If biofuels are to be a viable substitute for fossil fuels, it is essential that they retain their potential to mitigate climate change under future atmospheric conditions. Elevated atmospheric CO2 ...concentration CO2 stimulates plant biomass production; however, the beneficial effects of increased production may be offset by higher energy costs in crop management.
We maintained full size poplar short rotation coppice (SRC) systems under both current ambient and future elevated CO2 (550 ppm) and estimated their net energy and greenhouse gas balance. We show that a poplar SRC system is energy efficient and produces more energy than required for coppice management. Even more, elevated CO2 will increase the net energy production and greenhouse gas balance of a SRC system with 18%. Managing the trees in shorter rotation cycles (i.e., 2 year cycles instead of 3 year cycles) will further enhance the benefits from elevated CO2 on both the net energy and greenhouse gas balance.
Adapting coppice management to the future atmospheric CO2 is necessary to fully benefit from the climate mitigation potential of bio-energy systems. Further, a future increase in potential biomass production due to elevated CO2 outweighs the increased production costs resulting in a northward extension of the area where SRC is greenhouse gas neutral. Currently, the main part of the European terrestrial carbon sink is found in forest biomass and attributed to harvesting less than the annual growth in wood. Because SRC is intensively managed, with a higher turnover in wood production than conventional forest, northward expansion of SRC is likely to erode the European terrestrial carbon sink.
Temperate forest ecosystems have recently been identified as an important net sink in the global carbon budget. The factors responsible for the strength of the sinks and their permanence, however, ...are less evident. In this paper, we quantify the present carbon sequestration in Thuringian managed coniferous forests. We quantify the effects of indirect human‐induced environmental changes (increasing temperature, increasing atmospheric CO2 concentration and nitrogen fertilization), during the last century using BIOME‐BGC, as well as the legacy effect of the current age‐class distribution (forest inventories and BIOME‐BGC). We focused on coniferous forests because these forests represent a large area of central European forests and detailed forest inventories were available.
The model indicates that environmental changes induced an increase in biomass C accumulation for all age classes during the last 20 years (1982–2001). Young and old stands had the highest changes in the biomass C accumulation during this period. During the last century mature stands (older than 80 years) turned from being almost carbon neutral to carbon sinks. In high elevations nitrogen deposition explained most of the increase of net ecosystem production (NEP) of forests. CO2 fertilization was the main factor increasing NEP of forests in the middle and low elevations.
According to the model, at present, total biomass C accumulation in coniferous forests of Thuringia was estimated at 1.51 t C ha−1 yr−1 with an averaged annual NEP of 1.42 t C ha−1 yr−1 and total net biome production of 1.03 t C ha−1 yr−1 (accounting for harvest). The annual averaged biomass carbon balance (BCB: biomass accumulation rate‐harvest) was 1.12 t C ha−1 yr−1 (not including soil respiration), and was close to BCB from forest inventories (1.15 t C ha−1 yr−1). Indirect human impact resulted in 33% increase in modeled biomass carbon accumulation in coniferous forests in Thuringia during the last century. From the forest inventory data we estimated the legacy effect of the age‐class distribution to account for 17% of the inventory‐based sink. Isolating the environmental change effects showed that these effects can be large in a long‐term, managed conifer forest.
This paper provides the first steps toward a regional-scale analysis of carbon (C) budgets. We explore the ability of the ecosystem model BIOME-BGC to estimate the daily and annual C dynamics of four ...European coniferous forests and shifts in these dynamics in response to changing environmental conditions. We estimate uncertainties in the model results that arise from incomplete knowledge of site management history (for example, successional stage of forest). These uncertainties are especially relevant in regional-scale simulations, because this type of information is difficult to obtain. Although the model predicted daily C and water fluxes reasonably well at all sites, it seemed to have a better predictive capacity for the photosynthesis-related processes than for respiration. Leaf area index (LAI) was modeled accurately at two sites but overestimated at two others (as a result of poor long-term climate drivers and uncertainties in model parameterization). The overestimation of LAI (and consequently gross photosynthetic production (GPP)), in combination with reasonable estimates of the daily net ecosystem productivity (NEP) of those forests, also illustrates the problem with modeled respiration. The model results suggest that all four European forests have been net sinks of C at the rate of 100-300 gC/m^sup 2^/y and that this C sequestration capacity would be 30%-70% lower without increasing nitrogen (N) deposition and carbon dioxide (CO^sub 2^) concentrations. The magnitude of the forest responses was dependent not only on the rate of changes in environmental factors, but also on site-specific conditions such as climate and soil depth. We estimated that the modeled C exchange at the study sites was reduced by 50%-100% when model simulations were performed for climax forests rather than regrowing forests. The estimates of water fluxes were less sensitive to different initializations of state variables or environmental change scenarios than C fluxes. PUBLICATION ABSTRACT
Neutrino transfer via convective flow to the surface of a proto-neutron star is numerically simulated. The evolution of the neutrino distribution in a heated region rising from the center of the ...proto-neutron star to its surface is simulated using a kinetic equation with a Uehling-Uhlenbeck collision integral in a uniform, isotropic approximation. The composition of the matter in the region under consideration changes due to the 'burning' of electrons and protons by beta processes. The simulation results enable the estimation of the characteristic time required for the rising medium to become optically thin to neutrinos and the characteristic spectrum of the neutrinos that are emitted.
