LITERATURE CITED

1. Pre-Fire Fuel Manipulation Impacts on Alien Plant Invasion of Wildlands Jon E. Keeley and Kyle E. Merriam, USGS Western Ecological Research Center, Sequoia-Kings Canyon Field Station, Three Rivers, CA 93271 jon_keeley@usgs.gov, (559) 565-3170 Fuel Break Mendocino National Forest Shaded Fuel Break Lake Tahoe Basin Management Area Fuel Break Shasta-Trinity National Forest SUMMARY BACKGROUND LOCATIONS AND COOPERATORS • This study addresses the effect of fuel breaks on the invasion of alien plant species into wildland areas. Fuel breaks may be a critical factor in alien plant invasions because these disturbed areas could: • provide establishment sites for invasive species • act as corridors for alien species invasion into remote areas • harbor source populations that promote alien establishment into surrounding ecosystems following natural disturbances such as fire • To examine the impact of fuel breaks on alien plant invasion, we will investigate fuel breaks on federal, state, and private land throughout California. We will examine diverse fuel types, including shrublands, woodlands and coniferous forests. This study has three objectives: • to inventory the floristic composition of fuel breaks throughout California and relate patterns of alien plant distribution to fuel break parameters • to determine if fuel breaks act as source populations for the invasion of wildland areas • to educate resource managers about how fuel manipulations may be planned to minimize the negative impacts of invasive species on natural landscapes Fuel breaks and other pre-fire fuel manipulations are designed to break up landscape fuels and improve access for fire suppression. They vary in design from linear features created by bulldozers, to large thinned areas with up to sixty percent remaining canopy cover, sometimes referred to as shaded fuel breaks. Fuel breaks are an increasingly important component of state and federal fuels management programs, particularly in urban interface areas. However, it is possible these disturbed zones will contribute to the invasion of alien plant species into wildland areas, particularly after fires. Fuel breaks increase light levels and soil disturbance, factors necessary for the establishment of most invasive alien plants. Fuel break maintenance activities, such as thinning and prescribed burning, may provide disturbance regimes that favor invasive species. Given sufficient time many fuel breaks eventually harbor alien species and in some regions fuel breaks may be dominated by alien plants, particularly annual grasses (Giessow and Zedler 1997). • This is a three year study. We recently completed the first year of data collection at sites in central and northern California. During the next two years we plan to revisit several areas sampled this year and to establish new sites, particularly in southern California. Thanks to the generous assistance of our cooperators from the United States Forest Service (USFS) and the National Park Service (NPS) we completed surveys in the following locations during 2002: • Lake Tahoe Basin Management Area (USFS) • Mendocino National Forest (USFS) • Plumas National Forest (USFS) • Sequoia National Forest (USFS) • Sequoia and Kings Canyon National Parks (NPS) • Sierra National Forest (USFS) • Six Rivers National Forest (USFS) • Shasta-Trinity National Forest (USFS) • Whiskeytown National Recreation Area (NPS) • During the next two years we hope to establish • new sites in areas under the jurisdiction of the • USFS, NPS, the Bureau of Land Management (BLM), • and the California Department of Foresty (CDF), • including sites in the following areas: • Angeles National Forest (USFS) • Cleveland National Forest (USFS) • Hollister District (BLM) • Los Padres National Forest (USFS) • Pinnacles National Monument (NPS) • Santa Monica Mountains (NPS) • Sierra Nevada foothills (CDF) • Wofford Heights, Lake Isabella (BLM) • RECOMMENDATIONS WELCOME! A burned area adjacent to a fuel break in the Mendocino National Forest A shaded fuel break after a prescribed burn in the Plumas National Forest Historically, Western U.S. forests have not been highly threatened by invasive plant problems (Pierson and Mack 1990). However, this may in part be a result of fire exclusion that has eliminated natural disturbance regimes. An alarming increase in cheatgrass has been noted in recent years in Kings Canyon National Park that is correlated with an active prescription burning program (Caprio et al. 1998, Keeley et al. in review). Similar invasions of cheatgrass and other alien species have been reported following wildfires in ponderosa pine forests on the Mogollon