Temperate Vegetation Research Articles

Modeling of carbonaceous particles emitted by boreal and temperate wildfires at northern latitudes

For the first time, a spatial and monthly inventory has been constructed for carbonaceous particles emitted by boreal and temperate wildfires in forests, shrublands, and grasslands, with burned area data statistics, fuel load maps, fire characteristics, and particle emission factors. The time period considered is 1960–1997, and an important year‐to‐year variability was observed. On average, boreal and temperate vegetation fires represent 4% of global biomass burning, but during extreme years, their contribution may reach 12%, producing 9% and 20% of black carbon (BC) and particulate organic matter (POM), respectively, emitted by worldwide fires. The North American component of the boreal forest fires (Canada and Alaska) represents 4 to 122 Gg C yr‐1 of BC and 0.07 to 2.4 Tg yr‐1 of POM emitted, whereas the Eurasiatic component (Russia and northern Mongolia) may vary in the 16 to 474 Gg C yr‐1 range for BC and between 0.3 and 9.4 Tg yr‐1 for POM, with however great uncertainty. Temperate forests in conterminous United States and Europe have a much lower contribution with an average of 11 Gg C yr‐1 of BC and 0.2 Tg yr‐1 of POM. Grassland fires in Mongolia represent significant BC and POM sources which may reach 62 Gg C and 0.4 Tg, respectively. Finally, an annual average of BC emissions for shrubland fires in both the Mediterranean region and California is 20 Gg C yr‐1, with average POM emissions of 0.1 Tg yr‐1. These source maps obtained with a high spatial resolution (lox lo) can now be added to previous ones developed for other global carbonaceous aerosol sources (fossil fuel combustion, tropical biomass burning, agricultural and domestic fires) in order to provide global maps of particulate carbon emissions. Taking into account particle injection height in relation with each type of fire, our source map is a useful tool for studying the atmospheric transport and the impact of carbonaceous aerosols in three‐dimensional transport and climate models.

A phytogeographical characterization of the vine flora of the Sonoran and Chihuahuan deserts

Aim This study presents a phytogeographical characterization of the vine flora of two lower North American desert regions as a biogeographical framework for further ecological inquiry into desert vines. Location The phytogeography of the vine flora of the Sonoran and Chihuahuan Deserts was c haracterized based on 263 known species. Methods Checklists of the vines of each desert were developed. Represented genera were then grouped into 10 phytogeographical elements based on worldwide distribution patterns. To compare the floristic composition of the desert floras, an index of species similarity was calculated. Results About a third more species of vines occur in the Sonoran Desert than in the Chihuahuan Desert. Based on the analysis, cosmopolitan genera are the only group more numerous in absolute terms in the Chihuahuan Desert than in the Sonoran Desert. Tropical elements are represented in about the same proportion in each desert as the number of species, however, nearly twice as many pantropical and neotropical genera are represented in the Sonoran Desert as in the Chihuahuan Desert. Proportionately, more genera of temperate elements occur in the Chihuahuan Desert than in the Sonoran desert, although the absolute number of genera is slightly higher in the latter. Main conclusions As these deserts are relatively recent ecological formations and as vines evolved in forest ecosystems, the composition of the desert vine floras is the result of the interaction between historical vegetation types, their constituent taxa and climatic and geological history. The main differences in the vining floras of the present-day Sonoran and Chihuahuan Deserts appear to be the result of greater historical influence in the Sonoran Desert of (1) tropical vegetation types and (2) the emergence of the Gulf of California. The Chihuahuan Desert vine flora seems to be the result of (1) a more pronounced historical temperate vegetation, (2) the lack of an important isolating event, such as the creation of the Baja California peninsula, and (3) a cooler climate with shorter growing seasons.

