bluuebunny/crossref_metadata_2025_split huggingface dataset:
Human modification of the landscape and surface climate in the next fifty years
Authors: Defries R. S. , Bounoua L , Collatz G. J. 
Published: March 2003

AbstractHuman modification of the landscape potentially affects exchanges of energy and water between the terrestrial biosphere and the atmosphere. This study develops a possible scenario for land cover in the year 2050 based on results from the IMAGE 2 (Integrated Model to Assess the Greenhouse Effect) model, which projects land‐cover changes in response to demographic and economic activity. We use the land‐cover scenario as a surface boundary condition in a biophysically‐based land‐surface model coupled to a general circulation model for a 15‐years simulation with prescribed sea surface temperature and compare with a control run using current land cover. To assess the sensitivity of climate to anthropogenic land‐cover change relative to the sensitivity to decadal‐scale interannual variations in vegetation density, we also carry out two additional simulations using observed normalized difference vegetation index (NDVI) from relatively low (1982–83) and high (1989–90) years to describe the seasonal phenology of the vegetation.In the past several centuries, large‐scale land‐cover change occurred primarily in temperate latitudes through conversion of forests and grassland to highly productive cropland and pasture. Several studies in the literature indicate that past changes in surface climate resulting from this conversion had a cooling effect owing to changes in vegetation morphology (increased albedo). In contrast, this study indicates that future land‐cover change, likely to occur predominantly in the tropics and subtropics, has a warming effect governed by physiological rather than morphological mechanisms. The physiological mechanism is to reduce carbon assimilation and consequently latent relative to sensible heat flux resulting in surface temperature increases up to 2 °C and drier hydrologic conditions in locations where land cover was altered in the experiment. In addition, in contrast to an observed decrease in diurnal temperature range (DTR) over land expected with greenhouse warming, results here suggest that future land‐cover conversion in tropics could increase the DTR resulting from decreased evaporative cooling during the daytime. For grid cells with altered land cover, the sensitivity of surface temperature to future anthropogenic land‐cover change is generally within the range induced by decadal‐scale interannual variability in vegetation density in temperate latitudes but up to 1.5 °C warmer in the tropics.
Climate change and breeding parameters of great and blue tits throughout the western Palaearctic
Authors: Sanz Juan José 
Published: March 2003

AbstractIncreasing evidence suggests that climate change has consequences on avian breeding phenology. Here, variations in laying date and clutch size of great tit Parus major and blue tit Parus caeruleus within and between breeding populations through the western Palaearctic are examined in relation to climatic fluctuations, measured by the winter North Atlantic Oscillation (NAO) index. Within and across breeding sites, laying date was related to winter‐NAO index such that great and blue tit females lay earlier after warmer, moister winters (positive values of winter NAO‐index). The present study shows that for most populations there is an advancement of laying date, but the rate of change with respect to NAO significantly differed geographically across the western Palaearctic and did not differ between species. However, clutch size of great and blue tits was not affected by climatic fluctuations, presumably because the whole season is being shifted, but not in relation to food supplies. These combined analyses for the two species controlled for potentially confounding variables such as latitude, longitude, elevation and habitat of each study site.
Annual variation in soil respiration and its components in a coppice oak forest in Central Italy
Authors: Rey Ana , Pegoraro Emiliano , Tedeschi Vanessa , De Parri Ilaria , Jarvis Paul G. , Valentini Riccardo 
Published: March 2003

