Natural Terrestrial Ecosystems Research Articles

Assessing effects of temporal compositing and varying observation periods for large-area land-cover mapping in semi-arid ecosystems: Implications for global monitoring

Land-cover is an important parameter in analyzing the state and dynamics of natural and anthropogenic terrestrial ecosystems. Land-cover classes related to semi-arid savannas currently exhibit among the greatest uncertainties in available global land cover datasets. This study focuses on the Kalahari in northeastern Namibia and compares the effects of different composite lengths and observation periods with class-wise mapping accuracies derived from multi-temporal MODIS time series classifications to better understand and overcome quality gaps in mapping semi-arid land-cover types. We further assess the effects of precipitation patterns on mapping accuracy using Tropical Rainfall Measuring Mission (TRMM) observation data. Botanical field samples, translated into the UN Land Cover Classification System (LCCS), were used for training and validation. Different sets of composites (16-day to three-monthly) were generated from MODIS (MOD13Q1) data covering the sample period from 2004 to 2007. Land-cover classifications were performed cumulatively based on annual and inter-annual feature sets with the use of random forests. Woody vegetation proved to be more stable in terms of omission and commission errors compared to herbaceous vegetation types. Generally, mapping accuracy increases with increasing length of the observation period. Analyses of variance (ANOVA) verified that inter-annual classifications significantly improved class-wise mapping accuracies, and confirmed that monthly composites achieved the best accuracy scores for both annual and inter-annual classifications. Correlation analyses using piecewise linear models affirmed positive correlations between cumulative mapping accuracy and rainfall and indicated an influence of seasonality and environmental cues on the mapping accuracies. The consideration of the inter-seasonal variability of vegetation activity and phenology cycling in the classification process further increases the overall classification performance of savanna classes in large-area land-cover datasets. Implications for global monitoring frameworks are discussed based on a conceptual model of the relationship between observation period and accuracy.

Grasshoppers (Orthoptera: Acrididae) select vegetation patches in local‐scale responses to foliar nitrogen but not phosphorus in native grassland

Abstract Key elements such as nitrogen (N) and phosphorus (P) are often limiting relative to the nutritional needs of herbivores that feed on them. While N often limits insect herbivores in natural terrestrial ecosystems, the effect of P is poorly studied in the field, even though compelling hypotheses from the ecological stoichiometry literature predict its importance. We evaluated small‐scale spatial distributions of, and herbivory by, grasshoppers among neighboring plots that vary in foliar‐N and ‐P in tallgrass prairie. Grasshopper densities were 67% greater in N‐fertilized plots but detected no effect to grasshopper densities from P‐fertilizer. Leaf damage to the dominant grass Andropogon gerardii was 32% greater in N‐fertilized plots, but no response to foliar‐P was detected. Herbivore damage to a common forb, goldenrod (Solidago missouriensis), was not strongly linked by fertilizer treatments, although there was increased leaf damage in N‐fertilizer treatments when no P was applied (a significant N × P interaction). Under field conditions at local scales, we conclude that spatially heterogeneous distributions of grasshoppers are primarily affected by foliar‐N in host plants with little evidence that P‐levels contribute to the spatial patterns.

Water stress and harmful insects in agri-forest ecosystems

Present knowledge on ecological services supplied by insects to natural terrestrial ecosystems, allow us to identify many homeostatic mechanisms regulating biological balance as well as life perpetuation of the said ecosystems; at the same time, that knowledge represents a sound referring point to understanding how those mechanisms do work so as to manage them in the anthropized ecosystems (i.e., agriculture and forests), and especially in order to identify in the latter the natural meaning of the so called insect outbreaks, so as to forecast and possibly prevent them; as well as, when needed, to conceive and formulate efficient control strategies having minimal environmental impact. Water factor is crucial with genesis, configuration and conservation of a terrestrial ecosystem (both natural or anthropized) as a whole or in its individual components, but especially concerning plant life as well as plant interactions with phytophagous invertebrates, mainly insects. Insect-plant trophic interactions are principally influenced by the water conditions in the ecosystem, and the impact of phytophagous insects on crops is markedly affected. Extremely severe water stress, especially if prolonged, prevent insect life just like plant’s life but a moderate and not so prolonged water stress, while depressing plant vigour, paradoxically can improve development and multiplication of phytophagous arthropods, with severe consequences on woody plants especially, and forest trees markedly.

