bluuebunny/crossref_metadata_2025 huggingface dataset:
A numerical laboratory for simulation and visualization of seismic wavefields1
Authors: Serón F. J. , Badal J. , Sabadell F. J.
Published: April 2006

Computational seismic modelling (CSM) plays an important role in the geophysical industry as an established aid to seismic interpreters. Numerical solution of the elastic wave equations has proved to be a very important tool for geophysicists in both forward modelling and migration. Among the techniques generally used in CSM, we consider the finite‐element method (FEM) and investigate its computational and visualization requirements. The CSMFEM program, designed for this purpose and developed on an IBM 3090 computer with vector facility, is described in detail. It constitutes a numerical laboratory for performing computer experiments. Two Newmark type algorithms for time integration are compared with other time integration schemes, and both direct and iterative methods for solving the corresponding large sparse system of linear algebraic equations are analysed. Several numerical experiments to simulate seismic energy propagation through heterogeneous media are performed. Synthetics in the form of common shot gathers, vertical seismic profiles and snapshots are suitably displayed, since with the large amounts of data obtained from CSM research, methods for visualization of the computed results must be developed. The FEM is compared with other numerical tools, such as finite‐difference and pseudo‐spectral methods.
Climatic severity and the response to temperature elevation of Arctic aphids
Authors: STRATHDEE A.T. , BALE J.S. , STRATHDEE F.C. , BLOCK W.C. , COULSON S.J. , WEBB N.R. , HODKINSON I. D.
Published: April 2006

Theory suggests that any given rise in temperature resulting from climate change will have its greatest effect on high Arctic ecosystems where growing seasons are short and temperatures low.

 A small temperature rise, similar to that predicted for the middle of the next century, has profound effects on a population of the high Arctic, Dryas‐feeding aphid Acyrthosiphon svalbardicum on Spitsbergen (Strathdee et al. 1993a).

 Here comparative experiments on a closely related Dryas‐feeding species, A. brevicorne, at two contrasting sub‐Arctic sites are described. Together with the results from Spitsbergen these sites represent two colder sites (high Arctic and upland sub‐Arctic) and one warmer site (lowland sub‐Arctic).

 Differential responses in aphid population density and overwintering egg production to temperature elevation support the hypothesis that the ecological effects are greatest at sites with the most severe climates; however, there is no similar gradient in advancement of host plant phenology with warming.
Early‐season effects of supplemented solar UV‐B radiation on seedling emergence, canopy structure, simulated stand photosynthesis and competition for light
Authors: BARNES PAUL W. , FLINT STEPHAN D. , CALDWELL MARTYN M.
Published: April 2006

Mixtures and monocultures of wheat (Triticum aestivum) and wild oat (Avena fatua), a common weedy competitor of wheat, were exposed to enhanced solar UV‐B radiation simulating a 20% reduction in stratospheric ozone to assess the timing and seasonal development of the UV‐B effects on light competition in these species. Results from two years of field study revealed that UV‐B enhancement had no detectable effect on the magnitude or timing of seedling emergence in either species. End‐of‐season measurements showed significant UV‐B inhibition of leaf insertion height in wild oat in mixture and monoculture in the second year (irrigated year) but not in the first year (drought year). Leaf insertion height of wheat was not affected by UV‐B in either year. The UV‐B treatment had no detectable effect on monoculture or total (combined species) mixture LAI but did significantly increase (5–7%) the fractional contribution of wheat to the mixture LAI after four weeks of growth in both years. In addition, the UV‐B treatment had subtle effects on LAI height profiles with early season mixtures showing significant reductions in wild oat LAI in lower canopy layers in both years while midseason Year 2 mixtures showed significant reductions in wild oat LAI in upper canopy layers. The changes in canopy structure were found to significantly increase (6–7%) the proportional simulated clear sky canopy photosynthesis and light interception of wheat in mixture. These findings, and others, indicate that the effects of UV‐B enhancement on competition are realized very early in canopy development and provide additional support for the hypothesis that UV‐B enhancement may shift the balance of competition between these species indirectly by altering competitive interactions for light.
Leaf gas exchange and nitrogen dynamics of N2‐fixing, field‐grown Alnus glutinosa under elevated atmospheric CO2
Authors: VOGEL CHRISTOPH S. , CURTIS PETER S.
Published: April 2006

Few studies have investigated the effects of elevated CO2 on the physiology of symbiotic N2‐fixing trees. Tree species grown in low N soils at elevated CO2 generally show a decline in photosynthetic capacity over time relative to ambient CO2 controls. This negative adjustment may be due to a reallocation of leaf N away from the photosynthetic apparatus, allowing for more efficient use of limiting N. We investigated the effect of twice ambient CO2 on net CO2 assimilation (A), photosynthetic capacity, leaf dark respiration, and leaf N content of N2‐fixing Alnus glutinosa (black alder) grown in field open top chambers in a low N soil for 160 d.

