PRE-FIRE TREATMENT EFFECTS AND UNDERSTORY PLANT COMMUNITY RESPONSE ON THE RODEO-CHEDISKI FIRE, ARIZONA Amanda M. Kuenzi A Thesis Submitted in Partial Fulfillment Of the Requirements for the Degree of Master of Science in Forestry Northern Arizona University December 2006 Approved: _____________________________ Peter Z. Fulé, Ph.D., Co-Chair _____________________________ Carolyn Hull Sieg, Ph.D., Co-Chair _____________________________ Margaret M. Moore, Ph.D. ABSTRACT PRE-FIRE TREATMENT EFFECTS AND UNDERSTORY PLANT COMMUNITIY RESPONSE ON THE RODEO-CHEDISKI FIRE, ARIZONA AMANDA M. KUENZI High severity wildfires have been increasing across southwestern ponderosa pine forests in recent decades. As the effects of wildfire become more widespread across the landscape, the need for information about the ecological effects of fire on understory vegetation is mounting. We investigated understory plant community response to the Rodeo-Chediski fire by conducting parallel studies on the White Mountain Apache Tribal lands (WMAT) and the Apache-Sitgreaves National Forests (A-S). We estimated plant canopy cover by species and quantified total plant species richness on 1000m2 plots. We established 71 plots on WMAT lands. Plots were stratified by fire severity (low and high) and pre-fire treatment (cut/burned and untreated). We found significantly higher plant cover on areas that were burned by severe fire, but did not detect significant differences due to pre-fire treatment. There was no significant difference in cover of exotic species between high and low severity sites. Indicator species were primarily early successional species or species that were included in the post-fire seed mix. We established 84 plots on the A-S. This study consisted of 7 paired stands of treated (pre-fire fuel reduction) and untreated sites. These sites had been established by the USDA Forest Service in 2002 after the fire to assess effectiveness of fuel-reduction treatments in altering fire behavior. We found significantly higher plant cover on areas that had not been treated, and had therefore burned with higher severity. There was no 2 significant difference in cover of exotic species between treated and untreated stands. Indicator species were primarily early successional species or species that were included in the post-fire seed mix. In both studies we found a limited response of exotics, which is surprising given the history of active management by both land agencies. Other studies have shown higher exotic species presence following severe wildfires in areas with histories of active management that included practices such as logging, grazing, and seeding. The pre-fire plant community must not have had large populations of exotic species, despite past management practices to result in a native-dominated post-fire community. Whether the few exotic species we observed, including a number of species seeded following the fire, persist and spread in the post-fire plant community remains to be seen. 3 ACKNOWLEDGEMENTS I would like to thank my co-advisors, Dr. Peter Z. Fulé and Dr. Carolyn Hull Sieg, for their tireless efforts to produce this work. They have been incredibly supportive and informative; I feel blessed to have worked with such wonderful people. In addition, I thank Dr. Margaret M. Moore for serving as a committee member. Her advice has been most helpful. I also thank my colleague, Barbara A. Strom, for all of her hard work on this project, especially for her GIS work. I thank the White Mountain Apache Tribal Council for access to their land and logistical support for the project. I personally thank Paul Declay, WMAT Forest Manager; Jim Youtz, formerly of Ft. Apache Agency BIA Forestry; and Robert LaCapa. I thank Mary “Mama Baer” Stuever for her invaluable efforts and input. Thanks to the ERI field crew members and staff including: Steve Till, Mark Daniels, Daniel Laughlin, Susan Nyoka, Teresa Dekoker, Rob Hastings, Shawnte Greenway, Lang Suby, Jeff Rainey, Chris Gonzales, and Ken Baumgartner, for two long summers of data collection and plant keying. I thank Scott Curran for technical support, including designing the database, facilitating electronic data collection in the field, and many hours spent training me in the ways of query building. For statistical help I thank: Dr. Jonathon Bakker, Daniel Laughlin, Dr. Mike Kearsley, and Rudy King. I thank all my family and friends, and the loving community of Flagstaff, Arizona, a very nurturing place for learning. I also thank my loving boyfriend, Andrew M. Baker for keeping me a happy woman during the writing of this thesis. 4 TABLE OF CONTENTS LIST OF TABLES………………………………………………………………………...6 LIST OF FIGURES……………………………………………………………………….7 PREFACE…………...…………………………………………………………………….9 Chapter 1: Introduction…………………………………………………………………..10 Chapter 2: Limited response of exotic species after a severe landscape-scale wildfire…19 Chapter 3: Influence of pre-fire fuel reduction treatments on understory response following a severe wildfire, Apache-Sitgreaves National Forests, USA………………...51 Chapter 4: Conclusions and Management Implications…………………………………77 APPENDICES…………………………………………………………………………...82 5 LIST OF TABLES Chapter 2 Table 1. Plant canopy cover classes used to classify percent cover within a 20- by 50-cm quadrat (modified from Daubenmire 1959).