Competition in the regeneration niche between conifers and angiosperms: Bond's slow seedling hypothesis

What features of angiosperms have enabled them to dominate the biomass of much temperate and tropical vegetation despite the high productivity of many adult gymnosperms, especially conifers? Bond (1989) argued that slow-growing gymnosperm juveniles are poor competitors with angiosperms regenerating in forest gaps and other well lit, well watered habitats. Consequently, gymnosperms are restricted to areas where growth of angiosperm competitors is reduced, for example by cold or nutrient shortages. A historical implication of Bond's hypothesis is that angiosperms overran gymnosperms during the Cretaceous and Tertiary by invading their regeneration niche. Bond's (1989) 'slow seedling' hypothesis has considerable appeal because it seeks to explain major phytogeographical patterns and evolutionary trends in terms of observable vegetative traits. Data suitable for testing Bond's plausible arguments were then quite limited, and what was proposed as hypothesis has often been cited as fact in recent reviews of conifer biology (Enright & Hill 1995; Richardson 1998; Smith & Hinckley 1995). Studies of large-scale trends may be exploratory (generating hypotheses) or sceptical (testing hypotheses); both modes of inquiry are essential and indeed complementary (McShea 1998). This review emphasizes the sceptical mode, and aims to test some of the main premises and generalizations of Bond's (1989) slow seedling hypothesis. Although Bond's arguments embraced the polyphyletic gymnosperms, relevant data are mostly limited to the monophyletic conifers, also constraining this review. A key element of Bond's (1989) hypothesis is that conifer seedlings cannot match the fastest growth rates of angiosperms. This is supported here for earlysuccession angiosperms, but not for late-succession, north-temperate trees. Few comparative data are available from regions where both angiosperms and conifers have long-lived leaves, a trait that is correlated with reduced seedling growth rate (Reich 1998). Whether Bond's hypothesis can explain the rarity of conifers and gymnosperms in lowland tropical forests therefore remains uncertain. Bond (1989) attributed the slow growth of juvenile conifers to an inefficient transport system and a low

Correlation between Vegetation in Southwestern Africa and Oceanic Upwelling in the Past 21,000 Years

Dinoflagellate cyst and pollen records from marine sediments off the southwestern African coast reveal three major aridification periods since the last glaciation and an environmental correlation between land and sea. Abundant pollen of desert, semi-desert, and temperate plants 21,000–17,500 cal yr B.P. show arid and cold conditions in southwestern Africa that correspond to low sea surface temperatures and enhanced upwelling shown by dinoflagellate cysts. Occurrence of Restionaceae in the pollen record suggests northward movement of the winter-rain regime that influenced the study area during the last glacial maximum. Decline of Asteroideae, Restionaceae, and Ericaceae in the pollen record shows that temperate vegetation migrated out of the study area about 17,500 cal yr B.P., probably because of warming during the last deglaciation. The warming in southwestern Africa was associated with weakened upwelling and increased sea surface temperatures, 2000–2800 years earlier than in the Northern Hemisphere. Aridification 14,300–12,600 cal yr B.P. is characterized by a prominent increase of desert and semi-desert pollen without the return of temperate vegetation. This aridification corresponds to enhanced upwelling off Namibia and cooler temperatures in Antarctica, and it might have been influenced by oceanic thermohaline circulation. Aridification 11,000–8900 cal yr B.P. is out of phase with the northern African climate. Reduction of the water vapor supply in southwestern Africa at that time may be related to northward excursions of the Intertropical Convergence Zone.