and Kaibab Plateaus in central and northern Arizona (Griffis et al. 2001, Crawford et al. 2001). These studies also reported an extraordinary diversity of alien species that readily colonized burned sites but were absent from unburned forests. Post-fire studies have shown that alien plant establishment is through post-fire colonization, most often by wind dispersal (Crawford et al. 2001, Keeley et al. in review). Construction of fuel breaks may promote the invasion of alien plant species if fuel breaks act as sources of alien plant propagules after widespread disturbances such as fire. Road 2002 Study Sites 2003-2004 Proposed Sites A linear fuel break in the Shasta-Trinity National Forest A shaded fuel break in the Sierra National Forest This study is funded by theJoint Fire Science Program METHODS ANALYSIS • We will correlate the distribution of invasive plant species with fuel break parameters such as elevation, habitat type, slope, aspect, fire history, construction and maintenance method, (e.g. thinning, clearing, prescribed burning), and proximity to roads, urban areas, and other disturbed sites. Analysis will involve a combination of parametric and non-parametric statistics, including: • site variable correlations • simple linear regression • multivariate CANOCO analysis • GIS spatial analysis • We hope these analyses will determine which factors are most likely to promote alien plant invasions. We intend to use this information to develop recommendations on how pre-fire fuel manipulations may be planned and managed to minimize the negative impacts of invasive plant species on natural landscapes. Sampling is conducted along belt transects perpendicular to the fuel break. Transects are 1 meter (m) in width, and extend from the center of the fuel break 40m into the surrounding vegetation on both sides. Sampling points along each transect are established at -10, -5, 0, 5, 10, 20, and 40 m from the edge of the fuel break. At each sampling point a 1 x 1 m quadrat is placed. Shaded Fuel Break Plumas National Forest Shaded Fuel Break Six Rivers National Forest Fuel Break Shasta-Trinity National Forest Fuels thinned and chipped Whiskeytown National Recreation Area Sampling within a shaded fuel break Sierra National Forest Sampling perpendicular to a fuel break Sierra National Forest 250 M (Not to scale) LITERATURE CITED Fuel Break • Within each 1 x 1 m quadrat data are collected on plant species composition, percent cover, and density. Litter, bare ground, and canopy cover also are recorded. Additional data collected include: • slope, aspect, elevation • fire history • fuel break age • construction and maintenance method • general site conditions Caprio, A., S. Haultain, M. B. Keifer, and J. Manley. 1998. Problem evaluation and recommendations: invasive cheatgrass (Bromus tectorum) in Cedar Grove, Kings Canyon National Park. Report submitted to the Natural Resource Division, Sequoia-Kings Canyon national parks. Crawford, J. A., C.‑H. A. Wahren, S. Kyle, and W. H. Moir. 2001. Responses of exotic plant species to fires in Pinus ponderosa forests in northern Arizona. Journal of Vegetation Science 12:261‑268. Giessow, J. and P. Zedler. 1997. The effects of fire frequency and firebreaks on the abundance and species richness of exotic plant species in coastal sage scrub. Pages 86‑94 in J. Lovich, J. Randall, and M. Kelly, editors. Proceedings of the California Exotic Pest Plant Council Symposium. California Exotic Pest Plant Council, 2. Sacramento, CA. Griffis, K. L., J. A. Crawford, M. R. Wagner, and W. H. Moir. 2001. Understory response to management treatments in northern ponderosa pine forests. Forest Ecology and Management 146:239‑245. Keeley, J.E., D. Lubin, and C.J. Fotheringham. in review. Fire and grazing impacts on plant diversity and invasives in the southern Sierra Nevada. Ecological Applications. Pierson, E. A. and R. N. Mack. 1990. The population biology of Bromus tectorum in forests: distinguishing the opportunity for dispersal from environmental restriction. Oecologia 84:519‑525. Sampling perpendicular to a fuel break Mendocino National Forest 40 M Transect 1X1 M Plots Bull thistle (Cirisum vulgare) in burned area Lake Tahoe Basin Management Area Yellow star thistle (Centaurea solstitialis) Mendocino National Forest Fuels thinned and piled for burning Plumas National Forest Transects are placed at 250 m intervals from the origin nearest to a road corridor or urban area. A minimum of 8 transects per fuel break are established. Sampling within a fuel break Shasta-Trinity National Forest Thanks to Elizabeth Martin and Trent Draper for all their hard work during the 2002 field season!!!