Diversity by Design
by Larry Harrington
Our common goals
There are a number of reasons for fostering
diversity in agroecosystems. More diverse systems take better
advantage of ecological niches. Species adapted to different stresses
(e.g., waterlogging, soil acidity) can be positioned where they
have a comparative advantage. Greater system diversity can also
improve stability and resilience. Diverse agroecosystems offer
multiple pathways for energy and nutrient cycling; consequently
system productivity is not held hostage to the performance vagaries
of any particular species. When properly designed, more diverse
systems also can reduce problems associated with pests, diseases,
and weeds and can decrease reliance on external inputs. Such diverse systems may also be associated with in-situ conservation of foodgrain land races and folk varieties.
However, agroecosystem biodiversity is not an end in itself but a means of achieving productivity, stability,
resilience, improved environmental quality, and the conservation
of crop genetic diversity. These in turn are
part of larger societal goals -- sustainable food security, reduced
poverty, and improved public health.
Societies also value natural biological
diversity in the broader sense. People are concerned about the
possible extinction of species because of their potential future
benefits, their role in ecological balances, and simply because
people place a value in their continued existence, regardless of future human benefits.
Kinds of diversity
Agroecosystem biodiversity can be understood
in several different ways:
Crop genetic diversity.
This embraces such factors as varietal concentration; pace of
varietal change over time; genetic similarity among major cultivars;
the conservation and pyramiding of favorable genes in breeders'
varieties; the conservation and use of important genes present
in folk varieties, land races, and wild relatives;
and opportunities for expanding crop genetic diversity through
wide crosses and biotechnology.
Crop species diversity over space.
Spatial species diversity may be exceedingly narrow (e.g., a
monocropped rice field) or exceedingly broad (e.g., a home garden
featuring simultaneous cultivation of fruit trees, banana plants,
coffee, spices, and several food crops). Plots with low species diversity and high species diversity
often are found within the same farming system.
Crop species diversity over time.
Temporal species diversity may be narrow (e.g., one maize monocrop
crop per year, every year); broad within a year (e.g., an annual
sequence of multiple cropping involving cereals, legumes, and
horticultural crops); or broad over several years (e.g., rice-potato-wheat patterns, broken every
few years by a sugarcane crop). Crop species diversity over space
and over time are not necessarily related.
Agroecosystem biodiversity through crop-livestock
interactions. The presence of
livestock in a system tends to greatly enhance the value of non-crop
components (crop residues, grazing lands, forest resources) and
typically features nutrient cycling between rangeland and crop
land, thus fostering improved productivity and sustainability
of cropping systems and a higher potential for spatial and temporal
Natural biodiversity within agroecosystems.
More diverse agroecosystems -- particularly those with greater
spatial diversity, and those with trees -- may provide habitat
for a wider array of wildlife.
Natural biodiversity as indirectly affected
by agroecosystems. Highly productive
agroecosystems can indirectly foster natural biodiversity by making
it unnecessary to farm marginal or fragile areas, or to clear
new forest areas for agriculture. System diversity may be broadened
by increasing crop genetic diversity, expanding crop species diversity
over space and time, fostering crop-livestock interactions, or
improving productivity in favored agricultural areas to protect
biologically diverse fragile, marginal, or forested areas from
Sustainability in perspective
Partly because they are thought to be closely
linked to issues of biological diversity, sustainability issues
are commanding more attention from agricultural scientists. Many
agree that the ability to quantify sustainability is fundamental
to making the concept useful. Unfortunately little progress has
been made in this regard.
Most commonly, indicators of sustainability are narrowly driven by definitions. This often leads to arguments that are merely circular. For example:
All of these definitions, and their corresponding
indicators, are inadequate -- even when combined. They emphasize
the plot or farm community level of analysis, ignoring higher
levels. They succumb to the "fallacy of scale," in which
something that appears unsustainable at one level of analysis
may be a strong element in favor of sustainability at a higher
An example of "fallacy of scale"
Green Revolution technologies for rice and
wheat in South Asia often have been criticized as unsustainable.
At the agroecosystem level, these technologies may feature low
species diversity, high reliance on external inputs and energy
sources, and environmental pollution from pesticides and fertilizers.
However, at higher levels of analysis, the diffusion of Green
Revolution technologies in parts of South Asia has been associated
with accelerated economic development in Bangladesh; higher incomes
through employment generation in Uttar Pradesh; improvements in
income distribution in Pakistan; reduced population growth in
Green Revolution areas of India -- and, not least, the saving
of approximately 40 million ha from the plow (or woodcutter's
ax) in India alone. Without the Green Revolution technologies,
India would have needed another 40 million ha of rice and wheat
area to meet foodgrain demand.
The Green Revolution played a virtually
unrecognized role in reducing pressure to cultivate biologically
diverse fragile, marginal, or forested areas. In the absence of
the Green Revolution, food prices would have been higher, employment
growth (especially off-farm employment) would have been slower,
poverty more widespread, and population growth more rapid -- exacerbating
the threat to natural biological diversity.
