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

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.

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Invasive Cereal Aphids of North America: Ecology and Pest Management

Annual Review of Entomology ◽

10.1146/annurev-ento-011118-111838 ◽

2019 ◽

Vol 64 (1) ◽

pp. 73-93 ◽

Cited By ~ 10

Author(s):

Michael J. Brewer ◽

Frank B. Peairs ◽

Norman C. Elliott

Keyword(s):

North America ◽

Pest Management ◽

Great Plains ◽

Large Scale ◽

Production Systems ◽

Cereal Crops ◽

Cereal Aphids ◽

Sugarcane Aphid ◽

Cereal Production ◽

Abundance And Diversity

Aphid invasions of North American cereal crops generally have started with colonization of a new region or crop, followed by range expansion and outbreaks that vary in frequency and scale owing to geographically variable influences. To improve understanding of this process and management, we compare the invasion ecology of and management response to three cereal aphids: sugarcane aphid, Russian wheat aphid, and greenbug. The region exploited is determined primarily by climate and host plant availability. Once an area is permanently or annually colonized, outbreak intensity is also affected by natural enemies and managed inputs, such as aphid-resistant cultivars and insecticides. Over time, increases in natural enemy abundance and diversity, improved compatibility among management tactics, and limited threshold-based insecticide use have likely increased resilience of aphid regulation. Application of pest management foundational practices followed by a focus on compatible strategies are relevant worldwide. Area-wide pest management is most appropriate to large-scale cereal production systems, as exemplified in the Great Plains of North America.

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Climatology of Severe Local Storm Environments and Synoptic-Scale Features over North America in ERA5 Reanalysis and CAM6 Simulation

Journal of Climate ◽

10.1175/jcli-d-19-0986.1 ◽

2020 ◽

Vol 33 (19) ◽

pp. 8339-8365 ◽

Cited By ~ 1

Author(s):

Funing Li ◽

Daniel R. Chavas ◽

Kevin A. Reed ◽

Daniel T. Dawson II

Keyword(s):

United States ◽

North America ◽

Great Plains ◽

Large Scale ◽

Extreme Values ◽

Convective Available Potential Energy ◽

The United States ◽

Synoptic Scale ◽

Low Level ◽

High Bias

AbstractSevere local storm (SLS) activity is known to occur within specific thermodynamic and kinematic environments. These environments are commonly associated with key synoptic-scale features—including southerly Great Plains low-level jets, drylines, elevated mixed layers, and extratropical cyclones—that link the large-scale climate to SLS environments. This work analyzes spatiotemporal distributions of both extreme values of SLS environmental parameters and synoptic-scale features in the ERA5 reanalysis and in the Community Atmosphere Model, version 6 (CAM6), historical simulation during 1980–2014 over North America. Compared to radiosondes, ERA5 successfully reproduces SLS environments, with strong spatiotemporal correlations and low biases, especially over the Great Plains. Both ERA5 and CAM6 reproduce the climatology of SLS environments over the central United States as well as its strong seasonal and diurnal cycles. ERA5 and CAM6 also reproduce the climatological occurrence of the synoptic-scale features, with the distribution pattern similar to that of SLS environments. Compared to ERA5, CAM6 exhibits a high bias in convective available potential energy over the eastern United States primarily due to a high bias in surface moisture and, to a lesser extent, storm-relative helicity due to enhanced low-level winds. Composite analysis indicates consistent synoptic anomaly patterns favorable for significant SLS environments over much of the eastern half of the United States in both ERA5 and CAM6, though the pattern differs for the southeastern United States. Overall, our results indicate that both ERA5 and CAM6 are capable of reproducing SLS environments as well as the synoptic-scale features and transient events that generate them.

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Comparison of convective parameters derived from ERA5 and MERRA2 with rawinsonde data over Europe and North America

Journal of Climate ◽

10.1175/jcli-d-20-0484.1 ◽

2020 ◽

pp. 1-55

Author(s):

Mateusz Taszarek ◽

Natalia Pilguj ◽

John T. Allen ◽

Victor Gensini ◽

Harold E. Brooks ◽

...

