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1.
A simulation model based on satellite observations of monthly vegetation cover was used to estimate monthly carbon fluxes in terrestrial ecosystems from 1982 to 1998. The NASA–CASA model was driven by vegetation properties derived from the Advanced Very High Resolution Radiometer (AVHRR) and radiative transfer algorithms that were developed for Moderate Resolution Imaging Spectroradiometer (MODIS). For the terrestrial biosphere, predicted net ecosystem production (NEP) flux for atmospheric CO2 has varied widely between an annual source of −0.9 Pg C per year and a sink of +2.1 Pg C per year. The southern hemisphere tropical zones (SHT, between 0° and 30°S) have a major influence over the predicted global trends in interannual variability of NEP. In contrast, the terrestrial NEP sink for atmospheric CO2 on the North American (NA) continent has been fairly consistent between +0.2 and +0.3 Pg C per year, except during relatively cool annual periods when continental NEP fluxes are predicted to total to nearly zero. The predicted NEP sink for atmospheric CO2 over Eurasia (EA) increased notably in the late 1980s and has been fairly consistent between +0.3 and +0.55 Pg C per year since 1988. High correlations can be detected between the El Niño Southern Oscillation (ENSO) and predicted NEP fluxes on the EA continent and for the SHT latitude zones, whereas NEP fluxes for the North American continent as a whole do not correlate strongly with ENSO events over the same time series since 1982. These observations support the hypothesis that regional climate warming has had notable but relatively small-scale impacts on high latitude ecosystem (tundra and boreal) sinks for atmospheric CO2.  相似文献   

2.
The snow cover of the Northern Patagonia Icefield (NPI) was monitored after applying the Normalized Difference Snow Index (NDSI) and the Red/NIR band ratio to 134 Moderate Resolution Imaging Spectroradiometer (MODIS) images captured between 2000 and 2006. The final results show that the snow cover extent of the NPI fluctuates a lot in winter, in addition to its seasonal behaviour. The minimum snow cover extent of the period (3600 km2) was observed in March 2000 and the maximum (11,623 km2) in August 2001. We found that temperature accounts for approximately 76% of the variation of the snow cover extent over the entire icefield. We also show two different regimes of winter snow cover fluctuations corresponding to the eastern and the western sides of the icefield. The seasonality of the snow cover on the western side was determined by temperature rather than precipitation, while on the east side the seasonality of the snow cover was influenced by the seasonal behaviour of both temperature and precipitation. This difference can be explained by the two distinct climates: coastal and continental. The fluctuations in the winter snow cover extent were more pronounced and less controlled by temperature on the western side than on the eastern side of the icefield. Snow cover extent was correlated with temperature R2 = 0.75 and R2 = 0.74 for the western and eastern sides, respectively. Since limited meteorological data are available in this region, our investigation confirmed that the change in snow cover is an interesting climatic indicator over the NPI providing important insights in mass balance comprehension. Since snow and ice were distinguished snow cover fluctuations can be associated to fluctuations in the snow accumulation area of the NPI. In addition, days with minimum snow covers of summer season can be associated to the period in which Equilibrium Line Altitude (ELA) is the highest.  相似文献   

