Importance of species replication in understanding plant invasions into North American grasslands - Invasive Plants: Ecological and Agricultural Aspects - page 43

Importance of species replication in understanding
plant invasions into North American grasslands
Brian J. Wilsey
Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA 50011,
USA
Introduction
The global homogenization of the Earth's biota is expected to increase due to
the increase in movement of people and goods between regions, and many
introduced species are having a negative economic impact. The increase of
introduced species can be thought of as a major global change, because
ecosystems throughout the world are now impacted by exotics [1, 2].
Grasslands, which cover roughly 25% of the globe, contain perhaps the most
disrupted and homogenized communities in the world. Native grasslands have
been lost because of land conversion, and native species have been replaced or
displaced with introduced grasses and legumes. Many species were intention-
ally introduced during the early 20th century to prevent erosion or to improve
grazing, and many have undoubtedly done so. However, as management objec-
tives for grasslands have expanded to include wildlife habitat, biodiversity, and
C sequestration, it has become critical to understand how introduced species
are affecting these new objectives as well. For example, Christian and Wilson
[3] found that areas in Saskatchewan, Canada, dominated by the introduced
forage grass Agropyron cristatum are sequestering less C into their soils com-
pared to developing native prairie stands with similar land use histories.
Exotic species have been planted or have spread to become common or even
the dominant species in many grasslands in the US. For example, the grasses
Bromus inermis and Agropyron cristatum are dominant grasses in much of the
Northern Plains region (e.g., [3, 4]), species of the genus Centaurea dominate
some Rocky Mountain grasslands [5, 6], exotic annuals dominate California
(e.g., [7]), Agropyron desertorum dominates much of the inter-mountain west
(e.g., [8-10]), and the grass Bothriochloa ischaemum dominates most central
Texas grasslands [11]. The spread of these species has occurred within a very
short time span. For example, it is stated in the 1979 Flora of Texas that
Bothriochloa ischaemum was 'not persisting except in cultivation or along
roadsides'. The spreading of exotic species, their impact on native communi-
ties, and the global homogenization of the flora and fauna makes this an
important global issue [1, 12-14].