Agricultural management impacts on soil organic carbon storage under moist and dry climatic conditions of temperate and tropical regions

We conducted a meta-analysis to quantify the impact of changing agricultural land use and management on soil organic carbon (SOC) storage under moist and dry climatic conditions of temperate and tropical regions. We derived estimates of management impacts for a carbon accounting approach developed by the Intergovernmental Panel on Climate Change, addressing the impact of long-term cultivation, setting-aside land from crop production, changing tillage management, and modifying C input to the soil by varying cropping practices. We found 126 articles that met our criteria and analyzed the data in linear mixed-effect models. In general, management impacts were sensitive to climate in the following order from largest to smallest changes in SOC: tropical moist>tropical dry>temperate moist>temperate dry. For example, long-term cultivation caused the greatest loss of SOC in tropical moist climates, with cultivated soils having 0.58 ± 0.12, or 58% of the amount found under native vegetation, followed by tropical dry climates with 0.69 ± 0.13, temperate moist with 0.71 ± 0.04, and temperate dry with 0.82 ± 0.04. Similarly, converting from conventional tillage to no-till increased SOC storage over 20 years by a factor of 1.23 ± 0.05 in tropical moist climates, which is a 23% increase in SOC, while the corresponding change in tropical dry climates was 1.17 ± 0.05, temperate moist was 1.16 ± 0.02, and temperate dry was 1.10 ± 0.03. These results demonstrate that agricultural management impacts on SOC storage will vary depending on climatic conditions that influence the plant and soil processes driving soil organic matter dynamics.     

Changes in annual CO2 fluxes estimated from inventory data in South Korea

Using a slightly modified IPCC method, we examined changes in annual fluxes of CO_2and contributions of energy consumption, limestone use, waste combustion, land-use change, and forest growth to the fluxes in South Korea from 1990 to 1997. Our method required less data and resulted in a larger estimate of CO_2 released by industrial processes, comparing with the originalIPCC guideline. However, net CO_2 emission is not substantially different from the estimates of IPCC and modified methods. Net CO_2 emission is intimately related to GDP as Korean economyhas heavily relied on energy consumption and industrial activities, which are major sources of CO_2.Total efflux of CO_2 was estimated to be 63.6 Tg C/a in 1990 and amounted to 112.9 Tg C/a in 1997. Land-use change contributed to annual budget of CO_2 in a relatively small portion. Carbon dioxide was sequestered by forest biomass at the rate of 6.5 Tg C/a in 1990 and 8.5 Tg C/a in 1997. Al-though CO_2 storage in the forests increased, the sink effect was overwhelmed by extensive energy consumption, suggesting that energy-saving strategies will be more effective in reducing CO_2 emission in Korea than any other practices. It is presumed that plant uptake of CO_2 is underesti-mated as carbon contained in plant detritus and belowground living biomass were not fully consid-ered. Furthermore, the soil organic carbon stored in forest decomposes in various ways in rugged mountains depending on their conditions, such as slope, aspect and elevation, which could havean effect on decomposition rate and carbon stores in soils. Thus, carbon sequestration of forests deserves further attention.     

Changes in annual CO2 fluxes estimated from inventory data in South Korea

Using a slightly modified IPCC method, we examined changes in annual fluxes of CO2 and contributions of energy consumption, limestone use, waste combustion, land-use change, and forest growth to the fluxes in South Korea from 1990to 1997. Our method required less data and resulted in a larger estimate of CO2released by industrial processes, comparing with the original IPCC guideline. However, net CO2 emission is not substantially different from the estimates of IPCC and modified methods. Net CO2 emission is intimately related to GDP as Koreaneconomy has heavily relied on energy consumption and industrial activities, which are major sources of CO2. Total efflux of CO2 was estimated to be 63.6 Tg C/ain 1990 and amounted to 112.9 Tg C/a in 1997. Land-use change contributed to annual budget of CO2 in a relatively small portion. Carbon dioxide was sequesteredby forest biomass at the rate of 6.5 Tg C/a in 1990 and 8.5 Tg C/a in 1997. Although CO2 storage in the forests increased, the sink effect was overwhelmed by extensive energy consumption, suggesting that energy-saving strategies will be more effective in reducing CO2 emission in Korea than any other practices. It is presumed that plant uptake of CO2 is underestimated as carbon contained in plant detritus and belowground living biomass were not fully considered. Furthermore, the soil organic carbon stored in forest decomposes in various ways in rugged mountains depending on their conditions, such as slope, aspect and elevation, which could have an effect on decomposition rate and carbon stores in soils. Thus, carbon sequestration of forests deserves further attention.     