At growth CO2, A was always greater in elevated compared to ambient CO2 plants. Late season A vs. internal leaf p(CO2) response curves indicated no negative adjustment of photosynthesis in elevated CO2 plants. Rather, elevated CO2 plants had 16% greater maximum rate of CO2 fixation by Rubisco. Leaf dark respiration was greater at elevated CO2 on an area basis, but unaffected by CO2 on a mass or N basis. In elevated CO2 plants, leaf N content (μg N cm−2) increased 50% between Julian Date 208 and 264. Leaf N content showed little seasonal change in ambient CO2 plants. A single point acetylene reduction assay of detached, nodulated root segments indicated a 46% increase in specific nitrogenase activity in elevated compared to ambient CO2 plants. Our results suggest that N2‐fixing trees will be able to maintain high A with minimal negative adjustment of photosynthetic capacity following prolonged exposure to elevated CO2 on N‐poor soils.
Terrestrial ecosystems and the carbon cycle
Authors: SCHIMEL DAVID S.
Published: April 2006

The terrestrial biosphere plays an important role in the global carbon cycle. In the 1994 Intergovernmental Panel Assessment on Climate Change (IPCC), an effort was made to improve the quantification of terrestrial exchanges and potential feedbacks from climate, changing CO2, and other factors; this paper presents the key results from that assessment, together with expanded discussion. The carbon cycle is the fluxes of carbon among four main reservoirs: fossil carbon, the atmosphere, the oceans, and the terrestrial biosphere. Emissions of fossil carbon during the 1980s averaged 5.5 Gt y−1. During the same period, the atmosphere gained 3.2 Gt C y−1 and the oceans are believed to have absorbed 2.0 Gt C y−1. The regrowing forests of the Northern Hemisphere may have absorbed 0.5 Gt C y−1 during this period. Meanwhile, tropical deforestation is thought to have released an average 1.6 Gt C y−1 over the 1980s. While the fluxes among the four pools should balance, the average 198Ds values lead to a ‘missing sink’ of 1.4 Gt C y−1 Several processes, including forest regrowth, CO2 fertilization of plant growth (c. 1.0 Gt C y−1), N deposition (c. 0.6 Gt C y−1), and their interactions, may account for the budget imbalance. However, it remains difficult to quantify the influences of these separate but interactive processes. Uncertainties in the individual numbers are large, and are themselves poorly quantified. This paper presents detail beyond the IPCC assessment on procedures used to approximate the flux uncertainties.

Lack of knowledge about positive and negative feedbacks from the biosphere is a major limiting factor to credible simulations of future atmospheric CO2 concentrations. Analyses of the atmospheric gradients of CO2 and 13 CO2 concentrations provide increasingly strong evidence for terrestrial sinks, potentially distributed between Northern Hemisphere and tropical regions, but conclusive detection in direct biomass and soil measurements remains elusive.

Current regional‐to‐global terrestrial ecosystem models with coupled carbon and nitrogen cycles represent the effects of CO2 fertilization differently, but all suggest longterm responses to CO2 that are substantially smaller than potential leaf‐ or laboratory whole plant‐level responses. Analyses of emissions and biogeochemical fluxes consistent with eventual stabilization of atmospheric CO2 concentrations are sensitive to the way in which biospheric feedbacks are modeled by c. 15%. Decisions about land use can have effects of 100s of Gt C over the next few centuries, with similarly significant effects on the atmosphere.

Critical areas for future research are continued measurements and analyses of atmospheric data (CO2 and 13CO2) to serve as large‐scale constraints, process studies of the scaling from the photosynthetic response to CO2 to whole‐ecosystem carbon storage, and rigorous quantification of the effects of changing land use on carbon storage.
Elevated carbon dioxide affects leaf‐miner performance and plant growth in docks (Rumex spp.)
Authors: SALT D. T. , BROOKS G. L. , WHITTAKER J. B.
Published: April 2006

Exposure of R. crispus and R. obtusifolius to elevated CO2 (600 ppm) resulted in an increased C:N ratio of leaf tissue and greater leaf areas. Larvae of P. nigritarsis mining leaves of R. obtusifolius during exposure produced significantly bigger mines in elevated than in ambient (350 ppm) conditions. There were no significant treatment effects on pupal weight although in both host species mean weight was greater in ambient than in elevated conditions. These results are consistent with the hypothesis that insect herbivores compensate for increased C:N ratios by increased food consumption. This response by herbivores may partially offset predicted increases in plant biomass in a future high CO2 environment.
Climate change, interannual weather differences and conflicting responses among crop characteristics: the case of forage quality
Authors: SELIGMAN NO'AM G. , SINCLAIR THOMAS R.
Published: April 2006