Modeling of critical lead loads on natural ecosystems of Belarus

We give an outline of the model of behavior of heavy metals in terrestrial ecosystems and present the results derived from implementing it in estimating critical lead loads on natural ecosystems of Belarus. We provide the main methodological approaches, the algorithm, the composition of input information, the soil-geochemical, biogeocenotic, hydrological-climatic and other parameters used in the study as well as starting cartographic information. We provide the results of calculations in terms of the model as well as the maps of critical lead loads on the main types of natural terrestrial ecosystems of Belarus according to the effect-oriented and preservation approaches and demonstrate some cases where the existing levels exceed the calculated load standards.

Temporal isotopic variations of dissolved silicon in a pristine boreal river

It has previously been concluded that the stable Si isotopes are fractionated during geochemical and biogeochemical elemental transfers, such as weathering and precipitation of clays and biogenic Si, which has opened up the possibility of using Si as a tracer in natural terrestrial ecosystems. Furthermore, quantification of the biogenic impact on the biogeochemical Si cycle has attracted significant scientific interest since biological control has been suggested. Previous observations of seasonal variations in the dissolved Si isotopic pattern further imply that high-frequency riverine sampling during main hydrological events might provide important information about natural processes governing the fluvial biogeochemical Si cycle. Therefore, temporal variations in the isotopic composition of riverine dissolved Si were investigated for the Kalix River, Northern Sweden, the largest pristine river system in Europe, based on high-frequency sampling during a period of 25 weeks from early April to early October 2006. Temporal variations spanning 0.4‰ for δ 29Si and 0.8‰ for δ 30Si of dissolved Si in the Kalix River were observed during the period, suggesting that the riverine dissolved Si input to the oceans cannot be considered to have a constant Si isotopic composition on a short time scale. The results implicate biogeochemical Si-cycling via formation and dissolution of biogenic silica as processes significantly affecting the dissolved Si transport in boreal systems during April to early October. The Si budget in the river system appeared to be controlled by relative Si enrichment during high discharge events and relative Si depletions in the subarctic mountainous and lake dominated areas. The Si enrichments and depletions were accompanied by decreasing and increasing riverine δ 29Si and δ 30Si, respectively. These isotope variations can be explained by release of plant derived silica, depleted in heavier Si isotopes, during the spring snowmelt. Further, increased volumetric contribution from the headwater and losses of dissolved Si due to biogenic silica formation by diatoms in the subarctic lakes at a later period are expected to be responsible for the preferential losses of lighter isotopes, as further verified by land cover analysis.

The Soil: Nature, Sustainable Use, Management, and Protection – An Overview

Soil forms the outer skin of the earth's land surface. Often less than a metre in depth, it is essential to sustain natural terrestrial ecosystems and human life. Soils result from the interactions over time between climate, parent material, topography, vegetation, and biota. They vary from place to place. Mineral soils are composed of mineral matter, organic matter, and gas- or liquid-filled pores in varying proportions. Soils perform a wide range of functions and provide many ecosystem or environmental services; with the climate problem, the soil is increasingly being recognised as a potential sink for carbon from the atmosphere. In part because of humankind's (over)use of soils and in part because of natural and human-induced environmental change, there is a widespread decline in soil quality and an increasing number of threats to soil, which jeopardise both the soil's natural functions and its use by humans. As a limited resource, soils must be used sustainably. Soil protection strategies have been indirectly embodied in a number of United Nations conventions, and there are now national and supranational developments towards specific regulations and legislation to protect soils and their functions.

