Grasslands of the World.pdf - Disasters and Conflicts - UNEP

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Grasslands of the world
Balancing seasonal variations of forage supply
In more mesic situations, mixed operations are common, whereby animals are
raised under pasture or confined conditions in combination with cultivated
agriculture practices (Neumann and Lusby, 1986). In many cases, the number
of animals in these situations is relatively small.
Although grasslands have the potential to be grazed year long, they are
grazed mostly seasonally by livestock. In northern areas, inclement weather
largely precludes grazing during the winter (Holechek, Pieper and Herbel,
2001; Neumann and Lusby, 1986; Stoddart and Smith, 1955). Native grass hay
and alfalfa have been used extensively as winter feed in northern areas and as
supplemental feed in southern areas (Neumann and Lusby, 1986; Newell, 1948;
Rogler and Hurtt, 1948). Keller (1960) showed that wild hay (native grasses)
occupied over 3.6 million hectares in the six plains states, followed by alfalfa on
about 2.8 million hectares and cereal hay on about 0.4 million hectares.
Another factor involved in decisions for seasonal grazing is that of declining
nutritive quality of forage as the growing season progresses (Adams et
al., 1996; Rao, Harbers and Smith, 1973; Scales, Streeter and Denham, 1971).
Protein content of Great Plains forage generally reaches a peak during the early
summer period and declines sharply as the forage matures into winter (Adams
et al., 1996). During the late summer, forage quality was rated as moderate,
while in the winter it was rated as low quality. Other nutritional variables
often change in a similar pattern, such as phosphorus content, digestibility and
intake. Changes in nutritive quality of forage depend to some degree on species
composition: cool-season grasses (C3 ) have higher nutritive quality early
in the season than warm-season species (C4 ) that grow later, during the heat of
the summer. Presence of forbs may also increase mineral content of herbivore
diets (Pieper and Beck, 1980; Holechek, 1984). In New Mexico, protein and
phosphorus content of side-oats grama (Bouteloua curtipendula ) was significantly
lower than that of five other grass species (Pieper et al., 1978). Tall-grass
prairie plants often become coarse and relatively unpalatable late in the growing
season.
One approach to mitigation of the problems of low nutritive quality and
palatability of forage late in the growing season is intensive early stocking
(Bernardo and McCollum, 1987; Lacey, Studiner and Hacker, 1994; Smith and
Owensby, 1978; McCollum et al., 1990; Olson, Brethour and Launchbaugh,
1993). In Montana, early spring grazing was beneficial for most vegetational
characteristics compared with summer grazing, but livestock performance
was not reported (Lacey, Studiner and Hacker, 1994). In tall-grass prairie in
Kansas, intensive early grazing improved steer gains per unit area compared
with season-long grazing, resulted in more even utilization of the pastures
and increased desirable perennial grass production, but reduced gain per steer
(Smith and Owensby, 1978). Other studies in Kansas indicated that stocking
density could be increased 2 to 3 times by early-season grazing compared with