The Effect of Pre-Fire Fuel Manipulations on Alien Plant Invasion

Transcription

1 The Effect of Pre-Fire Fuel Manipulations on Alien Plant Invasion Kyle E. Merriam 1, Jon E. Keeley 1, and Jan L. Beyers 2 1 Western Ecological Research Center, Sequoia and Kings Canyon Field Station, Three Rivers, CA 2 USDA Forest Service, Pacific Southwest Research Station, Riverside Forest Fire Laboratory, Riverside, CA

2 Fuel Reduction High Priority National Fire Plan Healthy Forest Restoration Act Increased pre-fire fuel manipulation projects photo courtesy of Eric Knapp

3 Fuel Breaks

4 Fuel breaks and invasive plants? Reduce competition, alter soil properties, create sites for establishment, introduce nonnative seeds Act as nonnative seed source that promotes invasion of adjacent wildlands?

5 Research Questions Are nonnative plants more abundant on fuel breaks? Are some fuel breaks less likely to support nonnative species? Do nonnatives move into wildland areas adjacent to fuel breaks?

6 2-15 m (not to scale) Road Fuel Break 4 M Tr ansect 1X1 M plots Methods

7 Species composition, cover and density Ground cover Overstory canopy cover Litter and duff depth Soil N, C, moisture Slope, aspect, elevation Methods

8 Study Sites

9 General Results 737 species: 85% native, 11% nonnative, 4% unknown 1547 study plots, nonnatives present in 49% 12 of 79 nonnative species on Cal-IPC list

10 Most common nonnatives Cheat grass, Bromus tectorum Photo from Brossard et al. 2

11 Relative Nonnative Cover, Density 1 and Richness Percentage of Total On Fuel Break Off Fuel Break Cover Density Richness MANOVA, N=46, Wilk s λ=.2

12 Environmental factors associated with nonnatives Slope Elevation Solar Radiation Duff Depth Litter Cover Bare Ground Rock Cover Overstory Canopy Cover Soil Nitrogen

13 Overstory Canopy Cover and Relative Nonnative Cover Percent of Total Plant Cover R 2 =.695, p< Canopy Cover (%)

14 Overstory Canopy Cover Duff Depth 8 2 p<.1 18 p<.1 Percentage Closed Centimeters On Fuel Break Off Fuel Break On Fuel Break Off Fuel Break Slope Litter Cover p=.7 6 p=.4 Percentage Percentage Cover On Fuel Break Off Fuel Break On Fuel Break Off Fuel Break

15 Fuel Break Variation Study Sites Relative Nonnative Cover (%)

16 What anthropogenic factors associated with nonnatives? Construction Method Maintenance Frequency Fuel Break Age Distance to Roads Maintenance Method adjusted multiple r 2 =.666

17 Relative Nonnative Cover (%) Fuel Break Construction Method and Relative Nonnative Cover Bulldozers Hand Crews Mechanical Construction Method p<.1

18 Construction Method and Environmental Covariates Percentage Closed Overstory Canopy Cover 8 p< Percentage p<.1 Litter Cover Bulldozer Handcrew Mechanical Bulldozer Handcrew Mechanical Centimeters p<.1 Duff Depth Bulldozer Handcrew Mechanical Percentage Bare Ground p=.28 Bulldozer Handcrew Mechanical

19 Fire Number and Distance from Fuel Break Relative Nonnative Cover (%) P<.1 No Fires One Fire Two Fires Three or More Fires Plot Distance from Fuel Break (m)

20 Fuel Break Age Category and Distance from Fuel Break 5 Relative nonnative cover (%) p<.1 < 1 years 1-3 years >3 years Distance from Fuel Break (m)

21 Summary Nonnative plants are more abundant on fuel breaks. Some fuel breaks are less likely to support nonnative species. Nonnative plants are more abundant adjacent to fuel breaks after fire and with fuel break age.

22 Acknowledgements Joint Fire Science Program Angeles, Cleveland, Lassen, Los Padres, Mendocino, Plumas, San Bernadino, Sequoia, Shasta-Trinity, Sierra, and Six Rivers National Forests and the Lake Tahoe Basin Management Area; Whiskeytown National Recreation Area, Santa Monica National Recreation Area, and Sequoia and Kings Canyon National Parks; Bakersfield District of the Bureau of Land Management; San Luis Obispo District of the California Department of Forestry and Fire Protection; Los Angeles County Fire Department Division of Forestry; Orange County Department of Parks, Casper s Wilderness Park, Field assistance from Elizabeth Martin, Trent Draper, Lea Condon, and Katie Vinzant