The Environmental Complex - Agroecology: The Ecology of Sustainable Food Systems - page 167

open field, for example, increasing light levels during
the morning increase temperature, and the higher temper-
ature increases evaporation of water from the soil while
transpiration also increases. Thus the intensity of each
factor varies simultaneously with every change in the
intensity of solar radiation, and the relative effect of
each factor on the crop is practically inseparable from the
multiplicity of effects they have together.

FOOD FOR THOUGHT

1. What factors may have impacted seed before a

farmer buys it for planting? How may these
influences affect the performance of the seed
once it is planted?

2. What are some ways that a farmer can manage

an agroecosystem in a highly variable environ-
ment other than trying to control or homogenize
the conditions that create the heterogeneity?

12.3.3 F ACTOR P REDISPOSITION

3. What are some of the disadvantages for a farmer

who chooses to deal with or adapt to (rather
than overcome) spatial and temporal heteroge-
neity in the agroecosystem?

A particular environmental factor may cause a crop
response that renders the crop more susceptible to dam-
age by another factor. In such cases, the first factor is
said to predispose the plant to the effects of the second
factor. Low light levels caused by shading, for example,
can predispose a plant to fungal attack. The lower light
levels usually mean higher relative humidity for the plant
and cause it to develop thinner, larger leaves that then
may be more susceptible to attack by a pathogenic fungus
that occurs more commonly when excess moisture is
present in the environment. Similarly, research has
shown that some crop plants are more susceptible to
herbivore damage when they have been given large
amounts of nitrogenous fertilizer. The plant tissue
is predisposed to the herbivory due to its higher nitrogen
content — apparently the nitrogen serves as an attractant
for the pest (Scriber, 1984).

4. What are some ways in which a farmer can

successfully compensate for a limiting factor
by altering or managing one or several other
factors, and thus contribute to the sustainability
of a farming system?

INTERNET RESOURCES

Plant ecophysiology research group at the Univer-
sity of Wales
www.bangor.ac.uk/safs-new/research/
plecophys.php
A good example of a research group doing work
on the factors that impact plants in the envi-
ronment, a field known as ecophysiology.

12.4 MANAGING COMPLEXITY

RECOMMENDED READING

Sustainable agroecosystem management will require an
understanding not only of how individual factors affect
crop organisms but also of how all factors interact to form
the environmental complex. Part of this understanding
comes from knowing how factors interact with, compen-
sate for, enhance, and even counteract with each other.
Another part comes from knowing the extent of variability
present on the farm, from field to field and within each
field. Conditions vary from one season to another as well
as from one year to the next. From climate to soils, from
abiotic to biotic factors, and from plants to animals, factors
interact and vary in dynamic and ever-changing patterns.
Perhaps an important component of sustainability is
knowing not only the extent and form of factor interaction,
but also the range of variability in interactions that can
occur over time. Adapting the agroecosystem as much as
possible to take advantage of complexity and variability
where appropriate, and to compensate for both when not,
is in many ways the challenge that will be addressed in
the following chapters.

Daubenmire, R.F. 1974. Plants and Environment. 3rd ed. John
Wiley & Sons: New York. The topic that established
the foundation for an agroecological approach to
plant-environment relationships.
Forman, R.T.T. and M. Gordon. 1986. Landscape Ecology. John
Wiley & Sons: New York. Essential reading in understand-
ing the relationships between plant distribution and the
temporal and spatial complexity of the physical landscape.
Harper, J.L. l977. Population Biology of Plants . Academic Press:
London. The key reference for understanding the foun-
dations for modern plant population biology, with many
references to agricultural systems.
Larcher, W. 2003. Physiological Plant Ecology . 4th ed.. Springer:
New York. A very complete text of ecophysiology, cov-
ering plant adaptation to the factors of the environmental
complex.
Schmidt-Nielsen, K. 1997. Animal Physiology: Adaptations and
Environment. 5th ed. Cambridge University Press: New
York. An important review of the physiological ecology
of animals in the environment.