Reconstructions of biomass burning from sediment charcoal records to improve data-model comparisons

The location, timing, spatial extent, and frequency of wildfires are changing rapidly in many parts of the world, producing substantial impacts on ecosystems, people, and potentially climate. Paleofire records based on charcoal accumulation in sediments enable modern changes in biomass burning to be considered in their long-term context. Paleofire records also provide insights into the causes and impacts of past wildfires and emissions when analyzed in conjunction with other paleoenvironmental data and with fire models. Here we present new 1000 year and 22 000 year trends and gridded biomass burning reconstructions based on the Global Charcoal Database version 3, which includes 736 charcoal records (57 more than in version 2). The new gridded reconstructions reveal the spatial patterns underlying the temporal trends in the data, allowing insights into likely controls on biomass burning at regional to global scales. In the most recent few decades, biomass burning has sharply increased in both hemispheres, but especially in the north, where charcoal fluxes are now higher than at any other time during the past 22 000 {years}. We also discuss methodological issues relevant to data-model comparisons, and identify areas for future research. Spatially gridded versions of the global dataset from GCDv3 are provided to facilitate comparison with and validation of global fire simulations

Anthropogenic modifications to fire regimes in the wider Serengeti‐Mara ecosystem

Fire is a key driver in savannah systems and widely used as a land management tool. Intensifying human land uses are leading to rapid changes in the fire regimes, with consequences for ecosystem functioning and composition. We undertake a novel analysis describing spatial patterns in the fire regime of the Serengeti‐Mara ecosystem, document multidecadal temporal changes and investigate the factors underlying these patterns. We used MODIS active fire and burned area products from 2001 to 2014 to identify individual fires; summarizing four characteristics for each detected fire: size, ignition date, time since last fire and radiative power. Using satellite imagery, we estimated the rate of change in the density of livestock bomas as a proxy for livestock density. We used these metrics to model drivers of variation in the four fire characteristics, as well as total number of fires and total area burned. Fires in the Serengeti‐Mara show high spatial variability—with number of fires and ignition date mirroring mean annual precipitation. The short‐term effect of rainfall decreases fire size and intensity but cumulative rainfall over several years leads to increased standing grass biomass and fuel loads, and, therefore, in larger and hotter fires. Our study reveals dramatic changes over time, with a reduction in total number of fires and total area burned, to the point where some areas now experience virtually no fire. We suggest that increasing livestock numbers are driving this decline, presumably by inhibiting fire spread. These temporal patterns are part of a global decline in total area burned, especially in savannahs, and we caution that ecosystem functioning may have been compromised. Land managers and policy formulators need to factor in rapid fire regime modifications to achieve management objectives and maintain the ecological function of savannah ecosystems

The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard–Oeschger (D–O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D–O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73–15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U∕230Th, optically stimulated luminescence (OSL), 40Ar∕39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft AccessTM at https://doi.org/10.1594/PANGAEA.870867

The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard–Oeschger (D–O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D–O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73–15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U∕230Th, optically stimulated luminescence (OSL), 40Ar∕39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft AccessTM at https://doi.org/10.1594/PANGAEA.870867

Anthropogenic modifications to fire regimes in the wider Serengeti-Mara ecosystem

Fire is a key driver in savannah systems and widely used as a land management tool. Intensifying human land uses are leading to rapid changes in the fire regimes, with consequences for ecosystem functioning and composition. We undertake a novel analysis describing spatial patterns in the fire regime of the Serengeti‐Mara ecosystem, document multidecadal temporal changes and investigate the factors underlying these patterns. We used MODIS active fire and burned area products from 2001 to 2014 to identify individual fires; summarizing four characteristics for each detected fire: size, ignition date, time since last fire and radiative power. Using satellite imagery, we estimated the rate of change in the density of livestock bomas as a proxy for livestock density. We used these metrics to model drivers of variation in the four fire characteristics, as well as total number of fires and total area burned. Fires in the Serengeti‐Mara show high spatial variability—with number of fires and ignition date mirroring mean annual precipitation. The short‐term effect of rainfall decreases fire size and intensity but cumulative rainfall over several years leads to increased standing grass biomass and fuel loads, and, therefore, in larger and hotter fires. Our study reveals dramatic changes over time, with a reduction in total number of fires and total area burned, to the point where some areas now experience virtually no fire. We suggest that increasing livestock numbers are driving this decline, presumably by inhibiting fire spread. These temporal patterns are part of a global decline in total area burned, especially in savannahs, and we caution that ecosystem functioning may have been compromised. Land managers and policy formulators need to factor in rapid fire regime modifications to achieve management objectives and maintain the ecological function of savannah ecosystems.Natural Environment Research Council, Grant/Award Number: JZG10015; Leverhulme Trust, Grant/Award Number: IN‐2014‐022; Vetenskapsrådet; Sida and Formas, Grant/Award Number: 2016‐06355.http://wileyonlinelibrary.com/journal/gcbhj2019Zoology and Entomolog

African fire histories and fire ecologies

International audienc

African fire histories and fire ecologies

International audienc

Radiocarbon dating, macroscopic charcoal counts, pollen counts, and tree-establishment data from Little Trefoil Lake, Alberta, Canada

This dataset was developed from a sediment core collected from Little Trefoil Lake in Jasper, AB, Canada, and from tree-cores collected from the surrounding forest. The data includes radiocarbon dating information, sedimentary charcoal counts, pollen counts, and tree establishment dates

Time series animations of African vegetation change using pollen records for: "Asymmetric response of forest and grassy biomes to climate variability across the African Humid Period: influenced by anthropogenic disturbance?"

