scholarly journals Fire Dynamics in Boreal Forests Over the 20th Century: A Data-Model Comparison

2021 ◽  
Vol 9 ◽  
Author(s):  
Chiara Molinari ◽  
Stijn Hantson ◽  
Lars Peter Nieradzik
Keyword(s):  
North America ◽  
Data Model ◽  
Boreal Forests ◽  
Model Comparison ◽  
Fire Regime ◽  
Total Carbon ◽  
Time Interval ◽  
Fire Dynamics ◽  
Dynamic Global Vegetation Model ◽  
Fire Activity

Fire regimes across the world are expected to be altered by continuing variations in socio-economic conditions and climate. Current global fire-vegetation models are able to represent the present-day fire activity, but it is unclear how well they can simulate past or future scenarios. Here we use sedimentary charcoal-based biomass burning reconstructions to evaluate fire probability and total carbon flux emitted to the atmosphere per year simulated by the dynamic global vegetation model LPJ-GUESS with its incorporated fire model SIMFIRE-BLAZE across the boreal region during the last century. The analyses were run for the whole time period (1900–2000 CE), as well as for the intervals 1900–1950 CE and 1950–2000 CE. The data–model comparison for the 20th century reveals a general disagreement in trends between charcoal reconstructions (with decreasing or stable trends) and simulations (showing an overall increase) at both global (boreal forests) and continental scales (North America and Fennoscandia), as well as for most of the regional sub-areas (Canada, Norway and Sweden). The only exceptions are Alaska and Finland/Russia Karelia, where all the variables increase. Negative correlations between observations and model outputs are also recorded for the two different sub-periods, except for Alaska and North America during the time interval 1900–1950 CE, and Norway and Finland/Russia Karelia between 1950 and 2000 CE. Despite several uncertainties in charcoal records, main differences between modeled and observed fire activity are probably due to limitations in the representation of the human impact on fire regime (especially connected to forest management and landscape fragmentation) in the model simulations.

The Global Pollen Database in biogeographical and palaeoclimatic studies

2008 ◽  
Vol 32 (4) ◽  
pp. 379-402 ◽  
Author(s):  
K. Gajewski
Keyword(s):  
North America ◽  
Data Model ◽  
Model Comparison ◽  
Physical Geography ◽  
Taxonomic Resolution ◽  
Climate Effect ◽  
Data Synthesis ◽  
Major Transitions ◽  
Continental Scale ◽  
Past Conditions

The Global Pollen Database is an example of a successful data synthesis effort that has uses for biogeographical and climate change studies. Results are of interest in many fields of physical geography. Continental-scale maps of past conditions have been used in data-model comparison studies. Time series, developed by averaging quantitative reconstructions from many sites, have indicated that millennial-scale climate variability has affected the vegetation of Europe and North America during the Holocene. Major transitions in the vegetation of Europe and North America occurred at the same time, suggesting the overriding climate effect on the vegetation of both continents. The database can also be used to test biogeographical hypotheses, as several examples illustrate, without the need for collecting new data. Hundreds of studies over the past 50 years show that pollen analysis is more precise than frequently acknowledged: vegetation responds rapidly to climate variations, changes in vegetation are spatially coherent and the taxonomic resolution available in the database is greater than frequently acknowledged. The availability of a public, freely available database enables different analyses to be performed on the same data, thereby ensuring that results are not dependent on methodology.

The Neogene transition from C3 to C4 grasslands in North America: assemblage analysis of fossil phytoliths

Paleobiology ◽  
2011 ◽  
Vol 37 (1) ◽  
pp. 50-71 ◽  
Author(s):  
Caroline A. E. Strömberg ◽  
Francesca A. McInerney
Keyword(s):  
North America ◽  
Great Plains ◽  
Late Miocene ◽  
Vegetation Change ◽  
Stable Carbon Isotopes ◽  
Fire Regime ◽  
Tooth Enamel ◽  
Regional Scale ◽  
Grassland Ecosystems ◽  
Isotopic Records

The rapid ecological expansion of grasses with C4 photosynthesis at the end of the Neogene (8–2 Ma) is well documented in the fossil record of stable carbon isotopes. As one of the most profound vegetation changes to occur in recent geologic time, it paved the way for modern tropical grassland ecosystems. Changes in CO2 levels, seasonality, aridity, herbivory, and fire regime have all been suggested as potential triggers for this broadly synchronous change, long after the evolutionary origin of the C4 pathway in grasses. To date, these hypotheses have suffered from a lack of direct evidence for floral composition and structure during this important transition. This study aimed to remedy the problem by providing the first direct, relatively continuous record of vegetation change for the Great Plains of North America for the critical interval (ca. 12–2 Ma) using plant silica (phytolith) assemblages.Phytoliths were extracted from late Miocene-Pliocene paleosols in Nebraska and Kansas. Quantitative phytolith analysis of the 14 best-preserved assemblages indicates that habitats varied substantially in openness during the middle to late Miocene but became more uniformly open, corresponding to relatively open grassland or savanna, during the late Miocene and early Pliocene. Phytolith data also point to a marked increase of grass short cells typical of chloridoid and other potentially C4 grasses of the PACMAD clade between 8 and 5 Ma; these data suggest that the proportion of these grasses reached up to ∼50–60% of grasses, resulting in mixed C3-C4 and highly heterogeneous grassland communities by 5.5 Ma. This scenario is consistent with interpretations of isotopic records from paleosol carbonates and ungulate tooth enamel. The rise in abundance of chloridoids, which were present in the central Great Plains since the early Miocene, demonstrates that the “globally” observed lag between C4 grass evolution/taxonomic diversification and ecological expansion occurred at the regional scale. These patterns of vegetation alteration imply that environmental change during the late Miocene-Pliocene played a major role in the C3-C4 shift in the Great Plains. Specifically, the importance of chloridoids as well as a decline in the relative abundance of forest indicator taxa, including palms, point to climatic drying as a key trigger for C4 dominance.

