1. Results: The percentage of shrub and tree cover: Reference (unburned) plots Impact (burned) plots CSS 53% (se = 4.30) 13% (se = 3.7) CHAP 67% (se = 4.31) 30% (se = 3.89) GRASS 3.8% (se = 1.81) 2% (se = 1.26) WR 34% (se = 7.55) 24% (se = 6.35) Multivariate Community Analyses Multidimensional scaling graphs and hierarchial clustering showed that across vegetation types, the rodent communities from razed plots more closely resemble each other than the Corresponding nonrazed rodent communities (Figure 3). Community structure in burned plots differed from unburned plots in all vegetation types; CSS (Pseudo-F 1,23 = 6.51, P = 0.001, 30.5% of total variation) CHAP (Pseudo-F 1,11 = 4.37, P = 0.026, 18.5% of total variation) GRASS (Pseudo-F 1,15 = 4.53, P = 0.004, 21.6% of total variation) WOOD (Pseudo-F 1,13 = 2.73, P = 0.016, 14.0% of total variation). BIOENV showed that the percentage of shrub and tree cover was predictive of the change in rodent community composition for coastal sage scrub, (ρ = 0.195, p = 0.005; Figure 4). Postfire Changes in Relative Abundance of Rodent Species by Vegetation Type: CHAP: PEMA and DISI significantly increased in relative abundance CSS: PEMA and DISI significantly increased in relative abundance, while NELE and PECA significantly decreased. WOOD: PEMA significantly increased in relative abundance, while PEBO significantly decreased. GRASS: CHFA significantly decreased in relative abundance (Figure 5). Effects of Large-scale Wildfires on Rodents in Southern California Denise R. Clark*, Cheryl S. Brehme, Carlton J. Rochester, and Robert N. Fisher U.S. Geological Survey, Western Ecological Research Center, San Diego Field Station, 4165 Spruance Road, Suite 200, San Diego, California, 92101 U.S.A. * E-mail: drclark@usgs.gov Phone: (619) 225-6435 Fax: (619) 225-6436 Introduction: In October 2003, wildfires burned large areas of San Diego County. After the fires, we surveyed rodents in both burned and unburned control plots across four sites and four vegetation types using a combination of pitfall and Sherman live-traps. Prior to the 2003 wildfires, we conducted studies at one site that included rodent surveys, habitat quality assessments and vegetation characterization using established methods (Table 1). Based on previous studies, we expected to see shifts in community composition after fire and to see changes in the density and distribution of individual rodent species. The objectives of this study were to determine the effects of fire on the diversity, community composition and relative abundances of individual rodent species. Trapping Methods: Unbaited Pitfall Trap Array (Figure 2) Three 15-m arms of drift fence Seven 19-L pitfall traps Three hardware-cloth funnel traps Baited Sherman Traps (Figure 2) 9 small traps (8 x 9 x 30.5 cm) 9 large traps (10 x 11.5 x 38 cm) Data Collection: All captured animals were processed by recording species, sex, reproductive condition, age class, weight, length and hair clipping for identification of recapture. Figure 2. Study plot design. Study Area: Four study sites (Figure 1) Each site was impacted by 2003 wildfires in part or in whole Four vegetation types Chaparral (CHAP) Coastal sage scrub (CSS) Grassland (GRASS) Woodland/riparian (WR) Figure 1. The four study sites in San Diego, CA, were Little Cedar Ridge (CED), Elliott Chaparral Reserve (ELL), Rancho Jamul Ecological Reserve (RAJ), and Santa Ysabel Open Space Preserve (SYR). Prefire sampling Postfire sampling Unburned plots Burned Plots Elliot--010 Cedar--09 Rancho Jamul2010 Santa Ysabel01014 Total20 43 Discussion: Our study indicates that the coastal southern California rodent community exhibits a strong response to wildfire within the first two to three years after fire. Multivariate tests for the effects of fire on rodent communities showed significant differences in rodent community structure in coastal sage scrub, grassland, chaparral, and woodland vegetation types. Overall, the rodent communities in the burned habitats was more similar to each other than rodent communities in the unburned habitats. Postfire changes found in these rodent communities were likely caused by both direct and indirect effects of the fires. Direct effects include differences in species mortality, while indirect effects include changes in rodent competitive interactions and postfire habitat suitability. Individual rodent species largely responded in a manner consistent with their life history characteristics. Generalist and open habitat specialists generally increased in relative abundance, while closed habitat specialists decreased. Among habitats, significant increases in relative abundance were found for the Dulzura kangaroo rat (Dipodomys simulans) and deer mouse (Peromyscus maniculatus). In contrast, significant decreases in relative abundance were found for the