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

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Grasslands of the world
VEGETATION PATTERNS
While the Central Plains grassland of North America is often divided into three
subdivisions, as noted earlier, the patterns are more complex at finer scales.
For example, Sieg, Flather and McCanny (1999) show 24 major vegetation
types extending from Canada to the coastal prairies in Texas. Similar rangeland
also occurs in northern Mexico. Woody vegetation types embedded in the
grassland includes aspen parkland in the north, mesquite -acacia savannah,
shinnery oak savannah, cross timbers, mesquite-buffalo grass , juniper -oak
savannah, oak-hickory forest and oak-hickory-pine forest in the south (Sieg,
Flather and McCanny, 1999). These woodland types have been described in
more detail by Dahl (1994), McClendon (1994), Pettit (1994), Engle (1994)
and Smeins (1994). Several species of juniper have expanded into grasslands in
recent times. In Oklahoma some estimates of expansion of eastern red cedar
(Juniperus virginiana ) are as high as 113 000 ha annually (Engle, 2000; Gehring
and Bragg, 1992). In Texas, ash (Juniperus ashei ) and redberry (Juniperus
pinchoti ) junipers have also expanded into grasslands (Smeins, 2000). Reduced
fire intensity and frequency is considered one of the primary factors in this
expansion (McPherson, 1997).
Major grass dominants in the tall-grass prairie (Plate 6.6) are big bluestem
(Andropogon gerardii ) little bluestem (Schizachyrium scoparium ), Indian grass
(Sorghastrum nutans ) and switchgrass (Panicum virgatum ). In the mixed -grass
prairie (see Plates 6.7, 6.8 and 6.9), needle-and-thread grass (Stipa comata ) and
western wheatgrass (Pascopyrum smithii ) are common grasses, but many other
species are abundant on specific sites. Sims (1988) states that the vegetational
Plate 6.6
Tall-grass prairie – Sheyenne National Grassland area, North Dakota, USA .
JEFF PRINTZ, USDA-NRCS