Impacts on Weeds - Climate Resilient Agriculture for Ensuring Food Security - page 194

not occur at problem levels in the US Corn Belt.
Studies have shown that itch grass, a profusely
tillering, robust grass weed, could invade the cen-
tral Midwest and California with only a 3 °C
warming trend (Patterson 1995 ). Witch weed, a
root parasite of corn, is limited at this time to the
coastal plain of North and South Carolina. With
an increase of temperature of 3 °C, it is specu-
lated that this parasite could become established
in the Corn Belt with disastrous consequences.
The current distribution of both Japanese honey-
suckle and kudzu is limited by low winter tem-
peratures. Global warming could extend their
northern limits by several hundred miles.
As mean temperatures increase, some weeds
will be able to expand their range into new areas.
The tropical weed prickly acacia ( Acacia nilotica
ssp. indica ) is likely to spread south (Kriticos
et al. 2003 ) and athel pine could spread through-
out inland rivers as far south as the Murray River
in Victoria.

10.5 Expansion of Geographical

Distribution

Lowland species such as lantana ( Lantana
camara ) may be able to shift into the uplands
(McFadyen 2008 ). Weeds moving into alpine
areas could have a particularly severe impact
because many alpine plant communities are
localized with rare endemic species, and there are
numerous weed species at lower altitudes
(McDougall et al. 2005 ). On subantarctic Heard
Island, the weed winter grass ( Poa annua ) has
been spreading rapidly on deglaciated sites (Scott
and Kirkpatrick 2005 ).
The number of documented examples to pro-
mote potential range expansion in invasive plants
is increasing, and many of these are related to key
aspects of climate change, such as northward
range expansion in the northern hemisphere
(Table 10.2 ).

Table 10.2 Actual recorded range expansions of weeds or weed genotypes in the USA and Canada and associated
adaptive traits
Weed species Description of range expansion Adaptive traits References

Datura stramonium
(Jimsonweed)

Northward invasion
of Canadian and northeastern
US cropland since the 1950s

Heavier seeds, earlier
growth

Weaver et al. ( 1985 )
and Warwick ( 1990 )

Hypericum perforatum
(St John's wort)

Clinal variation across the
north-south axis of North
American distribution

Leaf size larger in
northern populations

Maron et al. ( 2004 )

Echinochloa
crus-galli
(barnyard grass)

Northward invasion
of Quebec from the USA
in the nineteenth century

More rapid maturation
at each life cycle stage

Potvin ( 1986 )

Panicum miliaceum
(proso millet)

Northward invasion into
Canadian cropland
by the early 1970s

Seed germination
and dispersal
characteristics

Bough et al. ( 1986 ),
McCanny et al. ( 1988 ),
and McCanny and Cavers
( 1988 )

Polygonum cuspidatum
(Japanese knotweed)

Range expansion in both
Ontario and British
Columbia, Canada

Genotypes with
different temperature
thresholds and
potential hybridization

Bourchier and
Van Hezewijk ( 2010 )

Setaria faberi
(giant foxtail)

Northward expansion
into Canadian cropland
by the 1970s

Varied life history
traits

Warwick et al. ( 1987 )

Setaria viridis
(green foxtail)

Survival at Churchill,
Manitoba at nearly 60N
latitude (normal range 45-55N)

Leaf production
at low temperatures

Douglas et al. ( 1985 )
and Swanton et al. ( 1999 )

Sorghum halepense
(Johnson grass)

Northward expansion by 5
latitude between 1926
and 1979

Northern populations
annual (versus perennial
southern population)

Warwick et al. ( 1986 )