AbstractIn order to investigate the annual variation of soil respiration and its components in relation to seasonal changes in soil temperature and soil moisture in a Mediterranean mixed oak forest ecosystem, we set up a series of experimental treatments in May 1999 where litter (no litter), roots (no roots, by trenching) or both were excluded from plots of 4 m2. Subsequently, we measured soil respiration, soil temperature and soil moisture in each plot over a year after the forest was coppiced. The treatments did not significantly affect soil temperature or soil moisture measured over 0–10 cm depth.Soil respiration varied markedly during the year with high rates in spring and autumn and low rates in summer, coinciding with summer drought, and in winter, with the lowest temperatures. Very high respiration rates, however, were observed during the summer immediately after rainfall events. The mean annual rate of soil respiration was 2.9 µmol m−2 s−1, ranging from 1.35 to 7.03 µmol m−2 s−1.Soil respiration was highly correlated with temperature during winter and during spring and autumn whenever volumetric soil water content was above 20%. Below this threshold value, there was no correlation between soil respiration and soil temperature, but soil moisture was a good predictor of soil respiration. A simple empirical model that predicted soil respiration during the year, using both soil temperature and soil moisture accounted for more than 91% of the observed annual variation in soil respiration.All the components of soil respiration followed a similar seasonal trend and were affected by summer drought. The Q10 value for soil respiration was 2.32, which is in agreement with other studies in forest ecosystems. However, we found a Q10 value for root respiration of 2.20, which is lower than recent values reported for forest sites. The fact that the seasonal variation in root growth with temperature in Mediterranean ecosystems differs from that in temperate regions may explain this difference. In temperate regions, increases in size of root populations during the growing season, coinciding with high temperatures, may yield higher apparent Q10 values than in Mediterranean regions where root growth is suppressed by summer drought.The decomposition of organic matter and belowground litter were the major components of soil respiration, accounting for almost 55% of the total soil respiration flux. This proportion is higher than has been reported for mature boreal and temperate forest and is probably the result of a short‐term C loss following recent logging at the site.The relationship proposed for soil respiration with soil temperature and soil moisture is useful for understanding and predicting potential changes in Mediterranean forest ecosystems in response to forest management and climate change.
Linking sequestration of 13C and 15N in aggregates in a pasture soil following 8 years of elevated atmospheric CO2
Authors: VAN GROENIGEN KEES‐JAN , HARRIS DAVID , HORWATH WILLIAM R. , HARTWIG UELI A. , VAN KESSEL CHRIS 
Published: March 2003

AbstractThe influence of N availability on C sequestration under prolonged elevated CO2 in terrestrial ecosystems remains unclear. We studied the relationships between C and N dynamics in a pasture seeded to Lolium perenne after 8 years of elevated atmospheric CO2 concentration (FACE) conditions. Fertilizer‐15N was applied at a rate of 140 and 560 kg N ha2−1 y2−1 and depleted 13C‐CO2 was used to increase the CO2 concentration to 60 Pa pCO2. The 13C–15N dual isotopic tracer enabled us to study the dynamics of newly sequestered C and N in the soil by aggregate size and fractions of particulate organic matter (POM), made up by intra‐aggregate POM (iPOM) and free light fraction (LF). Eight years of elevated CO2 did not increase total C content in any of the aggregate classes or POM fractions at both rates of N application. The fraction of new C in the POM fractions also remained largely unaffected by N fertilization. Changes in the fractions of new C and new N (fertilizer‐N) under elevated CO2 were more pronounced between POM classes than between aggregate size classes. Hence, changes in the dynamics of soil C and N cycling are easier to detect in the POM fractions than in the whole aggregates. Within N treatments, fractions of new C and N in POM classes were highly correlated with more new C and N in large POM fractions and less in the smaller POM fractions. Isotopic data show that the microaggregates were derived from the macro‐aggregates and that the C and N associated with the microaggregates turned over slower than the C and N associated with the macroaggregates. There was also isotopic evidence that N immobilized by soil microorganisms was an important source of N in the iPOM fractions. Under low N availability, 3.04 units of new C per unit of fertilizer N were sequestered in the POM fractions. Under high N availability, the ratio of new C sequestered per unit of fertilizer N was reduced to 1.47. Elevated and ambient CO2 concentrations lead to similar 15N enrichments in the iPOM fractions under both low and high N additions, clearly showing that the SOM‐N dynamics were unaffected by prolonged elevated CO2 concentrations.
Response of tundra ecosystem in southwestern Alaska to Younger‐Dryas climatic oscillation
Authors: HU F. S. , LEE B. Y. , KAUFMAN D. S. , YONEJI S. , NELSON D. M. , HENNE P. D. 
Published: March 2003