3.
Land use has a large impact on ecosystem functioning, though evidences of these impacts at the regional scale are scarce. The objective of this paper was to analyze the impacts of agricultural land use on ecosystem functioning (radiation interception and carbon uptake) in temperate areas of North and South America. From land cover maps generated using high-resolution satellite images we selected sites dominated by row crops (RC), small grain crops (SG), pastures (PA), and rangelands (RA) in the Central Plains of USA and the Pampas of Argentina. These two regions share climatic characteristics and the agricultural conditions (crop types) are also very similar. Both areas were originally dominated by temperate grasslands. In these sites we extracted the temporal series of the normalized difference vegetation index (NDVI) from the NOAA satellites for the period 1989–1998 and calculated the mean seasonal NDVI curve for each site. Additionally, we calculated the mean annual NDVI, the maximum NDVI, the date of the year when the max NDVI was recorded and the interannual variability of these three attributes. We compared the mean values of each NDVI-derived attribute between land cover types and between continents. The NDVI seasonal patterns for each land cover type were roughly similar between the Central Plains and the Pampas during the growing season. The largest differences were observed during the winter and spring, when the NDVI of all land cover types in the Central Plains remained at lower values than in the Pampas. This was probably caused by the high annual thermal amplitude in the Central Plains that results in a much more restricted growing season. As a result of these differences in the shape of the NDVI curve, the mean annual NDVI in the Central Plains was lower than in the Pampas for all land cover types but the maximum NDVI did not differ importantly. In both regions, row crops delayed the date of the NDVI peak, small grain crops advanced it and pastures did not change it importantly, compared with rangelands. The interannual variability of the NDVI attributes was higher for small grains than for row crops in both regions. However, small grains crops were consistently more variable between years in the Central Plains than in the Pampas. The opposite occurred with pastures and rangelands, which were more variable in the Pampas than in the Central Plains. This paper confirms and generalizes previous findings that showed important imprints of land use on ecosystem functioning in temperate ecosystems. Our results support the idea that the changes in land cover that have occurred in the Central Plains and the Pampas leaded to similar changes in the way that ecosystems absorb solar radiation and in the patterns of carbon uptake.  相似文献   

4.
The role of tropical ecosystems in global carbon cycling is uncertain, at least partially due to an incomplete understanding of climatic forcings of carbon fluxes. To reduce this uncertainty, we simulated and analyzed 1982–1999 Amazonian, African, and Asian carbon fluxes using the Biome-BGC prognostic carbon cycle model driven by National Centers for Environmental Prediction reanalysis daily climate data. We first characterized the individual contribution of temperature, precipitation, radiation, and vapor pressure deficit to interannual variations in carbon fluxes and then calculated trends in gross primary productivity (GPP) and net primary productivity (NPP). In tropical ecosystems, variations in solar radiation and, to a lesser extent, temperature and precipitation, explained most interannual variation in GPP. On the other hand, temperature followed by solar radiation primarily determined variation in NPP. Tropical GPP gradually increased in response to increasing atmospheric CO2. Confirming earlier studies, changes in solar radiation played a dominant role in CO2 uptake over the Amazon relative to other tropical regions. Model results showed negligible impacts from variations and trends in precipitation or vapor pressure deficits on CO2 uptake.  相似文献   

5.
Today, most land surface process models have prescribed seasonal change of vegetation with regard to the exchange processes between land and the atmosphere. However, in order to consider the real interaction between vegetation and atmosphere and represent it best in a climate model, the vegetation growth process should be included. In other words, “life” should be brought into climate models. In this study, we have coupled the physical and biological components of AVIM (Atmosphere–Vegetation Interaction Model), a land surface model including plant ecophysiological processes, into the IAP/LASG L9 R15 GOALS GCM. To exhibit terrestrial vegetation information, the vegetation is given a high resolution of 1.5° by 1.5° to nest and couple the fine grid cells of land with the coarse grid cells of atmosphere, which is 7.5° longitude and 4.5° latitude. The simulated monthly mean surface air temperature and precipitation is close to the observations. The monthly mean Leaf Area Index (LAI) is consistent with the observed data. The global annual mean net primary production (NPP) simulation is also reasonable. The coupled model is stable, providing a good platform for research on two-way interaction between land and atmosphere, and the global terrestrial ecosystem carbon cycle.  相似文献   