California mouse (Peromyscus californicus), California pocket mouse (Chaetodipus californicus), desert woodrat (Neotoma lepida) and the dusky footed woodrat (Neotoma macrotis) which prefer shrubs, trees and closed habitat. Currently, we are helping to assess whether current habitat conservation plans (HCPs) in southern California provide long term protection to covered species, as well as preserve ecosystem function. Federal and state laws currently require that HCPs be implemented within an adaptive management framework. This framework represents an iterative approach, where an information feedback loop between monitoring and management improves understanding of species dynamics and ecological systems. The future scenario of increased wildfires must be incorporated into this framework. This will likely require creativity in implementing fire minimization measures, creating of fire safe refugia in natural areas, and working with local and state firefighting agencies to include plans for defense of sensitive natural areas. Statistical Analyses: To reduce seasonal and daily variability, we averaged the number of unique captures for each species per sample session. Plots were treated as replicates. Prefire and postfire averaged capture rates were used as the basis for all further analyses. For multivariate analysis; We refer to plots as razed (postfire burn) and nonrazed (prefire burn, prefire and postfire reference plots) Effect of Burn on Community Composition (Multivariate Analyses) : Non-metric multidimensional scaling (MDS; Primer-E software) Analysis of variance routine (PERMANOVA) - To test whether the factors of burn status (burned/unburned), site, vegetation type, burn status × vegetation type, and percent shrub and tree cover were significantly predictive of community structure based upon a dissimilarity matrix of species abundance data at each sample array. Biological-environmental matching (BIOENV) - Percent shrub/tree cover Single Species Comparisons Plots compared by vegetation type and burn condition (postfire reference to postfire impact plots). Acknowledgements: We thank T. Matsuda, M. Mendelsohn, S. Schuster, D. Stokes, G. Turschak and D. Wood for their many hours of hard work. Thanks to Dr. J. Yee who provided statistical advice. This project benefited greatly from reviews by D. Schwilk and Dr. J. Yee and R. Klinger. For site access, we thank the managers of the four study sites (California Department of Fish & Game, San Diego County Parks & Recreation Department, University of California, San Diego - Elliott Chaparral Reserve, Bureau of Land Management). Funding for this project was provided in part by the San Diego MSCP Initiative and the San Diego Association of Governments. Use of trade names does not imply USGS endorsement. Table 1. Number of unburned and burned plots sampled by study site Reithrodontomys megalotis Dipodomys simulans Peromyscus californicus Neotoma lepida Figure 5. Species differences in relative abundance (impact minus reference) in postfire vegetation communities. Presented in the order of greatest change to smallest change. Levels of significance are indicated as follows: *** P < 0.01, ** P< 0.05, * P < 0.10. Figure 3. Multivariate Community Analysis. A) Nonmetric multi-dimensional scaling (MDS) with B) hierarchical clustering show how the rodent communities in razed plots (R) of coastal sage scrub (CSS), chaparral (CHAP), grassland (GRASS), and woodland (WOOD) have shifted away from the communities detected in the nonrazed plots (NR). C) Vectors of individual species abundances in relation to the razed (*) and nonrazed (◊) communities showed positive responses for both PEMA, and DISI toward the fire impacted communities, while PECA, PEBO, CHFA), MICA, NELE, CHCA, PEER showed positive responses toward nonrazed communities. *** ** *** * * Figure 4. Non-metric multi-dimensional scaling plots (MDS) based on Bray-Curtis similarity matrix using square root transformed capture data show how the rodent communities in razed plots (B) of coastal sage scrub have shifted away from the communities detected in the nonrazed plots (U). Bubble size represent the relative cover from shrubs and trees. Reduced cover was a significant predictor of the change in rodent community composition in burned plots. Distance between bubbles represents how similar plots are to each other. Species codes are Chaetodipus californicus (CHCA), Chaetodipus fallax (CHFA), Dipodomys simulans (DISI), Microtus californicus (MICA), Neotoma lepida (NELE), Neotoma macrotis (NEMA), Peromyscus boylii (PEBO), Peromyscus californicus (PECA), Peromyscus eremicus (PEER), Peromyscus maniculatus (PEMA) and Reithrodontomys megalotis (REME). Species differences in relative abundance RAJ array 36 (1 year postfire)RAJ array 36 (prefire) SYR array 11 (prefire) SYR array 11 (4 years postfire)