Land Use Pressure and Climate Impacts on Fire Regimes and Forest Regeneration in the Upper Tuul River Watershed, Mongolia

This dissertation is composed of three chapters addressing the broad issues of land use, climate variability, and wildfire in central Mongolia. The first chapter describes a GIS model developed to map human impacts in the Upper Tuul River watershed. Forest establishment data were used to validate the application of the model with results indicating a high level of correspondence with a field assessment of human disturbance. Chapter two is a tree-ring based reconstruction of Palmer Drought Severity Index (PDSI) for the central Khan Khentii Mountains from 1675-2000. Changes in moisture availability were more frequent during the 20th century than any other period of the reconstruction, suggesting a growing need for increased adaptability of the livestock industry and natural resource managers. In the final chapter, we used tree rings to reconstruct wildfire frequency and extent in the Upper Tuul River watershed during the period 1875-2009. Results indicate a recent decrease in wildfire frequency and extent; trends which might be observed in other arid regions where prolonged drought and human land use inhibit fuel accumulation. Chapter one was formatted for and submitted to The Geographical Journal on July 2, 2011, while the remaining two chapters are pending submission to peer-reviewed journals

Three centuries of shifting hydroclimatic regimes across the Mongolian Breadbasket

In its continuing move toward resource independence, Mongolia has recently entered a new agricultural era. Large crop fields and center-pivot irrigation have been established in the last 10 years across Mongolia's "Breadbasket": the Bulgan, Selenge and Tov aimags of northcentral Mongolia. Since meteorological records are typically short and spatially diffuse, little is known about the frequency and scale of past droughts in this region. We use six chronologies from the eastern portion of the breadbasket region to reconstruct streamflow of the Yeruu River. These chronologies accounted for 60.8% of May–September streamflow from 1959 to 1987 and 74.1% from 1988 to 2001. All split, calibration-verification statistics were positive, indicating significant model reconstruction. Reconstructed Yeruu River streamflow indicates the 20th century to be wetter than the two prior centuries. When comparing the new reconstruction to an earlier reconstruction of Selenge River streamflow, representing the western portion of the breadbasket region, both records document more pluvial events of greater intensity during 20th century versus prior centuries and indicate that the recent decade of drought that lead to greater aridity across the landscape is not unusual in the context of the last 300 years. Most interestingly, variability analyses indicate that the larger river basin in the western breadbasket (the Selenge basin) experiences greater swings in hydroclimate at multi-decadal to centennial time scales while the smaller basin in the eastern portion of the breadbasket (the Yeruu basin) is more stable. From this comparison, there would be less risk in agricultural productivity in the eastern breadbasket region, although the western breadbasket region can potentially be enormously productive for decades at a time before becoming quite dry for an equally long period of time. These results indicate that farmers and water managers need to prepare for both pluvial conditions like those in the late-1700s, and drier conditions like those during the early and mid-1800s. Recent studies have indicated that cultures with plentiful resources are more vulnerable when these resources become diminished. Thus, the instrumental records of the 20th century should not be used as a model of moisture availability. Most importantly, the geographic mismatch between precipitation, infrastructure, and water demand could turn out to be particularly acute for countries like Mongolia, especially as these patterns can switch in space through time

Advancing dendrochronological studies of fire in the United States

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Dendroecology is the science that dates tree rings to their exact calendar year of formation to study processes that influence forest ecology (e.g., Speer 2010 [1], Amoroso et al., 2017 [2]). Reconstruction of past fire regimes is a core application of dendroecology, linking fire history to population dynamics and climate effects on tree growth and survivorship. Since the early 20th century when dendrochronologists recognized that tree rings retained fire scars (e.g., Figure 1), and hence a record of past fires, they have conducted studies worldwide to reconstruct [2] the historical range and variability of fire regimes (e.g., frequency, severity, seasonality, spatial extent), [3] the influence of fire regimes on forest structure and ecosystem dynamics, and [4] the top-down (e.g., climate) and bottom-up (e.g., fuels, topography) drivers of fire that operate at a range of temporal and spatial scales. As in other scientific fields, continued application of dendrochronological techniques to study fires has shaped new trajectories for the science. Here we highlight some important current directions in the United States (US) and call on our international colleagues to continue the conversation with perspectives from other countries

The North American tree-ring fire-scar network

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree-ring fire scars provide valuable perspectives on fire regimes, including centuries-long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree-ring fire-scar network (NAFSN), which contains 2562 sites, >37,000 fire-scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000-m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire-scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under-sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non-Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually- to sub-annually-resolved tree-ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America

Hands-On Astrophysics: Variable Stars in the Math/Science Lab

Hands-OnAstrophysics: Variable Stars in Math/Science Lab. - being developed by the AAVSO and funded by the National Science Foundation - is an astronomy educational project which emphasizes student involvement and scientific discovery

Three centuries of shifting hydroclimatic regimes across the Mongolian Breadbasket

In its continuing move toward resource independence, Mongolia has recently entered a new agricultural era. Large crop fields and center-pivot irrigation have been established in the last 10 years across Mongolia's "Breadbasket": the Bulgan, Selenge and Tov aimags of northcentral Mongolia. Since meteorological records are typically short and spatially diffuse, little is known about the frequency and scale of past droughts in this region. We use six chronologies from the eastern portion of the breadbasket region to reconstruct streamflow of the Yeruu River. These chronologies accounted for 60.8% of May–September streamflow from 1959 to 1987 and 74.1% from 1988 to 2001. All split, calibration-verification statistics were positive, indicating significant model reconstruction. Reconstructed Yeruu River streamflow indicates the 20th century to be wetter than the two prior centuries. When comparing the new reconstruction to an earlier reconstruction of Selenge River streamflow, representing the western portion of the breadbasket region, both records document more pluvial events of greater intensity during 20th century versus prior centuries and indicate that the recent decade of drought that lead to greater aridity across the landscape is not unusual in the context of the last 300 years. Most interestingly, variability analyses indicate that the larger river basin in the western breadbasket (the Selenge basin) experiences greater swings in hydroclimate at multi-decadal to centennial time scales while the smaller basin in the eastern portion of the breadbasket (the Yeruu basin) is more stable. From this comparison, there would be less risk in agricultural productivity in the eastern breadbasket region, although the western breadbasket region can potentially be enormously productive for decades at a time before becoming quite dry for an equally long period of time. These results indicate that farmers and water managers need to prepare for both pluvial conditions like those in the late-1700s, and drier conditions like those during the early and mid-1800s. Recent studies have indicated that cultures with plentiful resources are more vulnerable when these resources become diminished. Thus, the instrumental records of the 20th century should not be used as a model of moisture availability. Most importantly, the geographic mismatch between precipitation, infrastructure, and water demand could turn out to be particularly acute for countries like Mongolia, especially as these patterns can switch in space through time

The North American tree‐ring fire‐scar network

Abstract Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree‐ring fire scars provide valuable perspectives on fire regimes, including centuries‐long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree‐ring fire‐scar network (NAFSN), which contains 2562 sites, >37,000 fire‐scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000‐m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire‐scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under‐sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non‐Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually‐ to sub‐annually‐resolved tree‐ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America