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

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Grasslands of the world
faults in the management system and is associated with high grazing pressures ;
several mechanisms are involved according to vegetation type and management
system. Unpalatable shrubs may increase when the more palatable ones are
overgrazed; if little dry herbage remains in the non-growing season there may
not be hot enough fires to control the bush. Goats browse much more than
cattle and mixed grazing is probably less favourable to bush establishment than
cattle alone; goats may be used to browse regrowth after fire . Herbicides are
used in some commercial systems ; they are favoured in South Africa and used to
prepare land for over-seeding in the Campos . Bush encroachment is mentioned
in many of the studies. Indigenous plants are usually involved but alien shrubs
and trees can be very invasive: the Australian study mentions Acacia nilotica ,
which is a highly respected source of browse and pods in Africa, Pakistan and
India ; Opuntia spp. are pasture weeds in many areas outside their homeland;
Prosopis velutina , which has been widely used for revegetation of degraded dry
areas in parts of Africa, northern India and Pakistan, invades grazing land and
forms dense thickets; in wetter areas, Lantana camara is a widespread pest; and
in high-rainfall zones , guava (Psidium spp. ) colonizes grazing land.
Fire
Controlled fire is a major factor in determining the composition of grasslands
and a widespread and powerful tool in grassland management . Its effect depends
on its intensity, seasonality, frequency and type . The intensity depends on the
type, structure and abundance of fuel. It is mentioned in most of the studies,
except in those with more arid climates. Fire is used to remove unpalatable
grass and enable regrowth and access to the young herbage by grazing stock.
It often stimulates regrowth and supplies a green bite when most needed.
Fire is also used, as discussed above, to control woody vegetation . Burning of
grassland must be carefully controlled and timed, otherwise it can cause serious
damage; this is not discussed in any of the studies, although planning burning
and controlling fire is difficult and labour-consuming. Since fire has so severe
an effect, burning must take the whole ecosystem into account, not only the
grass and the grazing livestock. Ill-timed fire can have a devastating effect on
wildlife , including nesting and young birds . Most developed countries have
regulations governing burning of natural vegetation. For example periodic
burning is necessary to maintain the Calluna -dominated pastures of the United
Kingdom; strips are burnt in different years to produce a mosaic of heather
of different ages. Burning is regulated by law and the season is defined to
minimize damage to wildlife according to a “Muirburn Code” (The Scottish
Executive 2003). Uncontrolled fire is, of course, a risk in many areas. It may
occur spontaneously through lightning strike, but very often it is due to
careless grassland burning, through fires lit to drive out game or through arson.
The Mongolia study mentions the care taken by herders to avoid grassland
fire – in Mongolia’s cold winter there would be no regrowth and burnt herbage