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End-Triassic nonmarine biotic events

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Journal of Palaeogeography 2015年第4期4卷 331-348页

作者： Spencer G.Lucas Lawrence H.Tanner New Mexico Museum of Natural History Department of Biological Sciences Le Moyne College

The Late Triassic was a prolonged interval of elevated extinction rates and low origination rates that manifested themselves in a series of extinctions during Carnian, Norian and Rhaetian time. Most of these extinctions took place in the marine realm, particularly affecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms. On land, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on tetrapod vertebrates（amphibians and reptiles）, though some workers advocate a sudden endTriassic（TJB） extinction of land plants. Nevertheless, an extensive literature does not identify a major extinction of land plants at the TJB, and a comprehensive review of palynological records concluded that TJB vegetation changes were non-uniform（different changes in different places）, not synchronous and not indicative of a mass extinction of land plants. Claims of a substantial perturbation of plant ecology and diversity at the TJB in East Greenland are indicative of a local change in the paleoflora largely driven by lithofacies changes resulting in changing taphonomic filters. Plant extinctions at the TJB were palaeogeographically localized events, not global in extent. With new and more detailed stratigraphic data, the perceived TJB tetrapod extinction is mostly an artifact of coarse temporal resolution, the compiled correlation effect. The amphibian, archosaur and synapsid extinctions of the Late Triassic are not concentrated at the TJB, but instead occur stepwise, beginning in the Norian and extending into the Hettangian. There was a disruption of the terrestrial ecosystem across the TJB, but it was more modest than generally claimed. The ecological severity of the end-Triassic nonmarine biotic events are relatively low on the global scale. Biotic turnover at the end of the Triassic was likely driven by the CAMP（Central Atlantic Magmatic Province） eruptions, which caused significant environmental perturbations（cooling, warming, acidification） through outgassing, but the effec

关键词： Triassic-Jurassic boundary mass extinction land plants East Greenland tetrapods Newark Supergroup CAMP volcanism

Spatial and temporal dynamics of growth of woody plant species (birch and willows) on the foreland of a retreating glacier in southern Iceland

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Ecological Processes 2021年第1期10卷 184-194页

作者： Haley E.Synan Mikael A.Melfi Lawrence H.Tanner Department of Biological and Environmental Sciences Le Moyne CollegeSyracuseNew York 13214USA

Background:The forelands of retreating glaciers are invaluable natural laboratories in which to explore the processes of primary succession.Numerous studies have been conducted on foreland chronosequences to identify temporal and spatial trends of the successional communities.This study focused on the spatio-temporal distribution of three woody plant species on the foreland of a retreating glacier in southern Iceland where historical observations provide precise age control of the moraines.To evaluate colonization and successional trends,we examined which species increase in abundance with time and tested the role of proximity to a seed source in colonization.Additionally,we quantified the rate at which biomass carbon is added to the landscape.Results:The density of stems of Betula pubescens increases with moraine age across the foreland chronosequence while the density of stems of both Salix lanata and Salix phylicifolia decreases.We found low statistical significance to the relationship between the density of B.pubescens and distance from a forested ridge nor did we find a relationship between the lengths of the stems and the moraine ages.Woody biomass increased fastest during early successional stages and reached a maximum of 28.5 g C m^(−2) on the oldest moraine.Conclusions:Early colonization of moraines was controlled by environmental filters which favored both Salix species.Colonization by B.pubescens followed as environmental factors,e.g.,favorable soil properties,improved.We found no conclusive evidence that proximity to a potential source of B.pubescens propagules was a significant factor in controlling colonization.The assumption that the abundance of individuals increased with time through later successional stages proved valid for B.pubescens,but not for either species of Salix.These findings are consistent with the classical spatial successional model of community homogenization.Thus,general successional processes at the landscape scale control the temporal dynamics of individual species.