Climate change and spotted owls: potentially contrasting responses in the Southwestern United States

Developing strategies that reduce the impacts of climate change on biodiversity will require projections of the future status of species under alternative climate change scenarios. Demographic models based on empirical data that link temporal variation in climate with vital rates can improve the accuracy of such predictions and help guide conservation efforts. Here, we characterized how population dynamics and extinction risk might be affected by climate change for three spotted owl (Strix occidentalis) populations in the Southwestern United States over the next century. Specifically, we used stochastic, stage‐based matrix models parameterized with vital rates linked to annual variation in temperature and precipitation to project owl populations forward in time under three IPCC emissions scenarios relative to contemporary climate. Owl populations in Arizona and New Mexico were predicted to decline rapidly over the next century and had a much greater probability of extinction under all three emissions scenarios than under current climate conditions. In contrast, owl population dynamics in Southern California were relatively insensitive to predicted changes in climate, and extinction risk was low for this population under all scenarios. The difference in predicted climate change impacts between these areas was due to negative associations between warm, dry conditions and owl vital rates in Arizona and New Mexico, whereas cold, wet springs reduced reproduction in Southern California. Predicted changes in population growth rates were mediated more by weather‐induced changes in fecundity than survival, and were generally more sensitive to increases in temperature than declines in precipitation. Our results indicate that spotted owls in arid environments may be highly vulnerable to climate change, even in core parts of the owl's range. More broadly, contrasting responses to climate change among populations highlight the need to tailor conservation strategies regionally, and modeling efforts such as ours can help prioritize the allocation of resources in this regard.     

Climate- and crop-responsive emission factors significantly alter estimates of current and future nitrous oxide emissions from fertilizer use

The current Intergovernmental Panel on Climate Change (IPCC) default methodology (tier 1) for calculating nitrous oxide (N₂O) emissions from nitrogen applied to agricultural soils takes no account of either crop type or climatic conditions. As a result, the methodology omits factors that are crucial in determining current emissions, and has no mechanism to assess the potential impact of future climate and land‐use change. Scotland is used as a case study to illustrate the development of a new methodology, which retains the simple structure of the IPCC tier 1 methodology, but incorporates crop‐ and climate‐dependent emission factors (EFs). It also includes a factor to account for the effect of soil compaction because of trampling by grazing animals. These factors are based on recent field studies in Scotland and elsewhere in the UK. Under current conditions, the new methodology produces significantly higher estimates of annual N₂O emissions than the IPCC default methodology, almost entirely because of the increased contribution of grazed pasture. Total emissions from applied fertilizer and N deposited by grazing animals are estimated at 10 662 t N₂O‐N yr^?1 using the newly derived EFs, as opposed to 6 796 t N₂O‐N yr^?1 using the IPCC default EFs. On a spatial basis, emission levels are closer to those calculated using field observations and detailed soil modelling than to estimates made using the IPCC default methodology. This can be illustrated by parts of the western Ayrshire basin, which have previously been calculated to emit 8–9 kg N₂O‐N ha^?1 yr^?1 and are estimated here as 6.25–8.75 kg N₂O‐N ha^?1 yr^?1, while the IPCC default methodology gives a maximum emission level of only 3.75 kg N₂O‐N ha^?1 yr^?1 for the whole area. The new methodology is also applied in conjunction with scenarios for future climate‐ and land‐use patterns, to assess how these emissions may change in the future. The results suggest that by 2080, Scottish N₂O emissions may increase by up to 14%, depending on the climate scenario, if fertilizer and land management practices remain unchanged. Reductions in agricultural land use, however, have the potential to mitigate these increases and, depending on the replacement land use, may even reduce emissions to below current levels.     

The production and emission of nitrous oxide from headwater streams in the Midwestern United States

The emission of nitrous oxide (N₂O) from streams draining agricultural landscapes is estimated by the Intergovernmental Panel on Climate Change (IPCC) to constitute a globally significant source of this gas to the atmosphere, although there is considerable uncertainty in the magnitude of this source. We measured N₂O emission rates and potential controlling variables in 12 headwater streams draining a predominantly agricultural basin on glacial terrain in southwestern Michigan. The study sites were nearly always supersaturated with N₂O and emission rates ranged from ?8.9 to 266.8 μg N₂O‐N m^?2 h^?1 with an overall mean of 35.2 μg N₂O‐N m^?2 h^?1. Stream water NO₃^? concentrations best‐predicted N₂O emission rates. Although streams and agricultural soils in the basin had similar areal emission rates, emissions from streams were equivalent to 6% of the anthropogenic emissions from soils because of the vastly greater surface area of soils. We found that the default value of the N₂O emission factor for streams and groundwater as defined by the IPCC (EF5‐g) was similar to the value observed in this study lending support to the recent downward revision to EF5‐g. However, the EF5‐g spanned four orders of magnitude across our study sites suggesting that the IPCC's methodology of applying one emission factor to all streams may be inappropriate.     

