A late-Holocene fire record from the Sierra de San Pedro Martir National Park, Baja California, Mexico

This research investigates a fire history and environmental disturbances of a ciénega in the Sierra de San Pedro Mártir National Park in Northern Baja California, Mexico. A fire regime was reconstructed through charcoal analysis. Other environmental disturbances were reconstructed using the geochemical proxies magnetic susceptibility and loss on ignition. For this project, a sediment core was collected from a dry ciénega called the Palo Atravezado at approximately 2,750 meters (9,000 feet) in elevation. Ciénegas are wetland ecosystems that exist in arid environments and are ideal locations for sediment core recovery because they preserve information of past climates, such as charcoal particles, through deposition. Using both charcoal analysis and other proxies allowed conclusions to be drawn about past disturbance patterns of the site. The Sierra de San Pedro Mártir National Park was chosen as the study site because it has historically experienced less human impact than ciénega ecosystems in the southwestern United States, making the paleoecological record from the collected sediment core more comprehensive. This project is a component of a larger body of research investigating past oscillations of the North American Monsoon and its forcing on vegetation and fire regimes in North America. The findings will be compared with other sites on the Baja Peninsula to investigate how vegetation changes, climatic changes, and land-use changes alter ecosystems and the impacts from the North American Monsoon in the region.

ABSTRACT This research investigates a fire history and environmental disturbances of a ciénega in the Sierra de San Pedro Mártir National Park in Northern Baja California, Mexico. A fire regime was reconstructed through charcoal analysis. Other environmental disturbances were reconstructed using the geochemical proxies magnetic susceptibility and loss on ignition. For this project, a sediment core was collected from a dry ciénega called the Palo Atravezado at approximately 2,750 meters (9,000 feet) in elevation. Ciénegas are wetland ecosystems that exist in arid environments and are ideal locations for sediment core recovery because they preserve information of past climates, such as charcoal particles, through deposition. Using both charcoal analysis and other proxies allowed conclusions to be drawn about past disturbance patterns of the site. The Sierra de San Pedro Mártir National Park was chosen as the study site because it has historically experienced less human impact than ciénega ecosystems in the southwestern United States, making the paleoecological record from the collected sediment core more comprehensive. This project is a component of a larger body of research investigating past oscillations of the North American Monsoon and its forcing on vegetation and fire regimes in North America. The findings will be compared with other sites on the Baja Peninsula to investigate how vegetation changes, climatic changes, and land-use changes alter ecosystems and the impacts from the North American Monsoon in the region. ii ACKNOWLEDGEMENTS I would first like to thank my parents, Susie Graves-Henneman and Dan Graves and my step-dad, Todd Henneman, for having the foresight to start a college fund for me and paying for my undergraduate education. I have felt endless support from all of them throughout my time at the University of Utah as well as through this project. Secondly, I would like to thank my partner, Bo Torrey, for providing me with emotional support and love throughout this project. I would not have been able to complete this senior thesis without the love and encouragement they have all given me. Thank you to Dr. Jennifer Watt for her dedication in mentorship and assistance in all aspects of this project including inviting me to travel to Baja, Mexico for field work. I would also like to thank Dr. Andrea Brunelle, Dr. Brett Clark, and Benjamin Marconi for their huge contributions to this project and my overall learning process in undergraduate research. Thank you to Jose Delgadillo and colleagues from the Autonomous University of Baja California for being translators, assisting in field work, and helping us work in the Sierra de San Pedro Mártir National Park. Huge thank you to Kaylee Barkett Jones, Jordin Hartley, and all the other folks in the RED Lab for teaching me a multitude of laboratory methods and consistently being around to help. Thanks to Dr. Michael E. Ketterer at Northern Arizona University for processing plutonium samples for dating and Dr. Mitchell Power for running fire analyses in the CharAnalysis program. Finally, thank you to the Undergraduate Research Opportunities Program for funding my research work. iii TABLE OF CONTENTS ABSTRACT………………………………………………………………...ii ACKNOWLEDGEMENTS………………………………………………..iii INTRODUCTION AND SETTING………………………………………...1 Introduction……………………………………………………….....1 Setting……………………………………………………………….2 Ciénegas……………………………………………………..2 The Sierra de San Pedro Mártir National Park…………........4 Mixed-conifer forest type…………………………………....7 Land management history…………………………………...8 METHODS………………………………………………………………….9 