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

Grasslands of central North America 249
changed little since European settlement, farming and other disturbances have
had a great effect. For example, Klopatek et al. (1979) showed that most counties
in the Great Plains had lost some of the potential natural vegetation , with
the greatest impact in the mesic eastern edge and the least disturbed being the
more xeric western short-grass plains. From 85 to 95 percent of the bluestem
prairie vegetation types had been converted to cropland (Sieg, Flather and
McCanny, 1999). These types of disturbance and vegetation shifts represent
habitat fragmentation for many wildlife species that developed in unbroken
tracts of grassland . Conversion to cropland created habitats for other species,
but loss of both plant and animal diversity in the grassland is a concern
(Sieg, Flather and McCanny, 1999; Leach and Givnish, 1996; Licht, 1997).
For example Sieg, Flather and McCanny (1999) reported that in the Canadian
province of Saskatchewan and six Great Plains states in the USA , 19 percent
of the breeding bird species declined in numbers from 1966 to 1996. However,
the number of listed, threatened and endangered (LT&E) plant and animal
species is relatively low compared with other regions of the country (Ostlie
et al., 1997; Sieg, 1999). No pattern of LT&E species could be discerned for
the Great Plains. Large blocks of counties showed no known LT&E species,
up to a maximum of 9–12 species. These counties were scattered throughout
the Great Plains (Sieg, 1999). Examples of LT&E species are the black -tailed
prairie dog (Cynomys ludovicianus), the black-footed ferret (Mustela nigrepes)
and the western prairie fringed orchid (Platanthera praeclara) (Sieg, Flather
and McCanny, 1999).
Other environmental concerns regard use of pesticides and herbicides, commercial
fertilizers, grazing by introduced domestic livestock, status of riparian
areas and introduction of invasive plants and animals. Crested wheatgrass was
introduced into the Great Plains in the early 1900s (Holechek, 1981; Rogler,
1960). The species played a major role in restoration of abandoned wheat fields
in the northern Great Plains in the 1930s (Rogler, 1960), but some workers
regard crested wheatgrass as an invader species leading to near monocultures.
One of the most troublesome introduced plant species is leafy spurge
(Euphorbia esula ) (Plate 6.22), a perennial forb accidentally introduced into the
USA from eastern Europe or western Asia (Biesboer and Koukkari, 1992). It is
an aggressive weed that currently infests over one million hectares in the USA
(DiTomaso, 2000) and over 650 000 ha in the northern Great Plains (Leistritz,
Leitch and Bangsund, 1995). Estimates of loss of livestock grazing because
of leafy spurge encroachment onto northern Great Plains rangelands were
736 000 Animal Unit Months (AUMs), or US$ 37 million annually (Leistritz,
Leitch and Bangsund, 1995).
Introduction of annual grasses such as Japanese brome (Bromus japonicus )
has also altered grassland vegetation (Haferkamp et al., 1993; Haferkamp,
Heitschmidt and Karl, 1997). Japanese brome occurs throughout the Great
Plains (Hitchcock, 1950) and often competes with native perennial grasses.