INTENSIVE AGRICULTURE

Much of the less spectacular desert land in the southern USA and northern Mexico has been converted to agricultural use, supported by irrigation canals that draw water from the major rivers such as the Colorado River. The crop yields can be very high because of the warm growing conditions in these regions. The high-value market crops grown in these conditions include onions, peppers, tomatoes, alfalfa, citrus crops, grapes and nuts such as pecans and walnuts. Some examples are shown in the images below.

However, the ecological impacts of this are raising concerns, for at least two reasons.

• Many of these intensively farmed crops rely on the use of insecticides and herbicides, which can seriously affect the populations of native pollinator species (moths and bees). The insecticides can kill these organisms, and the herbicides destroy the native "weed" plants that provide pollen and nectar for insects.

• The widespread conversion to agricultural use causes fragmentation of the desert habitat, which can seriously disrupt the migration of pollinators and other migratory species (e.g. hummingbirds, bats, hawkmoths, monarch butterflies). These animals need "corridors" of wild vegetation on which they can feed during their annual migrations.

Intensive agriculture in Northern Mexico

Irrigation canal near Yuma, USA, immediately next to the Mexican border

Irrigated fields (right) compared with the native vegetation (left of the irrigation ditch)

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