Field Methods…………………………………………………..........9 Lab Methods………………………………………………………..10 Stratigraphy and chronology……………………………….10 Charcoal analysis…………………………………………...11 Loss on ignition……………………………………….........12 Magnetic susceptibility…………………………………......13 RESULTS…………………………………………………………………..13 Stratigraphy and chronology………………………………………..13 Core description…………………………………………….13 Chronology…………………………………………………14 Sediment proxies…………………………………………………....15 iv Charcoal analysis…………………………………………......15 Loss on ignition……………………………………………....16 Magnetic susceptibility…………………………………….....17 DISCUSSION AND CONCLUSIONS……………………………………....19 Discussion………………………………………………….................19 Charcoal analysis……………………………………………..19 Loss on ignition ……………………………………………....21 Magnetic susceptibility……………………………………….22 Conclusions…………………………………………………...............22 REFERENCES…………………………………………………......................24 v 1 INTRODUCTION AND SETTING Introduction The climatic and environmental histories of an area can be reconstructed using sediment analysis. If sediment can deposit and accumulate in an area without being disturbed, a climatic history can typically be reconstructed. Paleoecological research is central in the understanding and analysis of environmental disturbance patterns such as fire regimes and climatic changes. Using paleoecological research methods along with historical analyses of land management practices, we can better understand how to manage and conserve vital ecosystems into the future while accounting for potential environmental disturbances and modern anthropogenic climate change. This project focused on reconstructing a late-Holocene (1035 cal yr BP to present) fire regime history and other environmental disturbance patterns of a ciénega, or desert wetland ecosystem, in the Sierra de San Pedro Mártir (SSPM) National Park in Baja California, Mexico. Ciénegas provide crucial habitat for an abundance of endangered and endemic plants and animals (Minckley & Brunelle, 2007). Thus, understanding the climate dynamics and fire regime through history is important in understanding how these ecosystems function and how they can be managed and conserved into the future. This research is part of a larger interdisciplinary project focused on climatic variability and the effects of climate change on desert wetland environments. Most fire reconstruction in this region has been conducted using tree ring analysis, or dendrochronology, focusing on fire regimes and fire events dating back to the mid-1600s CE. Much of this work has been done by Scott L. Stephens and colleagues in the SSPM National Park (Stephens, Skinner, & Gill, 2003; Evett, Franco-Vizcaíno, & 2 Stephens, 2007; Skinner, Burk, Barbour, Franco-Vizcaíno, & Stephens, 2008; and Stephens, Fry, & Franco-Vizcaíno, 2008). The majority of this research has focused on the influences of climate and land management practices on fire regimes in the SSPM National Park. This project used sedimentary analysis to reconstruct a fire history dating back to 1035 cal yr BP (915 CE), which allowed for interpretation of a more comprehensive and longer fire history. Setting Figure 1: Map and photo of the Palo Atravezado ciénega study site in the SSPM National Park, Baja California, Mexico. Ciénegas Ciénegas are wetland ecosystems that exist in otherwise arid landscapes. These ecosystems can act as archives for past climatic conditions and environments because they are repositories for macrofossils, pollen, and charcoal from thousands of years in the 3 past (Martin, 1963; Hall, 1985; Davis, Minckley, Moutous, Jull, & Kalin, 2002; Minckley & Brunelle, 2007; and Brunelle, Watt, & Clark, 2010). Ciénegas are classified as meadows with highly organic saturated soil and dominated by sedges and rushes. They are essential ecosystems because they provide water, a major limitation factor for biological activity, in otherwise arid landscapes (Minckley, Turner, & Weinstein, 2013). Ciénegas provide a host of important ecosystem services including habitats for native and/or endemic animals, flood control, migratory points for various birds, and water filtration. Today, unaltered ciénegas are virtually nonexistent in the desert southwest of the United States and the northwestern region of Mexico. Historical research indicates that before European colonization, there were many ciénegas in the Chihuahuan and Sonoran deserts of Mexico and the United States (Hendrickson & Minckley, 1985; Minckley et al. 2013). However, these ecosystems have been under threat since the arrival of European colonizers. As Europeans began to occupy the landscape, activities such as livestock grazing of sheep and cows, mining, water diversion, and railroad construction encouraged channelization, erosion, and desertification of these fragile ciénegas (Hendrickson & Minckley, 1985; Minckley et al. 2013). Rather than having wide, slow moving waterways, most ciénegas today look like small creeks or dried meadows. Although almost all ciénegas have been altered by humans, ciénegas in Mexico have experienced fewer human impacts than those in the United States. Thus, Mexican ciénegas may provide better paleoecological reconstructions than ciénegas in the United States. 