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

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Grasslands of the world
perennials does not exceed 20–40 percent. Steep slopes are covered by
Aristida rufescens and Loudetia simplex . The percentage of bare soil is high
(90 percent), indicating serious erosion. Colluvions are covered by Panicum
maximum and Hyparrhenia variabilis .
The southern savannahs are the largest of the regions. The topography
is vast plains. The region has low rainfall and few rainy days. Toliary is the
driest area, with 275 mm over 27 rainy days. There is great inter-year variability.
The rainiest months are December to February. Water is a problem
for stock between April and November. The south is renowned for its big
herds of zebus and small stock. The population live in “a cattle civilization”.
Heteropogon contortus is the commonest grass on soils not subject to
waterlogging. According to the topography and the degree of erosion, some
species can dominate; this is the case for Loudetia simplex and Aristida spp. ,
which occupy degraded slopes. Hyparrhenia rufa , Hyperthelia dissoluta and
Cynodon dactylon occupy areas that may receive runoff. Cacti (Opuntia
spp. ) are characteristic fodder plants. The extreme south, on limestone, has
characteristic thorn-scrub, with many endemic plants, dominated by tall
Didieraceae.
Many forages have been grown successfully, but only a few dairy farmers
grow them. Pasture improvement by over-sowing with Stylosanthes guyanensis
and S. humilis was tested on a large scale in the mid-west in the early
1970s, but, after initial promise, the legume was wiped out by anthracnose.
SOUTH AMERICA
The Llanos
The Llanos of Venezuela (Vera, 2003) are part of the 50 million hectares of
savannahs in the Orinoco River basin. The vegetation communities can be
divided into four main subregions.
The Piedmont Savannahs consist of large alluvial areas and terraces covered
originally by semi -deciduous forests and savannahs, though the latter
predominates. They are southeast of the Andes and descend gradually to the
plains. They are characterized by a rich tree flora, shrubs and grasses, most of
which are common to the other types of savannah. These include Andropogon
selloanus , A. semiberbis , Axonopus canescens , A. purpusii , Bulbostylis spp.,
Elyonurus adustus, Leptocoryphium lanatum , Panicum olyroides , Paspalum plicatulum
, P. gardnerianum , Trachypogon plumosus , T. vestitus and T. montufari.
On average, the maximum aboveground stand of savannah reaches 7 t/ha/yr,
with about twice that amount below ground.
The savannahs of the High Plains or Mesas are north of the Orinoco, at
150–270 m, descending into the Llanos de Monagas. They are covered by
a deciduous tree savannah where the herbaceous layer predominates and is
dominated by Trachypogon plumosus or T. vestitus , with Andropogon selloanus
, Axonopus canescens and Leptocoryphium lanatum as subdominant grasses.