Neotropical seasonally dry forests and Quaternary vegetation changes

AbstractSeasonally dry tropical forests have been largely ignored in discussions of vegetation changes during the Quaternary.We distinguish dry forests, which are essentially tree‐dominated ecosystems, from open savannas that have a xeromorphic fire‐tolerant, grass layer and grow on dystrophic, acid soils. Seasonally dry tropical forests grow on fertile soils, usually have a closed canopy, have woody floras dominated by the Leguminosae and Bignoniaceae and a sparse ground flora with few grasses. They occur in disjunct areas throughout the Neotropics. The Chaco forests of central South America experience regular annual frosts, and are considered a subtropical extension of temperate vegetation formations.At least 104 plant species from a wide range of families are each found in two or more of the isolated areas of seasonally dry tropical forest scattered across the Neotropics, and these repeated patterns of distribution suggest a more widespread expanse of this vegetation, presumably in drier and cooler periods of the Pleistocene.We propose a new vegetation model for some areas of the Ice‐Age Amazon: a type of seasonally dry tropical forest, with rain forest and montane taxa largely confined to gallery forest. This model is consistent with the distributions of contemporary seasonally dry tropical forest species in Amazonia and existing palynological data.The hypothesis of vicariance of a wider historical area of seasonally dry tropical forests could be tested using a cladistic biogeographic approach focusing on plant genera that have species showing high levels of endemicity in the different areas of these forests.

High-frequency sea-level fluctuations and plant habitats in Cenomanian fluvial to estuarine succession: Pecínov quarry, Bohemia

Abstract The succession of the Peruc and Korycany Members in the Pecinov quarry, Bohemia, reflects the interplay of 4th-order sea-level fluctuations, of approximately 100–120 ka periodicity, and a long-term (3rd-order) sea-level rise of the late middle through early late Cenomanian. The succession studied includes deposits of a shallow, gravelly braided river (unit 1), tide-influenced braided river (unit 2), supratidal marsh (unit 3), tidal flat (unit 4) and ebb-tidal delta to estuary mouth fill (unit 5). Units 1–5 are interpreted as parasequences of a single depositional sequence; units 1–4 together make up a transgressive systems tract and unit 5 is a highstand deposit, capped by a sequence boundary. The presence of deciduous plants attests to a certain degree of seasonality of the climate. The mixing of thermophile and temperate vegetation, together with the presumed palaeolatitudinal position of the Bohemian Massif, suggests a generally slightly semi-arid (i.e., seasonally wet) regional climatic conditions during the deposition of units 1–5; substrates in local habitats in alluvial valleys and estuary margins were damp due to high local water table. The plant habitat of the alluvial valley (units 1 and 2) was characterized by the Myrtophyllum assemblage, which included an angiosperm-dominated gallery forest and shrubs on braid bars and islands. The transition between fluvial and coastal environments was characterized by a taxodioid backswamp forest (the Ceratostrobus assemblage). Coastal vegetation (i.e., the marsh habitats of unit 3 and the upper part of unit 5), changes distinctly between the two units, although both represent similar facies of high intertidal to supratidal origin. The Frenelopsis assemblage of unit 3, representing shrubby marsh vegetation growing seaward of the Ceratostrobus forest, differs strongly from the more xerophytic Sphenolepis assemblage of unit 5, characterized by herbaceous pteridophytes growing in the marsh in front of a coastal taxodioid forest. We explain the differences between units 3 and 5 by the different sequence-stratigraphic position of the two units: a high groundwater table and eutrophic substrate of the transgressive systems tract (unit 3) compared with a lower or falling regional water table and oligotrophic substrate during the late highstand systems tract (unit 5). Thus, temporal changes in coastal plant assemblages of the Pecinov section do not merely reflect lateral shifts of facies belts, but show that similar depositional environments in different systems tracts hosted very different floras.

Middle Pleistocene temperate deposits at Dingé, Ille-et-Vilaine, northwest France: pollen, plant and insect macrofossil analysis

Nine cores were taken from a damp depression at Dinge, Ille-et-Vilaine, northwest France. Analyses of the pollen, plant macrofossil and Coleoptera remains preserved in the same organic samples of two profiles suggest a temperate vegetation characterised by a mixed deciduous forest with mesophilous taxa (Carpinus, Fagus, Quercus) followed by a coniferous forest with Pinus and Picea. The determination of plant taxa to species was made either directly through the identification of plant macrofossil remains and pollen or indirectly through the identification of phytophagous Coleoptera specifically related to certain plants. Stratigraphical information derived from pollen, plant macrofossil and insect data indicates that this sequence may be correlated with a temperate episode older than the Eemian and younger than the Holsteinian, possibly the Bouchet 2 (Oxygen Isotope Stage 7c) or Bouchet 3 (Oxygen Isotope Stage 7a) temperate periods or the Landos Interglacial (Oxygen Isotope Stage 9 pro parte). (C) 1997 by John Wiley & Sons, Ltd.