Transition (ecotone) zone between adjacent vegetation types is one of the most interesting topics for study and one of the most difficult objects for modelling. In this study we suggest and approach ...that could be useful for investigating the mechanisms defining the appearance of different ecotone types, and specific predictions about the dynamics of transitiion zones. The method allows discrete and continuous ecotone structure to be obtained under continuous change of climatic characteristiscs.
A widely used assumption in forestry is that the demand for timber will exceed the maximum level available from forests on a sustainable basis. In this study, measurements of extracted timber and ...modeled forest productivity were used to investigate the relationship between harvested timber and natural forest productivity for current conditions, and under global change scenario.
Information about the uncertainties associated with eddy covariance measurements of surface-atmosphere CO sub(2) exchange is needed for data assimilation and inverse analyses to estimate model ...parameters, validation of ecosystem models against flux data, as well as multi-site synthesis activities (e.g., regional to continental integration) and policy decision-making. While model residuals (mismatch between fitted model predictions and measured fluxes) can potentially be analyzed to infer data uncertainties, the resulting uncertainty estimates may be sensitive to the particular model chosen. Here we use 10 site-years of data from the CarboEurope program, and compare the statistical properties of the inferred random flux measurement error calculated first using residuals from five different models, and secondly using paired observations made under similar environmental conditions. Spectral analysis of the model predictions indicated greater persistence (i.e., autocorrelation or ''memory'') compared to the measured values. Model residuals exhibited weaker temporal correlation, but were not uncorrelated white noise. Random flux measurement uncertainty, expressed as a standard deviation, was found to vary predictably in relation to the expected magnitude of the flux, in a manner that was nearly identical (for negative, but not positive, fluxes) to that reported previously for forested sites. Uncertainty estimates were generally comparable whether the uncertainty was inferred from model residuals or paired observations, although the latter approach resulted in somewhat smaller estimates. Higher order moments (e.g., skewness and kurtosis) suggested that for fluxes close to zero, the measurement error is commonly skewed and leptokurtic. Skewness could not be evaluated using the paired observation approach, because differencing of paired measurements resulted in a symmetric distribution of the inferred error. Patterns were robust and not especially sensitive to the model used, although more flexible models, which did not impose a particular functional form on relationships between environmental drivers and modeled fluxes, appeared to give the best results. We conclude that evaluation of flux measurement errors from model residuals is a viable alternative to the standard paired observation approach.
Here we estimate the biospheric carbon dioxide balance of Hungary using the adapted BIOME-BGC process oriented ecological system model. The model was calibrated using the Hungarian measurements of ...biosphere-atmosphere carbon dioxide exchange. After calibration, the model was run for the four major land cover types such as croplands, grasslands, deciduous and coniferous forests for the period of 2002-2007. Our calculations suggest that all Hungarian ecological systems together formed a net carbon dioxide source during the time period studied. Since agricultural fields cover more than 50% of the total area of Hungary, the net carbon dioxide flux is dominated by the carbon balance of croplands. The average net release of CO sub(2) is 8.7 Mt per year with significant interannual variation: the highest net emission was 21.6 Mt CO sub(2) in 2003, while the lowest was 1.2 Mt CO sub(2) in 2006. Due to the model limitations, simulated CO sub(2) release from croplands is most likely overestimated, thus, the present results provide an upper limit for the potential range of the carbon balance of Hungary. The model results highlight the strong dependence of the biospheric carbon dioxide balance on the weather conditions. The results are compared with the carbon budget estimations previously published for Hungary as well as with those reported to the United Nations Framework Convention on Climate Change.
Seventeen global models of terrestrial biogeochemistry were compared with respect to annual and seasonal fluxes of net primary productivity (NPP) for the land biosphere. The comparison, sponsored by ...IGBP-GAIM/DIS/GCTE, used standardized input variables wherever possible and was carried out through two international workshops and over the Internet. The models differed widely in complexity and original purpose, but could be grouped in three major categories: satellite-based models that use data from the NOAA/AVHRR sensor as their major input stream (CASA, GLO-PEM, SDBM, SIB2 and TURC), models that simulate carbon fluxes using a prescribed vegetation structure (BIOME-BGC, CARAIB 2.1, CENTURY 4.0, FBM 2.2, HRBM 3.0, KGBM, PLAI 0.2, SILVAN 2.2 and TEM 4.0), and models that simulate both vegetation structure and carbon fluxes (BIOME3, DOLY and HYBRID 3.0). The simulations resulted in a range of total NPP values (44.4-66.3 Pg C year super(-1)), after removal of two outliers (which produced extreme results as artefacts due to the comparison). The broad global pattern of NPP and the relationship of annual NPP to the major climatic variables coincided in most areas. Differences could not be attributed to the fundamental modelling strategies, with the exception that nutrient constraints generally produced lower NPP. Regional and global NPP were sensitive to the simulation method for the water balance. Seasonal variation among models was high, both globally and locally, providing several indications for specific deficiencies in some models.
PDF
