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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 systemaltering species on the planet” Brooks et al. 2004 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 Grass-fire cycle: D’Antonio and Vitousek (1992) Grasses: standing dead material, can dry out quickly; recover quickly after fire Brooks et al. 2004 Change F I E W Intrinsic fuel properties ↑ Flammability ↑ ↑ ↑ ↓ Flammability ↓ ↓ ↓ Extrinsic fuel properties ↑ Fuel load ↑ ↓ Fuel load ↓ ↑ Horiz. continuity ↑ ↑ ↓ Horiz. continuity ↓ ↓ ↑ Vert. continuity ↑ ↑ ↓ Vert. continuity ↓ ↓ Packing ratio ↑↓ ↑↓ ↑↓ T surface to crown crown to surface F = Frequency; I = Intensity; E = Extent; W = Window of fire activity (seasonality); T = Type Brooks et al: Invasive Plant-Fire Regime Cycle Topography & Climate Ecosystem Properties Fire Regime Fuel Alien Plants Impact Invasive Naturalized Introduction Native Plants 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 Tunison et al. Fire Regime Cycle ‘Ohi’a Dominated Woodlands Feral goats Woodlands with Beardgrass Fire Woody Vegetation Reduced Molasses Grass Increased Broomsedge, Beardgrass, Molasses grass 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 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) Management Options Brooks 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 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 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?