Invasive and weedy plants and global change Potential impacts of invasive and weedy plants Causes of invasion success

1. 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

2. 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

3. 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

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

6. Invaded by cheatgrass Fire interval – 5 yrs Native sagebrush steppe Fire interval – 60 to 100 yrs

7. Cheatgrass invasion alters soil nitrogen cycling Soil depth (m) C3 C4 Invaded/ disturbed Sperry et al. 2006

8. Non-native weeds alter soil moisture regimes Annual grass dominated Dominated by perennial grass Dominated by yellow starthistle Centaurea solstitialis Enloe et al. 2004

9. Causes of plant invasions • Enemy release • High resource availability (disturbance, elevated CO2, nitrogen deposition) • Novel weapons (allelopathy)

10. Blumenthal 2005

11. 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

12. Response of grassland weeds to elevated CO2 Ziska 2003 Dashed line is the average response of other plants from literature

13. Increased snow inputs facilitate non-native dicot weeds Blumenthal et al. 2008 Non-native dicots Diffuse knapweed Baby’s breath Dalmation toadflax Native dicots Native monocots

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