Tropics

Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Tropics

  • australian wet tropic
  • dry tropic
  • humid tropic
  • semi-arid tropic
  • wet tropic


  • Selected Abstracts


    Soil-atmospheric exchange of CO2, CH4, and N2O in three subtropical forest ecosystems in southern China

    GLOBAL CHANGE BIOLOGY, Issue 3 2006
    XULI TANG
    Abstract The magnitude, temporal, and spatial patterns of soil-atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil-atmospheric CO2, CH4, and N2O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N2O sources and CH4 sinks. Annual mean CO2, N2O, and CH4 fluxes (mean±SD) were 7.7±4.6 Mg CO2 -C ha,1 yr,1, 3.2±1.2 kg N2O-N ha,1 yr,1, and 3.4±0.9 kg CH4 -C ha,1 yr,1, respectively. The climate was warm and wet from April through September 2003 (the hot-humid season) and became cool and dry from October 2003 through March 2004 (the cool-dry season). The seasonality of soil CO2 emission coincided with the seasonal climate pattern, with high CO2 emission rates in the hot-humid season and low rates in the cool-dry season. In contrast, seasonal patterns of CH4 and N2O fluxes were not clear, although higher CH4 uptake rates were often observed in the cool-dry season and higher N2O emission rates were often observed in the hot-humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO2 and N2O emissions and CH4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO2 effluxes by 17,44% in the three forests but had no significant effect on CH4 absorption and N2O emission rates. This suggests that microbial CH4 uptake and N2O production was mainly related to the mineral soil rather than in the surface litter layer. [source]


    Vegetation structure and biodiversity along the eucalypt forest to rainforest continuum on the serpentinite soil catena in a subhumid area of Central Queensland, Australia

    AUSTRAL ECOLOGY, Issue 3 2006
    RAY L. SPECHT
    Abstract The deep lateritic earths that cap the serpentinite outcrop in the Rockhampton , Marlborough area on the Tropic of Capricorn in Central Queensland have been eroded to expose the underlying ultramafic rock. Water-holding capacity of these nutrient-poor soils increases in a gradient from the skeletal soils to the deep lateritic earths and results in a continuum of structural formations from open-woodland to woodland to open-forest. A couple of closed-forest (rainforest) stands have developed where seepage into Marlborough Creek occurs throughout the year. Aerodynamic fluxes (frictional, thermal and evaporative) in the atmosphere as it flows over and through the vegetation influence the annual foliage growth in all strata in the continuum from skeletal soils to deep lateritic earths. The lateral growth of each plant is abraded so that the sum of the foliage projective covers of overstorey (FPCo) and understorey (FPCu) strata , that is ,(FPCo + FPCu) , remains constant throughout the serpentinite soil catena. As more water becomes available in the soil catena, the mineral nutrient levels in overstorey leaves increase, making developing leaves more vulnerable to insect attack. Although the number of leaves produced annually on each vertical foliage shoot in the overstorey increases along the soil-water gradient, ,(FPCo + FPCu) remains constant in all stands. The carbon isotope ratios (a measure of stomatal resistance) and leaf specific weights (LSWs) (a measure of the proportion of structural to cytoplasmic content in a leaf) of overstorey and understorey strata, however, are constant throughout the continuum. The well-watered rainforest pockets , where seepage occurs , form the end point of this serpentinite continuum. LSWs and carbon isotope ratios of the canopy trees are similar to those in the sheltered understorey in the eucalypt communities. A gradient of foliage attributes is observed from evergreen canopy trees (12 m) to subshrubs (2 m) in the sunlit life forms that compose the complex structure of the rainforest stands in the humid to subhumid climate of Central Queensland. As alpha diversity (number of species per hectare) is correlated with annual shoot growth per hectare, species richness along the serpentinite continuum is almost half that of nearby plant communities on medium-nutrient soils. The one to two eucalypt species per hectare are about a tenth of the number recorded on adjacent medium-nutrient soils. [source]


    Echinococcus granulosus in northern Queensland

    AUSTRALIAN VETERINARY JOURNAL, Issue 9 2006
    1. Prevalence in cattle
    Objective To determine the prevalence and geographical distribution of hydatidosis and investigate factors that might be expected to influence the prevalence of hydatids in cattle in Queensland north of the Tropic of Capricorn. To determine the effect of natural levels of infection on carcase weight and subsequent economic loss. Procedure An abattoir survey conducted in 1981 provided information on the distribution, prevalence and viability of hydatid cysts in cattle from all shires north of the Tropic of Capricorn in Queensland. Livers, lungs and spleens from 10,382 cattle were palpated at abattoirs in Cairns, Townsville and Rockhampton to detect hydatid cysts. Prevalence of infection in cattle in each shire was estimated from results of the abattoir study together with reports of infection in a further 22,185 cattle obtained from abattoir records. Linear modelling was used to define the effect of geographical origin, age, breed and sex on prevalence of infection. Differences in the weights of carcases between infected and non-infected cattle of the same age, sex, breed and property of origin were examined. The economic loss to the beef industry in the region surveyed was estimated. Results Cattle infected with hydatids originated almost entirely from regions to the east of the Great Dividing Range. The mean prevalence inside this zone was 28% compared with 3% in other areas. Viable protoscoleces were found in 0.7% of cysts. Geographical origin and age of the cattle were the most significant factors influencing prevalence. Infection with hydatids had no effect on carcase weight. Economic loss was limited to that associated with condemnations of organs at meat inspection, estimated to be $0.5 million per annum in 1981 and $6 million in 2004. The distribution of hydatids in Queensland north of the Tropic of Capricorn corresponded most closely with the distribution of small wallabies such as Macropus dorsalis (black-striped wallaby), M parryi (whiptail wallaby) and M rufogriseus (red-necked wallaby). Conclusions It was concluded that cattle are not an important part of maintaining the life-cycle of E granulosus in Queensland north of the Tropic of Capricorn. Within the endemic zone, which is almost all to the east of the Great Dividing Range, the local pattern of bovine echinococcosis is most likely to be determined by the presence or absence of small species of wallaby such as M dorsalis, M parryi and M rufogriseus. [source]