Yield and quality of cultivated forage crops are important determinants of animal production efficiency and both forage traits are sensitive to weather. Consequently, it can be presumed that these traits will respond to anticipated changes in the global environment associated with increases in [CO2] and temperature. Because of the large inter‐ and intra‐annual weather variation that exists in most agricultural regions, it is not clear what the forage production response will be to predicted changes. This uncertainty in forage response to global environment change as compared to interannual weather variation was analysed using a mechanistic simulation model of plant development and growth. The results indicated that low soil‐nutrient availability restricts forage production to such a degree that the global environment effects of higher [CO2] and temperature on quality are essentially irrelevant. When the nitrogen constraint was relaxed, higher [CO2] caused dry matter and digestibility to increase and protein concentration and leaf:stem ratio to decrease. Increased temperature had opposite effects. The combined effects of [CO2] and temperature were complex and annual weather variations were dominant, especially in rainfed situations. Limited reliability of predictions of crop response decades into the future indicates that it may be prudent to direct research effort to prepare for a wide range of climatic contingencies.
The effects of elevated CO2concentrations on the root growth of Lolium perenne and Trifolium repens grown in a FACE* system
Authors: JONGEN MARJAN , JONES MIKE B. , HEBEISEN THOMAS , BLUM HERBERT , HENDREY GEORGE
Published: April 2006

Lolium perenneandTrifolium repenswere grown in a Free Air CO2Enrichment (FACE) system at elevated (600 μimol mol‐1) and ambient (340 μmol mol‐1) carbon dioxide concentrations during a whole growing season. Using a root ingrowth bag technique the extent to which CO2enrichment influenced the growth ofL, perenneandT. repensroots under two contrasting nutrient regimes was examined. Root ingrowth bags were inserted for a fixed time into the soil in order to trap roots. It was also possible to follow the mortality of roots in bags inserted for different time intervals. Root ingrowth of bothL. perenneandT. repensincreased under elevated CO2conditions. InL. perenne, root ingrowth decreased with increasing nutrient fertilizer level, but forT. repensthe root ingrowth was not affected by the nutrient application rate. Besides biomass measurements, root length estimates were made forT, repens.These showed an increase under elevated CO2concentrations. Root decomposition appeared to decrease under elevated CO2concentrations. A possible explanation for this effect is the observed changes in tissue composition, such as the increase in the carbon: nitrogen ratio in roots ofL. perenneat elevated CO2concentrations.
Effects of global environmental change on carbon partitioning in vegetative plants of Triticum aestivum and closely related Aegilops species
Authors: LAMBERS HANS , VAN DEN BOOGAARD RIKI , VENEKLAAS ERIK J. , VILLAR RAFAEL
Published: April 2006

The use of fossil fuel is predicted to cause an increase of the atmospheric CO2 concentration, which will affect the global pattern of temperature and precipitation. It is therefore essential to incorporate effects of temperature and water supply on carbon partitioning of plants to predict effects of elevated [CO2] on growth and yield of Triticum aestivum.

Although earlier papers have emphasized that elevated [CO2] favours investment of biomass in roots relative to that in leaves, it has now become clear that these are indirect effects, due to the more rapid depletion of nutrients in the root environment as a consequence of enhanced growth. Broadly generalized, the effect of temperature on biomass allocation in the vegetative stage is that the relative investment of biomass in roots is lowest at a certain optimum temperature and increases at both higher and lower temperatures. This is found not only when the temperature of the entire plant is varied, but also when only root temperature is changed whilst shoot temperature is kept constant. Effects of temperature on the allocation pattern can be explained largely by the effect of root temperature on the roots' capacity to transport water. Effects of a shortage in water supply on carbon partitioning are unambiguous: roots receive relatively more carbon.

The pattern of biomass allocation in the vegetative stage and variation in water‐use efficiency are prime factors determining a plant's potential for early growth and yield in different environments. In a comparison of a range of T. aestivum cultivars, a high water‐use efficiency at the plant level correlates positively with a large investment in both leaf and root biomass, a low stomatal conductance and a large investment in photosynthetic capacity. We also present evidence that a lower investment of biomass in roots is not only associated with lower respiratory costs for root growth, but also with lower specific costs for ion uptake. We suggest the combination of a number of traits in future wheat cultivars, i.e. a high investment of biomass in leaves, which have a low stomatal conductance and a high photosynthetic capacity, and a low investment of biomass in roots, which have low respiratory costs. Such cultivars are considered highly appropriate in a future world, especially in the dryer regions. Although variation for the desired traits already exists among wheat cultivars, it is much larger among wild Aegilops species, which can readily be crossed with T. aestivum. Such wild relatives may be exploited to develop new wheat cultivars well‐adapted to changed climatic conditions.
Interaction between atmospheric CO2 concentration and water deficit on gas exchange and crop growth: testing of ecosys with data from the Free Air CO2 Enrichment (FACE) experiment
Authors: GRANT R.F. , GARCIA R.L. , PINTER J P.J. , HUNSAKER D. , WALL G.W. , KIMBALL B.A. , LaMORTE R.L.
Published: April 2006

