TheImprovement ofTropical and Subtropical Rangelands

118 IMPROVEMENT OF TROPICAL AND SUBTROPICAL RANGELANDS
and animals, and adjust schedules and livestock numbers to changing
conditions.
Forage production on rangelands, though controlled to a large
extent by range site characteristics, is critically tied to the health
of the root system in perennial forages and to seed production in
annual forages. Consequently, grazing strategies must be developed
to maintain a healthy root system in perennial forages and an optimal
seed yield in annual forages. Specific grazing practices to maintain
productivity will necessarily vary with the limitations of the site and
weather during the growing season. Roots can succe88fully grow and
support a forage crop under grazing when the intensity and time
of use is properly controlled. Individual plants need to grow, to
photosynthesize, and to replace damaged or senescent tissue every
year. This can be accomplished by closing an area to grazing during
the growing season, by stocking lightly enough that the livestock
remove forage at a rate slower than the growth rate of the forage, or
by rotating use 80 that forages are ungrazed during critical periods
of the growing season. Any of these approaches can be successful
when the specific growth patterns of the forages are known or can be
estimated.
Since most rangelands are made up of a complex of species,
grazing must consider availability and palatability of the vegetation
produced each year. Livestock will not graze all individual plant
species uniformly unless the pasture is overgrazed or grazing is carefully
designed to produce a uniform pattern of grazing that provides
for sufficient vigor to produce the next crop. Within a given site,
different plant species will maximize their growth at different times
of the growing season. As the plant community develops, there is
a continual change in relative proportions of different plants and,
therefore, a continually changing availability of forages. Along with
the changes in availability, there are changes in palatability among
species or changes in palatability related to the growth stages of the
constituent plants.
IT grazing is unmanaged or managed without consideration of the
dynamic nature of the plant community, some forages will be used
heavily while others are lightly used or not used at all during the
period when interspecific competition is critical. Desirable forages
that consistently are at a disadvantage because of differential grazing
will lose to the more competitive plants. This will change, and usually
reduce, the productivity of the range site. IT grazing is designed to
take advantage of the natural community dynamics of a range site,