    A Strategic Framework for Monitoring Coastal Change in Australia's Wet-dry Tropics , Concepts and Progress

    GEOGRAPHICAL RESEARCH, Issue 2 2009
    C. MAX FINLAYSON
    Abstract A strategic framework for monitoring natural and human-induced change in the coastal plains of the Alligator Rivers Region in the wet-dry tropics of northern Australia is presented. The framework also supports refinement of methods used to monitor the vulnerability of coastal areas to change, including human-induced climate change and sea-level rise. The information derived through the framework can be used to assess scenarios, highlight the potential significance and implications of changes, and assist land managers formulate management responses. The framework incorporates several large-scale studies for monitoring atmospheric and hydrodynamic processes as well as mapping and monitoring projects specific to environmental change in the freshwater wetlands and the floodplains of the Region. Monitoring is proposed to address processes influencing the stability and rate of change of the floodplain environments. These include large-scale processes, such as inter-annual variability in weather conditions affecting the morphology of the coastal plains, shoreline and riverbank stabilisation, headward expansion of tidal creeks, and salinisation of freshwater basins. Information management is also addressed, and a Geographic Information System structure proposed for effective data collation, analysis and management. The information management system will facilitate data sharing and participation of multiple agencies and organisations interested in coastal change, especially where a landscape perspective or whole ecosystem approach is advocated. [source]


    Managing Environmental Impacts of Recreation and Tourism in Rainforests of the Wet Tropics of Queensland World Heritage Area

    GEOGRAPHICAL RESEARCH, Issue 2 2005
    Stephen M. Turton
    Abstract This paper describes environmental impacts of tourism and recreation activities in the world heritage listed rainforests of northeast Australia and presents management strategies for sustainable visitor use of the protected area. Tropical rainforests are characterised by their low resistance and moderate to high resilience to impacts associated with human visitation. Visitor use in the World Heritage Area is mostly associated with walking tracks, camping areas, day use areas and off-road vehicle use of old forestry roads and tracks. Adverse environmental impacts range from vegetation trampling, soil compaction, water contamination and soil erosion at the local scale through to spread of weeds, feral animals and soil pathogens along extensive networks of old forestry roads and tracks at the regional scale. Concentration of visitor use is the most desirable management strategy for controlling adverse impacts at most World Heritage Area visitor nodes and sites, and includes methods such as site hardening and shielding to contain impacts. For dispersed visitor activities, such as off-road vehicle driving and long-distance walking, application of best practice methods by the tourist industry and recreational users such as removal of mud and soils from vehicle tyres and hiking boots before entering pathogen-free catchments, together with seasonal closure of roads and tracks, are the preferred management strategies. Retention of canopy cover at camping areas and day use areas, as well as along walking tracks and forestry roads is a simple, yet effective, management strategy for reduction of a range of adverse impacts, including dispersal of weeds and feral animals, edge effects, soil erosion and nutrient loss, road kill and linear barrier effects on rainforest fauna. [source]


    An Island of Green in the Sunburnt Country: The Rainforest of the Humid Tropics of Northeastern Australia and Their Response to Quaternary Environmental Change

    GEOGRAPHY COMPASS (ELECTRONIC), Issue 6 2008
    Patrick T. Moss
    The Humid Tropics of northeastern Australia is a region of exceptional diversity and productivity that reflects many of the characteristics of similar tropical biomes. In the Australian context, it is a unique environment being a virtual ,island of green' surrounded by the more typical sclerophyll (i.e. dry and fire prone) landscapes of Australia. This article will examine the modern ecological characteristics of the region, as well as providing historical context by discussing the response of the humid tropics communities to Quaternary environmental upheavals and the possible implications that these alterations have for understanding ecosystem response to future environmental change. [source]


    Long-term trends of synoptic-scale breaking Rossby waves in the Northern Hemisphere between 1958 and 2001

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2008
    F. Isotta
    Abstract Breaking synoptic-scale Rossby waves are frequent features of the upper troposphere and lower stratosphere (UTLS) which affect both global- and regional-scale dynamics. Furthermore, they directly influence ozone distribution through meridional transport of ozone-rich air towards the south and ozone-poor air towards the north. Here, trends in the frequency of these breaking waves are assessed by analysing a 44-year climatology (1958,2002) of potential vorticity (PV) streamers on isentropic surfaces from 310 to 350 K. These streamers are viewed as breaking Rossby waves, whereby stratospheric (tropospheric) streamers indicate southward (northward) breaking waves. Two complementary techniques are used to analyse the trends. First, linear trends are computed using the least-squares regression technique. Statistically significant linear trends are found to vary in location and magnitude between isentropic levels and the four seasons. In winter significant trends are detected in the eastern Pacific between 340 and 350 K. A positive trend of stratospheric streamers in the Tropics is related to an increase of total column ozone, whereas the positive trend of tropospheric streamers in the mid-latitudes is associated with a decrease of total ozone. Secondly, a nonlinear trend analysis is performed using the seasonal-trend decomposition procedure based on Loess (STL). With this technique, the low-frequency variability of the time series is analysed during the 44-year period. For instance, over the eastern Atlantic on 350 K, a phase of decreasing PV streamer frequencies in the 1950s and 1960s is followed by a positive streamer tendency after the 1970s. Additionally, trends of the zonal wind are investigated. One prominent outcome of this analysis is the observation that equatorial easterlies over the Atlantic are weakening. A dynamically meaningful link exists between the trends observed in both wind velocity and PV streamers. Copyright © 2008 Royal Meteorological Society [source]