6.
The global climate–vegetation model HadSM3_TRIFFID has been used to estimate the equilibrium states of climate and vegetation with pre-industrial and last glacial boundary conditions. The present study focuses on the evaluation of the terrestrial biosphere component (TRIFFID) and its response to changes in climate and CO2 concentration. We also show how, by means of a diagnosis of the distribution of plant functional types according to climate parameters (soil temperature, winter temperature, growing-degree days, precipitation), it is possible to get better insights into the strengths and weaknesses of the biosphere model by reference to field knowledge of ecosystems.The model exhibits profound changes between the vegetation distribution at the Last Glacial Maximum and today that are generally consistent with palaeoclimate data, such as the disappearance of the Siberian boreal forest (taiga), an increase in shrub cover in Europe and an increase of the subtropical desert area. The effective equatorial and sub-tropical tree area is reduced by 18%. There is also an increase in cover of wooded species in North-Western Africa and in Mexico. The analysis of bioclimatic relationships turns out to be an efficient method to infer the contributions of different climatic factors to vegetation changes, both at high latitudes, where the position of the boreal treeline appears in this model to be more directly constrained by the water stress than by summer temperature, and in semi-humid areas where the contributions of temperature and precipitation changes may partly compensate each other. Our study also confirms the major contribution of the decrease in CO2 to environmental changes and carbon storage through its selective impact on gross primary productivity of C3 and C4 plants and a reduction by 25% of water-use efficiency. Specifically, the reduction in CO2 concentration increases the amount of precipitation necessary to sustain at least 20% of grass fraction by 50 mm/year; the corresponding threshold for trees is increased by about 150 mm/year. As a consequence, a reduction in CO2 concentration considerably widens the climatic range where grasses and shrubs dominate.  相似文献   

7.
Peatlands play a major role in the global carbon cycle but are largely overlooked in current large-scale vegetation mapping efforts. In this study, we investigated the potential of the Moderate Resolution Imaging Spectroradiometer (MODIS) to capture the extent and distribution of peatlands in the St. Petersburg region of Russia by analyzing the relationships between peatland cover fractions derived from reference maps and  1-km resolution MODIS Nadir BRDF-Adjusted Reflectance (NBAR) data from year 2002.First, we characterized and mapped 50 peatlands from forest inventory and peat deposit inventory data. The peatlands represent three major nutritional types (oligotrophic, mesotrophic, eutrophic) and different sizes (0.6–7800 ha). In addition, parts of 6 peatlands were mined for peat and these were mapped separately. The reference maps provided information on peatland cover for 1105 MODIS pixels. We performed regression analysis on 50% of the pixels and reserved the remainder for model validation. Canonical correlation analysis on the MODIS reflectance bands and the peatland cover fractions produced a multi-spectral peatland cover index (PCI), which served as the predictor in a reduced major axis (RMA) regression model. The results suggest a high potential for mapping peatlands with MODIS. The RMA regression models explained much of the variance in the PCI (r2 = 0.74 for mined and r2 = 0.81 for unmined peatlands). Model validation showed high correlation between observed versus predicted peatland cover (mined: r = 0.87; unmined: r = 0.92). We used the models to derive peatland cover estimates for the St. Petersburg region and compared the results to current MODIS land cover maps.  相似文献   

8.
This study describes surface cyclone activity associated with the interannual variability in summer precipitation in northern Eurasia and how that activity may be connected to other climate signals. An east–west seesaw oscillation of precipitation across Siberia is the primary mode of interannual variability in the summer hydrological cycle over northern Eurasia. This variation occurs at sub-decadal timescales of about 6–8 years. The spatial characteristics of cyclone frequency and cyclone tracks at the two poles in variability [eastern Siberia (ES)-wet–western Siberia (WS)-dry and WS-wet–ES-dry] were examined, and temporal variability in regional cyclone frequency was compared to basin-scale precipitation variability. The analysis period was from 1973 to 2002, when the precipitation variability signal was predominant.Cyclone behavior suggested that the regions of enhanced (reduced) cyclone activity coincided with regions of increased (decreased) precipitation in each phase of the oscillation. Such behavior reflects the zonal displacement of the track of frequent storm activity that accompanies the changes in precipitation. Comparisons of the temporal characteristics confirmed the importance of regional cyclone frequency on precipitation variability in both eastern and western Siberia. Low-frequency changes in regional cyclone activity may produce the precipitation oscillation. We used various climate signals to explore connections between regional precipitation and cyclone activity in Siberia. Results suggest that the North Atlantic Oscillation (NAO) from the preceding winter is significantly and negatively correlated with summer surface cyclone frequency and precipitation over western Siberia. Enhanced (reduced) summer cyclone activity and precipitation in western Siberia follows low- (high-) winter NAO. However, the physical mechanisms linking summer cyclone activity and precipitation over western Siberia with the preceding climate conditions associated with the winter NAO remain unclear.  相似文献   