Soil water deficits are likely to influence the response of crop growth and yield to changes in atmospheric CO2 concentrations (Ca), but the extent of this influence is uncertain. To study the interaction of water deficits and Ca on crop growth, the ecosystem simulation model ecosys was tested with data for diurnal gas exchange and seasonal wheat growth measured during 1993 under high and low irrigation at Ca= 370 and 550 μmol mol−1 in the Free Air CO2 Enrichment (FACE) experiment near Phoenix, AZ. The model, supported by the data from canopy gas exchange enclosures, indicated that under high irrigation canopy conductance (gc) at Ca= 550 μmol mol−1 was reduced to about 0.75 that at Ca= 370 μmol mol−1, but that under low irrigation, gc was reduced less. Consequently when Ca was increased from 370 to 550 μmol mol−1, canopy transpiration was reduced less, and net CO2 fixation was increased more, under low irrigation than under high irrigation. The simulated effects of Ca and irrigation on diurnal gas exchange were also apparent on seasonal water use and grain yield. Simulated vs. measured seasonal water use by wheat under high irrigation was reduced by 6% vs. 4% at Ca= 550 vs. 370 μmol mol−1 but that under low irrigation was increased by 3% vs. 5%. Simulated vs. measured grain yield of wheat under high irrigation was increased by 16% vs. 8%, but that under low irrigation was increased by 38% vs. 21%. In ecosys, the interaction between Ca and irrigation on diurnal gas exchange, and hence on seasonal crop growth and water use, was attributed to a convergence of simulated gc towards common values under both Ca as canopy turgor declined. This convergence caused transpiration to decrease comparatively less, but CO2 fixation to increase comparatively more, under high vs. low Ca. Convergence of gc was in turn attributed to improved turgor maintenance under elevated Ca caused by greater storage C concentrations in the leaves, and by greater rooting density in the soil.
Plant growth chambers for the simultaneous control of soil and air temperatures, and of atmospheric carbon dioxide concentration
Authors: GORDON DENNIS C. , VAN VUUREN MARGRET M.I. , MARSHALL BRUCE , ROBINSON DAVID
Published: April 2006

Many facilities for growing plants at elevated atmospheric concentrations of CO2 ([CO2]) neglect the control of temperature, especially of the soil. Soil and root temperatures in conventional, free‐standing pots often exceed those which would occur in the field at a given air temperature. A plant growth facility is described in which atmospheric CO2 can be maintained at different concentrations while soil and air temperatures mimic spatial and temporal patterns seen in the field. It consists of glasshouse‐located chambers in which [CO2] is monitored by an infra‐red gas analyser and maintained by injection of CO2 from a cylinder. Air is cooled by a heat exchange unit. Plants grow in soil in 1.2 m long containers that are surrounded by cooling coils and thermal insulation. Both [CO2] and temperature are controlled by customized software. Air temperature is programmed to follow a sine function of diurnal time. Soil temperature at a depth of 0.55 m is programmed to be constant. Temperature at 0.1 m depth varies as a damped, lagged function of air temperature; that at 1.0 m as a similar function of the 0.55 m temperature. [CO2] is maintained within 20 μmol mol−1 of target concentrations during daylight. A feature of the system is that plant material is labelled with a 13C enrichment different from that of carbon in soil organic matter. The operation of the system is illustrated with data collected in an experiment with spring wheat (Triticum aestivum L., cv Tonic) grown at ambient [CO2] and at [CO2] 350 μmol mol−1 greater than ambient.
The importance of climate and soils for estimates of net primary production: a sensitivity analysis with the terrestrial ecosystem model
Authors: PAN YUDE , MCGUIRE A. DAVID , KICKLIGHTER DAVID W. , MELILLO JERRY M.
Published: April 2006

We used the Terrestrial Ecosystem Model (TEM) to investigate how alternative input data sets of climate (temperature/precipitation), solar radiation, and soil texture affect estimates of net primary productivity (NPP) for the conterminous United States. At the continental resolution, the climates of Cramer and Leemans (C&L) and of the Vegetation/ Ecosystem Modelling and Analysis Project (VEMAP) represent cooler and drier conditions for the United States in comparison to the Legates and Willmott (L&W) climate, and cause 5.2% and 2.3% lower estimates of NPP. Solar radiation derived from C&L and given in VEMAP is 32% and 60% higher than the solar radiation data derived from Hahn cloudiness. These differences cause ∼ 8% and 10% lower NPP because of radiation‐induced water stress. In comparison to the FAO/CSRC soil texture, which represents most biomes with loam soils, the soil textures are finer (more silt and clay) in the Zobler and VEMAP data sets. The use of VEMAP soil textures instead of FAO/CSRC soil textures causes ∼ 3% higher NPP because enhanced volumetric soil moisture causes higher rates of nitrogen cycling, but use of the Zobler soil textures has little effect. In general, NPP estimates of TEM are more sensitive to alternative data sets at the biome and grid cell resolutions than at the continental resolution. At all spatial resolutions, the sensitivity of NPP estimates represents the impact of uncertainty among the alternative data sets we used in this study. The reduction of uncertainty in input data sets is required to improve the spatial resolution of NPP estimates by process‐based ecosystem models, and is especially important for improving assessments of the regional impacts of global change.
Effects of enhanced ultraviolet radiation and carbon dioxide concentration on the moss Hylocomium splendens
Authors: SONESSON MATS , CALLAGHAN TERRY V. , CARLSSON BENGT Å.
Published: April 2006

In a laboratory experiment interaction effects of UV‐B and CO2 on photosynthesis and growth of the moss Hylocomium splendens were studied. The plants were exposed to two CO2 levels (350 ppm and 600 ppm) and three UV‐B levels (no UV‐B, ambient UV‐B and that corresponding to 20% ozone depletion) for 5 months. The effects were recorded by measuring the photosynthetic response and growth of the plants.

