Indicators of Sustainability - Agroecology: The Ecology of Sustainable Food Systems - page 307

sustainability it is, which of its aspects is least sustain-
able, exactly how its sustainability is being undermined,
and how it can be changed to move it toward sustainable
functioning. And once a system is designed with the
intent of being sustainable, we need to be able to monitor
it to determine if sustainable functioning has been
achieved.
The methodological tools for accomplishing this task
can be borrowed from the science of ecology. Ecology has
a well-developed set of methodologies for the quantifica-
tion of ecosystem characteristics such as nutrient cycling,
energy flow, population dynamics, species interactions,
and habitat modification. Using these tools, agroecosys-
tem characteristics — and how they are impacted by
humans — can be studied from a level as specific as that
of an individual species to a level as broad as that of the
global environment.
We can also borrow methodological tools from rural
and environmental sociologists who have developed a set
of methodologies for evaluation of societal characteristics
such as access to economic resources, social networks,
political or economic status, and empowerment. Using
these tools, broader agroecosystem characteristics — and
how the are affected by political and economic structures
and relationships — can be studied from a level as specific

as a household to a level as broad as that of global markets
and free trade agreements.
One approach is to analyze specific agroecosystems to
quantify at what level a particular ecological or social
parameter or set of parameters must be at for sustainable
function to occur. Many researchers have begun work in
this area, and some of their results are presented in
Table 21.5. Even though the results are given individually,
it is important to remember that such results must be used
and interpreted in the context of the whole system and the
complex of interacting factors of which they are only a part.
Another kind of approach is to begin with the whole
system. Some researchers, for example, have been work-
ing on developing methods for determining the probability
of an agroecosystem being sustainable over the long term
(Fearnside, 1986; Hansen and Jones, 1996). Using a sys-
tems framework for measuring the carrying capacity of a
particular landscape, they apply a methodology for inte-
grating the rates of change of a range of parameters of
sustainability and determine how quickly change is taking
place toward or away from a specific goal. Such an analy-
sis is limited by the difficulty of choosing which parame-
ters to integrate into the model, but has the potential for
becoming a tool allowing us to predict if a system will be
able to continue indefinitely or not.

TA B L E 2 1 . 5
Selected Quantifiable Parameters and Their Approximate Minimum Values for Sustainable Function of
Specific Agroecosystems

Minimum Level for
Sustainability Parameter Agroecosystem Ref.

Soil organic matter content 2.9% Strawberries in California (Gliessman, et al., 1996)

Spores of the disease Verticillium wilt Less than 1 spore per 100

grams of soil

Strawberries and vegetables
in California

(Koike and Sabbarao, 2000)

Input harvest loss ratio for each
macronutrient

Net positive balance over
time

Mixed arable crops in Costa Rica (Jansen et al., 1995)

Biocide Use Index a Maintain at a level less than 15 Mixed arable crops in Costa Rica (Jansen et al., 1995)

Ecosystem biophysical capital b GPP - NPP < 1 Variable (Giampietro, 2004)

Plant species diversity Shannon index > 5.0 Perennial pasture (Risser, 1995)

Ratio of renewable energy input
to total energy input

Should approach 1 Mixed crops, forage, and animals

in Central Italy

(Tellarini and Caporali, 2000)

Ratio of net energy output to total
external input c

Maintain as far above 1 as
possible

Mixed crops, forage, and animals
in Central Italy

(Tellarini and Caporali, 2000)

Female participation in farm activities Full acknowledgement of roles

and activities

Small-scale traditional farms
in NW Ethiopia

(Tsegaya, 1997)

Ratio of cost of all local inputs to
cost of total inputs d

As close to 1 as possible Mixed field crops in Bangladesh (Rasul and Thapa, 2003)

a Index based on several factors, including use rates, toxicity, and area sprayed; values above 50 are considered indicative of excessive biocide use.

b Defined as the capture of adequate solar energy to sustain cycles of matter in an ecosystem.

c An indicator of productivity.

d An indicator of input self-sufficiency.