    Patterns of variability in the satellite microwave sounding unit temperature record: comparison with surface and reanalysis data

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2003
    Giovanni Sturaro
    Abstract Principal component analysis is applied to global temperature records to study the differences in the patterns of variability between surface and troposphere. Surface, Microwave Sounding Unit (lower troposphere, channel 2 and channel 4) and National Centers for Environmental Prediction,National Center for Atmospheric Research reanalysis thickness data are studied in the common period 1979,2000. The patterns of variability are classified into geographical regions and compared. The series of their time coefficients are correlated to assess the existence of common and significant climate-change signals in the form of climatic trends. The objective is to identify the physical processes determining the records' variations and the differences between the surface and the satellite records that might be related to the discrepancy in their globally averaged trend. Major differences were found in the Tropics, where the surface warming is not paralleled in any other record. The surface record has two major patterns over the Tropics, one of which is connected to El Niño,southern oscillation. Satellite variability is instead described by only one pattern, most probably deriving from the merging of the two distinct patterns found for the near-surface records. In the eastern Antarctic a higher troposphere and lower stratosphere negative trend is found connected to ozone depletion. This signal prevails in the satellite record, despite evidence that it is confined only above 500 hPa. A pattern over Siberia is linked to the ,Euro-Siberian oscillation', i.e. the change in the pressure field determining the tracks of the Atlantic storms over the area Copyright © 2003 Royal Meteorological Society [source]


    Subtropical cold surges: regional aspects and global distribution

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2001
    René D. Garreaud
    Abstract Shallow surges of cold dry air are frequently observed to the east of the major mountain ranges, moving from mid-latitudes well into the Tropics in about 4 days. Because of their strong impact on weather, regional aspects of cold surges have received considerable attention, particularly over Southeast Asia, to the east of the Rockies and Mexican Sierras, and to the east of the subtropical Andes. Both observational and numerical studies reveal a similar structure and evolution of cold surges in different regions. These common aspects are reviewed in this work, as well as the mechanisms responsible for the development and subsequent advance of cold surges over the subtropics. Atmospheric reanalysis data are used to document the global distribution of cold surges on the basis of their continental-scale imprints on relevant fields, as well as to estimate their contribution on the regional and global energy balances. It is found that cold surges have a major cooling and drying effect over the regions where they are prevalent (e.g. subtropical South America) and represent a sizeable sink of energy for the Tropics. Copyright © 2001 Royal Meteorological Society [source]


    Maize Yields as Affected by Short- and Long-Term Improved Fallows: A Comparative Analysis in the Asian Humid Tropics

    JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2005
    R. Schelbert
    Abstract Improved short- or long-term fallows are considered suitable low external input technologies for maintaining productivity and sustainability of tropical smallholder upland cropping units, although comparisons on the benefits of this technology are not widely reported. A field study evaluated the impact of improved short (6 months) and long-term fallow (18 months) using Crotalaria juncea and Tithonia diversifolia, in relation to a natural fallow of the same durations, on the productivity of maize (Zea mays), the most important upland cereal in tropical Asia, over a minor season. The use of improved fallows, especially Tithonia, increased maize yields over the Crotalaria or natural fallow. While the overall yields of maize after a long fallow were greater, the beneficial impact of the green manures was significantly higher in the short fallows. The causal factors for this trend, including biomass production of the improved fallows and possible impact on soils, along with the greater benefits of short-term fallows for increasing maize yields in the tropics due to lower requirements of unproductive time are presented. [source]


    Impact of the Cropping Systems of a Minor Dry Season on the Growth, Yields and Nitrogen Uptake of Maize (Zea mays L) Grown in the Humid Tropics during the Major Rainy Season

    JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2003
    U. R. Sangakkara
    Abstract A field study evaluated the residual effect of a cropping system in two minor (dry) seasons on the productivity pattern and nitrogen utilization of a maize crop grown in the subsequent major (wet) seasons. The cropping systems established in the minor seasons, where evaporation exceeds rainfall, were either monocultures of maize (Zea mays L), or maize intercropped with either common bean (Phaseolus vulgaris L) or sunhemp (Crotolaria juncea L). In addition, monocultures of two green manures, namely sunhemp (Crotolaria juncea) or Tithonia (Tithonia diversifolia), were established. The residues of maize and beans and the green manures were incorporated at the end of the minor season; at the onset of rains in the major season, maize crops were established on the same plots. Germination of maize was not affected by the previous cropping system. In contrast, crop growth and yields of maize and nitrogen utilization were affected by the previous cropping system. Optimum growth and highest yields were procured in maize that was grown after a green manure crop. Similarly, although the yields were high, the planting of a green manure crop reduced nitrogen utilization by maize in the major season, thereby indicating its potential contribution to sustainability, due to its lower mining of soil nitrogen. On the basis of the results of this two-year study, the impact of cropping systems in minor seasons on the productivity of maize, a very important highland cereal in the tropics, grown under rain-fed conditions in a major season, is presented. [source]


    New approaches to understanding late Quaternary climate fluctuations and refugial dynamics in Australian wet tropical rain forests