So, at a higher level of analysis, resource
degradation and environmental pollution in Green Revolution areas
has been a cost associated with defusing longer-term threats to
resource quality and natural biological diversity in biologically
diverse fragile, marginal, or forested areas. Researchers and
farmers must reduce this cost. Plot-level threats to sustainability
in Green Revolution areas must be addressed. The challenge is
to generate a "doubly green revolution" that maintains
the powerful and favorable indirect consequences of highly productive
agricultural technology, while improving resource quality and
reducing pollution. Sustainability is not enough -- productivity
must increase as well.
Diversity by design
Greater agroecosystem biodiversity -- particularly crop genetic diversity and spatial and temporal species diversity -- often can help achieve sustainable improvements in agricultural system productivity. How, then, do we foster widespread use of more biologically diverse agroecosystems? There are at least two ways:
The path of "diversity by design"
is direct. It is the path taken by cropping systems and farming
systems research (FSR). In Asia such research sought to diversify
and intensify cropping patterns by introducing a second non-rice
crop into rice-based systems (an alternative made possible by
the introduction of short-duration, non-photoperiod sensitive
rice varieties). In Africa, the emphasis has been less on intensification
and more on reconciling food security and system sustainability
requirements. Even in Africa, however, diversity has been a major
theme in FSR. "Diversity by design" also has been characteristic
of research on agroecology.
The lessons learned from FSR and research
on agroecology have vastly improved researchers' capacity to work
with farmers in understanding and improving farming systems. However,
these lessons have not led to widespread adoption of more diverse,
productivity-enhancing resource-conserving agricultural systems.
Work is urgently needed to improve the effectiveness of research
(measured by widespread adoption) aimed at designing such agricultural
systems. Until then, the path of "diversity by design"
is unlikely to help achieve our common goals.
The path of "demand-led diversification"
is relatively indirect but has induced widespread change in farming
systems, particularly in Asia. Indonesia provides a classic example.
Increased rice productivity in favored lowland areas expanded
the supply of rice and reduced its price. Marginal rice areas,
often on hillsides, became unprofitable and farmers in these areas
ceased producing rice. However, higher incomes in rural and urban
areas -- largely resulting from improved rice productivity and
lower rice prices -- shifted the structure of demand for food
towards fruits and vegetables. Partly as a consequence, farmers
in hillside areas switched from growing rice to perennial fruit
trees. The same process is evident in other areas where new technology
has increased the productivity of basic grain production, for
instance in the Indian Punjab.
In contrast, stagnating grain (maize) productivity
in southern Africa provoked a chronic food security crisis, the
expansion of maize cultivation into wildlife areas, and a relative
absence of market signals that would induce farmers to diversify
into cash crops. Not by coincidence, "diversification out
of grain production" is not high on the southern Africa research
and policy agenda.
Success in demand-led diversification is sensitive to the policy environment, requiring:
Demand-led diversification will lead to
more biologically diverse agroecosystems at the aggregate (e.g.
regional) level but may not ensure increased biodiversity at the
plot or farm level. Moreover, plot-level trends in resource quality,
external input use, and environmental pollution may increase or
decrease, in accordance with practices adopted as farmers learn
to manage a new set of enterprises. The path of "demand-led
diversification," on its own, also may not lead to the attainment
of our common goals.
Complementarity and competition
As noted earlier, the goals of sustainable
food security, reduced poverty, improved public health, and conservation
of natural biological diversity will be attained through widespread
use of more productive, stable, resilient agroecosystems and the
conservation of crop genetic diversity.
This will require an emphasis on sustainable
productivity improvement in favored areas -- to reduce pressure
to cultivate biologically diverse areas unsuited to agriculture,
foster "demand-led diversification," and lead to the
"doubly green revolution" described previously.
Agricultural research and development --
scientists, extension workers, farmers, and policy makers -- can
help through: cereal varieties that are more tolerant to biotic
and abiotic stresses and use nutrients more efficiently; productivity-enhancing
resource-conserving crop management practices such as integrated
pest management (IPM) or reduced tillage; and more effective "diversity
by design" through adoption of new cropping patterns, farming
systems, and land management systems (featuring staple cereals)
that capitalize on the advantages of system diversity to sustainably
Sustainable productivity improvement in
marginal, fragile areas -- acknowledging that we can reduce but
not eliminate pressure to cultivate biologically diverse areas
unsuited to agriculture -- would again require varieties, crop
management practices, cropping patterns, farming systems, and
land management systems that can offer leverage points.
As "demand-led diversification"
takes hold, scientists, extension workers, farmers, and policy
makers must foster sustainable management strategies. A greater
temporal and spatial diversity of enterprises does not necessarily
imply improved sustainability. New fruit and vegetable crops can
exacerbate or ameliorate problems of erosion, soil fertility loss,
water-induced land degradation, external input dependence, or
In the end, it is not a case of competition, but of complementarity. It is not a case of "Green Revolution" vs. "alternative agriculture," or "diversity by design" vs. "demand-led diversification." We must use all of the tools at our disposal -- following all promising paths -- to reach our common goals.
Larry Harrington is Manager, Natural Resources Group, Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT)