Principles of terrestrial ecosystem ecology.pdf

16
Managing and Sustaining Ecosystems
Introduction
Humans depend on Earth’s ecosystems for
food, shelter, and other essential goods and
services. Ecosystems provide well-recognized
goods, including timber, forage, fuels, medicines,
and precursors to industrial products.
Ecosystems also provide underrecognized services,
such as recycling of water and chemicals,
mitigation of floods, pollination of crops, and
cleansing of the atmosphere (Daily 1997). The
harvest and management of these resources are
a major component of the global economy. Our
purposeful use and misuse of these resources
have endangered them, and many apparently
unrelated activities have had indirect and unintended
negative effects on them.
The overuse or misuse of resources can alter
the functioning of ecosystems and the services
they provide (see Chapter 1). Land use change,
for example, can degrade the capacity of watersheds
to purify water, leading to large treatment
costs to cities. Degradation and loss of
wetlands can expose communities to increased
damage from floods and storm surges. Decimation
of populations of insect pollinators has
reduced yields of many crops (Daily 1997).
Introductions and invasions of nonnative
species such as killer bees, fire ants, and zebra
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Human activities influence all of Earth’s ecosystems. This chapter summarizes the
nature of these impacts, the principles by which important ecological properties can
be sustained, and the management approaches that have been developed to maximize
sustainability.
mussels, through the actions of humans, cause
enormous damage to living resources and
threaten human health. Human activities also
indirectly affect ecosystem goods and services
through changes in the atmosphere, hydrologic
systems and climate (see Chapter 15).
The growing scale of human activities suggests
that all ecosystems are influenced, directly
or indirectly, by our activities. No ecosystem
functions in isolation, and all are influenced
by human activities taking place in adjacent
communities and around the world. Human
activities are leading to global changes in most
major interactive controls over ecosystem
processes: climate (global warming), soil and
water resources (nitrogen deposition, erosion,
diversions), disturbance regime (land use
change, fire control), and functional types of
organisms (species introductions and extinctions).
In many cases, at the scale of regions,
these global changes interact with each other
and with local changes. All ecosystems are
therefore experiencing directional changes in
ecosystem controls, creating novel conditions
and, in many cases, positive feedbacks that lead
to new types of ecosystems. These changes in
interactive controls will inevitably change the
properties of ecosystems; some of these
changes are detrimental to society.