    JOURNAL OF BIOGEOGRAPHY, Issue 2 2009
    Jeremy VanDerWal
    Abstract Aim, We created spatially explicit models of palaeovegetation stability for the rain forests of the Australia Wet Tropics. We accounted for the climatic fluctuations of the late Quaternary, improving upon previous palaeovegetation modelling for the region in terms of data, approach and coverage of predictions. Location, Australian Wet Tropics. Methods, We generated climate-based distribution models for broad rain forest vegetation types using contemporary and reconstructed ,pre-clearing' vegetation data. Models were projected onto previously published palaeoclimate scenarios dating to c. 18 kyr bp. Vegetation stability was estimated as the average likelihood that a location was suitable for rain forest through all climate scenarios. Uncertainty associated with model projections onto novel environmental conditions was also tracked. Results, Upland rain forest was found to be the most stable of the wet forest vegetation types examined. We provide evidence that the lowland rain forests were largely extirpated from the region during the last glacial maximum, with only small, marginally suitable fragments persisting in two areas. Models generated using contemporary vegetation data underestimated the area of environmental space suitable for rain forest in historical time periods. Model uncertainty resulting from projection onto novel environmental conditions was low, but generally increased with the number of years before present being modelled. Main conclusions, Climate fluctuations of the late Quaternary probably resulted in dramatic change in the extent of rain forest in the region. Pockets of high-stability upland rain forest were identified, but extreme bottlenecks of area were predicted for lowland rain forest. These factors are expected to have had a dramatic impact on the historical dynamics of population connectivity and patterns of extinction and recolonization of dependent fauna. Finally, we found that models trained on contemporary vegetation data can be problematic for reconstructing vegetation patterns under novel environmental conditions. Climatic tolerances and the historical extent of vegetation may be underestimated when artificial vegetation boundaries imposed by land clearing are not taken into account. [source]


    The Elusive Quest for Growth: Economists' Adventures and Misadventures in the Tropics, by William Easterly.

    JOURNAL OF POLICY ANALYSIS AND MANAGEMENT, Issue 2 2003
    $29.95., 342 pp., Cambridge, MA: MIT Press
    [source]


    Sexually Transmitted Diseases Diagnosed Among Travelers Returning from the Tropics

    JOURNAL OF TRAVEL MEDICINE, Issue 2 2009
    Séverine Ansart MD
    Objectives Data are lacking on the spectrum of sexually transmitted diseases (STDs) diagnosed in returning travelers. Study Design All consecutive travelers consulting our tropical unit between November 1, 2002 and October 31, 2003 were included if they presented within 1 month after their return from the tropics, with mucocutaneous signs suggesting STDs. Results Forty-nine patients (12 women and 37 men; median age 36.4 y, 35 heterosexuals) were included. Four patients had traveled with their usual sexual partner and 45 patients had casual sex while abroad (31 with locals and 14 with other tourists). The main diagnoses were gonococcal urethritis (n = 18), herpes simplex virus 2 infection (n = 12), urethritis of undetermined origin (n = 9), Chlamydia trachomatis infection (n = 4), primary syphilis (n = 4), and primary human immunodeficiency virus infection (n = 2). Conclusions These results illustrate the broad spectrum of STDs contracted by travelers to the tropics. They suggest the need to also inform travelers of the risks of STD and to promote the use of condoms in case of casual sex while abroad. [source]


    Infectious Mononucleosis,Like Syndromes in Febrile Travelers Returning From the Tropics

    JOURNAL OF TRAVEL MEDICINE, Issue 4 2006
    Emmanuel Bottieau MD
    Background Infectious mononucleosis (IM), resulting from Epstein,Barr virus (EBV) infection, and IM-like syndromes, mainly due to cytomegalovirus (CMV), Toxoplasma gondii, or human immunodeficiency virus (HIV), have been occasionally reported in travelers returning from the tropics. Our objective was to investigate the prevalence, outcome, and diagnostic predictors of these syndromes in febrile travelers. Methods Between April 2000 and March 2005, all febrile travelers and migrants presenting at our referral centers within 12 months after a tropical stay were prospectively included. We identified all patients serologically diagnosed with IM or IM-like syndrome and compared them with the rest of the cohort. Results During the 5-year period, 72/1,842 patients (4%) were diagnosed with an IM-like syndrome, including 36 CMV, 16 T gondii, 15 EBV, and 5 HIV primary infections. All patients were western travelers or expatriates. Mean delay before consultation was 2 weeks. Most patients had consulted other practitioners and/or received presumptive treatment. A minority of patients presented with IM clinical features. Lymphocytosis ,40% of the white blood cells (WBC) and reactive/atypical lymphocyte morphology were observed in 60 and 30% of the patients. The four diseases were indistinguishable. Protracted fever and asthenia were common but complications rarely occurred. IM-like syndromes were independently associated with fever >7 days, lymphadenopathy, elevated liver enzymes, and lymphocytosis ,40% of WBC. Diagnostic probability increased to >20% if at least three of these predictors were present. Conclusions Diagnosis of IM and IM-like syndrome is not uncommon in febrile travelers, with a higher proportion of primary CMV, T gondii, and HIV infections than in nonimported series. Consequently, classic IM clinical and laboratory features are often lacking. All four pathogens should be systematically considered because early diagnosis should avoid unnecessary investigations and treatment and allow early intervention in case of primary HIV infection. [source]