There was a statistically significant change in photosynthetic efficiency and maximum photosynthetic rates due to time and to enhanced CO2 concentration, whereas there was no effect due to UV‐B. There was a decreased growth due to both UV‐B and CO2 and an interaction effect on growth (in length). The UV‐B dose corresponding to the ambient level had a larger reducing effect on growth than the highest UV‐B dose. This was a counter‐intuitive result and the following tentative interpretation was made: differences in the measured UV‐A/UV‐B/PAR ratios between the treatments could explain the result provided there was a non‐linear response to UV over the range of irradiance levels used.
A new gas injection method to enhance spatial utilization within a Free‐Air CO2 Enrichment (FACE) system
Authors: WALKLATE P. J. , XU Z. G. , McLEOD A. R.
Published: April 2006

Visual observations of smoke dispersion in a wind tunnel and a computational fluid dynamics (CFD) model were used to evaluate methods of improving the performance of Free‐Air COT Enrichment (FACE) Systems for field studies of the effects of elevated CO2 on vegetation. A special baffle, named an Enhanced Local Mixing (ELM) system, was observed to increase the turbulence and consequent dilution of fumigant gas in the atmosphere. Modelling results suggest that the ELM design reduces the spatial variation of fumigant gas concentration in small experimental plots. The potential reduction in CO2 use and costs warrants further evaluation under Held conditions.
Coral reef bleaching: facts, hypotheses and implications
Authors: GLYNN PETER W.
Published: April 2006

Coral reef bleaching, the temporary or permanent loss of photosynthetic microalgae (zooxanthellae) and/or their pigments by a variety of reef taxa, is a stress response usually associated with anthropogenic and natural disturbances. Degrees of bleaching, within and among coral colonies and across reef communities, are highly variable and difficult to quantify, thus complicating comparisons of different bleaching events. Small‐scale bleaching events can often be correlated with specific disturbances (e.g. extreme low/high temperatures, low/high solar irradiance, subaerial exposure, sedimentation, freshwater dilution, contaminants, and diseases), whereas large scale (mass) bleaching occurs over 100s to 1000s of km2, which is more difficult to explain. Debilitating effects of bleaching include reduced/no skeletal growth and reproductive activity, and a lowered capacity to shed sediments, resist invasion of competing species and diseases. Severe and prolonged bleaching can cause partial to total colony death, resulting in diminished reef growth, the transformation of reef‐building communities to alternate, non‐reef building community types, bioerosion and ultimately the disappearance of reef structures. Present evidence suggests that the leading factors responsible for large‐scale coral reef bleaching are elevated sea temperatures and high solar irradiance (especially ultraviolet wavelengths), which may frequently act jointly.
Marine pollution and coral reefs
Authors: DUBINSKY ZVY , STAMBLER NOGA
Published: April 2006

Coral reefs are exposed to many anthropogenic stresses increasing in impact and range, both on local and regional scales. The main ones discussed here are nutrient enrichment, sewage disposal, sedimentation, oil‐related pollution, metals and thermal pollution. The stress comprising the main topic of this article, eutrophication, is examined from the point of view of its physiological and ecological mechanisms of action, on a number of levels. Nutrient enrichment can introduce an imbalance in the exchange of nutrients between the zooxanthellae and the host coral, it reduces light penetration to the reef due to nutrient‐ stimulated phytoplankton growth, and, most harmful of all, may bring about proliferation of seaweeds. The latter rapidly outgrow, smother and eventually replace, the slow‐growing coral reef, adapted to cope with the low nutrient concentrations typical in tropical seas.

Eutrophication seldom takes place by itself. Sewage disposal invariably results in nutrient enrichment, but it also enriches the water with organic matter which stimulates proliferation of oxygen‐consuming microbes. These may kill corals and other reef organisms, either directly by anoxia, or by related hydrogen sulfide production. Increased sediment deposition is in many cases associated with other human activities leading to eutrophication, such as deforestation and topsoil erosion.

Realistically achievable goals to ensure conservation, and in some instances, rehabilitation of coral reefs are listed.
Global change and coral reefs: impacts on reefs, economies and human cultures
Authors: WILKINSON CLIVE R.
Published: April 2006

Coral reefs have reconstituted themselves after previous large sea‐level variations, and climate changes. For the past 6000 years of unusually stable sea‐level, reefs have grown without serious interruptions. During recent decades, however, new stresses threaten localized devastation of many reefs. A new period of global climate change is occurring, stimulated by anthropogenic increases in greenhouse gases. Coral reefs will cope well with predicted sea‐level rises of 4.5 cm per decade, but reef islands will not. Higher sea levels will provide corals with greater room for growth across reef flats, but there are no foreseeable mechanisms for reef island growth to keep pace with sea‐level rise, therefore many low islands may ultimately become uninhabitable.

