Environmental Engineering Reference
In-Depth Information
SECTIONIV
SYNTHESIS
In reading the previous chapters about ecosystem energetics and biogeochemistry, you
may have noticed that some ideas and themes arose repeatedly. Examples of these cross-
cutting subjects include the creative use of boundaries to analyze ecosystems over different
scales of space and time; quantitative analysis, including mass balance; the use of multiple
approaches and tools to solve a single problem; the importance of human controls on eco-
systems; and so on. In the next three chapters, some of these important cross-cutting ideas
will be discussed explicitly. We hope that the explicit discussion of the cross-cutting sub-
jects that appeared implicitly in earlier chapters will make it easier for readers to under-
stand the central ideas of modern ecosystem science.
In Chapter 9, Michael Pace revisits some of the basic attributes of the ecosystem concept
that were introduced in Chapter 1, and shows how these simple attributes lend flexibility
and strength to ecosystem science. Pace reminds us that the fact that ecosystems contain
all living and nonliving materials within a boundary allows scientists to use the powerful
tools of budgets and mass balance to analyze ecosystems. He further emphasizes that flexi-
bility in choosing boundaries, formulating specific problems, and focusing on different
components of ecosystems allows the creative scientist to efficiently answer important
questions about ecosystem structure and function. Most importantly, Pace argues that this
flexibility and subjectivity does not prevent the development of robust generalities about
ecosystems, but rather speeds their development and testing.
In Chapter 10, Steward Pickett and Mary Cadenasso consider the implications of hetero-
geneity for ecosystems. Although most traditionally regarded as internally homogeneous
and surrounded by a uniform or neutral matrix, ecosystems are in fact both markedly het-
erogeneous and surrounded by varied, changing, and interactive neighbors. This internal
and external heterogeneity can have strong and varied effects on ecosystems. After
describing the nature and origins of ecological heterogeneity, Pickett and Cadenasso pro-
vide a framework for describing and understanding heterogeneity in space and time. They
also consider the central knotty question: when is heterogeneity important in ecosystems?
It is clear from this chapter that heterogeneity is important to ecosystems, and that its
effects are not yet satisfactorily understood.
Finally, Chapter 11 on the controls on ecosystem structure and function by Kathleen
Weathers and her coauthors closes this section of the topic. Understanding how ecosys-
tems are controlled is
important both for basic
science and for management.