4 The Sierra de San Pedro Mártir National Park The SSPM National Park is located within the Cordillera Baja California mountain range in the in the north-central region of the Baja Peninsula approximately 100 km southeast of Ensenada, Mexico. It is within the physiographic province that is known as the Planicie Hansen, or the Hansen Plain (Parque Nacional Constitución de 1857, 1962). The National Park was created by decree on April 26, 1947. The Mexican government protected 72,909 hectares of land in the SSPM through the creation of this National Park. The SSPM mountain range is a northwest-to-southeast fault block made of large granitic units and today at its highest point rises to 3100 m (10,153 ft) in elevation. It is also the highest mountain range in Baja California, Mexico. The range was uplifted as solid batholith, an igneous intrusion in the earth’s crust, and broke along fault lines into massive granitic blocks that were forced upward by pressure during the Mesozoic period in geologic history (Parque Nacional Constitución de 1857, 1962; SARH, 1993; Schwenkmeyer, 2000). The predominate soil type is regosol, which is weakly developed soil made of medium- to fine-grained, unconsolidated parent material deposited through alluvial processes (“Regosol: FAO Soil Group,” n.d.). The SSPM National Park is a sky island, or a terrestrial region that has been separated from related organisms through geographic isolation (Schwenkmeyer, 2000). In this case, organisms have been isolated from one another by their inability to cross hotter, drier and lower-elevation regions to reach the upper-elevations of the SSPM National Park (Schwenkmeyer, 2000). Through genetic drift, many species in the region are 5 endemic, or exist only in the National Park. The SSPM National Park is one of the only habitats of native Bighorn Sheep on the Baja Peninsula and is also home to the California Condor re-introduction program run by governmental and private conservation agencies. This project focused on a sediment core (PA-18-B) recovered from the Palo Atravezado ciénega, which is located on the western slope of the SSPM range at 30.9914720˚N, 115.5542780˚W (Figure 1). It is at an elevation of 2449 m (8035 ft). Palo Atravezado ciénega is approximately 0.7 hectares. The intended outcome of the field work was to recover three, one-meter long sediment cores. However, the Palo Atravezado ciénega site was dry and the ground was hard when the core was recovered. Only one significant precipitation event occurred in the 2017/18 winter precipitation season in March, producing 28 mm of rainfall and snow at higher elevations (Figure 2). This led to very little surface water recharge and dry conditions at the Palo Atravezado ciénega. The dry and medium- to fine-grain unconsolidated nature of the soil also contributed to shallow coring conditions. Thus, three sediment cores were collected, all about or less than half of a meter long. Sediment core PA-18-B is 53 cm and the longest core recovered. 7 since 2000. The observatory is approximately 10.5 km (6.5 mi) from the Palo Atravezado ciénega. Weather data from the observatory indicate that the average annual temperature of the region since 2000 has been ~20°C (68°F). Winter temperatures vary from 3˚C to 18°C (37˚F to 64 °F) and about 36% of precipitation falls during the winter as both rain and snow. Summer temperatures range from 18-32˚C (64 to 90˚F) and about 22.9% of precipitation falls as rain during this period (Instituto de Astronomía UNAM). However, temperatures and precipitation rates vary intensely across the National Park due to elevational, topographic, and regional changes (Instituto de Astronomía UNAM). These data do not accurately represent the average climate of the region because data has only been recorded and compiled for 18 years. Climatic data must be compiled for at least 30 years to be considered representative of the average climate of a region. Mixed-conifer forest type The SSPM National Park is comprised of 40,000 hectares of spatially heterogeneous California mixed-conifer forest (Thorne, Moran, & Minnich, 2010; Stephens et al., 2008). The western slope below 1900 m (6233 ft) is dominated by chaparral consisting of evergreen sclerophyllous, or woody, shrubs. As elevation increases, the western slope becomes dominated by manzanita chaparral (Arctostaphylos peninsularis), existing up to 2200–2400 m (7217 to 7874 ft) on steep, southern slopes (Thorne et al., 2010). Manzanita chaparral extends to the upper regions of the eastern slope of the SSPM National Park. The tree that dominates chaparral zones is the fourneedled pinyon (Pinus quadrifolia), which grows mostly in regions with chamise (Adenostoma fasciculatum) and red-shank chaparral (Adenstoma sparsifolium) as well as 8 on the eastern slope above 1800 m (5905 ft). Below 1500 m (4921 ft) one-needled pinyon (Pinus monophylla) dominates the eastern slope along with desert chaparral (Thorne et al., 2010). A mixed conifer forest dominates the landscape above the chaparral regions and in lower elevations without dense shrubs. Mixed-conifer forests above 2100 m (6889 ft) are dominated by Jeffrey pine (Pinus jeffreyi) on southern slopes, while northern slopes are home to more biodiverse forests