关键词： Glacial foreland Chronosequence Primary succession Spatial distribution Aboveground biomass Iceland

Successional trends and processes on a glacial foreland in Southern Iceland studied by repeated species counts

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Ecological Processes 2019年第1期8卷 138-148页

作者： Taylor G.Glausen Lawrence H.Tanner Jacobs School of Medicine and Biomedical Sciences State University of New York at BuffaloBuffaloNY 14203USA Department of Biological and Environmental Sciences Le Moyne CollegeSyracuseNY 13214USA

Introduction:Primary succession on glacial forelands is increasingly relevant as rapid glacial retreat is exposing growing land areas to plant colonization.We investigated temporal trends,controls,and outcomes in floral succession on a subarctic glacial foreland.Specifically,we examined changes in community composition(mosses,low shrubs,forbs,trees,and graminoids)over long-term(decadal)and short-term(les and attempted to identify the underlying processes responsible for the observed successional patterns.Methods:The study area was the foreland of the Skaftafellsjӧkull,located in Vatnajӧkull National Park near the south coast of Iceland.We established nine transect lines at varying distances from the ice front representing surfaces of age ranging from less than one decade to over 100 years.Each transect consisted of five measurement stations of 1 m2 where we measured vegetative cover(VC),species richness(SR),and species density(SD)and calculated species evenness(SE).Measurements were made initially in 2007 and repeated at the same geographic coordinates in 2014.Results:VC increased with distance from the ice front from 16%to over 90%.SR and SD increased from the youngest pioneer community through a mid-successional stage corresponding to an age of over 60 but less than 100 years.Increased VC but declining SR,SD,and SE characterized the oldest(over 100 years)bryophyte-dominated surfaces.Species turnover,which involved forbs almost exclusively,increased moderately from early through midsuccessional sites and declined on older sites.Comparison of the measurements made in 2014 to those made in 2007 demonstrates increased SR at mid-successional sites while SD remained relatively constant.Conclusion:At a small scale,colonization is controlled by local factors such as microtopography and aspect,particularly in proximity to the glacier.At the landscape level,changes in VC and community structure are controlled by time and nutrient availability.Low nutrient levels and limited site availability favor bryophyte

关键词： Primary succession Glacial foreland Species richness Species density Bryophyte

Paleosols of the upper Paleozoic Sangre de Cristo Formation,north-central New Mexico:Record of early Permian palaeoclimate in tropical Pangaea

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Journal of Palaeogeography 2017年第2期6卷 144-161页

作者： Lawrence H. Tanner Spencer G. Lucas Department of Biological Sciences Le Moyne CollegeSyracuseNY 13214USA New Mexico Museum of Natural History 1801 Mountain Road N.W.AlbuquerqueNM 87014USA

The lower Permian(Wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial plain.Locally,mudstones display a variety of pedogenic features.Common mudstone fabrics vary from platy to prismatic;some beds display prominent pedogenic slickensides.Drab-colored root traces are common throughout the section,as are calcareous nodules,which vary from small bodies with diffuse boundaries to vertically stacked,discrete,cm-scale nodules(rhizocretions),and less commonly form coalescing horizons.Vertisols occur only in the lower portion of the ca.90-m measured section.Most of the mudstone beds contain calcretes that are immature(calcic Protosols to calcic Argillisols),but the lower to middle portion of the section also contains mature calcrete horizons(argillic Calcisols and Calcisols).Intercalated micritic limestone beds with sharp contacts containing root traces,are of laterally variable thickness and grade to nodular calcretes.These are interpreted as floodplain pond carbonates that have undergone pedogenic alteration(palustrine limestones),indicating long periods of exposure under strongly seasonal climatic conditions.The isotopic composition of the pedogenic carbonate displays a substantial range of values,but most of the range of variation in isotopic composition is accounted for by isotopically heavier carbonate(both carbon and oxygen) precipitated in shallow ponds subject to intense pedogenic reworking(palustrine carbonate).During the early Permian,northern New Mexico was situated in a near equatorial position(ca.4° N).The overall character of the paleosols suggests a persistent warm,semi-humid,seasonal climate throughout most of the interval of deposition during the Wolfcampian,but with episodically increased aridity during formation of the more mature calcretes.No long-term trend of climate change is evident in the stratigraphic section examined for this study.

