TheImprovement ofTropical and Subtropical Rangelands

204 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS
prevent the establishment of the seeded species, should be planned
with a sensitivity for ways to maintain the overall diversity of the
plant community. Further, range techniciana who select species for
seeding should include those that will have a high degree of adaptability
and longevity on the lite to be revegetated. Where possible,
seeds of desirable species from the local area should be included in
the eeed mixture. Subsequent management practices should seek to
avoid highly selective grazing that damages only certain species that
are needed to maintain the diversity and the stability of the range
ecosystem.
PLANT IMPROVEMENT
Plant improvement consists for the most part ofdeveloping genotypes
that are superior when compared with the average of the
species or genetic entity. Although the selection of superior types
is the most expeditious way to obtain improved plants, by crossing
genotypes that have particularly valuable features, a new entity is
created that combines the desired features of the original parents into
one. Thus, the plant breeder is able to produce plants that are more
specialized than those that previously existed. However, this degree
of specialisation can limit the range of adaptation of the improved
genotype, unle88 its selection and performance testing are done in an
environment similar to that of the sites where the improved plant is
to be established.
Ideally, a species to be used in range seedings needs to possess
vigor, as well as considerable variation, in order to fit into the diverse
niches and environments of rangeland sites. Although it is desirable
to have uniform and highly productive species, it is also important
to have sufficient genetic diversity within a population that some
individuals survive and prosper in various rangeland situations. In
range plant improvement, it is possible to make selections from the
diverse gene pool of existing gr&88eB, forbs, trees, and shrubs in
order to identify the superior types available. A. newer techniques
in biotechnology become available, they can also be applied to the
challenge of unlocking the great reservoir of variability and uaeful
features in arid and semiarid plant populations. The breeding of
more specialized varieties, as has been done for pasture gr&88eB and
legumes, serves as an example of what can be done for tropical and
subtropical rangelands.