Invasive and weedy plants and global change

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REWM 3500 Rangeland Plant Ecophysiology November
23, 2009
Invasive and weedy plants and global
change Potential impacts of invasive and weedy
plants Causes of invasion success Interactions
with other global change factors
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Of the 400 million ha of rangeland in the U.S.
(42 of land area), more than 50 million ha is
infested with noxious weeds
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• Plant invaders can
• Completely alter the fire regime
• Alter nutrient cycling, hydrology, and energy
  budgets in a native ecosystem
• Greatly diminish the abundance or survival of
  native species

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Cheatgrass (Bromus tectorum) alters fire regimes
in the Intermountain West
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Invaded by cheatgrass Fire interval 5 yrs
Native sagebrush steppe Fire interval 60 to 100
yrs
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Cheatgrass invasion alters soil nitrogen cycling
Soil depth (m)
C3
C4
Invaded/ disturbed
Sperry et al. 2006
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Non-native weeds alter soil moisture regimes
Annual grass dominated
Dominated by perennial grass
Dominated by yellow starthistle Centaurea
solstitialis
Enloe et al. 2004
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• Causes of plant invasions
• Enemy release
• High resource availability (disturbance,
  elevated CO2, nitrogen deposition)
• Novel weapons (allelopathy)

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Blumenthal 2005
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Red brome (Bromus madritensis ssp. rubens) in the
Mojave desert is greatly enhanced by elevated
atmospheric CO2
Bromus versus native annuals
Bromus in fertile islands vs infertile interspaces
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Response of grassland weeds to elevated CO2
Ziska 2003
Dashed line is the average response of other
plants from literature
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Increased snow inputs facilitate non-native dicot
weeds
Blumenthal et al. 2008
Non-native dicots Diffuse knapweed Babys
breath Dalmation toadflax
Native dicots
Native monocots
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Novel weapons? Bais et al. (2003) - Allelopathy
in spotted knapweed (Centaurea maculosa)