Monsoon fluctuations over the past 350 kyr: High-resolution evidence from northeast asia/northwest Pacific climate proxies (marine pollen and radiolarians)

High-resolution analyses of pollen and radiolarians from northwest Pacific cores V28-304 and RC14-99 provide continuous, directly-linked evidence of oceanic-atmospheric climate processes through the past three Pleistocene glacial-interglacial cycles. Systematic fluctuations in marine pollen assemblages, which reflect changes in the forest communities of Japan, are compatible with fluctuations in faunal assemblages and inferred oceanographic properties offshore. Each interglacial has distinguishable characteristics which imply that the sequence, timing and magnitude of climatic change were not identical during the three most recent interglacial intervals. Most interglacials contain at least one 10–15 kyr period of exceptionally high percentages (>20%) of Cryptomeria, which we interpret as reflecting increased levels of precipitation in response to intensification of the summer monsoon. With the exception of Oxygen Isotope Substage 5e in RC14-99, interglacial summer sea-surface temperatures were similar to or slightly warmer than today. Glacial environments in central Japan and in the northern subtropical gyre were similar to those which now support cold-temperate and boreal forests on northernmost Japan and a dominant subpolar fauna and associated low sea-surface temperatures offshore. Climatic change was apparently not as severe in southern Japan (where temperate vegetation largely replaced warm-temperate flora) or in the southern subtropical gyre (where only winter SSTs were cooler than present). We attribute these changes in vegetation and surface-water conditions to shifts in the atmospheric polar and oceanographic subarctic fronts in response to the seasonal variations in the Siberian High. Maxima in Cryptomeria systematically lag maxima in solar insolation at 30°N. This correlation between our summer monsoon indicator and summer insolation substantiates the view that the strength of the Asian monsoon is linked to variations in northern hemisphere solar radiation.

Pollen Evidence of Changing Holocene Monsoon Climate in Sichuan Province, China

Pollen evidence from Lake Shayema, Mianning County, was obtained to examine postglacial vegetation and climatic change in southwestern Sichuan, China. The sclerophyllous character of the region's warm temperate vegetation today is a reflection of extreme drought in spring before the onset of the Asian monsoons. The pollen record displays several changes in the vegetation over the last 11,000 yr. From 11,000 to 9100 yr B.P., cold-tolerant species, such as Abies , Betula, and deciduous oaks, dominated the vegetation. Between 9100 and 7800 yr B.P., the abundance of deciduous oaks decreased and evergreen oaks increased, as did Tsuga and mesic deciduous species. This change suggests a warming climate with increased precipitation. From 7800 to 4000 yr B.P., sclerophyllous species increased at the expense of mesic deciduous species, an indication that precipitation was becoming more seasonal. Except for increased disturbance starting ca. 1000 yr B.P., the predominance of sclerophyllous vegetation continued until today. The pollen results are compatible with proposed global circulation hypotheses of a strengthened monsoon system during the early to mid Holocene.

Classification of the eastern alpine vegetation of Lesotho

Abstract Five vegetation communities in the alpine catchments of Lesotho were identified by hierarchical classification of the botanical composition data. Discriminant analysis indicated that these communities occupy particular topographic positions. The community‐environment relationships identified in this study were similar to those reported from other alpine areas of Lesotho. Grasslands at high altitudes are temperate in nature, with a high proportion of C3 grass species. Below 2 950 m on the warmer aspects and below 2 750 m on south‐facing slopes, subtropical grass species (C4) dominate the sward. Within the temperate and subtropical vegetation belts, slope orientation dictates the proportion of C3 species present in the sward. It is proposed that topography acts to modify the factors that directly influence plant growth by modifying solar radiation patterns.

