Agriculture Reference
In-Depth Information
Cyclones can create new opportunities for
weed invasion through associated fl ooding, soil
movement, and damage to native vegetation
communities. During cleanup activities, it is
important to limit further spread by minimizing
the movement of soil or plant material from one
area to another.
When native vegetation is stressed or
destroyed by droughts, fi res, fl oods, or severe
storms, weeds gain new opportunities to replace
native species.
There is a huge pool of invasive plants avail-
able to colonize bare spaces left by drought, fi re,
and storm damage, and wind and fl ooding waters
help spread weeds.
Many of Australia's worst weeds benefi t from
extreme events, including at least 13 of the coun-
try's 20 weeds of national signifi cance. Athel
pine (
Tamarix aphylla
), for example, spread
along 600 km of the Finke River in central
Australia after severe fl ooding in the 1970s and
1980s, replacing river red gums. It could spread
much further under climate change.
Serrated tussock (
Nassella trichotoma
)
benefi ts from bare patches created by droughts,
marram grass (
Ammophila arenaria
) and bitou
bush (
Chrysanthemoides monillfera rotundata
)
from storms, and willows (
Salix
spp.) from
fl oods. Climate change-altered fi re regimes will
also favor some weeds, particularly fi re-promoting
exotic pasture grasses.
10.6
Varying Precipitation
Patterns
Response to drought in agronomic conditions is
dependent on species and cultural conditions.
Any factor which increases environmental stress
on crops may make them less competitive with
weeds (Patterson
1995
).
Weeds constrained by rainfall may also fi nd
new habitats under new climate conditions.
Lantana and mist fl ower (
Eupatorium riparium
),
for example, could expand if rainfall increased in
some areas (McFadyen
2008
).
10.7
Increased Dispersal
If fruit-eating birds arrive earlier and leave later
for migration, as has been occurring, fruit-bearing
weeds may benefi t from greater dispersal.
Higher temperatures and other factors are likely
to increase insects' breeding cycles and provide
more weed pollination (Gallagher et al.
2006
).
As animals, including invasive species, move
into new areas in response to climate change,
they are likely to spread weeds or create distur-
bance advantageous for weeds.
10.8
Extreme Weather Events
Extreme events including droughts, fl oods, and
cyclones can sometimes create ideal conditions for
weeds to extend their range and invade new areas or
outcompete native species in their existing range.
Dry soil conditions caused by drought prolong
the longevity of weed seed banks; and importing
fodder and grain into drought areas can bring
new weed problems to the region. Drought can
reduce the competitiveness of native vegetation,
providing new opportunities for weed invasion.
Floods can spread weeds along water courses
into areas that were previously free of weeds. By
washing away vegetation and exposing areas of dis-
turbed soil, fl oods can also provide opportunities
for new weed invasions by reducing competition
from existing plants.
10.9
Human Health
Weeds are recognized by the general public as
signifi cantly affecting human health either
through allergenic reactions, skin irritations,
mechanical injury, or internal poisoning (Ziska
2001
). For the most part, we are only in the initial
stages of quantifying how changes in climate
and/or CO
2
may affect those specifi c weeds asso-
ciated with public health. One exception has been
changes in pollen production and allergenicity in
common ragweed (a recognized cause of allergic
rhinitis) with changing CO
2
and temperature in
both indoor (Ziska and Caulfi eld
2000
; Wayne
et al.
2002
) and in situ experiments (Ziska et al.
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