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

Fire History of Rhyolite Canyon, Chiricahua National Monument

"Final report to National Park Service, Contract PX 8601-7-0106"This item is part of the Natural History Reports collection. It was digitized from a physical copy provided by the Laboratory of Tree-Ring Research at The University of Arizona. For more information about items in this collection, please contact the Lab's Curator, (520) 621-1608 or see http://ltrr.arizona.edu/collection

Giant Sequoia Fire History: A Feasibility Study

Final Report to Sequoia and Kings Canyon National Park, National Park Service / Cooperative Agreement No. CA 8000-1-0002This item is part of the Natural History Reports collection. It was digitized from a physical copy provided by the Laboratory of Tree-Ring Research at The University of Arizona. For more information about items in this collection, please contact the Lab's Curator, (520) 621-1608 or see http://ltrr.arizona.edu/collection

Fire Scar Dates from Walnut Canyon National Monument, Arizona

Final Report to National Park Service, Southern Arizona Group OfficeEighteen samples of fire-scarred ponderosa pine (Pinus ponderosa Laws.) from Walnut Canyon National Monument (Fig. 1) were delivered to the Laboratory of Tree-Ring Research in September 1989. These partial cross section samples were prepared and dendrochronologically dated. This report contains a brief description of the methods used in this project, and a detailed listing of the dating results. Some preliminary observations of the character of fire history are offered.This item is part of the Natural History Reports collection. It was digitized from a physical copy provided by the Laboratory of Tree-Ring Research at The University of Arizona. For more information about items in this collection, please contact the Lab's Curator, (520) 621-1608 or see http://ltrr.arizona.edu/collection

Giant Sequoia Ring-Width Chronologies from the Central Sierra Nevada, California

Giant sequoia was one of the first species that A. E. Douglass examined in his pioneering tree- ring research. Recent attention to sequoia, stimulated by fire history studies in sequoia groves, has resulted in new ring-width chronologies based on both recently collected tree-ring material and Douglass' original samples. The development and characteristics of four new multimillennial sequoia chronologies are described here. Three of these chronologies are based on tree-ring series from individual sites: Camp Six (347 B.C. to A.D. 1989), Mountain Home (1094 B.C. to A.D. 1989), and Giant Forest (1235 B.C. to A.D. 1988). The fourth is a composite chronology (1235 B.C. to A.D. 1989) that includes radii from the other three chronologies. Sequoia ring series are generally complacent with occasional narrow rings ("signature years"). Ring-width standardization was complicated by growth releases, many of which are known to have been caused by fires. Such growth releases confuse climatic interpretation of low-frequency signals in the time series. Ring- width series were detrended with cubic splines with 50% frequency response function at 40 years to de-emphasize low-frequency variation and were fit with autoregressive time series models to remove persistence. The resulting prewhitened chronologies contain primarily a high frequency climate signal and are useful for assessing the past occurrence of extreme drought events and for dating applications. The dating chronology originally developed by Douglass is confirmed and the annual nature of giant sequoia tree rings unequivocally verified.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]

Giant Sequoia Fire History in Mariposa Grove, Yosemite National Park

We reconstructed a 1,438-year history of wildfire in the Mariposa Grove of giant sequoias (Sequoiadendron giganteum). Partial cross sections were taken from 18 dead fire-scarred trees, and the tree rings and fire scars were dated. The resulting master fire chronology shows that fires recurred at intervals ranging from 1 to 15 years. Changes in fire frequency on time scales of centuries are also apparent. This fire history documents the long-term importance of fire in sequoia-mixed conifer ecosystems and illustrates the temporal variability of fire regimes

Radiocarbon Dating and Intercomparison of Some Early Historical Radiocarbon Samples

ISSN:0033-822