including white fir (Abies concolor), sugar pine (Pinus lambertiana), and lodgepole pine (Pinus contorta) (Skinner, et al., 2008; Thorne et al., 2010). Other important tree species in the SSPM National Park include canyon live oak (Quercus chysolepis), peninsular oak (Quercus peninsularis, endemic), and Quaking Aspen (Populus tremuloides) (Thorne et al., 2010). More than 500 hectares of wet meadows exist in the forested region of the SSPM National Park, which are exposed to cattle grazing in the summer (Thorne et al., 2010). Dominant vegetation in meadows are rushes, sedges, and grasses. Meadows are also home to herbaceous perennials including yarrow (Achillea spp.), sunflower (Dieteria spp.), and Potentilla, much of which covers dry and overgrazed meadows (Thorne et al., 2010). Land management history The SSPM National Park is unique because the large mixed-conifer forest has not experienced logging nor organized, long-term fire suppression (Stephens et al., 2003). Unlike large forested regions in California and the wider United States, tree harvesting has never occurred in the SSPM range and very limited fire suppression started in the 9 1970s (Skinner et al., 2008). Thus, the SSPM has a more heterogeneous forest structure than forests in the United States. This structural heterogeneity allows the SSPM to serve as a model in the study of environmental disturbances and climatic changes because the ecosystem has remained more intact than most forested regions of the western United States (Minnich, Barbour, Burk, & Sosa-Ramirez, 2000a; Stephens et al., 2008). Although fire suppression has been heavily limited in the region, livestock grazing has occurred from the late 1700s to the present (Stephens et al., 2003). Grazing by cattle and sheep have impacted the ecosystems of the many wet meadows within the SSPM National Park. Sheep grazed in the park from 1915 to 1964, but were then denied access into the park. Thus, cattle grazing resurged in the middle to late 19th century and continues today (Meling, 1991; Stephens et al., 2003). The introduction of grazing into the SSPM region may have had effects on fire fuel continuity and forest heterogeneity. These effects are seen in the low productivity of herbaceous fuels in the area, with the exception of wet meadows (Stephens et al., 2003). Thus, the fire regime and vegetation in the SSPM may be influenced by grazing, especially after the late 19th century when the number of livestock significantly increased (Stephens et al., 2003). METHODS Field Methods One short sediment core (PA-18-B, 53 cm) was recovered from the Palo Atravezado ciénega in the SSPM National Park at 30.9914720˚N, 115.5542780˚W. Charcoal analysis, loss on ignition (LOI), and magnetic susceptibility (MS) were used to reconstruct a fire history and explain other environmental disturbances. The core was recovered using an aluminum tube (7.5 x 7.5 cm in diameter, 1 m long) attached to a 10 Vibracore engine. We attempted to recover a longer core, but due to dry conditions were unable to do so. The core was wrapped in plastic wrap, tin foil, and then capped on both ends. It was then transported back to the Department of Geography Records of Environment and Disturbance (RED) Lab via truck. Lab Methods The sediment core was cut in half lengthwise at the RED Lab. The core was then physically described by identifying distinct layers, colors, and sediment size. One half of the core was used for charcoal analysis as well as LOI, MS, and radiocarbon dating. 14 cm of the other (archival) half of the core was subsampled and used for plutonium dating to create an age model for the sediment core. The core is archived in a storage refrigerator in the Department of Geography RED Lab at the University of Utah. Stratigraphy and chronology The archival side of the core was subsampled at each centimeter for 0 to 14 cm to be analyzed for plutonium (Pu) dating. Subsamples were placed in whirlpaks prior to plutonium sample preparation. The procedure followed came from the RED Lab Plutonium Dating Sample Preparation Procedure. Scintillation vials (glass vials) were labeled and weighed to record the empty weight of each vial. Wet subsampled sediment from the archival core was taken out of whirlpaks and placed in weighed vials. The weight of the wet sediment and vial were recorded. The vials were then placed in a Gellenkamp Hotbox furnace preheated to 85˚C for 24 hours. After 24 hours, samples were weighed. This weight recorded the weight of the vial and dry sediment, but the 11 weight of the vial was subtracted for final values. All samples weighed more than 1 gram, so no additional sample preparation was needed. Caps were labeled and placed on the corresponding vials. Each vial was placed in a labeled whirlpak and shipped to Michael E. Ketterer’s lab in Department of Chemistry and Biochemistry at Northern Arizona University. 1cc was subsampled from centimeters 28 to 29 and 51 to 52, then processed for radiocarbon (14C) dating. The Schulze pollen processing technique was used for to process samples (Kapp, Davis, & King, 2000). Samples were put in glass scintillation vials and then placed in whirlpaks. Then samples were sent to the Center for Applied Isotope Studies (CAIS) at the University of Georgia for the pollen in the samples to be radiocarbon dated. Charcoal analysis The top half of sediment core PA-18-B was subsampled for charcoal analysis. 