Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
Land Use and Land Use Change
Blanchart, E., Bernoux, M., Sarda, Xavier, Neto, M. S., Cerri, C. C., Piccolo, M. De C., Douzet, J.-M., Scopel, E., Feller, C. (2007). Effect of direct seeding mulch-based systems on soil carbon storage and macrofauna in central Brazil. Agriculturae Conspectus Scientificus 72 (1): 81-87
ABSTRACT: Soils represent a large carbon pool, approximately 1500 Gt, equivalent to almost three times the quantity stored in terrestrial biomass and twice the amount stored in the atmosphere. Any modification of land-use or land management can induce variations in soil carbon stocks, even in agricultural systems that are perceived to be in a steady state. These modifications also alter soil macrofauna that is known to affect soil carbon dynamics. Direct seeding Mulch-based Cropping (DMC) systems with two crops per year without soil tillage have widely been adopted over the last 10 to 15 years in the Cerrado (central region) of Brazil. They are replacing the traditional soybean monocropping with fallow under conventional tillage (CT). The objective of this study was to examine how DMC practices affect soil organic carbon (SOC) dynamics and macrofauna (Rio Verde, Goias State). The approach was to determine soil C stocks and macrofauna in five fields under DMC aged 1, 5, 7, 11 and 13 years. In order to compare DMC systems with the native system of the region and previous land-use, a situation under native Cerrado (tree-savanna like vegetation) and a field conducted traditionally (CT) were also studied. Soil C stocks were calculated for the 0-10 and 0-40 cm soil depth and also for the first 400 kg m-2 of soil to compare the same amount of soil and to suppress the potential artefact of soil compaction when sample is based on fix layer depth. Soil macrofauna was hand-sorted from soil monoliths (30 cm depth, TSBF method). In our study, the annual rate of carbon storage was equal to ca. 1.6 Mg C ha-1 , which is in the range of values measured for DMC in different areas of Brazil, i.e., 0.4 to 1.7 Mg C ha-1 with the highest rates obtained in the Cerrado region. Compared to natural vegetation, soil macrofauna in cropped systems was strongly modified. In CT, biomass and density were very low and much lower than in DMC systems. With increasing age of DMC, total macrofauna density increased and then decreased while total macrofauna biomass continuously increased due to a strong increase in Coleoptera larvae biomass. These modifications in macrofauna density and biomass are discussed with regard to soil SOC dynamics (decomposition, mineralization and physical protection).
ABSTRACCT: Previous estimates of the flux of carbon from land use change in sub-Saharan Africa have been based on highly aggregated data and have ignored important categories of land use. To improve these estimates, we divided the region into four subregions (east, west, central, and southern Africa), each with six types of natural vegetation and five types of land use (permanent crops, pastures, shifting cultivation, industrial wood harvest, and tree plantations). We reconstructed rates of land use change and rates of wood harvest from country-level statistics reported by the Food and Agriculture Organization (FAO) (1961–2000) and extrapolated the rates from 1961 to 1850 on the basis of qualitative histories of demography, economy, and land use. We used a bookkeeping model to calculate the annual flux of carbon associated with these changes in land use. Country-level estimates of average forest biomass from the FAO, together with changes in biomass calculated from the reconstructed rates of land use change, constrained the average biomass of forests in 1850. Comparison of potential (predisturbance) forest areas with the areas present in 1850 and 2000 suggests that 60% of Africa's forests were lost before 1850 and an additional 10% lost in the last 150 years. The annual net flux of carbon from changes in land use was probably small and variable before the early 1900s but increased to a source of 0.3 ± 0.2 PgC/yr by the end of the century. In the 1990s the source was equivalent to about 15% of the global net flux of carbon from land use change.
M. Huang, J. Ji., K. Li, Y. Liu, F. Yang, B. Tao (2007). The ecosystem carbon accumulation after conversion of grasslands to pine plantations in subtropical red soil of South China. Tellus B 59 (3): 439-448
ABSTRACT: Since 1980s, afforestation in China has led to the establishment of over 0.53 × 108 ha of new plantation forests. While this leads to rapid accumulation of carbon (C) in vegetation, the effects of afforestation on soil C are poorly understood. In this study, a new version of the Atmosphere-Vegetation Interaction Model (AVIM2) was used to examine how changes in plant C inputs following afforestation might lead to changes in soil C at one of the Chinaflux sites and to estimate the effect of afforestation on ex-grassland. The potential total C accumulation of tree plantation was also predicted. The model was calibrated by net ecosystem exchange (NEE), ecosystem respiration (RE) and gross primary production (GPP) based on eddy-covariance measurements. The simulated vegetation C and soil C stocks were compared with the filed observations.