High‐Altitude bee fauna of southeastern Brazil: Implications for biogeographic patterns (Hymenoptera: Apoidea)

The bee fauna of two high altitude areas in southeastern Brazil is compared to that of surrounding lowlands. Four different geographic distribution patterns are recognized: species may be a) widespread in the region regardless of altitude; b) widespread in the lowland but not reaching altitudes above around 1300 m; c) restricted to the mountains of southeastern Brazil; or d) common to these mountains and to mountains and/or lowlands south of about 24’ latitude south. This last set of species may be a remnant fauna associated with the subtropical and temperate vegetation that advanced northward in cold periods. This relict fauna may be descendant of populations that have been trapped on the top of mountain ranges by the development of a warmer climate. It is also suggested that a relationship may exist between the bee fauna of the southeastern mountains fields and that of the “cerrado”; and related vegetations.

Relict floras of Atlantic islands: patterns assessed

St. Helena (South Atlantic Ocean) and Macaronesia have endemic plants that have been interpreted as relicts. This paper divides these relicts into three main types. It is suggested that type 1 relicts are of Miocene age. They are usually wet tropical forest trees, geographically and taxonomically highly disjunct from their nearest relatives. Type 2 relicts are of Late Miocene or Pliocene age, usually trees of tropical or subtropical seasonally dry vegetation, often with trans-African disjunction, and moderate taxonomic isolation. Type 3 relicts are of Late Pliocene or Pleistocene age, usually herbs of arid zone or temperate vegetation, with little taxonomic or geographical disjunction from their nearest relatives. Relict theory is defined, with discussion of its explanatory power to account for patterns of endemism, and more generally, taxonomic and geographical patterns of biodiversity.

Changing patterns of vegetation through Siwalik succession

The palaeobotanical record from the Neogene of Himalaya has been examined and an attempt has been made to reconstruct the vegetation patterns and throw light on palaeoclimate of the region during Siwalik time. Though the flora of the Pre-Siwalik Neogene from which the Siwalik flora evolved is poorly documented, a few palynofossils from the Kasauli and Dagshai formations indicate the existence of subtropical to temperate vegetation in the Upper reaches of the newly built Himalaya. On the contrary, a fairly rich assemblage of megafossils from the Siwalik indicates widespread tropical evergreen to moist deciduous mixed forest in the lowland sub-Himalayan zone during Middle Miocene-Pliocene The assemblage is dominated by wet evergreen dipterocarps and associated taxa, most of which are known to have entered the Indian subcontinent from southeast Asia during Miocene and subsequently spread all over and finally reached the lower slopes of sub-Himalaya. This has resulted increase in the diversity of tropical vegetation.
 The post-Pliocene orogeny of Himalaya brought great changes in the topography and climate which adversely affected the vegetation patterns of the region. The Early and Middle Siwalik tropical evergreen forest whose chief component are Anisoptera, Dipterocarpus, Hopea, Shorea (other than Shorea robusta), Polyalthia, Calophyllum, Aphanamixis, Dysoxylum, Gluta, Dracontomelum, Mangifera, Swintonia, Cynometra, Koompassia, Ormosia, Pongamia, Sindora, Duabanga, Diospyros spp., Myristica, etc. started dwindling towards the end of Middle Siwalik and subsequently disappeared from western and central sectors, though a few taxa like Mangifera, Litsea, Cinnamomum, Bauhinia, Dalbergia, Ficus, etc. continued to adjust to the new climatic conditions. Extinction of tropical evergreen taxa and further rise of Himalaya gave way to proliferation and diversification of tropical and subtropical moist deciduous to dry deciduous temperate vegetation in the lower and higher slopes respectively, as is also evidenced from the palynological record.

