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

MAE ELSINGER
Grasslands of central North America 235
Gutmann (1999) presented similar analyses for a much larger data set from
central USA grasslands for normal rainfall, favourable and unfavourable
rainfall patterns. The r2 values were 0.56 for normal years, 0.66 for favourable
years and 0.43 for unfavourable years (favourable years represent the wettest
10 percent of the years; unfavourable are the driest 10 percent of the years;
and normal the middle 80 percent (Soil Conservation Service, 1973)). Of
course, the ANPP–precipitation relationship is not linear over the complete
range of precipitation values, and often annual precipitation is a relatively
poor predictor of ANPP or end-of-season standing crop (Pieper, 1988).
For example, Smoliak (1956) found that May-June precipitation was highly
related to end-of-season standing crop in northern Great Plains short-grass
prairie (r2 = 0.86), while Hart and Samuel (1985) found a high correlation
between spring -summer precipitation and herbage yield in short-grass
vegetation in eastern Wyoming (r2 = 0.95). Since primary production is so
closely related to precipitation, the general pattern of primary production
(Plate 6.14) follows those gradients of precipitation, increasing from west to
east. Lauenroth (1979) reported that general average annual production was
about 200 g/m2 for short-grass, 300 g/m2 for mixed -grass prairie and 500 g/
m2 for USA International Biological Programme locations. These general
averages mask the tremendous variation across these grasslands. For example,
Risser et al. (1981) reported that above ground peak live standing crop for
23 tall-grass locations varied from 180 g/m2 at Junction, Kansas, to nearly
600 g/m2 in Oklahoma County, Oklahoma.
Plate 6.14
Estimating annual biomass productivity on the Monet Prairie Farm Rehabilitation
Area, Saskatchewan, Canada.