Invasive and weedy plants and global change

Potential impacts of invasive and weedy plants

Causes of invasion success

Interactions with other global change factors

REWM 3500Rangeland Plant EcophysiologyNovember 23, 2009

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

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

Cheatgrass (Bromus tectorum) alters fire regimes in the Intermountain West

Native sagebrush steppeFire interval – 60 to 100 yrs

Invaded by cheatgrassFire interval – 5 yrs

Sperry et al. 2006

Cheatgrass invasion alters soil nitrogen cyclingS

oil d

epth

(m

)

C3 C4 Invaded/disturbed

Non-native weeds alter soil moisture regimes

Enloe et al. 2004

Annual grass dominated

Dominated by yellow starthistleCentaurea solstitialis

Dominated by perennial grass

Causes of plant invasions

• Enemy release

• High resource availability (disturbance, elevated CO2, nitrogen deposition)

• Novel weapons (allelopathy)

Blumenthal 2005

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

Ziska 2003 Response of grassland weeds to elevated CO2

Dashed line is the average response of other plants from literature

Blumenthal et al. 2008

Native monocots

Native dicots

Non-native dicotsDiffuse knapweedBaby’s breathDalmation toadflax

Increased snow inputs facilitate non-native dicot weeds

Novel weapons? Bais et al. (2003) - Allelopathy in spotted knapweed (Centaurea maculosa)