Pollen analysis of a long upper Pleistocene continental sequence in a Velay maar (Massif Central, France)

A new 20 m sequence is presented which is based on 279 spectra derived from a coring at Le Bouchet lake (Massif Central, France). The vegetational history of this region is described back to the end of the last Interglacial (Ribains interglacial). The two Preglacial (early Glacial) forested interstadials (St-Geneys 1 and St-Geneys 2) are evidence for the first time in the Massif Central. In spite of the altitude of the site (1200 m), they suggest a quite temperate vegetation, with the same mesophilous character as during the Holocene. The Pleniglacial appears to be threefold, with two cold episodes (Lower and Upper Pleniglacial) divided by a long complex period of moderate climatic improvement. The vegetation history of this mountain region is compared with that evidenced for the same period on the basis of the sequence of Les Echets at a lower altitude (267 m). Botanical and climatic inferences are discussed.

North American terrestrial vegetation

Contributors Preface to the first edition Preface to the second edition 1. Arctic tundra and polar desert biome Lawrence C. Bliss 2. The taiga and boreal forest Deborah L. Elliot-Fisk 3. Forests and meadows of the Rocky Mountains Robert K. Peet 4. Pacific northwest forests Jerry F. Franklin and Charles B. Halpern 5. California upland forests and woodlands Michael G. Barbour and Richard A. Minnich 6. Chaparral Jon E. Keeley 7. Intermountain valleys and lower mountain slopes Neil E. West and James A. Young 8. Warm deserts James A. MacMahon 9. Grasslands Phillip L. Sims and Paul G. Risser 10. Eastern deciduous forests Hazel R. Delcourt and Paul A. Delcourt 11. Vegetation of the southeastern coastal plain Norman L. Christensen 12. Freshwater wetlands Curtis J. Richardson 13. Saltmarshes and mangroves Irving A. Mendelssohn and Karen L. McKee 14. Alpine vegetation William Dwight Billings 15. Mexican temperate vegetation Alejandro Velazquez, Victor Manuel Toledo and Isolda Luna 16. The Caribbean Ariel E. Lugo, Julio Figueroa Colon and Frederick N. Scatena 17. Tropical and subtropical vegetation of Mesoamerica Gary S. Hartshorn 18. Vegetation of the Hawaiian Islands Lloyd L. Loope Subject index Species index.

Comparisons of Interception Loss from Tropical and Temperate Vegetation Canopies

Abstract A multilayer crop model is used to investigate interception loss from oak, pine, wheat and grass canopies. It is shown that the evaporative properties of the full oak canopy are similar to those of the evergreen tropical rain forest. Evaporation from all the wet canopies is shown to be similar at low wind speeds but the loss from the tree canopies increases rapidly with increasing wind speed. In the low-wind-speed equatorial environment it would seem likely that changing vegetation type would cause little difference in interception loss and therefore runoff. Equatorial observations suggest that this is not so and the reasons for this are discussed. Possible hydrometeorological consequences of the deforestation of the Amazon basin are also considered.