Keyword(s):

North America ◽

Great Plains ◽

Wind Shear ◽

Extreme Values ◽

Absolute Error ◽

Coastal Zones ◽

Opposite Pattern ◽

The Balkans ◽

Low Level ◽

Lapse Rates

AbstractIn this study we compared 3.7 mln rawinsonde observations from 232 stations over Europe and North America with proximal vertical profiles from ERA5 and MERRA2 to examine how well reanalysis depicts observed convective parameters. Larger differences between soundings and reanalysis are found for thermodynamic theoretical parcel parameters, low-level lapse rates and low-level wind shear. In contrast, reanalysis best represents temperature and moisture variables, mid-tropospheric lapse rates, and mean wind. Both reanalyses underestimate CAPE, low-level moisture and wind shear, particularly when considering extreme values. Overestimation is observed for low-level lapse rates, mid-tropospheric moisture and the level of free convection. Mixed-layer parcels have overall better accuracy when compared to most-unstable, especially considering convective inhibition and lifted condensation level. Mean absolute error for both reanalyses has been steadily decreasing over the last 39 years for almost every analyzed variable. Compared to MERRA2, ERA5 has higher correlations and lower mean absolute errors. MERRA2 is typically drier and less unstable over central Europe and the Balkans, with the opposite pattern over western Russia. Both reanalyses underestimate CAPE and CIN over the Great Plains. Reanalyses are more reliable for lower elevations stations and struggle along boundaries such as coastal zones and mountains. Based on the results from this and prior studies we suggest that ERA5 is likely one of the most reliable available reanalysis for exploration of convective environments, mainly due to its improved resolution. For future studies we also recommend that computation of convective variables should use model levels that provide more accurate sampling of the boundary-layer conditions compared to less numerous pressure levels.

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Global fire emissions estimates during 1997–2015

10.5194/essd-2016-62 ◽

2017 ◽

Cited By ~ 10

Author(s):

Guido R. van der Werf ◽

James T. Randerson ◽

Louis Giglio ◽

Thijs T. van Leeuwen ◽

Yang Chen ◽

...

Keyword(s):

North America ◽

Fuel Consumption ◽

Fire Severity ◽

Emission Factors ◽

Trace Gas ◽

Burned Area ◽

Biogeochemical Model ◽

Fire Dynamics ◽

Fire Emissions ◽

Aerosol Emissions

Abstract. Climate, land use, and other anthropogenic and natural drivers have the potential to influence fire dynamics in many regions. To develop a mechanistic understanding of the changing role of these drivers and their impact on atmospheric composition, long term fire records are needed that fuse information from different satellite and in-situ data streams. Here we describe the fourth version of the Global Fire Emissions Database (GFED) and quantify global fire emissions patterns during 1997–2015. The modeling system, based on the Carnegie-Ames-Stanford-Approach (CASA) biogeochemical model, has several modifications from the previous version and uses higher quality input datasets. Significant upgrades include: 1) new burned area estimates with contributions from small fires, 2) a revised fuel consumption parameterization optimized using field observations, 3) modifications that improve the representation of fuel consumption in frequently burning landscapes, and 4) fire severity estimates that better represent continental differences in burning processes across boreal regions of North America and Eurasia. The new version has a higher spatial resolution (0.25°) and uses a different set of emission factors that separately resolves trace gas and aerosol emissions from temperate and boreal forest ecosystems. Global mean carbon emissions using the burned area dataset with small fires (GFED4s) were 2.2 x 1015 grams carbon per year (Pg C yr-1) during 1997–2015, with a maximum in 1997 (3.0 Pg C yr-1) and minimum in 2013 (1.8 Pg C yr-1). These estimates were 11 % higher than our previous estimates (GFED3) during 1997–2011, when the two datasets overlapped. This increase was the result of a substantial increase in burned area (37 %), mostly due to the inclusion of small fires, and a modest decrease in mean fuel consumption (–19 %) to better match estimates from field studies, primarily in savannas and grasslands. For trace gas and aerosol emissions, differences between GFED4s and GFED3 were often larger due to the use of revised emission factors. If small fire burned area was excluded (GFED4 without the "s" for small fires), average emissions were 1.5 Pg C yr-1. The addition of small fires had the largest impact on emissions in temperate North America, Central America, Europe, and temperate Asia. Our improved dataset provides an internally consistent set of burned area and emissions that may contribute to a better understanding of multi-decadal changes in fire dynamics and their impact on the Earth System. GFED data is available from http://www.globalfiredata.org.

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