…..…………………………………………40 Table 2. Overstory characteristics of sites on White Mountain Apache Tribal lands by pre-fire treatments and severities. Pre-fire data are based on standing live and dead trees. Post-fire data are based on live trees only. Data are means (standard error)…………….41 Table 3. A summary of the permuted p-values for DISTLM tests for univariate plant canopy cover and richness, by category. An asterisk indicates significance.....................42 Table 4. Summary of exotic species by fire severity. Classification of ‘noxious’ is based on designation in four southwestern states, according to Sieg et al. (2003). Species in the ‘seeded’ category may have been seeded throughout the known history of the WMAT lands, not uniquely as part of the BAER efforts (pers. comm., J. A. Youtz, 2006). A total of 31 exotic species were found on high severity plots and 24 on low severity plots..….43 Table 5a. Species present only in untreated or only in cut and burned sites….…………44 Table 5b. Species present only in high severity sites or only in low severity sites...........44 Table 6. Indicator species by year and level of fire severity..…………………………...45 Table 7: A comparison of cover and richness of exotic plant species following severe wildfires in the Southwest ……………………………………………………………….46 Chapter 3 Table 1. Cover classes and midpoints used to classify percent cover within a 20- by 50- cm quadrat (modified from Daubenmire 1959).…………………………………………70 Table 2. Pre- and post-fire overstory characteristics, on treated and untreated sites. Pre- fire values were estimated after the fire by combining living and fire-killed tree data.....71 Table 3. Indicator Species1 of treated and untreated areas on the Apache-Sitgreaves National Forest (table structure modified from Huisinga et al., 2005)…………………..72 6 LIST OF FIGURES Chapter 2 Figure 1. a) Average (+SE) richness on 1000m2 plot by fire severity (H= high, L= low), treatment, and year on the WMAT plots. No significant difference was found for treatment or severity in either year. b) Average (+SE) plant canopy cover on 20- by 50- cm quadrats by fire severity (H= high, L= low), treatment, and year on the WMAT plots.In 2004, a significant difference was found for the severity effect (p=.0002). The interaction between severity and treatment was significant (p=.0233) in 2005………………………...…………………………………………………………….47 Figure 2. Average (+SE) cover, by plant groups, fire severity (H= high, L= low), treatment, and year. a) Exotic forbs: no significant differences. b) Exotic graminoids: no significant differences. c) All forbs: a significant difference was found between high and low severity in 2004 at p=.007 and in 2005 at p=.0002. d) All graminoids: a significant difference was found between high and low severity in 2004 at p=.0137 and in 2005 at p=.0014. e) Shrubs: a significant difference was found between high and low severity in 2004 at p=.025 and in 2005 at p=.009. f) Tree regeneration (<1.4m tall): the interaction between fire severity and treatment was significant in 2004 at p=.0137 and in 2005 at p=.0014…………………………..………………………………………………………48 Figure 3. Ordinated plant communities based on plant cover data by severity level. Vector length indicates strength of correlation. a) 2004 data. Stress level is 19.71 for a 3- d solution. Low severity plots were positively correlated with basal area and trees per hectare. b) 2005 data. Stress level is 19.31 for a 3-d solution. Low severity plots were also positively correlated with basal area and trees per hectare……….………………...49 Figure 4. Average frequency (proportion of quadrats + SE) of Triticum aestivum, or common wheat, by year, fire severity (H = high, L = low) and treatment……...……….50 Chapter 3 Figure 1. Total richness (no. species/1000m2) (a) and total plant canopy cover (20- by 50- cm quadrats) (b) for treated and untreated sites in 2004 and 2005. An asterisk (*) indicates a significant difference. Error bars are standard errors………………………...73 Figure 2. Percent cover (mean + standard error) of a) exotic forbs b) exotic graminoids c) all forbs d) all graminoids e) shrubs and f) tree regeneration < 1.4 m tall for untreated and treated sites in 2004 and 2005……………………………………………………………74 Figure 3. Percent cover (mean + standard error) of a) annual and biennial forbs b) perennial forbs c) legumes d) C4 graminoids and e) C3 graminoids for untreated and treated sites in 2004 and 2005…………………………………………………………....75 7 Figure 4. Ordinated plant community cover data by treatment using the Bray-Curtis distance measure. Vector length indicates strength of correlation. a) 2004 data, stress level is 20.33 for a 3-d solution. Treated plots were positively correlated with basal area and trees per hectare. Untreated plots were positively correlated with overstory canopy openness.