AbstractClimatic warming during the last glacial–interglacial transition (LGIT) was punctuated by reversals to glacial‐like conditions. Palaeorecords of ecosystem change can help document the geographical extent of these events and improve our understanding of biotic sensitivity to climatic forcing. To reconstruct ecosystem and climatic variations during the LGIT, we analyzed lake sediments from southwestern Alaska for fossil pollen assemblages, biogenic‐silica content (BSiO2%), and organic‐carbon content (OC%). Betula shrub tundra replaced herb tundra as the dominant vegetation of the region around 13 600 cal BP (cal BP: 14C calibrated calendar years before present), as inferred from an increase of Betula pollen percentages from << 5% to >> 20% with associated decreases in Cyperaceae, Poaceae, and Artemisia. At c. 13 000 cal BP, a decrease of Betula pollen from 28 to << 5% suggests that shrub tundra reverted to herb tundra. Shrub tundra replaced herb tundra to resume as the dominant vegetation at 11 600 cal BP. Higher OC% and BSiO2% values suggest more stable soils and higher aquatic productivity during shrub‐tundra periods than during herb‐tundra periods, although pollen changes lagged behind changes in the biogeochemical indicators before c. 13 000 cal BP. Comparison of our palaeoecological data with the ice‐core dδ18O record from Greenland reveals strikingly similar patterns from the onset through the termination of the Younger Dryas (YD). This similarity supports the hypothesis that, as in the North Atlantic region, pronounced YD climatic oscillations occurred in the North Pacific region. The rapidity and magnitude of ecological changes at the termination of the YD are consistent with greenhouse experiments and historic photographs demonstrating tundra sensitivity to climatic forcing.
Northern hemisphere photosynthetic trends 1982–99
Authors: Slayback Daniel A. , Pinzon Jorge E. , Los Sietse O. , Tucker Compton J. 
Published: March 2003

AbstractWe examined trends in the averaged May–September AVHRR normalized difference vegetation index (NDVI) from 1982 to 1999 for the northern hemisphere. NDVI is closely related to the amount of absorbed photosynthetically active radiation; hence, trends in NDVI reflect trends in photosynthetic activity of land‐surface vegetation. Linear and nonlinear trend analysis techniques were applied to four differently processed and corrected Advanced Very High Resolution Radiometer (AVHRR) NDVI data sets. The results were compared in order to evaluate the effects of trends in NDVI unrelated to vegetation activity. We consistently found significant positive trends in averaged NDVI for latitude bands above 35°N in all but one data set; this one data set lacked corrections for sensor drift and instrument calibration. An impressive improvement in data quality was achieved by applying calibration and corrections for atmospheric effects.Conservative estimates of the trends over the 1982–99 period range from 0.0015 to 0.0045 NDVI units year−1 for global latitude bands from 35 to 75°N, with trends generally higher in the 1990s than in the 1980s; trends in NDVI were larger than trends explained by artefacts. In the 1980s, North American and Eurasian trends were roughly comparable, whereas in the 1990s the North American trends were generally higher. A pixel‐level analysis shows the trends to be widespread, with large areas of Canada, Europe and northern Asia experiencing significant positive increases across all vegetated landcovers.
Nitrous oxide emission factors for agricultural soils in Great Britain: the impact of soil water‐filled pore space and other controlling variables
Authors: Dobbie Karen E. , Smith Keith A. 
Published: March 2003

AbstractMeasurements were made of nitrous oxide (N2O) emissions from N‐fertilised ungrazed grassland and arable land at sites widely distributed across Great Britain during 1999–2001. The closed static chamber method was used throughout. Emissions varied widely throughout the year at each site, and between sites. Daily fluxes up to 1200 g N2O–N ha−1 d−1 were recorded. The highest annual flux was 27.6 kg N2O–N ha−1 at a grassland site in Wales, whereas the lowest, 1.7 kg N2O–N ha−1, occurred on a soil overlying chalk in southern England. The key factors affecting N2O emissions from agricultural soil were soil WFPS, temperature and soil NO3––N content. On grassland, rainfall (particularly around the time of N application), with its consequent effect on water‐filled pore space (WFPS), was the main driving factor during the growing season. Annual emission factors (EFs), uncorrected for background emission, varied from 0.4 to 6.5% of the nitrogen (N) applied, covering a similar range for grassland to that found previously for sites restricted to Scotland. Continued monitoring at a grassland reference site near Edinburgh showed that annual EFs vary greatly from year to year, even with similar management, and that several years' data are required to produce a robust mean EF. The overall distribution of EFs in this and previous studies was log‐normal. The EFs for small‐grain cereals (and oilseed rape) peaked at a much lower value than those for grassland, whereas the values for leafy vegetables and potato crops fitted well into the grassland distribution. These differences in EF between various types of crop should be taken into account when compiling regional or national N2O emission inventories.
Development of region‐specific emission factors and estimation of methane emission from rice fields in the East, Southeast and South Asian countries
Authors: Yan Xiaoyuan , Ohara Toshimasa , Akimoto Hajime 
Published: March 2003