关键词： Sangre de Cristo Formation Wolfcampian Vertisol Argillisol Calcisol Protosol

Fossil charcoal from the Middle Jurassic of the Ordos Basin,China and its paleoatmospheric implications

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Geoscience Frontiers 2012年第4期3卷 493-502页

作者： Lawrence H. Tanner Xin Wang Alesha C. Morabito Department of Biological Sciences Le Moyne College Syracuse NY 13214 USA State Key Laboratory of Palaeobiology and Stratigraphy Nanjing Institute of Geology and Palaeontology Chinese Academy of SciencesNanjing 210008 China

The Yah＇an Formation of the Ordos Basin is a sequence of four members, consisting of si- liciclastic sediments deposited in alluvial, lacustrine and mire settings during the Middle Jurassic. Samples collected from Members Two and Four contain abundant blackened plant material identified through standard analytical techniques as fusain （fossil charcoal）. The occurrence of fusain in fluvial sandstones at multiple horizons in the outcrops, combined with the previously reported high concentra- tion of inertinite in the coals of Member One, indicates that paleowildfire was a common occurrence in the Ordos Basin during Yan＇an deposition. Sedimentary evidence from Yan＇an outcrops suggests that the paleoclimate was seasonal during deposition of Members Two through Four, which may have contributed to the wildfire frequency. The presence of fusain in the Yah＇an Formation indicates that atmospheric oxygen levels were clearly above the minimum required for sustained combustion during the Middle Jurassic. This conclusion contradicts previous geochemical models for paleoatmospheric composition, but supports more recent studies.

关键词： Fusain Paleoatmospheric oxygen Wildfire Ordos Basin Yan＇an Formation Charcoal

Effect of Land Use Change on Carbon Content and CO<sub>2</sub>Flux of Cloud Forest Soils, Santa Elena, Costa Rica

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Open Journal of Soil Science 2014年第2期4卷 64-71页

作者： Lawrence H. Tanner David L. Smith Jessica Curry Justin Twist Department of Biological Sciences Le Moyne College Syracuse USA Pottstown Memorial Medical Center Pottstown USA

We investigated the effects of land-use changes on soil carbon storage and soil CO2 flux by comparing soils from mature cloud forest and 31-year-old secondary forest, both in the Santa Elena Forest Reserve, a municipallyowned reserve at an elevation of 1600 to 1700 m near the town of Monteverde, and a clear-cut pasture near the reserve. Soils in the mature forest exhibit only weak horizonation but typically thick A horizons;they also consistently yield the highest carbon contents in the upper 30 cm. Soil CO2 flux was the highest in these soils, but also displayed the highest spatial variability. Secondary forest soils contain substantially less soil carbon than mature forest soils, but more than pasture soils. CO2 flux in the secondary forest soils was more similar to that of the mature forest, but displayed lower spatial variability. The pasture soils contain less soil carbon and produced lower CO2 flux levels than either of the forest soils. The pasture soils typically contain a well-defined coarse sandy layer 10 to 20 cm below the surface that we interpret as a sediment layer deposited across much of the landscape following a widespread erosion event, likely a consequence of the clear-cutting. Soil nitrogen concentrations are more than an order of magnitude lower than soil carbon concentrations, and display no trends between the different landscapes examined. Our preliminary results suggest that reforestation does restore soil carbon to clear-cut landscapes, but returning soil carbon levels to pre-land use levels occurs at a time scale of centuries, rather than decades.

关键词： Cloud Forest Secondary Succession Soil Carbon Soil Nitrogen Soil CO2 Flux

Changes in Soil Composition and Floral Coverage on a Glacial Foreland Chronosequence in Southern Iceland

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Open Journal of Soil Science 2013年第4期3卷 191-198页

作者： Lawrence H.Tanner Ann E.Walker Morgan Nivison David L.Smith Department of Biological Sciences Le Moyne CollegeSyracuseUSA Department of Earth&Planetary Sciences and Science Alliance Center of ExcellenceUniversity of TennesseeKnoxvilleUSA

The land surface in front of the Skaftafellsj?kull in southern Iceland, exposed by ice recession commencing about the start of the twentieth century, constitutes a foreland with a maximum age of about 100 years and a more distal outwash plain. The ages of different surfaces within this sequence are constrained by moraines of known or estimated ages. Across this chronosequence, we measured at various sites the extent of floral coverage of the surface, the soil carbon and nitrogen contents of the substrate and the soil CO2 flux rate. All measured parameters exhibit values increasing with distance from the ice front, which correlates approximately with age. The strongest correlations are seen between distance and the carbon and nitrogen concentrations of the soil. Marked horizonation of the soil is observed only on the oldest surfaces (100+ years).

关键词： Skaftafellsjokull Glacial Foreland Chronosequence Soil Carbon Soil CO_(2) Flux