石狩平野南東部に分布するしお見層および下安平層の花粉学的研究

In the present paper, a pollen analytical study was made on 55 samples obtained from the upper member of the Shimoabira Formation, and the lower and the upper member of the Shiomi Formation belonging to the late Pleistocene in SE Ishikari Plain, Hokkaido, and palaeoenvironmental changes were discussed, being based on three pollen zones or divisions recognized, which were comparable to the three geological divisions mentioned already.Successive palaeoenvironmental changes are suggested from the pollen diagrams that the climatic condition have changed from warm to cool temperature condition. This thermal change, however, was considered to be a change within the Fagus crenata=Sasa Class in a phytosociological sense. Thus, the palaeoclimatic environments were possibly corresponding to the present climatic environments of the Kuromatsunai Area which is a significant demarcation area separating the Cool Temperate vegetation with Fagus crenata from the Cold Temperate vegetation with Quercus crispula, P. glehnii and P. jezoensis but lacking F. crenata in natural habitats in Hokkaido. The conclusion mentioned above was abstracted from the following: (1) gradual increasing of the ratio Picea/Abies from older periods to recent periods or from the pollen zone III to the zone I, although more or less irregular fluctuations were recognizable often in pollen diagrams, (2) conspicuous and nearly constant mixture of Picea, Tsuga, Abies, Cryptomeria, Pterocarya, Fagus, Quercus, etc. which was believed to be a proof of long existence of the Mixed forest, not pure boreal coniferous forests like the Taiga nor exclusive Temperate Summergreen forests, and (3) drastic decrease of maritime Chenopodiaceous pollen grains in the sample number just above the lowest sample number of the upper member of the Shimoabira Formation, showing palaeoenvironmental change from the high sea-level condition to low sea-level condition.Two exceptional pollen diagrams were shown: Ka-II' and Ni-I'. The pollen diagram of Ka-II' was considerably different from diagrams of the remaining 4 diagrams and was characterized by a tendency with increased amount of pollen grains of Picea and Cryptomeria, even though a species list of pollen grains was very similar to the remainder. The diagram of the lower part of Ni-I' pollen zone was characterized by complete lack of conifer grains. Elucidation of these exceptional cases was not tried in the present discussion and remained to be solved.Through the Shiomi Formation Period, it was supposed that bog vegetations were constantly developed; one is Picea-Sphagnum bog and the other is Alnus-Cyperaceae bog. As a result of the present study, it was shown that constant and extensive spreading of bog was considered to be the most characteristic palaeoenvironmental feature of the Shiomi Formation. Thus, the authors proposed that the Shiomi Formation Period should be called“Shiomi Bog Period”in pollen diagrams. This Period was contemporary with the Biraotori Bog Period and dated a period from the Riss-Wurm Interglacial to WI Subglacial Period.

Cenozoic evolution of Antarctic glaciation, the circum-Antarctic Ocean, and their impact on global paleoceanography

Deep-sea drilling in the Antarctic region (Deep-Sea Drilling Project legs 28, 29, 35, and 36) has provided many new data about the development of circum-Antarctic circulation and the closely related glacial evolution of Antarctica. The Antarctic continent has been in a high-latitude position since the middle to late Mesozoic. Glaciation commenced much later, in the middle Tertiary, demonstrating that near-polar position is not sufficient for glacial development. Instead, continental glaciation developed as the present-day Southern Ocean circulation system became established when obstructing land masses moved aside. During the Paleocene (t = ∼65 to 55 m.y. ago), Australia and Antarctica were joined. In the early Eocene (t = ∼55 m.y. ago), Australia began to drift northward from Antarctica, forming an ocean, although circum-Antarctic flow was blocked by the continental South Tasman Rise and Tasmania. During the Eocene (t = 55 to 38 m.y. ago) the Southern Ocean was relatively warm and the continent largely nonglaciated. Cool temperate vegetation existed in some regions. By the late Eocene (t = ∼39 m.y. ago) a shallow water connection had developed between the southern Indian and Pacific oceans over the South Tasman Rise. The first major climatic-glacial threshold was crossed 38 m.y. ago near the Eocene-Oligocene boundary, when substantial Antarctic sea ice began to form. This resulted in a rapid temperature drop in bottom waters of about 5°C and a major crisis in deep-sea faunas. Thermohaline oceanic circulation was initiated at this time much like that of the present day. The resulting change in climatic regime increased bottom water activity over wide areas of the deep ocean basins, creating much sediment erosion, especially in western parts of oceans. A major (∼2000 m) and apparently rapid deepening also occurred in the calcium carbonate compensation depth (CCD). This climatic threshold was crossed as a result of the gradual isolation of Antarctica from Australia and perhaps the opening of the Drake Passage. During the Oligocene (t = 38 to 22 m.y. ago), widespread glaciation probably occurred throughout Antarctica, although no ice cap existed. By the middle to late Oligocene (t = ∼30 to 25 m.y. ago), deep-seated circum-Antarctic flow had developed south of the South Tasman Rise, as this had separated sufficiently from Victoria Land, Antarctica. Major reorganization resulted in southern hemisphere deep-sea sediment distribution patterns. The next principal climatic threshold was crossed during the middle Miocene (t = 14 to 11 m.y. ago) when the Antarctic ice cap formed. This occurred at about the time of closure of the Australian-Indonesian deep-sea passage. During the early Miocene, calcareous biogenic sediments began to be displaced northward by siliceous biogenic sediments with higher rates of sedimentation reflecting the beginning of circulation related to the development of the Antarctic Convergence. Since the middle Miocene the East Antarctic ice cap has remained a semipermanent feature exhibiting some changes in volume. The most important of these occurred during the latest Miocene (t = ∼5 m.y. ago) when ice volumes increased beyond those of the present day. This event was related to global climatic cooling, a rapid northward movement of about 300 km of the Antarctic Convergence, and a eustatic sea level drop that may have been partly responsible for the isolation of the Mediterranean basin. Northern hemisphere ice sheet development began about 2.5–3 m.y. ago, representing the next major global climatic threshold, and was followed by the well-known major oscillations in northern ice sheets. In the Southern Ocean the Quaternary marks a peak in activity of oceanic circulation as reflected by widespread deep-sea erosion, very high biogenic productivity at the Antarctic Convergence and resulting high rates of biogenic sedimentation, and maximum northward distribution of ice-rafted debris.