9.
Forest ecosystems play an important role in global carbon cycle regulation. Clarifying the dynamics and mechanism of carbon sink is of both scientific and political importance. In this paper, we have investigated the spatiotemporal change of forest net primary production (NPP) in China for recent two decades based on the geographically weighted regression (GWR) with a cumulative remote sensing index, the maximum normalized difference vegetation index (NDVImax). GWR is a recently developed regression method with special emphasis on spatial non-stationarity. Outputs of forest NPP at three different stages was generated by the GWR model with NDVImax for the 1980s, early and late 1990s which were consequently analyzed. Our results indicated a wave-like pattern of change in forest NPP in the three stages with a trough-like depression for the early 1990s. The average forest NPP increased by about 0.72% from the 1980s to the late 1990s. A continuously increasing trend at a pace of 0.07% and 0.22% yr− 1 was observed in the tropical and subtropical zones from the 1980s to late 1990s respectively, while a continuously decreasing trend (− 0.05% yr− 1) was noted for the temperate zone. From forest type perspective, only the deciduous broadleaf forests exhibited a continuously decreasing trend of 0.18% yr− 1. The complex spatiotemporal patterns revealed by this study suggest the need for further research in this direction in order to build in-depth insights into the revealed complexities.  相似文献   

10.
Hannu Savijärvi 《Icarus》2012,221(2):617-623
The daytime convective boundary layer (CBL) of Mars and the transition to it after the cold night is studied on a warm dusty sol at the rover Spirit using temperature profiles from the miniature thermal emission spectrometer (mini-TES) and a 1-D model. The model’s net solar fluxes are linear in z in the CBL while the thermal fluxes decay logarithmically from about 8 m upward, due mainly to the emissivity properties and density of CO2. The induced strong radiative heating of the lower CBL is so well compensated by turbulent cooling (with an elevated maximum in the sensible heat flux H) that the growth of the CBL is uniform by the model, as observed by the mini-TES. Hence the net energy fluxes are linear and the shape of H in the lower CBL can be obtained as a residual. Moisture evolution is also considered although without validation.  相似文献   

11.
The effects of elevated atmospheric CO2 concentrations on plant polyphenolic, tannin, nitrogen, phosphorus and total nonstructural carbohydrate concentrations were investigated in leaves of subtropical grass and fynbos shrub species. The hypothesis tested was that carbon-based secondary compounds would increase when carbon gain is in excess of growth requirements. This premise was tested in two ecosystems involving plants with different photosynthetic mechanisms and growth strategies. The first ecosystem comprised grasses from a C4-dominated, subtropical grassland, where three plots were subjected to three different free air CO2 enrichment treatments, i.e., elevated (600 to 800 μmol mol−1), intermediate (400 μmol mol−1) and ambient atmospheric CO2. One of the seven grass species, Alloteropsis semialata, had a C3 photosynthetic pathway while the other grasses were all C4. The second ecosystem was simulated in a microcosm experiment where three fynbos species were grown in open-top chambers at ambient and 700 μmol mol−1 atmospheric CO2 in low nutrient acid sands typical of south western coastal and mountain fynbos ecosystems. Results showed that polyphenolics and tannins did not increase in the grass species under elevated CO2 and only in Leucadendron laureolum among the fynbos species. Similarly, foliar nitrogen content of grasses was largely unaffected by elevated CO2, and among the fynbos species, only L. laureolum and Leucadendron xanthoconus showed changes in foliar nitrogen content under elevated CO2, but these were of different magnitude. The overall decrease in nitrogen and phosphorus and consequent increase in C:N and C:P ratio in both ecosystems, along with the increase in polyphenolics and tannins in L. laureolum in the fynbos ecosystem, may negatively affect forage quality and decomposition rates. It is concluded that fast growing grasses do not experience sink limitation and invest extra carbon into growth rather than polyphenolics and tannins and show small species-specific chemical changes at elevated atmospheric CO2 concentrations. Responses of fynbos species are varied and were species-specific.  相似文献   

