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

The South American Campos ecosystem 193
faster regrowth after grazing. Animal type , their genetics and aptitudes condition
the development of natural grasslands. Society is now promoting conservation
of natural ecosystems in managed recreation areas, where herbivores are
always landscape modellers. A number of technical reports on this situation
are available.
Forage from natural grasslands can only be marketed in the form of animal
products. Nationally, there is still an instinctive resistance, if not dislike,
to exploitation and use of natural grasslands through pastoralism (Tothill,
Dzowela and Diallo, 1989). The measure of communal grazing is yield per unit
of area, as the number of animals represents the economic value of the activity.
In the philosophy of managed ecosystems (ranching), yield per animal and
commercial value of the product represent the economic value. This philosophy
of forage use is based on management of pastures and stock in delimited areas,
with the possibility of external inputs. There are still many natural grassland
properties operating with the philosophy and yield of pastoralism, which could
attain the yield of managed ecosystems.
Until recently, stock rearers did not understand basic grassland management
technology: to maintain vegetation and make long-term decisions on sustainability
. The need is now appreciated of understanding natural grasslands and
recognizing the availability level that does not restrict animal intake, in order to
attain high individual performance and high per-hectare production.
Dry matter accumulation in natural grasslands
The climatic transition strip in the south of Brazil favours summer grasses,
which explains the seasonal differences in forage production (Apezteguia,
1994; Correa and Maraschin, 1994; Maraschin et al., 1997). In the cool season,
which covers from a third to half of the year, there is slower growth due to
low temperature, frost and irregular rainfall . Rejected forage increases errors
in pasture evaluation (Moojen, 1991). Native winter species contributed
17 percent of yearly DM production in Uruguay (Berretta and Bemhaja, 1991)
and 18 percent in Rio Grande do Sul (Gomes, 1996). But the warm season
covers two-thirds to half the year (Maraschin et al., 1997). Daily growth is
termed the DM Accumulation Rate (AR) and represents what can be grazed.
Table 5.6 shows ARs (in kg DM/ha/day) in a Rio Grande do Sul natural
grassland , influenced by forage offer (FO) levels per head and per day, with
corresponding residual DM (Moojen, 1991; Correa and Maraschin, 1994).
ARs increase with increasing levels of FO until more than 12 percent of
liveweight, and tends to decrease after FO exceeds 16 percent of liveweight.
Maximum recorded AR was 16.3 kg DM/ha/day, with an FO of 13.5 percent
of liveweight, which corresponded to forage availability of 1 400–1 500 kg DM/
ha at any time.
Unfertilized natural grasslands produced 2 075 to 3 393 kg DM/ha considered
as available forage, defining the number of animals that could be grazed on