South American native bumblebees (Hymenoptera: Apidae) infected by Nosema ceranae (Microsporidia), an emerging pathogen of honeybees (Apis mellifera)

As pollination is a critical process in both human-managed and natural terrestrial ecosystems, pollinators provide essential services to both nature and humans. Pollination is mainly due to the action of different insects, such as the bumblebee and the honeybee. These important ecological and economic roles have led to widespread concern over the recent decline in pollinator populations that has been detected in many regions of the world. While this decline has been attributed in some cases to changes in the use of agricultural land, the effects of parasites could play a significant role in the reduction of these populations. For the first time, we describe here the presence of Nosema ceranae, an emerging honeybee pathogen, in three species of Argentine native bumblebees. A total of 455 bumblebees belonging to six species of genus Bombus were examined. PCR results showed that three of the species are positive to N. ceranae (Bombus atratus, Bombus morio and Bombus bellicosus). We discuss the appearance of this pathogen in the context of the population decline of this pollinators.

Ecological risks in anthropogenic disturbance of nitrogen cycles in natural terrestrial ecosystems

AbstractAnthropogenic addition of reactive nitrogen (Nr) to the biosphere is increasing globally and some terrestrial ecosystems are suffering from a state of excess Nr for biological nitrogen (N) demand, termed N saturation. Here, we review the ecological risks in relation to N saturation and prospective responses to N saturation. Excess Nr increases the risks of local extinction of rare plant species, encouragement of exotic plant species, disturbance of nutrient balance in plant organs, and increase of herbivory in plant communities. On the ecosystem scale, excess bioavailable N induces forest decline, disturbance of nutrient cycling within ecosystems, depending on vegetation, soil, land‐use, and N‐loading history. These Nr risks will increase in the Asian region, where impacts of Nr in natural terrestrial ecosystems have been scarcely studied. Whether much of the terrestrial ecosystems on a global level are in the sate of N saturation or not is still controversial, but the potential risks of excess Nr seem to be increasing. The fundamental ways to mitigate Nr risks are to reduce Nr production, prevent Nr translocation, and promote conversion of Nr to N2. Temporal, but promising actions against ecological N risks may include management of forests and riparian zones, and carbon addition in grassland.

A gap analysis comparing Natura 2000 vs National Protected Area network with potential natural vegetation

We performed a gap analysis of protected area networks in Italy to assess the representativeness of potential natural vegetation (PNV) types of the European Natura 2000 network compared with the National Protected Area network. In this context, the PNV map, reflecting the diversity and spatial arrangement of the natural terrestrial ecosystems, can be considered as an appropriate proxy of environmental and biogeographical diversity of Italy. In this country, 775 protected areas are registered in the Official List of Protected Areas (OLPA), 2281 sites are listed as Sites of Community Interest and 590 as Special Protection Areas, constituting the Natura 2000 network. The adopted conservation target considered that any PNV type included for less than the 10% in the PAs network (OLPA, Natura 2000) was defined as a gap in the system. In particular we defined four categories of PNV protection: any PNV types with a representation of less than 10% in both the OLPA and N2000 was defined as a “total gap” (i.e., under-protected); any PNV type with a representation of less than 10% in either the OLPA or the N2000 was defined as a “partial gap”; any PNV type with a representation of between 10 and 50% in both the OLPA and N2000 was defined as “protected”; lastly, any PNV type with a representation of more than 50% in both the OLPA and N2000 was defined as “widely-protected”. Digital overlays of PNV and PAs networks were separately performed and statistics produced, indicating the current state of protection of Potential Natural Vegetation types in the two networks (OLPA and Natura 2000). We found that more than 59% of PNV types recognized on the Italian territory is not protected by the OLPA network. On the contrary, regarding Natura 2000 network, 68% of PNV types are protected, accounting for 27% more than OLPA. Compared to the National network of OLPA, the European network Natura 2000 is characterized by a larger percentage of territory in terms of area (18% of the Italian territory for Natura 2000 vs 10% of OLPA) but also by a smaller size of the sites, allowing for a more coherent distribution and efficiency in the protection of habitat remnants (68% PNV types protected by Natura 2000 vs 41% by OLPA). The proposed PNV approach can help guiding decisions on where and how to spend scarce conservation management resources.