12.
In this account we present estimates of nannofossil fluxes in four sections and one borehole all belonging to the Early Jurassic western Tethys. This study aims to map the distribution of pelagic carbonate production across the Early Toarcian anoxic event (T-OAE), and to understand which environmental parameters did control such production. Our results indicate important changes in carbonate production by nannoplankton occurring within the western Tethys and its variations through time. Nannofossil fluxes (specimens per m2 per year) are extremely low during the T-OAE in all the studied settings. Higher fluxes are encountered in the westernmost part of the Tethys Ocean before the T-OAE, whilst pelagic carbonate production shifted towards the northern margin of the Tethys after the recovery from anoxic conditions. The dramatic decrease in nannoplankton production during the T-OAE has been interpreted in previous works as a biocalcification crisis related to high pCO2 in the atmosphere/hydrosphere system. Although a high pCO2 may have lowered the carbonate saturation state of Early Jurassic oceans and finally hampered biocalcification, we speculate that the most important effects of CO2 increase were indirect, and affected pelagic producers via changes on climate and sea-level. Namely, it seems that precipitation/evaporation budgets and continental runoff that controlled nutrient levels and salinity in surface oceanic waters were important factors for pelagic biocalcifiers.  相似文献   

13.
It has been reported by several groups that methane in the Martian atmosphere is both spatially and temporally variable. Gough et al. (2010) suggested that temperature dependent, reversible physical adsorption of methane onto Martian soils could explain this variability. However, it is also useful to consider if there might be chemical destruction of methane (and compensating sources) operating on seasonal time scales. The lifetime of Martian methane due to known chemical loss processes is long (on the order of hundreds of years). However, observations constrain the lifetime to be 4 years or less, and general circulation models suggest methane destruction must occur even faster (<1 year) to cause the reported variability and rapid disappearance. The Martian surface is known to be highly oxidizing based on the Viking Labeled Release experiments in which organic compounds were quickly oxidized by samples of the regolith. Here we test if simulated Martian soil is also oxidizing towards methane to determine if this is a relevant loss pathway for Martian methane. We find that although two of the analog surfaces studied, TiO2·H2O2 and JSC-Mars-1 with H2O2, were able to oxidize the complex organic compounds (sugars and amino acids) used in the Viking Labeled Release experiments, these analogs were unable to oxidize methane to carbon dioxide within a 72 h experiment. Sodium and magnesium perchlorate, salts that were recently discovered at the Phoenix landing site and are potential strong oxidants, were not observed to directly oxidize either the organic solution or methane. The upper limit reaction coefficient, α, was found to be <4×10?17 for methane loss on TiO2·H2O2 and <2×10?17 for methane loss on JSC-Mars-1 with H2O2. Unless the depth of soil on Mars that contains H2O2 is very deep (thicker than 500 m), the lifetime of methane with respect to heterogeneous oxidation by H2O2 is probably greater than 4 years. Therefore, reaction of methane with H2O2 on Martian soils does not appear to be a significant methane sink, and would not destroy methane rapidly enough to cause the reported atmospheric methane variability.  相似文献   