Nitrous oxide fluxes from a grain–legume crop (narrow‐leafed lupin) grown in a semiarid climate

Understanding nitrous oxide (N₂O) fluxes from grain–legume crops in semiarid and arid regions is necessary if we are to improve our knowledge of global terrestrial N₂O losses resulting from biological N₂ fixation. N₂O fluxes were measured from a rain‐fed soil, cropped to a grain–legume in a semiarid region of southwestern Australia for 1 year on a subdaily basis. The site included plots planted to narrow‐leafed lupin (Lupinus angustifolius; ‘lupin’) and plots left bare (no lupin). Fluxes were measured using soil chambers connected to a fully automated system that measured N₂O by gas chromatography. Daily N₂O fluxes were low (?0.5 to 24 g N₂O‐N ha^?1 day^?1) and not different between treatments, culminating in an annual loss of 127 g N₂O‐N ha^?1. Greatest daily N₂O fluxes occurred from both treatments in the postharvest period, and following a series of summer and autumn rainfall events. At this time of the year, soil conditions were conducive to soil microbial N₂O production: elevated soil water contents, increased inorganic nitrogen (N) and dissolved organic carbon concentrations, and soil temperatures generally > 25 °C; furthermore, there was no active plant growth to compete for mineralized N. N₂O emissions from the decomposition of legume crop residue were low, and approximately half that predicted using the currently recommended IPCC methodology. Furthermore, the contribution of the biological N₂ fixation process to N₂O emissions appeared negligible in the present study, supporting its omission as a source of N₂O from the IPCC methodology for preparing national greenhouse gas inventories.     

Vulnerability of African mammals to anthropogenic climate change under conservative land transformation assumptions

Recent observations show that human‐induced climate change (CC) and land transformation (LT) are threatening wildlife globally. Thus, there is a need to assess the sensitivity of wildlife on large spatial scales and evaluate whether national parks (NPs), a key conservation tools used to protect species, will meet their mandate under future CC and LT conditions. Here, we assess the sensitivity of 277 mammals at African scale to CC at 10′ resolution, using static LT assumptions in a ‘first‐cut’ estimate, in the absence of credible future LT trends. We examine the relationship between species' current distribution and macroclimatic variables using generalized additive models, and include LT indirectly as a filter. Future projections are derived using two CC scenarios (for 2050 and 2080) to estimate the spatial patterns of loss and gain in species richness that might ultimately result. We then apply the IUCN Red List criteria A3(c) of potential range loss to evaluate species sensitivity. We finally estimate the sensitivity of 141 NPs in terms of both species richness and turnover. Assuming no spread of species, 10–15% of the species are projected to fall within the critically endangered or extinct categories by 2050 and between 25% and 40% by 2080. Assuming unlimited species spread, less extreme results show proportions dropping to approximately 10–20% by 2080. Spatial patterns of richness loss and gain show contrasting latitudinal patterns with a westward range shift of species around the species‐rich equatorial zone in central Africa, and an eastward shift in southern Africa, mainly because of latitudinal aridity gradients across these ecological transition zones. Xeric shrubland NPs may face significant richness losses not compensated by species influxes. Other NPs might expect substantial losses and influxes of species. On balance, the NPs might ultimately realize a substantial shift in the mammalian species composition of a magnitude unprecedented in recent geological time. To conclude, the effects of global CC and LT on wildlife communities may be most noticeable not as a loss of species from their current ranges, but instead as a fundamental change in community composition.     

Invited review: Intergovernmental Panel on Climate Change,agriculture, and food—A case of shifting cultivation and history

Since 1990, the Intergovernmental Panel on Climate Change (IPCC) has produced five Assessment Reports (ARs), in which agriculture as the production of food for humans via crops and livestock have featured in one form or another. A constructed database of the ca. 2,100 cited experiments and simulations in the five ARs was analyzed with respect to impacts on yields via crop type, region, and whether adaptation was included. Quantitative data on impacts and adaptation in livestock farming have been extremely scarce in the ARs. The main conclusions from impact and adaptation are that crop yields will decline, but that responses have large statistical variation. Mitigation assessments in the ARs have used both bottom‐up and top‐down methods but need better to link emissions and their mitigation with food production and security. Relevant policy options have become broader in later ARs and included more of the social and nonproduction aspects of food security. Our overall conclusion is that agriculture and food security, which are two of the most central, critical, and imminent issues in climate change, have been dealt with an unfocussed and inconsistent manner between the IPCC five ARs. This is partly a result of not only agriculture spanning two IPCC working groups but also the very strong focus on projections from computer crop simulation modeling. For the future, we suggest a need to examine interactions between themes such as crop resource use efficiencies and to include all production and nonproduction aspects of food security in future roles for integrated assessment models.     

Environmental policy and the greenhouse effect

Emissions, resulting from human activity, are substantially increasing the atmospheric concentration of greenhouse gases. This, in turn, is causing an additional average warming of the Earth's surface. This article presents an overview of recent developments in the international discussion on climate change, taking into account the work of other organizations such as the Intergovernmental Panel on Climate Change (IPCC).The long term and global character of the climate change problem requires an international long term strategy based on internationally agreed principles such as sustainable development and the precautionary principle. Research is needed to further develop risk assessment and environmental quality standards, from which emission targets can be derived.As a first step, governments of many industrialized countries have already set provisional national CO₂ emission targets, aimed at stabilization at present levels by the year 2000 and, in some cases, reductions thereafter.Under the auspices of United Nations, negotiations have begun on an international framework climate convention and associated agreements, on, for example, greenhouse gas emissions, forestry and funding mechanisms. Obligations imposed on individual nations may be expected to reflect their responsibility for greenhouse warming; this paper presents some views on the equity of burden sharing.