Environmental Engineering Reference
In-Depth Information
Still, animals may have an easier time adjusting to a changing climate because many have the ability to move.
As the climate shifts, animals can more easily change their territory as long as suitable habitat is within reach.
Even the smallest of animals have shown evidence of moving as climate changes.
Ecological Succession
Communities are not static but are constantly changing. Species of plants and animals come and go, evolve and
die out. Change is constant, although often slow by human standards. Change in a given geographical area that
is predictable is described as
ecological succession.
Two types of ecological succession have been identified:
•
Primary succession
is the process that starts with bare rock where no soil or life are present, such as a
new volcanic island, an area emerging from beneath a retreating glacier, or the Earth when it was very
young.
•
Secondary succession
is the re-growth of an area after an event has wiped out an existing community,
but soil and some life remain. The "event" might be a fire, tornado, volcanic eruption, or human activity.
Examples of human activities are abandoning an agricultural field to regrow on its own, clear-cutting a -
forest, or setting a fire.
The organisms that start succession in both types are called
pioneer species.
These species typically have a
wide range of environmental tolerances and generally include lichens, mosses, algae, and bacteria. The pioneer
species lay the foundation of nutrients on which succeeding species come and settle. Grasses are typically
second; they add organic material to the developing soil and hold the new soil in place with their root systems.
Small herbaceous plant species appear next, and they continue to add organic matter to the soil. Small bushes
join the mix, adding still more organic matter but, more important, adding shelter and shade to the area for oth-
er plants yet to come. Conifers appear and add to the growing habitat. Short-lived hardwoods move in (such as
the maples), and finally the climax community of long-lived hardwoods (such as the oaks) is reached. The suc-
cession of animals follows a similar pattern: insects are the first to arrive, and then small rodents and lizards.
Birds come and bring with them the seeds of new plants for the community. As the community becomes more
complex, larger mammals join the changing ecosystem.
How long this process takes depends on whether the area is undergoing primary or secondary succession.
Another driving force is the climate; areas in dry climates take longer to develop than those in moist climates.
Areas that receive large amounts of precipitation may also take longer to develop because the newly accumu-
lating nutrients can be washed away by flowing water. Obviously an area undergoing primary succession will
take much longer to fully develop than one in secondary succession. Secondary succession is also driven by the
proximity of returning organisms. The size of the disturbed area and how close the former members of the
community are to the area will play a determining factor in the succession of the area.
Biogeochemical Cycles
Biogeochemical cycles
(nutrient cycles) describe the movement of nutrients throughout ecosystems (move-
ment between Earth's abiotic and biotic systems). The word
biogeochemical
is a combination of
bio
(meaning
"life"),
geo
(meaning "earth"), and
chemical
(meaning "elements or compounds that cycle through the living
and nonliving world"). While many nutrients are essential for life and health on our planet, five nutrient cycles
are vital for ecosystem function and survival: carbon, oxygen, nitrogen, phosphorus, and sulfur. These five nu-
trient cycles are being altered by human activity.