    Practice Guidelines for Evaluation of Fever in Returning Travelers and Migrants

    JOURNAL OF TRAVEL MEDICINE, Issue 2003
    Valérie D'Acremont
    Background Fever upon return from tropical or subtropical regions can be caused by diseases that are rapidly fatal if left untreated. The differential diagnosis is wide. Physicians often lack the necessary knowledge to appropriately take care of such patients. Objective To develop practice guidelines for the initial evaluation of patients presenting with fever upon return from a tropical or subtropical country in order to reduce delays and potential fatal outcomes and to improve knowledge of physicians. Target audience Medical personnel, usually physicians, who see the returning patients, primarily in an ambulatory setting or in an emergency department of a hospital and specialists in internal medicine, infectious diseases, and travel medicine. Method A systematic review of the literature,mainly extracted from the National Library of Medicine database,was performed between May 2000 and April 2001, using the keywords fever and/or travel and/or migrant and/or guidelines. Eventually, 250 articles were reviewed. The relevant elements of evidence were used in combination with expert knowledge to construct an algorithm with arborescence flagging the level of specialization required to deal with each situation. The proposed diagnoses and treatment plans are restricted to tropical or subtropical diseases (nonautochthonous diseases). The decision chart is accompanied with a detailed document that provides for each level of the tree the degree of evidence and the grade of recommendation as well as the key points of debate. Participants and consensus process Besides the 4 authors (2 specialists in travel/tropical medicine, 1 clinical epidemiologist, and 1 resident physician), a panel of 11 European physicians with different levels of expertise on travel medicine reviewed the guidelines. Thereafter, each point of the proposed recommendations was discussed with 15 experts in travel/tropical medicine from various continents. A final version was produced and submitted for evaluation to all participants. Conclusion Although the quality of evidence was limited by the paucity of clinical studies, these guidelines established with the support of a large and highly experienced panel should help physicians to deal with patients coming back from the Tropics with fever. [source]


    Speciation, hybrid zones and phylogeography , or seeing genes in space and time

    MOLECULAR ECOLOGY, Issue 3 2001
    Godfrey M. Hewitt
    Abstract The origins and development of the study of speciation, hybrid zones and phylogeography are outlined using evolutionary iconography. This traces the ideas in this field from Lamarck and Darwin through to the present as represented in diagrams and figures. A ,tree of trees' summarizes this growth and current vitality. The new facility to use various DNA sequences from nuclear, mitochondrial and chloroplast genomes to determine genetic variation throughout a species range is examined particularly. There is great genomic subdivision across species distributions, which can be interpreted in the light of the recent demonstrations of severe palaeoclimatic oscillations. Refugia and postglacial colonization routes are proposed for several organisms across Europe. The role of geography in speciation through the Pleistocene is considered. These emerging principles and analyses are applied to data available on a variety of organisms in other regions of the world, such as the Arctic, North America and the Tropics, and including the progress of Homo sapiens through the last ice age. Some suggestions are made for future research directions. [source]


    Development of eight polymorphic microsatellites for an Australasian rainforest tree species, Cryptocarya mackinnoniana (Lauraceae)

    MOLECULAR ECOLOGY RESOURCES, Issue 6 2007
    J. A. WELLS
    Abstract We developed eight microsatellite markers for Cryptocarya mackinnoniana to study the spatial genetic structure and ecological correlates of parentage in secondary rainforests in Australia's Wet Tropics. The microsatellite loci were screened in 99 trees, and 623 seedlings < 0.24 m tall, at a site extending from primary rainforest into adjacent 50-year-old secondary rainforest. The eight loci were polymorphic, exhibiting between three and 11 alleles, and gene diversity (HE) from 0.25 to 0.84. For the trees, no departures from Hardy,Weinberg equilibrium were detected, except at locus Cm03, which had an estimated null allele frequency of 0.0903. No locus combinations exhibited linkage disequilibrium. [source]


    Effects of a Severe Frost on Riparian Rainforest Restoration in the Australian Wet Tropics: Foliage Retention by Species and the Role of Forest Shelter

    RESTORATION ECOLOGY, Issue 4 2010
    Timothy J. Curran
    Restoration of ecological communities that can withstand future climate and land use changes requires information on species responses to various natural disturbances. Frost is an important disturbance that regulates plant species distributions, and although rare in tropical rainforest, it can occur in upland areas, especially where deforestation has occurred. We report the impacts of a severe frost that occurred in June and July 2007 on the Atherton Tablelands, Queensland, Australia and caused extensive damage to riparian restoration plots of upland rainforest species. We estimated proportion foliage retention to (1) compare impacts across 45 species; (2) examine the influence of plant height on frost effects; and (3) determine if plantings under shelterbelts of mature trees received less damage. Species exhibited different levels of foliage retention. Species that were particularly frost resistant included those from riparian habitats and a conifer. Some heavily impacted species are deciduous and may survive frost by shedding leaves; this warrants further investigation. Plant canopy height above ground level was only weakly correlated to foliage retention. Sheltered plants were much less damaged than unsheltered conspecifics, suggesting a useful way to mitigate frost impacts. These principles should help guide the development of resilient ecological communities in frost-prone areas. [source]


    Simulation of the Madden, Julian Oscillation and its teleconnections in the ECMWF forecast system

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 649 2010
    Frédéric Vitart
    Abstract A series of 46-day ensemble integrations starting on the 15th of each month from 1989 to 2008 has been completed with the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast system. The Madden, Julian Oscillation (MJO) simulated by the hindcasts is diagnosed using an index based on combined empirical orthogonal functions (EOFs) of zonal winds at 200 and 850 hPa and outgoing long-wave radiation. Results indicate that the dynamical model is able to maintain the amplitude of the MJO during the 46 days of integrations and the model displays skill for up to about 20 days to predict the evolution of the MJO. However, the MJO simulated by the model has a too slow eastward propagation and has difficulties crossing the Maritime Continent. The MJO teleconnections simulated by the ECMWF forecast system have been compared to reanalyses. In the Tropics, the impact of the MJO on precipitation is generally consistent with reanalysis. In the Northern Extratropics, the MJO simulated by the model has an impact on North Atlantic weather regimes, but with a smaller amplitude than in reanalysis which can be partly explained by the too slow eastward propagation of the simulated MJO events. The impact of the MJO on the probabilistic skill scores has been assessed. Results indicate that the MJO simulated by the model has a statistically significant impact on weekly mean probabilistic skill scores in the Northern Extratropics, particularly at the time range 19, 25 days. At this time range, the reliability of the probabilistic forecasts over Europe depends strongly on the presence of an MJO event in the initial conditions. This result confirms that the MJO is a major source of predictability in the Extratropics in the sub-seasonal time-scale. Copyright © 2010 Royal Meteorological Society [source]


