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

234
Plate 6.13
Grassland with sagebrush near Salt Lake City, Utah.
Grasslands of the world
prairie vegetation in North Dakota. Agropyron smithii , Carex pennsylvanica and
Stipa comata were dominant species on rolling upland with fine-textures soils,
while sites at lower elevations with medium-textured soils supported stands of
Sporobolus heterolepis . In short-grass vegetation in New Mexico, blue grama was
present in all topographic positions, while Lycurus phleoides , Aristida wrightii ,
Stipa neomexicana and Bouteloua curtipendula occurred on upper slopes.
Sporobolus cryptandrus and Muhlenbergia torrey i along with blue grama were
dominant on lower slopes, with blue grama and buffalo grass , Muhlenbergia
repens and Hilaria jamesii in moister depressions (Beavis et al., 1981).
There is also a north-south gradient in the relative proportion of C3 and
C4 species (Sims, Singh and Lauenroth, 1978). C4 species comprise more than
80 percent of the flora from 30° to 42°N, while C3 species increase dramatically
north of 42°N (Sims, 1988).
PRIMARY PRODUCTION
Several environmental variables act to control primary production in the
Central Plains grasslands in North America. Precipitation, as it is translated
into soil water content through infiltration, is often considered the main
control for primary production (Laurenroth, 1979; Sims, Singh and Lauenroth,
1978; Sims and Singh, 1978a, b). Several studies have provided regression
analyses showing the relationship between precipitation and above ground
net primary productivity (ANPP ). Lauenroth (1979) showed a linear
relationship between ANPP and mean annual precipitation for 52 grassland
sites around the world, with r 2 of 0.51 under mean annual precipitation
ranging from about 100 mm to about 1500 mm. Later, Lauenroth, Burke and
DUANE McCARTNEY