The simulates indicate that after 22 yr of conversion of grassland to needle leaf forests (Pinus massoniana andPinus elliottii ), the net carbon accumulation in tree ecosystem was 1.96 times more than that in grassland. The soil C in the initial 7 yr of planting decreased at a rate of 0.1871 kg C m−2 yr−1 , and after that it increased at a rate of 0.090 kg C m−2 yr−1 . The C accumulation in the studied plantation ecosystem is estimated to be 76–81% of that value in equilibrium state (the net ecosystem productivity approaches to zero).
Sensitivity analyses show that conversion from grassland to plantation caused an initial (7 or 8 yr) periods of decrease in soil C stocks in wider red soil area of southern China. The soil C stocks were reduced between 19.2 and 20.4% in the initial decreasing period. After 7 or 8 yr C loss, the increased in soil C stocks was predicted to be between 0.073 and 0.074 kg C m−2 yr−1 .
ABSTRACT: The type of land use and soil cultivation are important factors controlling organic carbon storage in soils and they may also change the relative importance of different mechanisms of soil organic matter stabilization. Our objectives were: i) to quantify the soil organic carbon (SOC) and nitrogen (N) storage in silty soils under wheat, maize, grassland and spruce, ii) to determine the SOC and N storage in water-stable aggregates of different size (<53μm, 53–250μm, 250–1000μm, 1000–2000μm, >2000 μm) and in density fractions (Mineral-associated soil organic matter >2 g cm−3 (Mineral-SOM), free particulate organic matter <1.6 g cm−3 (free POM), light occluded particulate organic matter <1.6 g cm−3 (occluded POM<1.6) and dense occluded particulate organic matter 1.6 to 2.0 g cm−3 (occluded POM1.6–2.0)) and iii) to analyse the stability and turnover of these SOC fractions in the maize soil on the basis of thed13 C values. Total SOC stocks down to a depth of 60 cm and including the humus layer were larger at the spruce site (10.3 kg C m−2 ) as compared with the grassland, wheat and maize (7 to 8 C kg m−2 ). However, SOC stocks in the mineral soil were smaller in the forest soil than in the agricultural soils. In the arable soils, the aggregate fractions 53–250μm and 250–1000μm were the most abundant size fractions, whereas aggregates >1000 μm were most abundant in the grassland and forest soil. The SOC concentration and the C/N ratio were greater for macroaggregates (>250 μm) than microaggregates (<250 μm) in the field and grassland soils. At the maize site the percentage of maize-derived C was smallest in the fraction <53 μm with 24% and steadily increased with increasing aggregate size to 47% in the fraction >1000 μm.The major part (86–91%) of the SOC was associated with the heavy mineral fraction at the grassland, maize and wheat site. In the A horizon of the spruce stand, the particulate organic matter accounted for 52% of the total SOC content. The C/N ratios of density fractions decreased in the order free POM<1.6>occluded POM>Mineral-SOM for all soils and depths.
The mean age of organic carbon in the water-stable aggregates in the Ap horizon of the maize site increased with decreasing aggregate size from 35 yr (>1000μm) to 86 yr (<53 μm). For the density fractions the order was free POM (22 yr)
ABSTRACT: Wildfires and alien grass invasion threaten dry tropical forests throughout Central America. Efforts to preserve and restore these forests will require a better understanding of how conversion to grassland changes key belowground processes and organisms such as soil organic matter, nutrient cycling, and mycorrhizae. We studied forest, edge, and grassland soils from five 60-m transects perpendicular to abrupt forest–grassland boundaries in Guanacaste Province, Costa Rica. Nutrient concentrations, N mineralization dynamics, and mycorrhizal fungal communities were compared across vegetation type (forest, edge, and grassland). The dynamics of N mineralization were measured in year-long laboratory incubations, and the diversity of mycorrhizal fungal communities was assessed from populations of soil-borne spores. Soil C, N, and K were lower, while many base cations and micronutrients were higher in grassland plots than in forest plots. Although differences in the quantity of total soil C and N occurred mainly in the forest-to-edge transition, differences in the quality of soil organic matter, as reflected by soil C:N ratios and mineralization rates, occurred in the edge-to-grassland transition. Beta diversity of mycorrhizal spore communities (measured by Sorenson’s similarity index) was lower in the grassland plots than in the forest plots, indicating that grass invasion had caused some convergence. However, total spore density and alpha diversity of mycorrhizal spore communities (measured by species richness and Simpson’s diversity index) were not altered by wildfires and grass invasion. These results suggest that persistence and regeneration of forest plant species in the grasslands may not be constrained to a significant degree by the lack of mycorrhizal symbionts. These grasslands appear to be sustainable, alternative stable states for these areas. Positive feedbacks between the alien grassland vegetation and both fire and nutrient cycling maintain and reinforce this alternative state.
