UNIVERSITY OF CALIFORNIA Santa Barbara Multi-temporal Remote Sensing of Vegetation Regrowth After a Large Wildfire A Thesis submitted in partial satisfaction of the requirements for the degree Master of Arts in Geography by Christopher Linscott Kibler Committee in charge: Professor Dar A. Roberts, Chair Professor Stuart H. Sweeney Professor Carla M. D’Antonio June 2019 The thesis of Christopher Linscott Kibler is approved. _____________________________________________ Stuart H. Sweeney _____________________________________________ Carla M. D’Antonio _____________________________________________ Dar A. Roberts, Committee Chair June 2019 Multi-temporal Remote Sensing of Vegetation Regrowth After a Large Wildfire Copyright © 2019 by Christopher Linscott Kibler iii ACKNOWLEDGEMENTS I would like to thank the people whose guidance and support made this thesis possible. I would like to thank my advisor, Professor Dar Roberts, for his valuable mentorship and guidance over the last three years. Professors Stuart Sweeney and Carla D’Antonio also provided valuable advice about how to design and implement this study. In addition to my committee members, several other people made substantial contributions to this research. Anne-Marie Parkinson worked tirelessly to organize the fieldwork trips and analyze the field survey data. She was assisted by field technicians Monica Goodwin and Payton Thomas, whose diligence and perseverance enabled us to collect excellent data. Seth Peterson provided valuable advice about how to design and implement the remote sensing analyses. Members of the VIPER laboratory also provided useful guidance on many occasions. Finally, I would like to thank my girlfriend, Claire, for her encouragement and enthusiasm as I completed this project. I would also like to thank my parents for their unwavering love and support during all of my endeavors. To everyone who supported me as I created this thesis, thank you. iv ABSTRACT Multi-temporal Remote Sensing of Vegetation Regrowth After a Large Wildfire by Christopher Linscott Kibler Large wildfires occur regularly in southern California and disturb a variety of vegetation communities that exist in different environmental conditions across the landscape. Different plant species have different functional adaptations to fire that affect their recovery. Chaparral shrublands are well adapted to high intensity crown fires and will recover rapidly in the years following a fire. Other vegetation types, such as coniferous forests, are less adapted to severe fires and will take longer to regenerate in areas of canopy mortality. As large wildfires become more frequent across the western United States, it is important to monitor how these fires affect different vegetation communities. Changes in the species composition of individual patches affect carbon and nutrient cycling, local hydrology, and other aspects of ecosystem function. In some cases, patches of vegetation may not return to their pre-fire conditions. This study examines how patches of chaparral shrubland and mixed conifer forest recovered from the 2007 Zaca wildfire in Santa Barbara County, California. It combines multi-temporal remote sensing imagery and field survey data to identify characteristic recovery signals for different vegetation types. Landsat imagery from 2000-2018 was used to v compute the relative differenced normalized burn ratio, green vegetation fractions, and shade fractions for the entire burn scar. Land cover data for the chaparral shrublands were collected from 82 field survey transects in the summer of 2018. Land cover data for the mixed conifer forests were created by manually classifying high resolution aerial imagery. The resulting remote sensing trajectories were used to compare recovery behavior across different vegetation types. The conifer land cover data was also used to develop a statistical model that identified the environmental predictors of conifer mortality during the fire. Finally, I quantified the fractional cover of standing dead wood in Quercus chrysolepis crowns to determine if standing dead wood affects remote sensing estimates of green vegetation regrowth. The chaparral shrub species recovered rapidly from 2007-2011, but recovery stalled from 2011-2017 because of a severe drought. Cercocarpus betuloides was the most resilient species during the drought. C. betuloides is well adapted to dry conditions, which suggests that droughts may affect which species successfully regenerate after wildfires. Both the remote sensing data and the field surveys revealed widespread mortality of mixed conifer forest. In general, the conifer stands did not recover to the levels of vegetation greenness seen before the fire. In total, 34.6% of the stands analyzed experienced partial or complete canopy loss as a result of the fire. A statistical model of conifer mortality revealed that insolation, maximum temperature, and local topographic position were important environmental determinants of post-fire canopy cover. These variables all control water availability on the landscape, which suggests that conifers in relatively wet areas are more likely to survive large wildfires. Field surveys indicated that many areas of conifer mortality are converting to shrubland. Some shrub species, such as Ceanothus palmeri, may even be inhibiting conifer vi regeneration. The mean fractional cover of standing dead wood in Quercus chrysolepis crowns was 0.25. As a result, remote sensing models may be underestimating green vegetation regrowth by as much as 25% for some vegetation types. vii TABLE OF CONTENTS 1 Introduction ..................................................................................................1 2 Methods........................................................................................................5 2.1 Study Area ........................................................................................5 2.2 Land Cover Reference Data .............................................................5 2.2.1 Conifer Reference Data ..............................................................6 2.2.2 Shrub and Herbaceous Plant Reference Data .............................7 2.2.3 Standing Dead Wood Cover Data ............................................10 2.3 Remote Sensing ..............................................................................12 2.3.1 Imagery Data ............................................................................12 2.3.2 Normalized Burn Ratio ............................................................13 2.3.3 Spectral Mixture Analysis ........................................................14 2.3.4 Multiple Endmember Spectral Mixture Analysis.....................17 2.3.5 Spectral Library Development .................................................18 2.3.6 Characteristic Recovery Trajectories .......................................23 2.4 Environmental Modeling of Type Conversion ...............................23 3 Results ........................................................................................................25 3.1 Land Cover Reference Data ...........................................................25 3.2 Characteristic Recovery Trajectories..............................................27 3.2.1 RdNBR Trajectories .................................................................29 3.2.2 Green Vegetation Trajectories .................................................31 3.2.3 Shade Trajectories ....................................................................34 viii 3.3 Fractional Cover of Standing Dead Wood .....................................37 3.4 Predictors of Conifer Mortality ......................................................38 4 Discussion ..................................................................................................43 4.1 Regrowth of Green Vegetation .......................................................43 4.2 Remote Sensing of Vegetation Structure ........................................47 4.3 Type Conversion of Mixed Conifer Forests ...................................49 4.4 Implications for Management and Future Research .......................53 5 Conclusion .................................................................................................55 Appendices ...................................................................................................................57 Bibliography ................................................................................................................64 ix LIST OF FIGURES Figure 1: Map showing the burn scar in relation to California county boundaries. ......4 Figure 2: Flowchart of the process used to develop spectral libraries for this study. ..19 Figure 3: PCA biplot of species cover for species that were dominant (>25% cover) in at least one field survey transect. .....................................................................................27 Figure 4: Diagram of a hypothetical recovery trajectory demonstrating ΔVIshort, ΔVIrecovery, and ΔVIlong. I use this framework to quantify changes in vegetation spectral indices, but it can also be used to analyze other metrics of change after disturbance. ...........28 Figure 5: Mean RdNBR trajectories for conifer stands with different combinations of pre-fire and post-fire stand densities. The stands with no canopy cover before the fire (bottom left subplot) appear to have been misclassified by CALVEG. They contain mixtures of shrubs, grasses, and barren ground. .....................................................................30