14.
The energy components of sixteen Soil-Vegetation Atmospheric Transfer (SVAT) schemes were analyzed and intercompared using 10 years of surface meteorological and radiative forcing data from the Red-Arkansas River basin in the Southern Great Plains of the United States. Comparisons of simulated surface energy fluxes among models showed that the net radiation and surface temperature generally had the best agreement among the schemes. On an average (annual and monthly) basis, the estimated latent heat fluxes agreed (to within approximate estimation errors) with the latent heat fluxes derived from a radiosonde-based atmospheric budget method for slightly more than half of the schemes. The sensible heat fluxes had larger differences among the schemes than did the latent heat fluxes, and the model-simulated ground heat fluxes had large variations among the schemes. The spatial patterns of the model-computed net radiation and surface temperature were generally similar among the schemes, and appear reasonable and consistent with observations of related variables, such as surface air temperature. The spatial mean patterns of latent and sensible heat fluxes were less similar than for net radiation, and the spatial patterns of the ground heat flux vary greatly among the 16 schemes. Generally, there is less similarity among the models in the temporal (interannual) variability of surface fluxes and temperature than there is in the mean fields, even for schemes with similar mean fields.  相似文献   

15.
This study utilizes the NCAR Land Surface Model (LSM1.2) integrated with dynamic global vegetation to recreate the early Paleogene global distribution of vegetation and to examine the response of the vegetation distribution to changes in climate at the Paleocene–Eocene boundary (∼ 55 Ma). We run two simulations with Eocene geography driven by climatologies generated in two atmosphere global modeling experiments: one with atmospheric pCO2 at 560 ppm, and another at 1120 ppm. In both scenarios, the model produces the best match with fossil flora in the low latitudes. A comparison of model output from the two scenarios suggests that the greatest impact of climate on vegetation will occur in the high latitudes, in the Arctic Circle and in Antarctica. In these regions, greater accumulated summertime warmth in the 1120 ppm simulation allows temperate plant functional types to expand further poleward. Additionally, the high pCO2 scenario produces a greater abundance of trees over grass at these high latitudes. In the middle and low latitudes, the general distribution of plant functional types is similar in both pCO2 scenarios. Likely, a greater increment of greenhouse gases is necessary to produce the type of change evident in the mid-latitude paleobotanical record. Overall, differences between model output and fossil flora are greatest at high latitudes.  相似文献   

16.
Recent detection of methane (CH4) on Mars has generated interest in possible biological or geological sources, but the factors responsible for the reported variability are not understood. Here we explore one potential sink that might affect the seasonal cycling of CH4 on Mars - trapping in ices deposited on the surface. Our apparatus consisted of a high-vacuum chamber in which three different Mars ice analogs (water, carbon dioxide, and carbon dioxide clathrate hydrates) were deposited in the presence of CH4 gas. The ices were monitored for spectroscopic evidence of CH4 trapping using transmission Fourier-Transform Infrared (FT-IR) spectroscopy, and during subsequent sublimation of the ice films the vapor composition was measured using mass spectrometry (MS). Trapping of CH4 in water ice was confirmed at deposition temperatures <100 K which is consistent with previous work, thus validating the experimental methods. However, no trapping of CH4 was observed in the ice analogs studied at warmer temperatures (140 K for H2O and CO2 clathrate, 90 K for CO2 snow) with approximately 10 mTorr CH4 in the chamber. From experimental detection limits these results provide an upper limit of 0.02 for the atmosphere/ice trapping ratio of CH4. If it is assumed that the trapping mechanism is linear with CH4 partial pressure and can be extrapolated to Mars, this upper limit would indicate that less than 1% is expected to be trapped from the largest reported CH4 plume, and therefore does not represent a significant sink for CH4.  相似文献   

