s canopy—the upper level of leaves and
surface (FIGURE 12.2). Forests occur on all continents except branches in the treetops—beetles, caterpillars, and other
Antarctica. leaf-eating insects abound, providing food for birds such as
warblers and tanagers, while arboreal mammals from squir-
Forests are ecologically complex rels to sloths to monkeys consume fruit and leaves. Animals
also live and feed in the subcanopy (the middle and lower
Because of their structural complexity and their capacity to portions of trees), in shrubs and small trees of the understory,
provide many niches for organisms, forests comprise some and among groundcover plants on the forest floor. Other ani-
of the richest ecosystems for biodiversity (FIGURE 12.3). The mals utilize the bark, branches, and trunks of trees. Cavities
leaves, fruits, and seeds of trees, shrubs, and forest-floor plants in trunks and limbs provide nest and shelter sites for a wide
furnish food and shelter for an immense diversity of insects, variety of animals. Dead and dying trees (called snags) are
birds, mammals, and other animals. Plants are also colonized especially valuable; insects that break down the wood provide

Treefall gap

Canopy
Snag

Subcanopy CHAPTER 12 • FOREST S, FOREST MAN A GEMENT, AND PR O TECTED AREAS

Understory

Shrub layer
Forest floor
Soil

Ground- Leaf litter Moss and Roots Fallen log
cover epiphytes

FIGURE 12.3 A cross-sectional diagram shows the complexity of a mature forest. Crowns of tall trees form
the canopy, and trees beneath them form the shaded subcanopy and understory. Shrubs and groundcover grow
just above the forest floor, and vines, mosses, lichens, and epiphytes cover portions of trees and the forest floor.
Snags (dead trees) provide food and nesting sites for woodpeckers and other animals, and logs nourish the soil.
Fallen trees create openings called treefall gaps, letting light through and allowing early successional plants to grow. 327

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