5 cubic centimeter (cc) sediment samples was taken for each centimeter increment of core PA-18-B. However, the top 4 cm (0 to 4 cm) of the core had collapsed lithology, thus that section of the core was subsampled together and subsequently analyzed together. Subsamples were placed in whirlpaks and stored in the RED Lab storage cooler. Each subsample was then sieved with 125-µm and 250-µm screens to divide the different sized particles. Both >125-µm and >250-µm charcoal particles were counted. 5cc of sediment was counted for the top 14 cm of the sediment core, then because of very high charcoal counts, 1cc of sediment was counted for the remaining 39 samples. Both morphology and number of charcoal particles were counted and identified. Morphology 12 types were categorized as fibrous, lattice, branched, dark, and cellular. Charcoal particles were identified and counted using a Lecia S6E dissecting microscope. The CharAnalysis program was run to reconstruct a fire return interval (FRI), or the number or times fires occur in an area over time, and decipher peaks in charcoal (Higuera, 2009). A 250-year parameter was used to smooth the estimated background charcoal concentrations and a 500-year parameter was used to smooth fire frequency and FRI in the program. Loss on ignition The purpose of loss on ignition (LOI) is to measure water, organic carbon, and carbonate content from heating sediment samples at various temperatures. The weight loss of sediment after each heating shows an estimation of the amount of water, carbon, and carbonate content and allows for a low-cost compositional profile to be created (LacCore, National Lacustrine Core Facility, 2013). The RED Lab Loss on Ignition Instructions were followed for this process. Sediment samples of 1 cm3 were taken from each centimeter of the PA18B sediment core and placed into clean ceramic crucibles. Samples were dried at 100˚C for 24 hours in a Gellenkamp Hotbox furnace and weighed to determine water content. Samples were then combusted at 550˚C in a Barnstead/Thermolyne 30400 furnace for two hours and weighed to determine organic carbon content. Finally, samples were combusted at 900˚C for two hours and weighed to determine carbonate content. 13 Magnetic susceptibility Magnetic susceptibility (MS) is a measure in which the concentration of magnetic minerals can be obtained through non-destructive and rapid means (Lecoanet, Lévêque, & Segura, 1999). This method is based on how easily sediments can be magnetized, which varies with the amount of iron-bearing minerals in the sediment (Zolitschka, Mingram, van der Gaast, Jansen, & Naumann, 2002). MS can be useful to reconstruct periods of runoff into a system. MS readings were taken using the Bartington Multisus2 computer software, MS2 Bartington Magnetic Susceptibility Meter, and Bartington MS2E2 Single Sample Sensor. Whirlpaks containing subsamples sampled at 1 cm increments were warmed at room temperature for approximately 24 hours. Each sample, still in whirlpaks, were scanned using the MS2E2 Single Sample Sensor three times at a 0.1 to one-meter range. MS readings for the air and samples were taken three times for each sample. Then, the sample MS readings were averaged for the 0.1 m range and recorded. RESULTS Stratigraphy and Chronology Core description The top 4 cm of the sediment core is unconsolidated and was therefore combined into one sample. Thus, the top 4 cm of the sediment core were subsampled as one sample. The lithology of the top 24 cm of the sediment core is composed of mostly fine grained, sub-rounded, poorly sorted sandy particles. At 4 cm, a streak of very dark in color, fineto very fine-grained, well sorted particles exists and becomes the dominant lithological 14 composition starting at 24 cm. Throughout the darker, fine- to very fine-grained sediment, some larger granular particles and organic matter was identified. Large plant particles including sticks, grasses, and roots were identified at the surface (0 to 4 cm), 13 to 16 cm, and a piece of wood approximately 3 cm long was identified from 46 to 49 cm. Figure 3: A sediment core diagram depicting identified layers and wood pieces in core PA-18-B. Chronology The resulting age model with the corresponding age table from radiometric dating (Pu and 14C) was generated using the CLAM software (Figure 4) (Blaauw, 2010). An additional anchor point was added at 6 cm based on the age-depth in the plutonium dating 16 cal yr BP, 903 to 862 cal yr BP, 653 to 598 cal yr BP, 298 cal yr BP, -8 - -47 cal yr BP, and -53 cal yr BP (Figure 5). These peaks were gathered from charcoal influx data. Results from the CharAnalysis program were only useful in reconstructing the FRI for core PA-18-B. CharAnalysis calculated an FRI of approximately 200 to 250 years up until 180 cal yr BP (1770 AD), where the fire regime changes. Peaks represented from CharAnalysis were not used in interpreting charcoal data because they did not accurately represent the peaks seen in charcoal influx data (Higuera, 2009). Charcoal influx data more accurately represented