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

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Grasslands of the world
Semi-deserts and shrub steppes
Semi-deserts and shrub steppes (Units Kg 11 and Kf 11 in Figure 4.5) exhibit
similar latitudinal extents; together, both variants of semi -desert cover 22 percent
of the region, with plant communities of low diversity, including, on average,
19 plant species (Golluscio, León and Perelman, 1982). The MAP of much of
the area is less than 150 mm. Patagonian semi-deserts are less productive than
shrub steppes; ANPP calculated from NDVI -I values by Paruelo, Jobbágy and
Sala (1998b) are 450 and 390 kg/ha/yr for units Kg 11 and Kf 11, respectively
(Table 4.1). From a species composition standpoint, Kf 11 is the most typical
and less degraded semi-desert type , in spite of being less productive (Soriano,
1983). Dwarf shrubs with cushion habits are typical of this vegetation type in the
Kg 11 and Kf 11 units. Nassauvia glomerulosa , N. ulicina and Chuquiraga aurea
are dominant, accompanied by others such as Chuquiraga kingii , Brachyclados
caespitosus and Perezia lanigera (León et al., 1998). Grasses such as Stipa
humilis , S. ibarii , S. ameghinoi and shrubs such as Chuquiraga avellanedae ,
Schinus polygamus and Lycium chilense are secondary species in semi-desert
plant communities . Some co-dominant species occur, but only in the Kg 11
semi-deserts: dwarf shrubs such as Azorella caespitosa , Mullinum microphyllum
and Frankenia sp. , grasses such as Poa dusenii , P. ligularis and, less frequently,
Stipa neaei , and shrubs such as Junellia tridens , which occur in clumps on paleodepressions
and natural drainage networks (León et al., 1998; Roig, 1998).
Shrub-grass and grass-shrub steppes
Shrub-grass and grass-shrub steppes span almost the entire latitudinal extent
of Patagonia and cover approximately 20 percent of the arid area (Units Jf 11
and Jd 12 in Figure 4.5). According to Paruelo, Jobbágy and Sala (1998b), both
types have similar ANPP levels (650 kg/ha/yr), although NDVI values peak
somewhat later in the growing season in grass-shrub steppes . Vegetation cover
of the shrub-grass steppes is 47 percent, with plant communities that contain
about 26 vascular plant species (Golluscio, León and Perelman, 1982). Adesmia
campestris , Mullinum spinosum , Senecio filaginoides , Berberis heterophylla ,
Colleguaya integerrima , Trevoa patagonica and Schinus polygamus are the
most conspicuous shrubs (León et al., 1998). The most important grasses are
Stipa speciosa , S. humilis , Poa ligularis , P. lanuginosa , Festuca argentina and
F. pallescens , and occur with sedges of the genus Carex (León et al., 1998).
Grass -shrub steppes are a transition between the shrub steppes and grass
steppes on the one hand and the grass-steppes and the Nothophagus subantarctic
forest ecotone on the other (Figure 4.5) (Roig, 1998). Paruelo, Jobbágy and
Sala (1998b) combine the latter (Chiliotrichum diffusum grass-shrub steppes)
and the steppe-forest ecotones in southern Santa Cruz and northern Tierra
del Fuego into a single biozone (unit Ha 12). Physiognomically, these are
different domains; they may exhibit similar functional attributes and should
be significantly more productive than the grass-shrub steppes at the opposite