Agriculture Reference
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ecological presence of alien grasses has been attributed to rangeland deterioration
caused by land use changes associated with plowing, landscape clearing and
burning, and soil nutrient enrichment resulting from fertilizer run-off and
nitrogen-fixing leguminous species (Milton 2004 ).
Concern has been raised that while alien grasses may not represent a major issue
in landscape flammability today in the Cape region, this problem of grass invasion
may increase in the future with global climate change. A recent study addressing
this issue used climate modeling to predict the future distributions of 29 species of
C 3 annual grasses from the Mediterranean Basin (Parker-Allie et al. 2009 ). The
authors concluded that future climate warming will broadly hinder the spread of
mediterranean annual grasses in South Africa, with all but one species predicted to
have a contraction in their current range of distribution. However, the predicted
shifts in distributions of these grasses into pristine higher elevations with climate
warming in the Cape region may alter existing fire regimes and thus pose a threat
to the natural vegetation. The authors also pointed out that rising atmospheric
CO 2 levels could mitigate the negative impacts of climate warming and thus allow
alien C 3 grasses to persist in more arid lowlands.
Southwestern Australia
Much like the situation in South Africa where oligotrophic soils have restricted the
extent and relative dominance of establishment of annual grasses from the Medi-
terranean Basin, the extensive areas of heathland, mallee, and eucalypt woodland
growing on poor soils in the MTC region of southwestern Australia have
been relatively impervious to the invasion of alien annual grasses. However, one
exception to this pattern lies with local areas of eucalypt woodlands on richer
soils which are readily invaded by mediterranean alien grasses (Abensperg-Traun
et al. 1998 ).
Banksia woodlands of southwestern Australia have been impacted by many
changes since European settlement 150 yrs ago. These changes included fire
frequency and intensity, nutrient inputs, and the introduction of alien species
(Bridgewater & Backshall 1981 ) followed by an increase in exotic propagules
(Fisher et al. 2009a ). While Banksia woodlands are dominated by native species
that are fire adapted (Hobbs & Atkins 1990 ), when fires become too frequent
(Hopkins & Griffin 1989 ) or there are impacts from human activities that enrich
soil nutrient pools, the resulting increase in resource availability makes the com-
munity vulnerable to invasion (Milberg & Lamont 1995 ).
As a result of impacts associated with frequent fire and nutrient enrichment,
many areas of Banksia woodland have become altered from a species-rich, sclero-
phyllous, tree and shrub dominated community to one with an understory dom-
inated by alien annuals and/or herbaceous perennials (Bridgewater & Backshall
1981 ; Fisher et al. 2009b ). The invasion of these species has been described as an
example of a classic grass fire feedback cycle, with the light grass fuels promoting
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