AbstractRice cultivation areas in East, Southeast and South Asia account for 89% of the world total, and field measurements of methane (CH4) emission from rice cultivation have been widely performed in this area. In this paper, we assembled most of the measurements and developed region‐specific CH4 emission factors. Efforts were made in order to regionalize rice fields by climate and soil properties, and to incorporate the effect of organic input and water regime on emission. Data on rice cultivation areas of 1995 were collected at subdivision level (province, state, prefecture, etc.). Total emission from these areas was estimated at 25.1 Tg CH4 year−1, of which 7.67 Tg was emitted from China and 5.88 Tg from India. Irrigated and rainfed rice fields contributed 70.4 and 27.5% to the total emission, respectively. Deepwater rice fields had a very small share. A high‐resolution and quality emission distribution map was constructed as the emission was directly estimated at province level and below that, a 30‐second land‐use dataset was used in order to translate the emission to grid format. As the rice cultivation area in the study region accounts for 89% of the world total, extrapolating the estimate to the global scale indicates a global emission of 28.2 Tg CH4 year−1.The estimate was compared with country reports made by local scientists. For some countries – such as Indonesia, Myanmar, Thailand, Vietnam, Japan, South Korea, Pakistan and the Philippines – the results of this estimate agree reasonably well with their country reports (CV < 15%). For some other countries – such as China, India and Bangladesh – there is relatively large disagreement between our estimate and their country reports. The reasons for the discrepancies were discussed.
Evaluation of ecosystem dynamics, plant geography and terrestrial carbon cycling in the LPJ dynamic global vegetation model
Authors: Sitch S. , Smith B. , Prentice I. C. , Arneth A. , Bondeau A. , Cramer W. , Kaplan J. O. , Levis S. , Lucht W. , Sykes M. T. , Thonicke K. , Venevsky S. 
Published: March 2003

AbstractThe Lund–Potsdam–Jena Dynamic Global Vegetation Model (LPJ) combines process‐based, large‐scale representations of terrestrial vegetation dynamics and land‐atmosphere carbon and water exchanges in a modular framework. Features include feedback through canopy conductance between photosynthesis and transpiration and interactive coupling between these ‘fast’ processes and other ecosystem processes including resource competition, tissue turnover, population dynamics, soil organic matter and litter dynamics and fire disturbance. Ten plants functional types (PFTs) are differentiated by physiological, morphological, phenological, bioclimatic and fire‐response attributes. Resource competition and differential responses to fire between PFTs influence their relative fractional cover from year to year. Photosynthesis, evapotranspiration and soil water dynamics are modelled on a daily time step, while vegetation structure and PFT population densities are updated annually.Simulations have been made over the industrial period both for specific sites where field measurements were available for model evaluation, and globally on a 0.5°° × 0.5°° grid. Modelled vegetation patterns are consistent with observations, including remotely sensed vegetation structure and phenology. Seasonal cycles of net ecosystem exchange and soil moisture compare well with local measurements. Global carbon exchange fields used as input to an atmospheric tracer transport model (TM2) provided a good fit to observed seasonal cycles of CO2concentration at all latitudes. Simulated inter‐annual variability of the global terrestrial carbon balance is in phase with and comparable in amplitude to observed variability in the growth rate of atmospheric CO2. Global terrestrial carbon and water cycle parameters (pool sizes and fluxes) lie within their accepted ranges. The model is being used to study past, present and future terrestrial ecosystem dynamics, biochemical and biophysical interactions between ecosystems and the atmosphere, and as a component of coupled Earth system models.
Potential effects of warming and drying on peatland plant community composition
Authors: Weltzin Jake F. , Bridgham Scott D. , Pastor John , Chen Jiquan , Harth Calvin 
Published: March 2003

