Livestock grazing for weed management - Ecological Management of Agricultural Weeds - page 409

9
Livestock grazing for weed management
Introduction
Cattle, sheep, goats, and other domesticated vertebrates graze more
than 50% of the earth's total land area, 20% in managed pastures and 30% in
rangelands (Snaydon, 1981). Animal production and cropland management
are also frequently linked. Animals graze the herbaceous understory in tree
crops and feed on residues and remnant vegetation in annual crop fields.
Animal manures are applied to croplands, and pastures and forage crops are
rotated with annual crops.
Domesticated herbivores can accentuate weed problems for humans. They
disperse weed seeds (Chapter 2). They graze preferred species heavily, but
leave unpalatable species to grow and reproduce. They compact soil around
watering holes, at resting sites, and along trails, which fosters grazing- and
trampling-tolerant unpalatable weedy vegetation. Introduced forage species
naturalize to become weedy invaders (Low, 1997).
However,through managed grazing animals can also reduce weedy vegeta-
tion and promote desirable forage species. This chapter illustrates three prin-
ciples for the use of livestock to reduce weeds in annual and perennial crops
and on grazing lands:
1. A weed's susceptibility to control by grazing depends on its growth habit , its life
cycle stage and the growing conditions at the time of grazing , and its palatability to
different herbivore species. The identification ofa weed's particular vulner-
abilities to grazing contributes to understanding why it has become a
problem or might become a problem.Whether a weed is vulnerable to
control by grazing also depends on the other plant species in the same
grazed area and their ability to tolerate and avoid grazing.In fact,a weed
in one context may be a primary forage species in another.
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