Nitrogen Fixing Lichen Roles from Desert to Alpine in the Sangre de Cristo Mountains, New Mexico

Nitrogen Fixing Lichen Roles from Desert to Alpine in the Sangre de Cristo Mountains, New Mexico

Arctic Mesozoic Floras: ABSTRACT

Mesophytic floras (Late Triassic-Early Cretaceous) of the Arctic are irregularly distributed and poorly studied. The floras studied in more detail are Carnian-Norian of Spitsbergen, Rhaetian and early Lias of East Greenland, Late Jurassic of the Lena basin, and Early Cretaceous of West Greenland, Spitsbergen, Franz Josef Land, and the Lena and Kolyma basins. Mesozoic floras of Arctic Islands were not isolated from continental ones. Undoubtedly close connection existed between the Late Triassic floras of Spitsbergen and Franz Josef Land and the middle Keuper floras of Western Europe; the Early Cretaceous floras of Spitsbergen, Kong Karls Land, Franz Josef Land, and Kotel'nyy Island were connected with coeval floras of northern Asia. Botanic-geographic zonation was more prominent during the second phase (Late Jurassic-Early Cretaceous) of the mesophytic floras than during the first phase (Late Triassic-Middle Jurassic). It is assumed that Late Triassic floras of Spitsbergen and Franz Josef Land comprised a special part of the European province of the Indo-European paleofloristic area. Late Triassic thermophilic vegetation traces are preserved in the southern Lena basin (Aldan River). Beginning in the Early Jurassic temperate vegetation formed in the Lena basin (Vilyuy trough) and farther south (South Yakutsk basin and other regions); later, in the Middle Jurassic temperate vegetation appeared farther north (lower Yenisey River), and then more widely in the Late Jurassic, and especially in the Early Cretaceous Arctic and Subarctic floras. The Early Jurassic flora of northeastern USSR (west bank of the Kolyma River) is similar to the Indo-European area floras; it is possible that an Indo-European and Siberian area boundary is farther north than Central Siberia, or that a special area existed which included Early Jurassic floras of southern Alaska. Late Jurassic and Early Cretaceous Arctic floras (except West Greenland floras) are typical floras of the Siberian paleofloristic area. The Arctic climate changed between Late Triassic and Early Cretaceous times from a hot (possibly tropical) climate to a temperate warm and humid climate favorable for profuse woody plant development. End_of_Article - Last_Page 2511------------