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

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 T

Intrinsic fuel properties

↑ Flammability ↑ ↑   ↑  

↓ Flammability ↓ ↓   ↓  

Extrinsic fuel properties

↑ Fuel load   ↑      

↓ Fuel load   ↓      

↑ Horiz. continuity ↑   ↑    

↓ Horiz. continuity ↓   ↓    

↑ Vert. continuity   ↑ ↑   surface to crown

↓ Vert. continuity   ↓ ↓   crown to surface

Packing ratio ↑ ↓ ↑ ↓   ↑ ↓  

F = Frequency; I = Intensity; E = Extent;

W = Window of fire activity (seasonality); T = Type

Alien Plants

Introduction

Brooks et al: Invasive Plant-Fire Regime Cycle

Fire Regime

Native PlantsFuelEcosystem Properties

Naturalized

Invasive

Impact

Topography & Climate

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

Fire

Woodlands with Beardgrass

Feral goatsBroomsedge, Beardgrass, Molasses grass

Woody Vegetation Reduced Molasses Grass Increased

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 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

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?