true peaks and troughs in fire activity because it comes from direct measurement of charcoal particles within sediment. Whereas CharAnalysis was a program created to analyze fire regimes in boreal forests, unlike the region this project focused on (Higuera, 2009). The morphology of charcoal particles was also taken into account. Charcoal morphology is split into two categories: those representative of arboreal vegetation (hardwood, pine, etc.) and those representative of non-arboreal vegetation (grasses, shrubs, sedges, etc.). Lattice, dark, and branched charcoal particles represent arboreal vegetation, while cellular and fibrous charcoal particles represent non-arboreal vegetation (Mueller, Long, Williams, Nurse, & Mclauchlan, 2014). The majority, 94% of the charcoal identified in core PA-18-B, was either lattice, branched, or dark. While about 6% of the charcoal particles identified were identified as fibrous or cellular. Loss on ignition Organic carbon was generally between 1% to 6% throughout most of the sediment core. There are peaks in organics ranging from 8% to 13%. Notable peaks in organics 17 occur at 998 cal yr BP (~8%), 334 to 193 cal yr BP (7.5% to 9%), 100 cal yr BP (~12%), -20 cal yr BP (13%), and -44 cal yr BP (9%). Carbonate content was also generally low, ranging between 0.05% to 0.7% throughout most of the sediment core. There are a few notable peaks of carbonates occurring at 998 cal yr BP, 903 cal yr BP, 227 to 193 cal yr BP, 100 cal yr BP, and -34 cal yr BP. Magnetic susceptibility The magnetic susceptibility values from sediment core PA-18-B mostly ranged from 4 to 9, with the lowest reading being 3.2 at 799 cal yr BP. Peaks in magnetics occurred at 753 cal yr BP (12.8), 474 cal yr BP (16.9), 73 cal yr BP (14.1), and from -28 to -44 cal yr BP (17.7 to 22.6). 18 0 100 post-grazing 200 pre-grazing Age (cal yr BP) 300 400 500 600 700 800 900 1000 0 20 40 60 Charcoal Influx (cm2 yr-1) 80 0 4 8 1216 0 0.4 0.8 % Organics % Carbonates 0 8 16 24 MS Figure 5: Charcoal influx, LOI, and magnetic susceptibility (MS) data plotted against the PA-18-B age model from CLAM (Blaauw, 2010). 19 DISCUSSION AND CONCLUSIONS Discussion Charcoal analysis Most of the fire history work conducted in the SSPM National Park has been reconstructed using aerial photography and dendrochronology, while this project relied on sedimentary analysis of charcoal. Using charcoal analysis to reconstruct a fire history allowed for a much longer fire history than can be captured by dendrochronology and aerial photography. Thus, the charcoal analysis for this project reconstructed a fire history dating back to 1035 cal yr BP (915 CE). 94% of the charcoal particles in sediment core PA-18-B were categorized as lattice, branched, or dark. This result indicates that, throughout the late-Holocene, vegetation at the Palo Atravezado ciénega was mostly arboreal, or made up of trees. This finding is consistent with the makeup of the modern mixed-conifer forest type of the SSPM National Park. However, at this time, there is no pollen record from this site, so conclusions cannot be drawn about a specific and a potentially changing vegetation regime throughout the late-Holocene at the Palo Atravezado ciénega. The reconstructed fire record shows that periods of high fire activity were followed by years, usually many decades, of low fire activity. This relationship remains true throughout the late-Holocene, and is especially pronounced in the mid-1900s to the early 2000s. This relationship aligns with findings in Skinner et al. (2008). Throughout the earlier segment of the record (1035 cal yr BP to 150 cal yr BP), the FRI of 200 to 250 20 years from CharAnalysis holds true (Higuera, 2009). Peaks in fire events are followed by decades of low fire activity. Around 1800 (150 cal yr BP), when there appears to be a gradual increase in fire events until modern day. The FRI for the SPPM from 150 cal yr BP to the present ranged from 4 to 23.5 years (Gucker, 2007). As noted previously, grazing began in the SSPM National Park in the late 1700s and fire suppression began in the mid-1970s (Stephens et al., 2003; Skinner, et al., 2008). Research has also supported the hypothesis that climatic drivers such as the El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and changing climate regimes have led to an increase in fires in the SSPM National Park (Stephens et al., 2003; Evett et al., 2007; Skinner et al., 2008). Livestock grazing in the SSPM significantly increased in the middle- to late1800s, which likely reduced the amount of herbaceous vegetation, such as grasses and shrubs. This reduced vegetation could be a contributing factor to the size and distribution of wildfires in the SSPM. With less understory vegetation to burn, fires would burn larger trees, resulting in larger wildfires (Stephens et al., 2003). Limited fire suppression starting in the 1970s may also be a contributor to a changing fire regime. Although fire suppression in the SSPM has been less widespread than fire exclusion in the United States, it still has an impact on the fire regime of the SSPM (Stephens et al., 2003; Skinner et al., 2008). The mid-1900s appears to have experienced the most frequent activity in the fire