ABSTRACT: Society is increasingly turning attention toward greenhouse gas emission control with for example the Kyoto Protocol has entered into force. Since many of the emissions come from energy use, high cost strategies might be required until new technological developments reduce fossil fuel dependency or increase energy utilization efficiency. On the other hand biologically based strategies may be used to offset energy related emissions. Agricultural soil and forestry are among the largest carbon reservoirs on the planet; therefore, agricultural and forest activities may help to reduce the costs of greenhouse gas emission mitigation. However, sequestration exhibits permanence related characteristics that may influence this role. We examine the dynamic role of carbon sequestration in the agricultural and forest sectors can play in mitigation. A 100-year mathematical programming model, depicting U.S. agricultural and forest sectoral activities including land transfers and greenhouse gas consequences is applied to simulate potential mitigation response. The results show that at low cost and in the near term agricultural soil and forest management are dominant sectoral responses. At higher prices and in the longer term biofuels and afforestation take over. Our results reveal that the agricultural and forest sector carbon sequestration may serve as an important bridge to the future helping to hold costs down until energy emissions related technology develops.
Luo, Y., Su, B., Currie, W.S., Dukes, J,S., Finzi, A., Hartwig, U., Hungate, B. A., McMurtrie, R.E., Oren, R., Parton, W.J., Pataki, D.E., Shaw, M.R., Zak, D. R., Field, C. B. (2004). Progressive nitrogen limitation of ecosystem responses to rising atmospheric carbon dioxide. BioScience 54 (8): 731-739
ABSTRACT: A highly controversial issue in global biogeochemistry is the regulation of terrestrial carbon (C) sequestration by soil nitrogen (N) availability. This controversy translates into great uncertainty in predicting future global terrestrial C sequestration. We propose a new framework that centers on the concept of progressive N limitation (PNL) for studying the interactions between C and N in terrestrial ecosystems. In PNL, available soil N becomes increasingly limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. Our analysis focuses on the role of PNL in regulating ecosystem responses to rising atmospheric carbon dioxide concentration, but the concept applies to any perturbation that initially causes C and N to accumulate in organic forms. This article examines conditions under which PNL may or may not constrain net primary production and C sequestration in terrestrial ecosystems. While the PNL-centered framework has the potential to explain diverse experimental results and to help researchers integrate models and data, direct tests of the PNL hypothesis remain a great challenge to the research community.
Hillier, J., C. Whittaker, G. Dailey, M. Aylott, E. Casella, G.M. Richter, A. Riche, R. Murphy, G. Taylor, P. Smith (2009). Greenhouse gas emissions from four bioenergy crops in England and Wales: Integrating spatial estimates of yield and soil carbon balance in life cycle analyses. Global Change Biology - Bioenergy 1 (4): 267-281
ABSTRACT: Accurate estimation of the greenhouse gas (GHG) mitigation potential of bioenergy crops requires the integration of a significant component of spatially varying information. In particular, crop yield and soil carbon (C) stocks are variables which are generally soil type and climate dependent. Since gaseous emissions from soil C depend on current C stocks, which in turn are related to previous land management it is important to consider both previous and proposed future land use in any C accounting assessment. We have conducted a spatially explicit study for England and Wales, coupling empirical yield maps with the RothC soil C turnover model to simulate soil C dynamics. We estimate soil C changes under proposed planting of four bioenergy crops,Miscanthus (Miscanthus×giganteus ), short rotation coppice (SRC) poplar (Populus trichocarpa Torr. & Gray ×P. trichocarpa , var. Trichobel), winter wheat, and oilseed rape. This is then related to the former land use – arable, pasture, or forest/seminatural, and the outputs are then assessed in the context of a life cycle analysis (LCA) for each crop. By offsetting emissions from management under the previous land use, and considering fossil fuel C displaced, the GHG balance is estimated for each of the 12 land use change transitions associated with replacing arable, grassland, or forest/seminatural land, with each of the four bioenergy crops. Miscanthus and SRC are likely to have a mostly beneficial impact in reducing GHG emissions, while oilseed rape and winter wheat have either a net GHG cost, or only a marginal benefit. Previous land use is important and can make the difference between the bioenergy crop being beneficial or worse than the existing land use in terms of GHG balance.