scholarly journals Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors in the Central Great Plains of North America

2014 ◽  
Vol 102 (6) ◽  
pp. 1374-1385 ◽  
Author(s):  
Zak Ratajczak ◽  
Jesse B. Nippert ◽  
John M. Briggs ◽  
John M. Blair
Keyword(s):  
North America ◽  
Great Plains ◽  
Fire Dynamics

Data-model Comparison for the mid-Pliocene Warm Period

2021 ◽  
Author(s):  
Julia Tindall ◽  
Alan Haywood ◽  
Ulrich Salzmann ◽  
Aisling Dolan
Keyword(s):  
Data Model ◽  
Model Comparison ◽  
Surface Air Temperature ◽  
High Latitudes ◽  
Orbital Forcing ◽  
Local Site ◽  
Modern Analogue ◽  
Intercomparison Project ◽  
Global Mean ◽  
Good Agreement

<p>Modelling results from PlioMIP2 (the Pliocene Model Intercomparison Project Phase 2) focussing on MIS KM5c; ~3.205Ma, suggest that global mean surface air temperature was 1.7 – 5.2 °C higher than the preindustrial.  This warming was amplified at the poles and over land.  The results are in reasonable agreement with paleodata over the ocean.   </p><p>Over the land the situation is more complicated.  Model and data are in very good agreement at lower latitudes, however at high latitudes an initial data-model comparison shows much warmer mPWP temperatures from data than from models.   </p><p>Here we consider possible reasons for this data-model discord at high latitudes.  These include uncertainties in model boundary conditions (such as CO<sub>2 </sub>and orbital forcing), and whether there are local site-specific conditions which need to be accounted for.  We also show that the seasonal cycle in mPWP temperatures at these high latitude sites has no modern analogue.  This could lead to inaccuracies when comparing model derived mean annual temperatures with quantitative climatic estimates from palaeobotanical data using Nearest Living Relative methods.</p>

scholarly journals Comparing modelled fire dynamics with charcoal records for the Holocene

2014 ◽  
Vol 10 (2) ◽  
pp. 811-824 ◽  
Author(s):  
T. Brücher ◽  
V. Brovkin ◽  
S. Kloster ◽  
J. R. Marlon ◽  
M. J. Power
Keyword(s):  
Land Surface ◽  
Burned Area ◽  
Surface Model ◽  
Model Output ◽  
Z Score ◽  
Fire Dynamics ◽  
Anthropogenic Forcing ◽  
Natural Fire ◽  
Fire Activity ◽  
Z Scores

Abstract. An earth system model of intermediate complexity (CLIMate and BiosphERe – CLIMBER-2) and a land surface model (JSBACH), which dynamically represent vegetation, are used to simulate natural fire dynamics through the last 8000 yr. Output variables of the fire model (burned area and fire carbon emissions) are used to compare model results with sediment-based charcoal reconstructions. Several approaches for processing model output are also tested. Charcoal data are reported in Z-scores with a base period of 8000–200 BP in order to exclude the strong anthropogenic forcing of fire during the last two centuries. The model–data comparison reveals a robust correspondence in fire activity for most regions considered, while for a few regions, such as Europe, simulated and observed fire histories show different trends. The difference between modelled and observed fire activity may be due to the absence of anthropogenic forcing (e.g. human ignitions and suppression) in the model simulations, and also due to limitations inherent to modelling fire dynamics. The use of spatial averaging (or Z-score processing) of model output did not change the directions of the trends. However, Z-score-transformed model output resulted in higher rank correlations with the charcoal Z-scores in most regions. Therefore, while both metrics are useful, processing model output as Z-scores is preferable to areal averaging when comparing model results to transformed charcoal records.

scholarly journals Mid-Holocene climate change in Europe: a data-model comparison

2007 ◽  
Vol 3 (3) ◽  
pp. 499-512 ◽  
Author(s):  
S. Brewer ◽  
J. Guiot ◽  
F. Torre
Keyword(s):  
Climate Change ◽  
Data Model ◽  
General Circulation ◽  
Model Comparison ◽  
General Circulation Models ◽  
Growing Degree Days ◽  
Degree Days ◽  
European Continent ◽  
Holocene Climate Change ◽  
Correct Location

Abstract. We present here a comparison between the outputs of 25 General Circulation Models run for the mid-Holocene period (6 ka BP) with a set of palaeoclimate reconstructions based on over 400 fossil pollen sequences distributed across the European continent. Three climate parameters were available (moisture availability, temperature of the coldest month and growing degree days), which were grouped together using cluster analysis to provide regions of homogenous climate change. Each model was then investigated to see if it reproduced 1) similar patterns of change and 2) the correct location of these regions. A fuzzy logic distance was used to compare the output of the model with the data, which allowed uncertainties from both the model and data to be taken into account. The models were compared by the magnitude and direction of climate change within the region as well as the spatial pattern of these changes. The majority of the models are grouped together, suggesting that they are becoming more consistent. A test against a set of zero anomalies (no climate change) shows that, although the models are unable to reproduce the exact patterns of change, they all produce the correct signs of change observed for the mid-Holocene.

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