record. From 1970 to the mid-1990s there is a large spike in charcoal influx, which indicates a period of high fire activity (Figure 5). I hypothesize that fire suppression, 21 which led to a buildup in fire fuel, and increases in livestock grazing have contributed to the higher fire activity and more frequent FRI seen in the late 1900s. The 2003 fire, which was the first wildfire to occur in the SSPM in over a decade, was captured in the charcoal data from the Palo Atravezado ciénega (Figure 5). This fire appears to be less severe than fires that occurred in the SSPM from the mid-1970s to mid1990s, even though it occurred in July of 2003 after a severe drought that lasted from 1999 to 2003 (Stephens and Fulé, 2005). Loss on ignition Minckley & Brunelle (2007) explain that LOI data can provide information on sedimentation history through providing a proxy of the production of organic material through time. The LOI readings in organics from sediment core PA-18-B is generally low, indicating that the Palo Atravezado ciénega did not have many increases in organic materials for most of the late-Holocene. However, there were some notable peaks in organics. Peaks in organics at 998 cal yr BP (~8%), 334 to 193 cal yr BP (7.5% to 9%), 100 cal yr BP (~12%), -20 cal yr BP (13%), and -44 cal yr BP (9%). The increasing concentration in organics near the top of the core (-20 to -44 cal yr BP) indicates that the Palo Atravezado ciénega may have been increasing in size during that time interval (Figure 5). This finding is somewhat surprising, given that most ciénegas have been shrinking in modern history due to land-use changes. The LOI readings of carbonates, or inorganic materials, is much more variable than readings of organics. Yet, there is no decipherable, consistent trend throughout this record. Without a vegetation history, it is difficult to conclude or discuss any significant 22 findings from the fluctuating percentage of carbonate material throughout the late-Holocene. Magnetic susceptibility High MS may reflect ciénega growth rates, since they are indicative of sediment input into a system (Minckley & Brunelle, 2007). MS readings throughout PA-18-B were variable and fluctuating throughout the sediment core, with four significant peaks in the record. The peaks near the bottom and middle of the record indicate two instances when sediment accumulation from runoff or other environmental disturbances may have occurred (753 cal yr BP and 474 cal yr BP). Yet, these peaks in MS do not correlate with peaks in LOI data, thus their ability to reconstruct environmental disturbances and sediment input may not be credible (Minckley & Brunelle, 2007). Near the top of the record, MS readings peak more frequently at 73 cal yr BP and -28 to -44 cal yr BP, with the largest peak occurring at -34 cal yr BP (Figure 5). These peaks in MS correlate with peaks and troughs in LOI data, potentially making these data more credible in reconstructing periods of high sediment accumulation into the Palo Atravezado ciénega. Conclusions This project focused on reconstructing a late-Holocene (1035 cal yr BP to present) fire regime and other environmental disturbance patterns from the Palo Atravezado ciénega in the SSPM National Park in Baja California, Mexico. The fire history was reconstructed using sedimentary analysis of charcoal from sediment core PA-18-B, which 23 made for a longer fire history than had been previously recorded. Other environmental disturbances were reconstructed using LOI and MS proxies. The findings from this project show that a consistent FRI (200 to 250 years) occurred at this site from the beginning of the record (1035 cal yr BP, 915 CE) until 150 cal yr BP (1800 CE). After 1800, fire events become more frequent. I hypothesize that fire suppression, which led to a buildup in fire fuel, and large increases in livestock grazing contributed to the higher fire activity and a more frequent FRI seen in the late 1900s. LOI data from core PA-18-B show that organic material at this site has generally remained low throughout the late-Holocene. Yet, some notable peaks occur, indicating increases in organic material and potential ciénega growth during these peak times (Figure 5). However, interpreting LOI and MS data may not be fully credible, since no comprehensive vegetation record exists for the time being. A vegetation record, which will be reconstructed in the future, will allow for further interpretation of LOI and MS data to reconstruct environmental disturbances at the site. Researching the changing fire regime and other environmental disturbance patterns at the Palo Atravezado ciénega is important because ciénega ecosystems are home to a host of endangered and endemic plants and animals (Minckley & Brunelle, 2007). Understanding the climate dynamics, fire regime, and environmental disturbance patterns is critical in knowing how these ecosystems function and how they can be managed and conserved into the future. 24 REFERENCES Blaauw, M., 2010. Methods and code for ‘classical’ age-modelling of radiocarbon sequences. Quaternary Geochronology 5: 512-518 Brunelle, A., Minckley, T., Blissett, S., Cobabe, S. and Guzman, B., 2010. An 8000year fire history of a southwestern U.S. desert wetland. Journal of Arid Environments 74: 475-481. Brunelle, A., Watt, J., and Clark, B., 2017. Sierra de San Pedro Collaborative Research Project. 