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

Trends in draft and extent of seasonal pack ice

[1] Continuous observations by sub-sea sonar form a 12-year draft record for seasonal pack ice in the Beaufort Sea. There has been a small trend (0.07 m/decade) to thinner ice, but this has low statistical significance; net change is comparable to the uncertainty of measurement. Although ice concentration at the monitoring site has increased by 0.14 since 1991, there is little evidence for trend in ice-covered area over the continental shelf in the longer (36-year) ice-chart record. However, local air temperature has increased by 1.6 ± 0.6°C during the last three decades. Clearly longer time series are needed to detect and understand change. Changing snow cover, ice circulation and ice deformation may obscure the direct effects of warming climate on seasonal pack ice

Controlled Breaking of Mummified Wood For Use In Paleoenvironmental Analysis

The discovery of exceptionally well-preserved Paleogene wood fossils (ca. 55–53 Ma) within Canadian Arctic diamond-bearing kimberlites prompted a paleoclimatic study of the Paleocene-Eocene Transition. The samples are not petrified, but have been “mummified” by their inclusion in pyroclastic debris and still contain primordial wood material. However, preferential cellulose loss has rendered the wood very fragile, precluding the use of standard dendrochronological methods of surface preparation. Similar to archaeological charcoal, breaking the mummified wood allows superior visualization of tree-ring boundaries and wood anatomy, but often produces irregular surfaces making microscopic examination difficult. Therefore, a simple aluminum clamp was constructed to break radial wood transects in a controlled manner for the purpose of collecting dendrochronological and wood-anatomical data for paleoclimatic reconstructions. Because it does not require the use of chemical treatments or stabilizing resins, the wood remains chemically unaltered, allowing chemical and isotopic analyses to be undertaken. Future studies of fragile woods may benefit from this method of controlled breaking if sanding is ineffective.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]

Stable isotope paleoclimatology of the earliest Eocene using kimberlite-hosted mummified wood from the Canadian Subarctic

The recent discovery of well-preserved mummified wood buried within a subarctic kimberlite diamond mine prompted a paleoclimatic study of the early Eocene "hothouse" (ca. 53.3 Ma). At the time of kimberlite eruption, the Subarctic was warm and humid producing a temperate rainforest biome well north of the Arctic Circle. Previous studies have estimated that mean annual temperatures in this region were 4–20 °C in the early Eocene, using a variety of proxies including leaf margin analysis and stable isotopes (δ¹³C and δ¹⁸O) of fossil cellulose. Here, we examine stable isotopes of tree-ring cellulose at subannual- to annual-scale resolution, using the oldest viable cellulose found to date. We use mechanistic models and transfer functions to estimate earliest Eocene temperatures using mummified cellulose, which was well preserved in the kimberlite. Multiple samples of <i>Piceoxylon</i> wood within the kimberlite were crossdated by tree-ring width. Multiple proxies are used in combination to tease apart likely environmental factors influencing the tree physiology and growth in the unique extinct ecosystem of the Polar rainforest. Calculations of interannual variation in temperature over a multidecadal time-slice in the early Eocene are presented, with a mean annual temperature (MAT) estimate of 11.4 °C (1 &sigma; = 1.8 °C) based on &delta;¹⁸O, which is 16 °C warmer than the current MAT of the area (−4.6 °C). Early Eocene atmospheric δ¹³C (δ¹³C_atm) estimates were −5.5 (±0.7) &permil;. Isotopic discrimination (&Delta;) and leaf intercellular <i>p</i>CO₂ ratio (<i>c</i>_i/<i>c</i>_a) were similar to modern values (&Delta; = 18.7 ± 0.8 &permil;; <i>c</i>_i/<i>c</i>_a = 0.63 ± 0.03 %), but intrinsic water use efficiency (Early Eocene iWUE = 211 ± 20 μmol mol^&minus;1) was over twice the level found in modern high-latitude trees. Dual-isotope spectral analysis suggests that multidecadal climate cycles somewhat similar to the modern Pacific Decadal Oscillation likely drove temperature and cloudiness trends on 20–30-year timescales, influencing photosynthetic productivity and tree growth patterns

Fire and climate variation in western North America from fire-scar and tree-ring networks

Fire regimes (i.e., the pattern, frequency and intensity of fire in a region) reflect a complex interplay of bottom-up and top-down controls (Lertzman et al., 1998; Mc Kenzie et al., in press). Bottom-up controls include local variations in topographic, fuel and weather factors at the time of a burn (e.g., fuel moisture and continuity, ignition density and local wind and humidity patterns). Bottom-up regulation is manifest as fine-scale spatial and temporal heterogeneity in fire behavior and effects within landscapes subject to the same general climate. Examples include variation in fuel consumption, tree mortality and soil effects, which create complex burn severity legacies that can influence subsequent fires (Collins and Stephens, 2008; Scholl and Taylor, 2010).Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Loop learning in adaptive management

No abstract available

Five Hundred Years of Hydrological Drought in the Upper Colorado River Basin

This article evaluates drought scenarios of the Upper Colorado River basin (UCRB) considering multiple drought variables for the past 500 years and positions the current drought in terms of the magnitude and frequency. Drought characteristics were developed considering water-year data of UCRB’s streamflow, and basin-wide averages of the Palmer Hydrological Drought Index (PHDI) and the Palmer Z Index. Streamflow and drought indices were reconstructed for the last 500 years using a principal component regression model based on tree-ring data. The reconstructed streamflow showed higher variability as compared with reconstructed PHDI and reconstructed Palmer Z Index. The magnitude and severity of all droughts were obtained for the last 500 years for historical and reconstructed drought variables and ranked accordingly. The frequency of the current drought was obtained by considering two different drought frequency statistical approaches and three different methods of determining the beginning and end of the drought period (annual, 5-year moving, and ten year moving average). It was concluded that the current drought is the worst in the observed record period (1923-2004), but 6th to 14th largest in terms of magnitude and 1st to 12th considering severity in the past 500 years. Similarly, the current drought has a return period ranging from 37 to 103 years based on how the drought period was determined. It was concluded that if the 10-year moving average is used for defining the drought period, the current drought appears less severe in terms of magnitude and severity in the last 500 years compared with the results using 1- and 5-year averages.National Science Foundation/[CMS-0239334]/NSF/Estados UnidosUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones Geofísicas (CIGEFI