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 3500 Rangeland Plant Ecophysiology November 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 steppe Fire interval – 60 to 100 yrs Invaded by cheatgrass Fire interval – 5 yrs

Sperry et al Cheatgrass invasion alters soil nitrogen cycling Soil depth (m) C3C4Invaded/ disturbed

Non-native weeds alter soil moisture regimes Enloe et al Annual grass dominated Dominated by yellow starthistle Centaurea solstitialis Dominated by perennial grass

Causes of plant invasions Enemy release High resource availability (disturbance, elevated CO 2, nitrogen deposition) Novel weapons (allelopathy)

Blumenthal 2005

Red brome (Bromus madritensis ssp. rubens) in the Mojave desert is greatly enhanced by elevated atmospheric CO 2 Bromus versus native annuals Bromus in fertile islands vs infertile interspaces

Ziska 2003 Response of grassland weeds to elevated CO 2 Dashed line is the average response of other plants from literature

Blumenthal et al Native monocots Native dicots Non-native dicots Diffuse knapweed Baby’s breath Dalmation toadflax Increased snow inputs facilitate non-native dicot weeds

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