1-3. Davis, O.K., Minckley, T., Moutoux, T., Jull, T., Kalin, T. B. 2002. The transformation of Sonoran Desert wetlands following the historic decrease of burning. Journal of Arid Environments 50, 393-412. Evett RR, Franco-Vizcaino, E., and Stephens S.L. 2007. Phytolith evidence for the absence of a prehistoric grass understory in a Jeffrey pine-mixed conifer forest in the Sierra San Pedro Martir, Mexico. Canadian Journal of Forest Research 37: 306–317. Gucker, Corey L. 2007. Pinus jeffreyi. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Retrieved April 17, 2019, from https://www.fs.fed.us/database/feis/plants/tree/pinjef/all.htm. Hall, S.A. 1985. Quaternary Pollen Analysis and Vegetational History of the Southwest. In V.M. Bryant Jr, and Holloway, R.G. (eds.) Pollen Records of Late-Quaternary North American Sediments. American Association of Stratigraphic Palynologists. Hendrickson, D.A., and Minckley, W.L. 1985. Cienegas-vanishing climax communities of the American Southwest. Desert Plants 6, 130-176. Higuera, P. 2009. CharAnalysis 0.9: Diagnostic and analytical tools for sedimentat charcoal analysis Instituto de Astronomía UNAM San Pedro Martir, B.C, Mexico. n.d. Retrieved January 27, 2019, from http://tango.astrosen.unam.mx/weather15/. Kapp, R., Davis, O., & King, J. 2000. Pollen and Spores (2nd ed.). American. Lecoanet, H., Lévêque, F., & Segura, S. 1999. Magnetic susceptibility in environmental applications: Comparison of field probes [Abstract]. Physics of the Earth and Planetary Interiors,115(3-4). doi:10.1016. Loss-on-Ignition Standard Operating Procedure [Standard Operating Procedure]. 2013 (November 11). LacCore, National Lacustrine Core Facility. 25 Martin, P.S., 1963. The Last 10,000 Years: A fossil pollen record from the American Southwest. The University of Arizona Press, 87 Meling, D. 1991. Raising cattle on the Sierra San Pedro Martir. In Memoirs of the International Conference of the Potential of the Peninsular Range of the California’s as a Biosphere Reserve, 18-19 Mar. 1991, Ensenada, Mexico. Edited by E. Franco-Vizcaíno and J. Sosa-Ramírez. Center for Scientific Research and Higher Education of Ensenada (CICESE) CICESE09101, Ensenada, Baja California, Mexico. pp. 16-17. Minckley, T.A., and Brunelle, A. 2007. Paleohydrology and growth of a desert ciénega. Journal of Arid Environments 69, 420-431. Minckley, T., Turner, D., & Weinstein, S. 2013. The relevance of wetland conservation in arid regions: A re-examination of vanishing communities in the American Southwest. Journal of Arid Environments, 88, 213-221. doi:10.1016/j.jaridenv. Minnich, R.A., Barbour, M.G., Burk, J.H. & Sosa-Ramirez, J. 2000a. California mixedconifer forests under unmanaged fire regimes in the Sierra San Pedro Martir, Baja California, Mexico. Journal of Biogeography, 27, 105-129. Mueller, J. R., Long, C. J., Williams, J. J., Nurse, A., & Mclauchlan, K. K. 2014. The relative controls on forest fires and fuel source fluctuations in the Holocene deciduous forests of southern Wisconsin, USA. Journal of Quaternary Science, 29(6), 561–569. https://doi.org/10.1002/jqs.2728. Parque Nacional Constitución de 1857. (August 27, 1962). Retrieved January 25, 2019, from https://web.archive.org/web/20081210101124/http://www.ine.gob.mx/ueajei/publ icaciones/libros/108/bc.html. RED Lab Loss-on-Ignition (LOI) Instructions [Standard Operating Procedure]. n.d. University of Utah, Salt Lake City. Regosol: FAO Soil Group. n.d. In Encyclopaedia Britannica. Retrieved January 25, 2019, from https://www.britannica.com/science/Regosol. SARH. 1993. Diagnóstico del Parque Nacional Constitución de 1857. [Report]. Schwenkmeyer, D. 2000. Sierra de San Pedro Mártir. Retrieved January 25, 2019, from https://www.sdnhm.org/oceanoasis/fieldguide/sanpedromartir.html. 26 Skinner, C. N., Burk, J. H., Barbour, M. G., Franco-Vizcaíno, E., & Stephens, S. L. 2008. Influences of climate on fire regimes in montane forests of north-western Mexico. Journal of Biogeography, 35(8), 1436-1451. doi:10.1111/j.13652699.2008.01893.x. Stephens, S. L., Fry, D. L., & Franco-Vizcaíno, E. 2008. Wildfire and Spatial Patterns in Forests in Northwestern Mexico: The United States Wishes It Had Similar Fire Problems. Ecology and Society,13(2). doi:10.5751/es-02380-130210. Stephens, S. L., and P. Z. Fulé. 2005. Western pine forests with continuing frequent fire regimes: possible reerence sites for management. Journal of Forestry. 103, 357362. Stephens, S. L., Skinner, C. N., & Gill, S. J. 2003. Dendrochronology-based fire history of Jeffrey pine - mixed conifer forests in the Sierra San Pedro Martir, Mexico. Canadian Journal of Forest Research,33(6), 1090-1101. doi:10.1139/x03-031. Thorne, R. F., Moran, R. V., & Minnich, R. A. 2010. Vascular Plants of the High Sierra San Pedro Mártir, Baja California, Mexico: An Annotated Checklist. Aliso: A Journal of Systematic and Evolutionary Botany,28(1), 1-51. doi:10.5642/aliso.20102801.02. Zolitschka, B., Mingram, J., van der Gaast, S., Jansen, F., & Naumann, R. 2001. Sediment Logging Techniques (Vol. 1). https://doi.org/10.1007/0-306-47669-X_.