Page 329 - Environment: The Science Behind the Stories

food for woodpeckers, which create cavities that other ani- plants grow (whether in forest, grassland, or other biomes),
mals may later use. Much of a forest’s biodiversity resides their roots stabilize the soil and help to prevent erosion. When
on the forest floor, where the fallen leaves and branches of rain falls, leaves and leaf litter slow runoff by intercept-
the leaf litter nourish the soil. A multitude of soil organisms ing water. This prevents flooding, helps water soak into the
helps decompose plant material and cycle nutrients (p. 236). ground to nourish roots and recharge aquifers, reduces soil
Tropical rainforests feature additional complexity not erosion, and helps keep streams and rivers clean.
shown in Figure 12.3. In tropical rainforests, particularly tall Forest plants also filter pollutants and purify water as they
individual trees called emergent trees protrude here and there take it up from the soil and release it to the atmosphere in
above the canopy. Epiphytes, plants specialized to grow atop transpiration (p. 138). Plants draw carbon dioxide from the air
other plants, add to the biomass and species diversity at all for use in photosynthesis (p. 50), release the oxygen that we
levels of a rainforest. Epiphytes include many ferns, mosses, breathe, regulate moisture and precipitation, and moderate cli-
lichens, orchids, and bromeliads. mate. Trees’ roots draw minerals up from deep soil layers and
Forests with a greater diversity of plants tend to host a deliver them to surface soil layers where other plants can use
greater diversity of organisms overall. As forests change over them. Plants also return organic material to the topsoil when
time through the process of succession (pp. 103, 106), their they die or drop their leaves.
species composition changes along with their structure. In By performing all these ecological functions, forests are
general, old-growth forests host more biodiversity than young indispensable for our survival. Forests also enhance our quality
forests, because older forests contain more structural diversity of life by providing us with cultural, aesthetic, health, and rec-
and thus more microhabitats and resources for more species. reation values (pp. 168–169). People seek out forests for adven-
Old-growth forests also are home to more species that today ture and for spiritual solace alike—to admire beautiful trees, to
are threatened, endangered, or declining, because old forests observe wildlife, to enjoy clean air, and for many other reasons.
have become rare relative to young forests.
Carbon storage limits climate change
Forests provide ecosystem services
Of all the ecosystem services that forests provide, their stor-
Besides hosting biodiversity, forests supply us with many vital age of carbon has elicited great interest as nations debate how
ecosystem services (p. 21, 134–135, 170, 308; FIGURE 12.4). As to control global climate change (Chapter 18). Because trees
absorb carbon dioxide from the air during photosynthesis and
then store carbon in their tissues, forests serve as a major res-
Store ervoir for carbon. Scientists estimate that the world’s forests
O 2 CO carbon Support store over 280 billion metric tons of carbon in living tissue,
2
biodiversity
which is more than the atmosphere contains. When plant mat-
ter is burned or when plants die and decompose, carbon diox-
Produce
oxygen Provide fuel wood, ide is released—and thereafter less vegetation remains to soak
lumber, paper, it up. Carbon dioxide is the primary greenhouse gas contrib-
medicines, dyes,
H O foods, fibers uting to global climate change (p. 503). Therefore, when we
2
cut forests, we worsen climate change. The more forests we
preserve or restore, the more carbon we keep out of the atmos-
Purify water, phere, and the better we can address climate change.
filter pollution
Forests provide us valuable resources

Return organic Carbon storage and other ecosystem services alone make for-
matter to soil
ests priceless to our society, but forests also provide many
economically valuable resources. Among these are plants for
medicines, dyes, and fibers; animals, plants, and mushrooms
Provide health, for food; and, of course, wood from trees. For millennia, wood
Slow runoff, beauty, recreation from forest trees has fueled our fires, keeping us warm and well
prevent flooding
fed. It has built the houses that keep us sheltered. It built the
ships that carried people and cultures between continents. And
it gave us paper, the medium of the first information revolution.
In recent decades, industrial harvesting has allowed us to
extract more timber than ever before, supplying all these needs
Transport
minerals to Stabilize soil, of a rapidly growing human population and its expanding econ-
soil surface prevent erosion omy. The extraction of forest resources has been instrumental in
helping our society achieve the standard of living we now enjoy.
Nations maintain and use forests for all these economic and
FIGURE 12.4 Forests provide us a diversity of ecosystem ecological reasons. An international survey in 2010 found that
328 services, as well as resources that we can harvest. globally, 30% of forests were designated primarily for timber

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