17.
Starting with analysis on the evolving course of oasis and the characteristics and evolution of transitional zone between oasis and desert, in consideration of ecological elements including plant stomata resistance, area covered by vegetation, and physical elements including albedo of vegetation and bare soil, atmosphere temperature, and humidity, under the condition of the balance among net radiation flux, latent heat flux, and sensible heat flux, the following are calculated: temperatures of vegetation and bare soil in different conditions, as well as the evapotranspiration rate of ecosystem. Analysis on evapotranspiration rate indicates that it depends on both the climate of environment and the physiological and ecological conditions of plants. On certain conditions, the evapotranspiration rate of transitional zone between oasis and desert (i.e. area covered by vegetation less than 20%), in some parameter domains, appears in bifurcation or multiequilibrium state. Meanwhile, in such area, ecosystem is extremely unstable. Any minor change to the balance will cause either increase or reduction of area covered by vegetation in ecosystem, on the basis of discussion on the emergency of these phenomena. This paper is attempting to propose an effective way of destruction and rebuilt ecosystem in transitional zone. The way is to control the evaporation of plant through selecting anti-drought country plant with big stomata resistance, and modify the roughness of the underlying surface in ecosystem by establishing rational interspace structure of plant community, so as to put the degenerative ecosystem into the natural succession track. This primary theory is being verified through observation and analysis on historical data.  相似文献   

18.
The northern treeline is generally limited by available warmth. However, in recent years, more and more studies have identified drought stress as an additional limiting factor for tree growth in northern boreal forests and at treelines. Three growth responses to warming have been identified: increase in growth, decrease in growth, and nonsignificant correlation of tree growth with climate. Here we investigate the effect of drought stress on radial growth of white spruce at northern treelines along a longitudinal gradient spanning the entire Brooks Range in Alaska. We systematically sampled 687 white spruce at seven treeline sites. Where possible, we sampled three site types at a given site: high-density forest, low-density forest, and floodplain forest. We investigated the relationship of site and site type to tree growth responses. In the western part of our study area, we found very high numbers of trees responding with increase in growth to recent warming; while in the eastern part, trees responding with decrease in growth to recent warming are predominant. Within a given site, more trees reacting positively to warming grow on site types characterized by low tree density. These patterns coincide with precipitation decreases from west to east and local water availability gradients, therefore pointing to drought stress as the controlling factor for the distribution of trees responding with increase or decrease in growth to recent warming. Compared to 20th century climate, we project a 25–50% basal area (BA) increase in the western region for the 21st century due to climate warming as projected by five general circulation models, 4–11% in the central region and decreases (+1 to −11%) in the eastern region. The overall net change in projected 21st century BA increase at each site seems to be controlled by the relative proportion of responder groups. If these are similar, differences in the magnitude of increase versus decrease in growth control BA projections for that site. This study highlights the importance of regional-scale investigations of biosphere–climate interactions, since our results indicate a substantial gain in aboveground biomass as a result of future warming only in the western regions; while in the eastern regions, climate warming will decrease overall wood production and therefore carbon uptake potential.  相似文献   

19.
Iceland is facing severe land degradation in many parts of the country. This study aims to increase the understanding of the complex interactions and interconnectivity between the critical factors that help maintain the land degradation processes in sub-arctic environments. A holistic approach in the form of a causal loop diagram (CLD) is applied for diagnosing the influencing factors. To further study the relationship between vegetation cover and its degradation, a dynamic model that uses a long-term temperature data as the main indicator function is constructed to simulate potential vegetation cover during the Holocene. The results depict an oscillating vegetation cover. Gradual degradation in potential vegetation cover begins ca. 3000 BP and accelerates greatly after ca. 2500 BP. From the time of the Norse settlement in the latter halve of the 9th century to present time, the simulated vegetation cover retreats ca. 25% in relation to climatic cooling.  相似文献   

20.
We analyze the arrival directions of cosmic rays with energies E 0≈(1–4)×1017 eV and zenith angles θ≤53≤ detected with the Yakutsk extensive air shower (EAS) array during 1974–2001. We show that ～10% of them form many clusters correlated with the Supergalactic plane. Enhanced particle fluxes arrive from the Supergalactic plane and the regions that are symmetrically adjacent to it at angles ±b SG ≈ 6°.5. The relatively high concentrations of clusters of galaxies and quasars that bear a relationship to the large-scale structure of the Universe are observed in these regions.  相似文献   

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