The Environmental Complex - Agroecology: The Ecology of Sustainable Food Systems - page 163

12 The Environmental Complex

Previous chapters have considered the separate influ-
ences of individual environmental factors — light, tem-
perature, precipitation, wind, soil, soil moisture, fire, and
other organisms — on the crop plant. Although it is
important to understand the impact that each of these
factors has by itself, rarely does any factor operate alone
or in a consistent manner on the organism. Moreover, all
the factors that have been discussed as separate compo-
nents of the environment also interact with and affect
each other. Therefore, the environment in which an indi-
vidual organism occurs needs to be understood as a
dynamic, ever-changing composite of all the interacting
environmental factors — that is, as an environmental
complex .
When all the factors that confront a crop plant are
considered together, it is possible to examine characteris-
tics of the environment that emerge only from the inter-
action of these factors. These characteristics — which
include complexity, heterogeneity, and dynamic change
— are the main topics of this chapter. Their examination
in terms of their impact on the crop plant, represents the
final step in analyzing agroecosystems autecologically,
and prepares us for the synecological level of analysis that
begins in the following chapter.

F ACTORING THE E NVIRONMENT

The concept of an environmental complex is presented
schematically in Figure 12.1. Although lines represent-
ing connections have not been drawn, the figure is
intended to show that interactions occur between factors
themselves, as well as between each factor and the crop
organism. The component factors of the environment
discussed in the previous chapters are all included, as
well as several others. Since it is impossible to divide
the entire environment neatly into components, or to
include every possible factor, the factors shown in
Figure 12.1 involve some simplification and overlap.
Furthermore, each of the factors is not of equal impor-
tance at any particular time. For this reason, time is not
listed as an independent factor, but should instead be
considered as the background context within which the
entire complex of factors is changing.
Because of the complexity of the environment, it is
clear that its factors can combine to affect organisms in
the environment in addition to doing so independently.
Factors can work together simultaneously and synergisti-
cally to affect an organism, or they can make their effects
felt through a cascade of changes in other factors. An
example of such factor interaction is the lush weed growth
on the north-facing side of the furrow illustrated in
Figure 4.4. In this particular microclimatic site, lower tem-
peratures, higher moisture, higher biological activity, and
possibly higher nutrient availability were simultaneously
associated with the small amount of shading that occurred,
and this combination of factors effectively altered the con-
ditions for plant growth. As another example, an allelo-
pathic compound released from the roots of a crop can
interact with shading, moisture stress, herbivory, suscep-
tibility to disease, and other factors to either enhance or
reduce the effectiveness of the phytotoxic compound
in limiting weed growth in a cropping system. Because
of such interactions, it is often a challenge to predict
the consequences of any single modification of the agro-
ecosystem.
One of the weaknesses of the conventional agronomic
approach to managing agroecosystems is that it ignores
factor interactions and environmental complexity. The
needs of the crop are considered in terms of isolated,
individual factors, and then each factor is managed sepa-
rately to achieve maximum yield. Agroecological

THE ENVIRONMENT AS A COMPLEX
OF FACTORS

The environment of an organism can be defined as the sum
of all external forces and factors, both biotic and abiotic,
which affect the growth, structure, and reproduction of that
organism. In agroecosystems, it is vital to understand which
factors in this environment — due to their condition or level
at the time — might be limiting an organism, and to know
what levels of certain factors are necessary for optimum
performance. Agroecosystem design and management are
based largely on such information. The foundations of this
understanding have been presented in the earlier chapters
of this topic. Individual factors have been explored, and
many agricultural options for their management have been
reviewed. Since the environment is a complex of all of these
factors, it becomes just as important to understand how each
factor affects or is affected by others, singly or in complex
combinations that vary in time and place. It is the complex
interactions of factors that make up the total environment
of the organism.

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