AbstractBoreal peatlands may be particularly vulnerable to climate change, because temperature regimes that currently constrain biological activity in these regions are predicted to increase substantially within the next century. Changes in peatland plant community composition in response to climate change may alter nutrient availability, energy budgets, trace gas fluxes, and carbon storage. We investigated plant community response to warming and drying in a field mesocosm experiment in northern Minnesota, USA. Large intact soil monoliths removed from a bog and a fen received three infrared warming treatments crossed with three water‐table treatments (n = 3) for five years. Foliar cover of each species was estimated annually.In the bog, increases in soil temperature and decreases in water‐table elevation increased cover of shrubs by 50% and decreased cover of graminoids by 50%. The response of shrubs to warming was distinctly species‐specific, and ranged from increases (for Andromeda glaucophylla) to decreases (for Kalmia polifolia). In the fens, changes in plant cover were driven primarily by changes in water‐table elevation, and responses were species‐ and lifeform‐specific: increases in water‐table elevation increased cover of graminoids – in particular Carex lasiocarpa and Carex livida– as well as mosses. In contrast, decreases in water‐table elevation increased cover of shrubs, in particular A. glaucophylla and Chamaedaphne calyculata. The differential and sometimes opposite response of species and lifeforms to the treatments suggest that the structure and function of both bog and fen plant communities will change – in different directions or at different magnitudes – in response to warming and/or changes in water‐table elevation that may accompany regional or global climate change.
Above‐ and below‐ground responses of C3–C4 species mixtures to elevated CO2 and soil water availability
Authors: DERNER JUSTIN D. , JOHNSON HYRUM B. , KIMBALL BRUCE A. , PINTER PAUL J. , POLLEY H. Wayne , TISCHLER CHARLES R. , BOUTTON THOMAS W. , LAMORTE ROBERT L. , WALL GERALD W. , ADAM NEIL R. , LEAVITT STEVEN W. , OTTMAN MICHAEL J. , MATTHIAS ALLAN D. , BROOKS TALBOT J. 
Published: March 2003

AbstractWe evaluated the influences of CO2[Control, ∼ 370 µmol mol−1; 200 µmol mol−1 above ambient applied by free‐air CO2 enrichment (FACE)] and soil water (Wet, Dry) on above‐ and below‐ground responses of C3 (cotton, Gossypium hirsutum) and C4 (sorghum, Sorghum bicolor) plants in monocultures and two density mixtures. In monocultures, CO2 enrichment increased height, leaf area, above‐ground biomass and reproductive output of cotton, but not sorghum, and was independent of soil water treatment. In mixtures, cotton, but not sorghum, above‐ground biomass and height were generally reduced compared to monocultures, across both CO2 and soil water treatments. Density did not affect individual plant responses of either cotton or sorghum across the other treatments. Total (cotton + sorghum) leaf area and above‐ground biomass in low‐density mixtures were similar between CO2 treatments, but increased by 17–21% with FACE in high‐density mixtures, due to a 121% enhancement of cotton leaf area and a 276% increase in biomass under the FACE treatment. Total root biomass in the upper 1.2 m of the soil was not influenced by CO2 or by soil water in monoculture or mixtures; however, under dry conditions we observed significantly more roots at lower soil depths (> 45 cm). Sorghum roots comprised 81–85% of the total roots in the low‐density mixture and 58–73% in the high‐density mixture. CO2‐enrichment partly offset negative effects of interspecific competition on cotton in both low‐ and high‐density mixtures by increasing above‐ground biomass, with a greater relative increase in the high‐density mixture. As a consequence, CO2‐enrichment increased total above‐ground yield of the mixture at high density. Individual plant responses to CO2 enrichment in global change models that evaluate mixed plant communities should be adjusted to incorporate feedbacks for interspecific competition. Future field studies in natural ecosystems should address the role that a CO2‐mediated increase in C3 growth may have on subsequent vegetation change.