Climate change will introduce localized variations in weather patterns, but changes to individual reefs cannot be predicted. Reefs on average should cope well with regional climate change, as they have coped with similar previous fluctuations. Air temperature increases of 0.2–0.3 °C/decade will induce slower increases in sea‐surface temperatures, which may cause localized, or regional increases in coral bleaching. Changes in rainfall will impact on reefs near land masses. Likewise, increased storms and variations in El Nino Southern Oscillation (ENSO) may stress some reefs, but not others.

The greatest impact of climate change will be a synergistic enhancement of direct anthropogenic stresses (excessive sediment and pollution from the land; over‐fishing, especially via destructive methods; mining of coral rock and sand; and engineering modifications), which currently cause most damage to coral reefs. Many of the world's reefs have been degraded and more will be damaged as anthropogenic impacts increase under the ‘demophoric’ increases in population (demos) and economic (phoric) activity. This biotic and habitat loss will result in severe economic and social losses. Reefs, however, have considerable recovery powers and losses can be minimized by effective management of direct human impacts and reducing indirect threats of global climate change.
Reef coral diversity and global change
Authors: CHADWICK‐FURMAN NANETTE E.
Published: April 2006

Regional anthropogenic processes such as pollution, dredging, and overfishing on coral reefs currently threaten the biodiversity of stony corals and other reef‐associated organisms. Global climate change may interact with anthropogenic processes to create additional impacts on coral diversity in the near future. In order to predict these changes, it is necessary to understand the magnitude and causes of variation in scleractinian coral diversity throughout their 240 million year history. The fossil record documents long periods of speciation in corals, interrupted repeatedly by events of mass extinction. Some of these events relate clearly to changes in global climate. Diversity in reef corals has increased since their last period of extinction at the end of the Cretaceous (65 My bp), and is still rising. During the last 8 million years, the fragmentation of the once pantropical Tethys Sea separated corals into two major biogeographical provinces. Periods of glaciation also have caused major changes in sea level and temperature. Accumulated evidence supports the theory that relative habitat area and changing patterns of oceanic circulation are mainly responsible for the two observed centres of recent coral diversity at the western tropical margins of the Atlantic and Pacific oceans. At predicted rates of climate change in the near future, coral reefs are likely to survive as an ecosystem. Increases in sea level may actually benefit corals and lead to regional increases in diversity if new habitat area on back reefs is opened to increased water circulation and thus coral dispersal. Rising temperature may cause higher rates of coral mortality and even local extinction in isolated, small populations such as those on oceanic islands. The effects of increases in ultraviolet radiation (UV) are largely unknown, but likely to be negative. UV may damage planktonic coral propagules in oceanic surface waters and thus decrease rates of gene flow between coral populations. This may result in increased local extinctions, again with the strongest impact on widely separated reefs with small coral populations. The largest threats to coral diversity are regional anthropogenic impacts, which may interact with global climate change to exacerbate rates of local species extinctions. Centres of high reef coral diversity coincide with human population centres in south‐east Asia and the Caribbean, and thus the greatest potential for species loss lies in these geographical areas.
Coral skeletons: storage and recovery of environmental information
Authors: BARNES D.J. , LOUGH J.M.
Published: April 2006

Understanding the nature and causes of past global change is a key to understanding what may happen in the future. The discovery, nearly 25 years ago, of annual density bands in skeletons of long‐lived, massive corals promised high‐resolution proxy climate records for tropical oceans. The tropics are regions of major importance to the global climate system and they are poorly represented by high‐resolution proxy climate records such as tree rings, ice cores and historical documents.

In this review we examine the principles and procedures underlying routine recovery and interpretation of information from proxy environmental recorders. We summarize an extensive literature which indicates that coral skeletons are excellent archives for considerable and diverse environmental information. We show that this potential has not been fully realized, largely because corals seemed to yield inconsistent, sometimes conflicting, information. We discuss ways in which much of this confusion is resolved by new understanding of coral skeletal growth mechanisms. We also examine several records which indicate that corals can meet requirements for reconstruction of useful, reliable environmental information.
Strategies for measuring and modelling carbon dioxide and water vapour fluxes over terrestrial ecosystems
Authors: BALDOCCHI DENNIS , VALENTINI RICCARDO , RUNNING STEVE , OECHEL WALT , DAHLMAN ROGER
Published: April 2006

Continuous and direct measurements of ecosystem carbon dioxide and water vapour fluxes can improve our ability to close regional and global carbon and hydrological budgets. On this behalf, an international and multidisciplinary group of scientists (micrometeorologists, ecophysiologists and biogeochemists) assembled at La Thuile, Italy to convene a workshop on ‘Strategies for Monitoring and Modelling CO2 and Water Vapour Fluxes over Terrestrial Ecosystems’. Over the course of the week talks and discussions focused on: (i) the results from recent field studies on the annual cycle of carbon dioxide and water vapour fluxes over terrestrial ecosystems; (ii) the problems and pitfalls associated with making long‐term flux measurements; (iii) alternative methods for assessing ecosystem carbon dioxide and water vapour fluxes; (iv) how direct and continuous carbon dioxide and water vapour flux measurements could be used by the ecological and biogeochemical modelling communities; and (v) if, how and where to proceed with establishing a network of long‐term flux measurement sites. This report discusses the purpose of the meeting and summarizes the conclusions drawn from the discussions by the attending scientists.

