Invasive Plants and Fire Regimes

1. Invasive Plants and Fire Regimes Biol 255 October 28, 2004 Jen Costanza “Invaders that alter fire regimes are widely recognized as some of the most important system-altering species on the planet” Brooks et al. 2004

2. Overview • Effects of invasives on fire regimes • Mechanisms • Implications for management and restoration • Brooks et al. (2004) provide a synthesis • Tunison et al. (2001) show a parallel case study

3. Grass-fire cycle:D’Antonio and Vitousek (1992) Grasses: standing dead material, can dry out quickly; recover quickly after fire

4. Brooks et al. 2004

5. F = Frequency; I = Intensity; E = Extent; W = Window of fire activity (seasonality); T = Type

6. Fire Regime Ecosystem Properties Fuel Native Plants Alien Plants Impact Invasive Naturalized Introduction Brooks et al: Invasive Plant-Fire Regime Cycle Topography & Climate

7. Tunison et al. 2001 - HAVO • Some fire history, but a dramatic increase in frequency and extent since 1960 • Exotic grasses: beardgrass and broomsedge affected woodlands most • Native grasses rare, especially in woodlands • Cover and density of vegetation sampled for four ecosystems

8. ‘Ohi’a Dominated Woodlands Woodlands with Beardgrass Woody Vegetation Reduced Molasses Grass Increased Feral goats Broomsedge, Beardgrass, Molasses grass Fire Tunison et al. Fire Regime Cycle

9. Tunison et al. – Fire Effects on Other Ecosystems • Coastal Lowlands: Increase in native pili grass; native shrub species able to establish by resprouting • Rainforest: Rapid recovery of native vegetation • Montane Mesic Forest: Shift in native species; no increase in alien cover

10. Effects of Invasive Plant – Fire Regime Cycle • Localized extirpation of species that cannot persist under new regime • Alternative stable states/change in succession • Alterations to climate (D’Antonio and Vitousek 1992) After Huston (1979)

11. Management OptionsBrooks et al. • Phase 1: Evaluate intrinsic properties of invader • Species Exclusion • Phase 2: Evaluate potential for significant impact • Qualitative vs. quantitative damage • Species eradication • Phase 3: Evaluate potential to alter fire regime • Revegetation and restoration • Phase 4- Promotion or suppression of fire regime: • Manage fuels • Manage ignition sources • Range of management options available • Tradeoff between cost and prob. of success

12. HAVO Post-fire Management • Phase 4 – Manage fuels, ignition sources • Woodlands: • Reintroduction of fire-tolerant natives to burned areas • Prescribed burning to remove dense grass • Herbicides, mechanical methods • Coastal Grasslands: • Enhance native pili grass with prescribed burning • Focus on timing and intensity of burns

13. Discussion Questions • How could “invasive traits” or screening systems be changed to accommodate potential to alter fire regimes? • Are Brooks et al.’s management recommendations useful? How could we save time in systems where the fire regime has been altered? • Is restoring new natives better than living with invasive aliens? Is it worth the cost? • What is “native” in Hawaii’s case? • How could changes to fire regimes cause changes in species richness? At what scales?