    Horizontal resolution impact on short- and long-range forecast error

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 649 2010
    Roberto Buizza
    Abstract The impact of horizontal resolution increases from spectral truncation T95 to T799 on the error growth of ECMWF forecasts is analysed. Attention is focused on instantaneous, synoptic-scale features represented by the 500 and 1000 hPa geopotential height and the 850 hPa temperature. Error growth is investigated by applying a three-parameter model, and improvements in forecast skill are assessed by computing the time limits when fractions of the forecast-error asymptotic value are reached. Forecasts are assessed both in a realistic framework against T799 analyses, and in a perfect-model framework against T799 forecasts. A strong sensitivity to model resolution of the skill of instantaneous forecasts has been found in the short forecast range (say up to about forecast day 3). But sensitivity has shown to become weaker in the medium range (say around forecast day 7) and undetectable in the long forecast range. Considering the predictability of ECMWF operational, high-resolution T799 forecasts of the 500 hPa geopotential height verified in the realistic framework over the Northern Hemisphere (NH), the long-range time limit ,(95%) is 15.2 days, a value that is one day shorter than the limit computed in the perfect-model framework. Considering the 850 hPa temperature verified in the realistic framework, the time limit ,(95%) is 16.6 days for forecasts verified in the realistic framework over the NH (cold season), 14.1 days over the SH (warm season) and 20.6 days over the Tropics. Although past resolution increases have been providing continuously better forecasts especially in the short forecast range, this investigation suggests that in the future, although further increases in resolution are expected to improve the forecast skill in the short and medium forecast range, simple resolution increases without model improvements would bring only very limited improvements in the long forecast range. Copyright © 2010 Royal Meteorological Society [source]


    Evolution of the stable water isotopic composition of the rain sampled along Sahelian squall lines,

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue S1 2010
    Camille Risi
    Abstract In the Tropics, the stable isotopic composition (HDO, HO) of precipitation is strongly modulated by convective activity. To better understand how convective processes impact the precipitation isotopic composition, we analyze the isotopic composition of rain collected during the passage of four squall lines over the Sahel (Niamey, Niger) in August 2006 during the African Monsoon Multidisciplinary Analysis (AMMA) campaign. The high-frequency sampling (5,10 min) of the precipitation allows us to investigate the evolution of the precipitation isotopic composition in different phases of the squall lines. Despite a large variability among the different squall lines, some robust isotopic features appear: the W shape of the ,18O evolution and the deuterium excess decrease in the first part of the stratiform zone. To understand more quantitatively how convective processes impact the precipitation isotopic composition, a simple stationary two-dimensional transport model including a representation of cloud microphysics and isotopic fractionation is developed and forced by three-dimensional winds retrieved from the Massachusetts Institute of Technology (MIT) radar on 11 August 2006. The model reproduces the robust observed features and a large sensitivity to the squall-line dynamics. This model suggests that the main controlling factors of the isotopic evolution are (1) squall-line dynamics, especially the downward advection of air at the rear of the squall lines, affecting the vapour composition and, by isotopic equilibration, the subsequent precipitation composition and (2) rain re-evaporation. This suggests that water isotopes have the potential to better constrain squall-line dynamics and rain re-evaporation, and to evaluate the representation of convective processes in numerical models. Copyright © 2009 Royal Meteorological Society [source]


    Characterization of the impact of geostationary clear-sky radiances on wind analyses in a 4D-Var context

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 644 2009
    C. Peubey
    The impact of geostationary clear-sky radiances (CSRs) on 4D-Var wind analyses has been investigated by running a set of observing system experiments. Analysis scores have been calculated to measure the ability of individual satellite datasets to improve the wind analysis, starting from a no-satellite baseline. In this context, the assimilation of CSRs from the two water-vapour channels on Meteosat-9 has been found to improve the wind analysis throughout the troposphere, with the strongest signal at 300 and 500 hPa. Indeed, for the Northern Hemisphere and the Tropics, the CSR impact at these levels exceeds that of the Meteosat-9 atmospheric motion vectors (AMVs), the sampling of the latter in the assimilation being rather limited. Conversely, the impact of AMVs exceeds that of CSRs in the lower troposphere, where the latter provide very little direct information. This demonstrates the complementarity of the two datasets in the operational 4D-Var wind analysis. The mechanisms through which the assimilation of CSRs can impact wind analyses have been isolated. The dominant effect is that of humidity-tracer advection, by which the wind field is adjusted in order to fit observed humidity features via the minimization of the 4D-Var cost function. Other mechanisms, such as balance constraints and the cycling of the forecast model that links the humidity and wind variables, have been found to play a minor role. The benefit of having frequent CSR images within the assimilation window has also been demonstrated. Copyright © 2009 Royal Meteorological Society [source]