There was a consensus that recent advances in instrumentation and software make possible long‐term measurements of carbon dioxide and water vapour fluxes over terrestrial ecosystems. At this writing, eight research teams have conducted long‐term carbon dioxide and water vapour flux experiments and more long‐term studies are anticipated. The participants advocated an experimental design that would make long‐term flux measurement valuable to a wider community of modelers, biogeochemists and ecologists. A network of carbon dioxide and water vapour flux measurement stations should include ancillary measurements of meteorological, ecological and biological variables. To assess spatial representativeness of the long term and tower‐based flux measurements, periodic aircraft‐based flux experiments and satellite‐based assessments of land cover were recommended. Occasional cuvette‐based measurements of leaf‐level carbon dioxide and water vapour fluxes were endorsed to provide information on the biological control of surface fluxes. They can also provide data to parameterize ecophysiological models. Flask sampling of stable carbon isotopes was advocated to extend the flux measurements to the global scale.
The use of eddy covariance to infer the net carbon dioxide uptake of Brazilian rain forest
Authors: GRACE JOHN , MALHI YADVINDER , LLOYD JON , McINTYRE JOHN , MIRANDA ANTONIO C. , MEIR PATRICK , MIRANDA HELOISA S.
Published: April 2006

Eddy covariance measurements of CO2 flux, based on four and six week campaigns in Rondôdnia, Brazil, have been used in conjunction with a model to scale up data to a whole year, and thus estimate the carbon balance of the tropical forest ecosystem, and the changes in carbon balance expected from small interannual variations in climatological conditions.

 One possible source of error in this estimation arises from the difficulty in measuring fluxes under stably stratified meteorological conditions, such as occur frequently at night. Flux may be ‘lost’ because of low velocity advection, caused by nocturnal radiative cooling at sites on raised ground. Such effects may be detected by plotting the net ecosystem flux of CO2, Feco is a function of wind speed. If flux is ‘lost’ then Feco is expected to decline with wind speed. In the present data set, this did not occur, and Feco was similar to the nocturnal flux estimated independently from chamber measurements.

 The model suggests that in 1992/3, the Gross Primary Productivity (GPP) was 203.3 mol C m−2 y−1 and ecosystem respiration was 194.8 mol C m−2 y−1, giving an ecosystem carbon balance of 8.5 mol C m−2 y−1, equivalent to a sink of 1.0 ton C ha−1 y−1. However, the sign and magnitude of this figure is very sensitive to temperature, because of the strong influence of temperature on respiration.

 The model also suggests that the effect of temperature on the net carbon balance is strongly dependent on the partial pressure of CO2.
The propagation of errors in long‐term measurements of land‐atmosphere fluxes of carbon and water
Authors: MONCRIEFF J.B. , MALHI Y. , LEUNING R.
Published: April 2006

For surface fluxes of carbon dioxide, the net daily flux is the sum of daytime and nighttime fluxes of approximately the same magnitude and opposite direction. The net flux is therefore significantly smaller than the individual flux measurements and error assessment is critical in determining whether a surface is a net source or sink of carbon dioxide. For carbon dioxide flux measurements, it is an occasional misconception that the net flux is measured as the difference between the net upward and downward fluxes (i.e. a small difference between large terms). This is not the case. The net flux is the sum of individual (half‐hourly or hourly) flux measurements, each with an associated error term. The question of errors and uncertainties in long‐term flux measurements of carbon and water is addressed by first considering the potential for errors in flux measuring systems in general and thus errors which are relevant to a wide range of timescales of measurement. We also focus exclusively on flux measurements made by the micrometeorological method of eddy covariance. Errors can loosely be divided into random errors and systematic errors, although in reality any particular error may be a combination of both types. Systematic errors can be fully systematic errors (errors that apply on all of the daily cycle) or selectively systematic errors (errors that apply to only part of the daily cycle), which have very different effects. Random errors may also be full or selective, but these do not differ substantially in their properties. We describe an error analysis in which these three different types of error are applied to a long‐term dataset to discover how errors may propagate through long‐term data and which can be used to estimate the range of uncertainty in the reported sink strength of the particular ecosystem studied.
Transpiration of trees and forest stands: short and long‐term monitoring using sapflow methods
Authors: GRANIER A. , BIRON P. , BRÉDA N. , PONTAILLER J.‐Y. , SAUGIER B.
Published: April 2006

We show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (i) it gives access to the spatial variability within a forest stand, (ii) it can be used even on steep slopes, and (iii) when combined with eddy correlation measurements over forests, it allows separation of individual tree transpiration from the total water loss of the stand. Moreover, sapflow techniques are quite easy to implement.

Four sapflow techniques currently coexist, all based on heat diffusion in the xylem. We found a good agreement between three of these techniques. Most results presented here were obtained using the radial flow meter (Granier 1985).

