Landscape Diversity and Agroecosystem Management - Agroecology: The Ecology of Sustainable Food Systems - page 317

inputs, relying on biological controls, diversifying crop-
ping systems, allowing successional processes to proceed
further — all these practices contribute to creating more
environmentally friendly agroecosystems. Assuming this
agroecologically based management, we will focus first
on the first principle — diversifying the agricultural land-
scape — and then later in the section, explore the ways
that the alternative management described in the second
principle can enhance the ability of the landscape to
provide environmental services.
The noncrop habitat patches in a diverse agricultural
landscape can interact with areas of agricultural produc-
tion in a variety of ways. An area of noncrop habitat
adjacent to a crop field, for example, can harbor popula-
tions of a native parasitic wasp species that can move into
the field and parasitize a pest. A riparian corridor vege-
tated by native plant species provides an example of a
more complex relationship: the corridor can filter out dis-
solved fertilizer nutrients leaching from crop fields, pro-
mote the presence of beneficial species, and allow the
movement of native animal species into and through the
agricultural components of the landscape.
As can be seen in these examples, landscape-level
diversification offers benefits to both native species and
agroecosystems. When diversification is carefully planned
and managed, these benefits can be maximized, and the
possible negative effects minimized. Effective landscape-
level management is thus an important part of achieving
sustainability.

of the farm by establishing and protecting appropriate
habitats (Jackson and Jackson, 2002). These habitats can
be within the farm fields, between fields, along road-
ways, in ditches, along property lines, or at the boundary
separating farm fields from housing areas. The habitats
can be permanent strips or blocks planted to diverse
noncrop perennials, or temporary patches within the farm
fields. Methods of creating such habitats include the
following:

• Plant a cover crop during the winter months.

The crop may provide critical food or cover for
a range of animal species, especially ground
nesting birds.

• Leave strips of unharvested crops such as corn

or wheat; these can provide resources for native
animal species.

• Where erosion control is necessary on a farm,

plant grassed waterways to enhance diversity and
achieve important environmental protection goals.

• On terraced hillsides, plant perennial grasses or

shrubs on the walls separating the terraces.

• Plant perennials on land that is marginal or

susceptible to erosion, or restore this land to a
more natural state by allowing natural succes-
sion of native species.

• Restore poorly drained or semipermanent

wetland sites on the farm to natural wetlands.

• Retain native trees in and around fields as nesting,

perch, and hunting sites for native birds.

• Provide artificial perches for native raptors,

and bird boxes for other potentially beneficial
bird species.

O N -F ARM D IVERSIFICATION

The farmer can actively encourage and maintain the pres-
ence of native species on the intensively managed areas

LANDSCAPE DIVERSITY IN TLAXCALA, MEXICO

In Tlaxcala, Mexico, rain comes in periodic heavy bursts capable of causing severe erosion. In addition, many local
farmers must grow their food on steep, erosion-prone slopes. To deal with this situation, they cultivate hillside terrace
systems that not only prevent soil erosion, but also effectively conserve rainfall runoff and provide the basis for
exceptional landscape diversity (Figure 22.4). These systems, which make use of water- and sediment-trapping catch-
ment basins called cajetes , have enabled traditional farmers in this region to maintain the integrity and fertility of the
soil for centuries without relying on imported, commercially produced inputs such as fertilizers (Mountjoy and Gliess-
man, 1988).
The high degree of landscape diversity in the Tlaxcala terrace systems comes from having a large amount of
permanent border space between cultivated terraces covered in natural vegetation. The border areas occupy the edges
of the terraces, above and below the cajetes. They are vegetated with a highly diverse mixture of perennials, trees,
and weeds, achieved by allowing natural succession to occur. The plants in the borders help cycle nutrients, prevent
erosion, and provide habitat for beneficial organisms. Wild relatives of the crop plants often flourish in the border
areas also, providing a potential source of gene flow that may help the crops maintain their hardiness and resistance.
Because the terraces are long and narrow, no crop plant is ever more than 6.5 m from a field border. Approximately
30% of the farming landscape is made up of border vegetation, while at any one time about 60% or less of the land is
being farmed and 10% or more left fallow. By all measures, these hillside systems are very diverse, and designed
to take full advantage of all that landscape-level diversity has to offer.