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Show COLLEGE OF SOCIAL & BEHAVIORAL SCIENCE UNDERGRADUATE RESEARCH ABSTRACTS Mary Mclntyre Shira Maezumi Mitchell Power 92 PALEOECOLOGICAL ANALYSIS OF FIRE REGIMES IN THE AMAZON RIVER BASIN OF BOLIVIA Mary Mclntyre (Shira Maezumi, Mitchell Power) Department of Geography University of Utah The Amazon River Basin is comprised of over 11 biomes and is home to the greatest plant and animal biodiversity in the world. Amazon ecosystems play a significant role in the global carbon cycle acting as the largest terrestrial carbon sink. Long-term paleoecological studies can provide a better understanding of h o w these crucial ecosystems respond to climatic variability on centennial to millennial scales. The purpose of this research is to compile data about ecosystem response to past disturbances in order to understand h o w the region may respond to future changes. The resiliency of the savanna ecosystem in the Amazon River Basin can be determined using paleoecological proxies of past disturbance events and subsequent recovery patterns. Lake sediment cores provide an excellent indicator of natural ecosystem variability because sediment accumulation can reveal changes in vegetation composition, fire regimes, and climatic variability through long-term paleoecological records. Characteristic connections between climate change and fire history can help researchers understand the effects of climatic variation on different ecosystems within the Amazon River Basin. A sediment core from the remote highlands of Huanchaca Mesetta, Bolivia was examined to determine savanna fire history in this region. The charcoal record from this sediment core was analyzed using Charanalysis to identify past fire regimes. Preliminary radiocarbon dates estimate the age of the Huanchaca Mesetta core to be approximately 31,500 cal yr BP. Reconstructed fire history of Huanchaca Mesetta was compared to existing regional precipitation records from lake and marine sediment cores. The data indicate increased fire frequency at end of the last glacial period (14,500-13,500 cal yrBP) when regional moisture likely enabled increased fuel accumulation (Figure 1). During the Younger-Dryas wet period 13,000-11,500 cal yr BP increased charcoal accumulation is accompanied by two fire episodes with a fire return internal of less than 100 years (Figure 1). Fire is absent from the record from 8000-7300 cal yr BP during the mid-Holocene drought, one of the most severe regional droughts in the Amazon during the Holocene. Fire frequency slowly increased between 6700-6250 cal yr BP, before slowly decreasing from 6250-5750 cal yr BP (Figure 2). This pattern of increased fire frequency followed by a sharp decrease could be attributed to increased regional precipitation following the end of the mid-Holocene drought. Drought may have initially increased fire frequency around 8000 cal yr BP, as hot, dry weather created flammable conditions, but lack of precipitation likely reduced plant growth and available fuels, causing fire frequency to decrease and become absent on the landscape for almost 1000 years during the peak of the drought period. Fire frequency reached a period of relative stability between 2500-2000 cal yr BP (Figure 3). Fire frequency decreased significantly from 1500-1000 cal yr BP, followed by a rapid increase from 1000-500 cal yr BP (Figure 3). This increase in fire frequency correlates with warming temperatures during the Medieval Climate Anomaly (MCA). The high level of charcoal accumulation during this time period indicates an increase in fuels as well as fire frequency in the last millennia. Preliminary findings demonstrate that the Huanchaca Mesetta savanna ecosystem is responding to regional climate variability. After charcoal analysis is completed for the remainder of the sediment core, a more comprehensive fire history of this study site will be generated. Since the region surrounding Huanchaca Mesetta was devoid of human impact, this fire history provides an example of natural fire regimes. These data can then be compared to sites with known anthropogenic impacts to determine h o w human presence m a y have affected the natural fire regimes. The resiliency of savanna ecosystems in the Amazon depends on fire maintaining an active role in the region. Anomalies in Huanchaca Mesetta fire regimes in comparison with regional fire data are likely due to vegetation and precipitation differences as well as edaphic controls (variation in soil type). Future research comparing fire regimes from the cerrado savanna to seasonally dry tropical forests m a y help explain the relationship between climate change and fire frequency in maintaining these major Amazon ecosystems. |