    A contribution by ice nuclei to global warming

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 643 2009
    Xiping Zeng
    Abstract Ice nuclei (IN) significantly affect clouds via supercooled droplets, that in turn modulate atmospheric radiation and thus climate change. Since the IN effect is relatively strong in stratiform clouds but weak in convective ones, the overall effect depends on the ratio of stratiform to convective cloud amount. In this paper, ten years of TRMM (Tropical Rainfall Measuring Mission) satellite data are analyzed to confirm that stratiform precipitation fraction increases with increasing latitude, which implies that the IN effect is stronger at higher latitudes. To quantitatively evaluate the IN effect versus latitude, large-scale forcing data from ten field campaigns are used to drive a cloud-resolving model to generate long-term cloud simulations. As revealed in the simulations, the increase in the net downward radiative flux at the top of the atmosphere from doubling the current IN concentrations is larger at higher latitude, which is attributed to the meridional tendency in the stratiform precipitation fraction. Surface warming from doubling the IN concentrations, based on the radiative balance of the globe, is compared with that from anthropogenic CO2. It is found that the former effect is stronger than the latter in middle and high latitudes but not in the Tropics. With regard to the impact of IN on global warming, there are two factors to consider: the radiative effect from increasing the IN concentration and the increase in IN concentration itself. The former relies on cloud ensembles and thus varies mainly with latitude. In contrast, the latter relies on IN sources (e.g. the land surface distribution) and thus varies not only with latitude but also longitude. Global desertification and industrialization provide clues on the geographic variation of the increase in IN concentration since pre-industrial times. Thus, their effect on global warming can be inferred and can then be compared with observations. A general match in geographic and seasonal variations between the inferred and observed warming suggests that IN may have contributed positively to global warming over the past decades, especially in middle and high latitudes. Copyright © 2009 Royal Meteorological Society [source]


    A self-consistent scattering model for cirrus.

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 629 2007
    I: The solar region
    Abstract In this paper a self-consistent scattering model for cirrus is presented. The model consists of an ensemble of ice crystals where the smallest ice crystal is represented by a single hexagonal ice column. As the overall ice crystal size increases, the ice crystals become progressively more complex by arbitrarily attaching other hexagonal elements until a chain-like ice crystal is formed, this representing the largest ice crystal in the ensemble. The ensemble consists of six ice crystal members whose aspect ratios (ratios of the major-to-minor axes of the circumscribed ellipse) are allowed to vary between unity and 1.84 for the smallest and largest ice crystal, respectively. The ensemble model's prediction of parameters fundamental to solar radiative transfer through cirrus such as ice water content and the volume extinction coefficient is tested using in situ based data obtained from the midlatitudes and Tropics. It is found that the ensemble model is able to generally predict the ice water content and extinction measurements within a factor of two. Moreover, the ensemble model's prediction of cirrus spherical albedo and polarized reflection are tested against a space-based instrument using one day of global measurements. The space-based instrument is able to sample the scattering phase function between the scattering angles of approximately 60° and 180° , and a total of 37 581 satellite pixels were used in the present analysis covering latitude bands between 43.75°S and 76.58°N. It is found that the ensemble model phase function is well able to minimize significantly differences between satellite-based measurements of spherical albedo and the ensemble model's prediction of spherical albedo. The satellite-based measurements of polarized reflection are found to be reasonably described by more simple members of the ensemble. The ensemble model presented in this paper should find wide applicability to the remote sensing of cirrus as well as more fundamental solar radiative transfer calculations through cirrus, and improved solar optical properties for climate and Numerical Weather Prediction models. Copyright © 2007 Royal Meteorological Society [source]


    A study of departures from the inverse-barometer response of sea level to air-pressure forcing at a period of 5 days

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 597 2004
    E. L. Mathers
    Abstract The response of the sea level to atmospheric forcing is investigated through the cross-spectral analysis of tide-gauge data from around 100 island and deep-ocean stations and atmospheric pressure records. The focus is at a period of 5 days, coinciding with an atmospheric pressure oscillation (Madden,Julian wave) of the same frequency. Outside the Tropics the energy in synoptic weather systems masks the small amplitude of the pressure wave, resulting in a response indistinguishable from that of an inverse barometer (IB). Within the Tropics, variability of air pressure is smaller in comparison with the amplitude of the pressure wave and departures from the IB model are found. Analysis of several sub-surface pressure records in the tropical Atlantic also yields departures at this time-scale, and indicates the barotropic nature of the response. Findings from a near-global barotropic numerical model forced with realistic air pressure and wind-stress fields show reasonable agreement with results at tide-gauge locations, and provide a more complete view of the sea-level response. These results indicate the possibility of providing an improved simulation of sea-level response to atmospheric-pressure forcing at this time-scale than is currently provided by the IB model, for example in the field of satellite altimetry. Copyright © 2004 Royal Meteorological Society [source]


    The ECMWF operational implementation of four-dimensional variational assimilation.

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 564 2000
    I: Experimental results with simplified physics
    Abstract This paper presents results of a comparison between four-dimensional variational assimilation (4D-Var). using a 6-hour assimilation window and simplified physics during the minimization, and three-dimensional variational assimilation (3D-Var). Results have been obtained at ,operational' resolution T213L31/T63L31. (T defines the spectral triangular truncation and L the number of levels in the vertical, with the first parameters defining the resolution of the model trajectory, and the second the resolution of the inner-loop.) The sensitivity of the 4D-Var performance to different set-ups is investigated. In particular, the performance of 4D-Var in the Tropics revealed some sensitivity to the way the adiabatic nonlinear normal-mode initialization of the increments was performed. Going from four outer-loops to only one (as in 3D-Var), together with a change to the 1997 formulation of the background constraint and an initialization of only the small scales, helped to improve the 4D-Var performance. Tropical scores then became only marginally worse for 4D-Var than for 3D-Var. Twelve weeks of experimentation with the one outer-loop 4D-Var and the 1997 background formulation have been studied. The averaged scores show a small but consistent improvement in both hemispheres at all ranges. In the short range, each two- to three-week period has been found to be slightly positive throughout the troposphere. The better short-range performance of the 4D-Var system is also shown by the fits of the background fields to the data. More results are presented for the Atlantic Ocean area during FASTEX (the Fronts and Atlantic Storm-Track Experiment), during which 4D-Var is found to perform better. In individual synoptic cases corresponding to interesting Intensive Observing Periods, 4D-Var has a clear advantage over 3D-Var during rapid cyclogeneses. The very short-range forecasts used as backgrounds are much closer to the data over the Atlantic for 4D-Var than for 3D-Var. The 4D-Var analyses also display more day-to-day variability. Some structure functions are illustrated in the 4D-Var case for a height observation inserted at the beginning, in the middle or at the end of the assimilation window. The dynamical processes seem to be relevant, even with a short 6-hour assimilation period, which explains the better overall performance of the 4D-Var system. [source]