Movies: for all mapped movies (movie S1 - S6): white circles indicate the presence of a pollen record; blue dots indicate archaeological remains of wild terrestrial ungulates; and red dots indicate the remains of domestic animals. The distribution of the faunal remains was based on summed probability distributions of radiocarbon dates at 100-year time intervals (see Phelps et al. in press for further methodological information). Movie S1a: The climatic envelope of forest mapped at 100-year intervals, using the direct methodology with WorldClim data (black background). Movie S1b: The climatic envelope of forest mapped at 100-year intervals, using the direct methodology with WorldClim data (white background). Movie S1c: The climatic envelope of forest mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (black background). Movie S1d: The climatic envelope of forest taxa mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (white background). Movie S1e: The climatic envelope of forest taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (black background). Movie S1f: The climatic envelope of forest taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (white background). Movie S1g: The climatic envelope of forest taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (black background). Movie S1h: The climatic envelope of forest taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (white background). ______________________________________________________________________________________ Movie S2a: The climatic envelope of grassy biomes (savanna- and steppe-associated taxa) mapped at 100-year intervals, using the direct methodology with WorldClim data (black background). Movie S2b: The climatic envelope of grassy biomes (savanna- and steppe-associated taxa) mapped at 100-year intervals, using the direct methodology with WorldClim data (white background). Movie S2c: The climatic envelope of grassy biomes (savanna- and steppe-associated taxa) mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (black background). Movie S2d: The climatic envelope of grassy biomes (savanna- and steppe-associated taxa) mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (white background). ______________________________________________________________________________________ Movie S3a: The climatic envelope of savanna-associated taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (black background). Movie S3b: The climatic envelope of savanna-associated taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (white background). Movie S3c: The climatic envelope of savanna-associated taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (black background). Movie S3d: The climatic envelope of savanna-associated taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (white background). ______________________________________________________________________________________ Movie S4a: The climatic envelope of steppe-associated taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (black background). Movie S4b: The climatic envelope of steppe-associated taxa mapped mapped at 100-year intervals, using the indirect methodology, WorldClim data (white background). Movie S4c: The climatic envelope of steppe-associated taxa mapped mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (black background). Movie S4d: The climatic envelope of steppe-associated taxa mapped mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (white background). ______________________________________________________________________________________ Movie S5a: The climatic envelope of desert-associated taxa mapped mapped at 100-year intervals, using the direct methodology with WorldClim data (black background). Movie S5b: The climatic envelope of desert-associated taxa mapped at 100-year intervals, using the direct methodology with WorldClim data (white background). Movie S5c: The climatic envelope of desert-associated taxa mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (black background). Movie S5d: The climatic envelope of desert-associated taxa mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (white background). Movie S5e: The climatic envelope of desert-associated taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (black background). Movie S5f: The climatic envelope of desert-associated taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (white background). Movie S5g: The climatic envelope of desert-associated taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (black background). Movie S5h: The climatic envelope of desert-associated taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (white background). ______________________________________________________________________________________ Movie S6a: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the direct methodology with WorldClim data (black background). Movie S6b: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the direct methodology with WorldClim data (white background). Movie S6c: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (black background). Movie S6d: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the direct methodology with TraCE-21ka climate information (white background). Movie S6e: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (black background). Movie S6f: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the indirect methodology, WorldClim data (white background). Movie S6g: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (black background). Movie S6h: The climatic envelope of xeric-associated taxa mapped at 100-year intervals, using the indirect methodology, TraCE-21ka climate information (white background). ______________________________________________________________________________________ Movie S7a: Multivariate environmental similarity surface (MESS) analyses plotted in geographic space using the direct methodology with repeated, modern-day WorldClim data. White areas demonstrate neutrality: i.e., neither similarity nor dissimilarity. Movie S7b: Multivariate environmental similarity surface (MESS) analyses plotted in geographic space using the direct methodology with TraCE-21ka climate information. White areas demonstrate neutrality: i.e., neither similarity nor dissimilarity. Movie S7c: Multivariate environmental similarity surface (MESS) analyses plotted in geographic space using the indirect methodology with repeated, modern-day WorldClim data. White areas demonstrate neutrality: i.e., neither similarity nor dissimilarity. Movie S7d: Multivariate environmental similarity surface (MESS) analyses plotted in geographic space using the indirect methodology with TraCE-21ka climate information. White areas demonstrate neutrality: i.e., neither similarity nor dissimilarity. ______________________________________________________________________________________ Movie S8a: Climatic envelope overlap between forest and grassy biomes (savanna and steppe) plotted in climate space. Envelopes were generated using the direct methodology and TraCE-21ka climate information. Red areas indicate the presence of grassy biomes only, whereas purple indicates overlap between grassy biomes and forest. For reference to the climatic variables used to define the climate space, see the TraCE-21ka correlation circle in figure A2. Movie S8b: Climatic envelope overlap between forest and savanna only, plotted in climate space. Envelopes were generated using the indirect methodology and TraCE-21ka climate information. Red areas indicate the presence of savanna only, whereas purple indicates overlap between savanna and forest. For reference to the climatic variables used, see the TraCE-21ka correlation circle in figure A2