M.D.A. Rounsevell, I. Reginster, M.B. Araújo, T.R. Carter, N. Dendoncker, F. Ewert, J.I. House, S. Kankaanpääc, R. Leemans, M.J. Metzger, C. Schmit, P. Smith, G. Tuck (2005). A coherent set of future land use change scenarios for Europe. 114 (1): 57-68
ABSTRACT: This paper presents a range of future, spatially explicit, land use change scenarios for the EU15, Norway and Switzerland based on an interpretation of the global storylines of the Intergovernmental Panel on Climate Change (IPCC) that are presented in the special report on emissions scenarios (SRES). The methodology is based on a qualitative interpretation of the SRES storylines for the European region, an estimation of the aggregate totals of land use change using various land use change models and the allocation of these aggregate quantities in space using spatially explicit rules. The spatial patterns are further downscaled from a resolution of 10 min to 250 m using statistical downscaling procedures. The scenarios include the major land use/land cover classes urban, cropland, grassland and forest land as well as introducing new land use classes such as bioenergy crops.
The scenario changes are most striking for the agricultural land uses, with large area declines resulting from assumptions about future crop yield development with respect to changes in the demand for agricultural commodities. Abandoned agricultural land is a consequence of these assumptions. Increases in urban areas (arising from population and economic change) are similar for each scenario, but the spatial patterns are very different. This reflects alternative assumptions about urban development processes. Forest land areas increase in all scenarios, although such changes will occur slowly and largely reflect assumed policy objectives. The scenarios also consider changes in protected areas (for conservation or recreation goals) and how these might provide a break on future land use change. The approach to estimate new protected areas is based in part on the use of models of species distribution and richness. All scenarios assume some increases in the area of bioenergy crops with some scenarios assuming a major development of this new land use.
Several technical and conceptual difficulties in developing future land use change scenarios are discussed. These include the problems of the subjective nature of qualitative interpretations, the land use change models used in scenario development, the problem of validating future change scenarios, the quality of the observed baseline, and statistical downscaling techniques.
ABSTRACT: Forests currently absorb billions of tons of CO2 globally every year, an economic subsidy worth hundreds of billions of dollars if an equivalent sink had to be created in other ways. Concerns about the permanency of forest carbon stocks, difficulties in quantifying stock changes, and the threat of environmental and socioeconomic impacts of large-scale reforestation programs have limited the uptake of forestry activities in climate policies. With political will and the involvement of tropical regions, forests can contribute to climate change protection through carbon sequestration as well as offering economic, environmental, and sociocultural benefits. A key opportunity in tropical regions is the reduction of carbon emissions from deforestation and degradation.
Rhemtullaa, J. M., Mladenoff, D. J., Clayton, M. K. (2009). Historical forest baselines reveal potential for continued carbon sequestration. Proceedings of the National Academy of Sciences 106 (15): 6082-6087
ABSTRACT: One-third of net CO2 emissions to the atmosphere since 1850 are the result of land-use change, primarily from the clearing of forests for timber and agriculture, but quantifying these changes is complicated by the lack of historical data on both former ecosystem conditions and the extent and spatial configuration of subsequent land use. Using fine-resolution historical survey records, we reconstruct pre-EuroAmerican settlement (1850s) forest carbon in the state of Wisconsin, examine changes in carbon after logging and agricultural conversion, and assess the potential for future sequestration through forest recovery. Results suggest that total above-ground live forest carbon (AGC) fell from 434 TgC before settlement to 120 TgC at the peak of agricultural clearing in the 1930s and has since recovered to approximately 276 TgC. The spatial distribution of AGC, however, has shifted significantly. Former savanna ecosystems in the south now store more AGC because of fire suppression and forest ingrowth, despite the fact that most of the region remains in agriculture, whereas northern forests still store much less carbon than before settlement. Across the state, continued sequestration in existing forests has the potential to contribute an additional 69 TgC. Reforestation of agricultural lands, in particular, the formerly high C-density forests in the north-central region that are now agricultural lands less optimal than those in the south, could contribute 150 TgC. Restoring historical carbon stocks across the landscape will therefore require reassessing overall land-use choices, but a range of options can be ranked and considered under changing needs for ecosystem services.