    The ECMWF operational implementation of four-dimensional variational assimilation.

    THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 564 2000
    II: Experimental results with improved physics
    Abstract A comprehensive set of physical parametrizations has been linearized for use in the European Centre for Medium-Range Weather Forecasts (ECMWF's) incremental four-dimensional variational (4D-Var) system described in Part I. The following processes are represented: vertical diffusion, subgrid-scale orographic effects, large-scale precipitation, deep moist convection and long-wave radiation. The tangent-linear approximation is examined for finite-size perturbations. Significant improvements are illustrated for surface wind and specific humidity with respect to a simplified vertical diffusion scheme. Singular vectors computed over 6 hours (compatible with the 4D-Var assimilation window) have lower amplification rates when the improved physical package is included, due to a more realistic description of dissipative processes, even though latent-heat release contributes to amplify the potential energy of perturbations in rainy areas. A direct consequence is a larger value of the observation term of the cost-function at the end of the minimization process when improved physics is included in 4D-Var. However, the larger departure of the analysis state from observations in the lower-resolution inner-loop is in better agreement with the behaviour of the full nonlinear model at high resolution. More precisely, the improved physics produces smaller discontinuities in the value of the cost-function when going from low to high resolution. In order to reduce the computational cost of the linear physics, a new configuration of the incremental 4D-Var system using two outer-loops is defined. In a first outer-loop, a minimization is performed at low resolution with simplified physics (50 iterations), while in the second loop a second minimization is performed with improved physics (20 iterations) after an update of the model trajectory at high resolution. In this configuration the extra cost of the physics is only 25%, and results from a 2-week assimilation period show positive impacts in terms of quality of the forecasts in the Tropics (reduced spin-down of precipitation, lower root-mean-square errors in wind scores). This 4D-Var configuration with improved physics and two outer-loops was implemented operationally at ECMWF in November 1997. [source]


    Deeply divergent mitochondrial lineages reveal patterns of local endemism in chironomids of the Australian Wet Tropics

    AUSTRAL ECOLOGY, Issue 3 2009
    MATT N. KROSCH
    Abstract The Wet Tropics bioregion of north-eastern Australia has been subject to extensive fluctuations in climate throughout the late Pliocene and Pleistocene. Cycles of rainforest contraction and expansion of dry sclerophyll forest associated with such climatic fluctuations are postulated to have played a major role in driving geographical endemism in terrestrial rainforest taxa. Consequences for the distributions of aquatic organisms, however, are poorly understood. The Australian non-biting midge species Echinocladius martini Cranston (Diptera: Chironomidae), although restricted to cool, well-forested freshwater streams, has been considered to be able to disperse among populations located in isolated rainforest pockets during periods of sclerophyllous forest expansion, potentially limiting the effect of climatic fluctuations on patterns of endemism. In this study, mitochondrial COI and 16S data were analysed for E. martini collected from eight sites spanning the Wet Tropics bioregion to assess the scale and extent of phylogeographic structure. Analyses of genetic structure showed several highly divergent cryptic lineages with restricted geographical distributions. Within one of the identified lineages, strong genetic structure implied that dispersal among proximate (<1 km apart) streams was extremely restricted. The results suggest that vicariant processes, most likely due to the systemic drying of the Australian continent during the Plio-Pleistocene, might have fragmented historical E. martini populations and, hence, promoted divergence in allopatry. [source]


    Does biogeographical history matter?

    AUSTRAL ECOLOGY, Issue 1 2005
    Diversity, distribution of lotic midges (Diptera: Chironomidae) in the Australian Wet Tropics
    Abstract We examined broad scale patterns of diversity and distribution of lotic Chironomidae (Diptera) within the Wet Tropics bioregion of northern Queensland, Australia. Field surveys across broad latitudinal and altitudinal gradients within the Wet Tropics revealed a fauna of 87 species-level taxa in 49 genera comprising three main elements: a small genuinely tropical fraction, and larger cosmopolitan and Gondwanan components. The latter group originated when Australia, as part of the ancient Gondwana supercontinent, was situated over Antarctic latitudes with a cooler, wetter climate than today. In the Wet Tropics, cool Gondwanan taxa occurred predominantly in upland and shaded lowland sites, but no species appeared narrowly temperature restricted, and there was no faunal zonation with altitude. Most chironomid species occurred at all latitudes within the Wet Tropics, with no evidence for an enduring effect of the historical rainforest contractions on current-day distribution patterns. These findings contrast with those for aquatic faunas elsewhere in the world and for the terrestrial Wet Tropics fauna. We relate this to the generally broad environmental tolerances of Australian chironomids, and comment on why the latitudinal diversity gradient does not apply to the Australian chironomid fauna. [source]