TheImprovement ofTropical and Subtropical Rangelands

REHAB1LlTATlON TECHNIQUES 161
Plant Materiah The plant Ipecies selected for seeding must be
compatible with management objectives (for example, palatability
and growth period). It is important to use only those species and
varieties well adapted to the lOil, climate, and topography of the
specific lite being revegetated. If native species are chosen, seed
of local origin should be used. Improved ecotypes, varieties, and
introduced species may be available for revegetation and should be
used. Species chosen for seeding must not only be adapted to the site
but also appropriate for the future use and management capabilities
of the lite. (See chapter 8 for more details on plant selection.)
Plant DifJernt, A diverse ground cover will generally result
in reduced lOil erosion, and mixtures of grasses, forbs, and shrubs
will better meet the multiple needs of the land user. The danger
in monocultural seeding is that disease or insect infestation can
eliminate the one species planted, whereas in a mixture, the differing
characteristics of the various speciel would better assure a higher
percentage of survival. The numerous ecological niches of variable
terrain generally support higher levels of species diversity.
Seetl Treatment The dormancy of most seeds can be overcome
through the use of pretreatmentl designed to IOften, puncture, wear
away, or Iplit the seed coat in order to render it permeable without
damaging the embryo and endosperm within. They include physical
and biological methods, dry heating, and soaking in water or chemicallOlutions.
For further information, see Willan (1985). Various
microbial treatments, IUch as nitrogen-fixing bacteria or mycorrhizal
fungi, may enhance seedling lurvival.
Seetling Rates It is important to use enough seed to establish
adequate plant densities, but not more seed than necessary to accomplish
this. Too much seed can produce a Itand of seedlings 10
thick that individual plants compete with each other. Species of
plants, the number of pure live seedl (PLS) per kilogram, and the
potential productivity ofthe site are major factors in determining the
rate of seeding. PLS il determined by multiplying the germination
of a lot of seed by its purity. Seeding rates providing 125-250 PLS
per m 2 should be used when the seed is placed in the lOil with a
drill. Broadcast seeding is an inefficient method of revegetation, and
should be used only where other methods cannot be used. Many
broadcast seeds are left on the soil surface where germination and