Tree sapflow is computed as sap flux density times sapwood area. To scale up from trees to a stand, measurements have to be made on a representative sample of trees. Thus, a number of trees in each circumference class is selected according to the fraction of sapwood they represent in the total sapwood area of the stand. The variability of sap flux density among trees is usually low (CV. 10–15%) in close stands of temperate coniferous or deciduous forests, but is much higher (35–50%) in a tropical rain forest. It also increases after thinning or during a dry spell.

A set of 5–10 sapflow sensors usually provides an accurate estimate of stand transpiration. Transpiration measured on two dense spruce stands in the Vosges mountains (France) and one Scot's pine plantation in the Rhine valley (Germany) showed that maximum rate was related to stand LAI and to local climate. Preliminary results comparing the sapflow of a stand of Pinus banksiana to the transpiration of large branches, as part of the BOREAS programme in Saskachewan, Canada showed a similar trend.

For modelling purposes, tree canopy conductance (gc) was calculated from Penman‐Monteith equation. In most experiments, calculated canopy conductance was dependent on global radiation (positive effect) and on vapour pressure deficit (negative effect) in the absence of other limiting factors. A comparison of the vapour pressure deficit response curves of gc for several tree species and sites showed only small differences among spruce, oak and pine forests when including understorey. Tropical rainforests exhibited a similar behaviour.
The use of CO2 flux measurements in models of the global terrestrial carbon budget
Authors: RUIMY ANNE , KERGOAT LAURENT , FIELD CHRISTOPHER B. , SAUGIER BERNARD
Published: April 2006

CO2 flux measurements give access to two critical terms of the carbon budget of terrestrial ecosystems, the gross primary productivity (GPP) and the net ecosystem productivity (NEP). CO2 fluxes measured by micrometeorological methods have spatial and temporal characteristics that make them potentially useful in modelling the global terrestrial carbon budget. The first use is in parameterizing ecosystem physiological processes. We present an example, based on parameterizing the mean light response of GPP. This parameterization can be used in diagnostic, satellite‐based GPP models. A global application leads to realistic estimates of global GPP. The second use is in testing the seasonality of fluxes predicted by global models. Our example of this use tests two global GPP models. One is a diagnostic, satellite‐based model, and one is a prognostic, process‐based model. Despite the limitations of the models, both agree reasonably well with the measurements. The agreements and disagreements are useful in addressing the problems of available input datasets and representation of processes, in global models. Long‐term CO2 flux measurements give access to key variables of terrestrial vegetation models and therefore offer exciting perspectives.
Modelling temporal variability in the carbon balance of a spruce/moss boreal forest
Authors: FROLKING S. , GOULDEN M.L. , WOFSY S.C. , FAN S‐M. , SUTTON D.J. , MUNGER J.W. , BAZZAZ A. M. , DAUBE B.C. , CRILL P. M. , ABER J. D. , BAND L.E. , WANG X. , SAVAGE K. , MOORE T. , HARRISS R.C.
Published: April 2006

A model of the daily carbon balance of a black spruce/feathermoss boreal forest ecosystem was developed and results compared to preliminary data from the 1994 BOREAS field campaign in northem Manitoba, Canada. The model, driven by daily weather conditions, simulated daily soil climate status (temperature and moisture profiles), spruce photosynthesis and respiration, moss photosynthesis and respiration, and litter decomposition. Model agreement with preliminary field data was good for net ecosystem exchange (NEE), capturing both the asymmetrical seasonality and short‐term variability. During the growing season simulated daily NEE ranged from ‐4 g C m‐2d‐1(carbon uptake by ecosystem) to + 2 g C m‐2d‐1(carbon flux to atmosphere), with fluctuations from day to day. In the early winter simulated NEE values were + 0.5 g C m‐2d‐1, dropping to + 0.2 g C m‐2d‐1in mid‐winter. Simulated soil respiration during the growing season (+ 1 to + 5 g C m‐2d‐1) was dominated by metabolic respiration of the live moss, with litter decomposition usually contributing less than 30% and live spruce root respiration less than 10% of the total. Both spruce and moss net primary productivity (NPP) rates were higher in early summer than late summer. Simulated annual NEE for 1994 was ‐51 g C m‐2y‐1, with 83% going into tree growth and 17% into the soil carbon accumulation. Moss NPP (58 g C m‐2y‐1) was considered to be litter (i.e. soil carbon input; no net increase in live moss biomass). Ecosystem respiration during the snow‐covered season (84 g C m‐2) was 58% of the growing season net carbon uptake. A simulation of the same site for 1968–1989 showed = 10–20% year‐to‐year variability in heterotrophic respiration (mean of + 113 g C m‐2y‐1). Moss NPP ranged from 19 to 114 g C m‐2y‐1; spruce NPP from 81 to 150 g C m‐2y‐1; spruce growth (NPP minus litterfall) from 34 to 103 g C m‐2y‐1; NEE ranged from +37 to ‐142 g C m‐2y‐1. Values for these carbon balance terms in 1994 were slightly smaller than the 1969–89 means. Higher ecosystem productivity years (more negative NEE) generally had early springs and relatively wet summers; lower productivity years had late springs and relatively dry summers.