Reservoirs and human well being: new challenges for evaluating impacts and benefits in the neotropics

As in many other continents, neotropical ecosystems are impacted by the construction of reservoirs. These artificial ecosystems change considerably the natural terrestrial and aquatic ecosystems and their biodiversity. The multiple uses of reservoirs promote benefits for the human beings in terms of economic development, income, jobs and employment. Services of reservoirs are important assets for the regional ecosystem. Evaluation of ecosystem services produced by artificial reservoirs, are new challenges to the understanding of the cost/benefit relationships of reservoir construction in the neotropics. Regulating and other services promoted by reservoirs lead to new trends for 'green technology' and the implementation of ecohydrological and ecotechnological developments. This approach can be utilized with better success as a substitute for the usual impact/benefit evaluation of the reservoirs. Better and diversified services can be achieved with 'green technology' applied to the construction.

Deriving Vegetation Dynamics of Natural Terrestrial Ecosystems from MODIS NDVI/EVI Data over Turkey.

The 16-day composite MODIS vegetation indices (VIs) at 500-m resolution for the period between 2000 to 2007 were seasonally averaged on the basis of the estimated distribution of 16 potential natural terrestrial ecosystems (NTEs) across Turkey. Graphical and statistical analyses of the time-series VIs for the NTEs spatially disaggregated in terms of biogeoclimate zones and land cover types included descriptive statistics, correlations, discrete Fourier transform (DFT), time-series decomposition, and simple linear regression (SLR) models. Our spatio-temporal analyses revealed that both MODIS VIs, on average, depicted similar seasonal variations for the NTEs, with the NDVI values having higher mean and SD values. The seasonal VIs were most correlated in decreasing order for: barren/sparsely vegetated land > grassland > shrubland/woodland > forest; (sub)nival > warm temperate > alpine > cool temperate > boreal = Mediterranean; and summer > spring > autumn > winter. Most pronounced differences between the MODIS VI responses over Turkey occurred in boreal and Mediterranean climate zones and forests, and in winter (the senescence phase of the growing season). Our results showed the potential of the time-series MODIS VI datasets in the estimation and monitoring of seasonal and interannual ecosystem dynamics over Turkey that needs to be further improved and refined through systematic and extensive field measurements and validations across various biomes.

Evidence of Enhanced Atmospheric Ammoniacal Nitrogen in Hells Canyon National Recreation Area: Implications for Natural and Cultural Resources

Agriculture releases copious fertilizing pollutants to air sheds and waterways of the northwestern United States. To evaluate threats to natural resources and historic rock paintings in remote Hells Canyon, Oregon and Idaho, deposition of ammonia (NH3), nitrogen oxides (NOx), sulfur dioxide (SO2), and hydrogen sulfide (H2S) at five stations along 60 km of the Snake River valley floor were passively sampled from July 2002 through June 2003, and ozone data and particulate chemistry were obtained from the Interagency Monitoring of Protected Visual Environments (IMPROVE) station at Hells Canyon. NH3 concentrations were high; biweekly averages peaked at 5–19 ppb in spring and summer and the nutrient-laden Snake River is a likely source. Fine particulate ammonium nitrate (NH4NO3) averaged 2.6 µg/m3 during the 20% of worst visibility days with winter drainage of air masses from the Snake River Basin and possibly long distance transport from southern California. Other pollutants were within background ranges. NH3 is corrosive to clay-based picto-graphs; nitrogen deposition can alter natural biotic communities and terrestrial ecosystem processes at levels reported here.

A reappraisal of the terrestrial nitrogen cycle: What can we learn by extracting concepts from Gaia theory?

Although soil scientists and most environmental scientists are acutely aware of the interactions between the cycling of carbon and nitrogen, for conceptual convenience when portraying the nitrogen cycle in text books the N cycle tends to be considered in isolation from its interactions with the cycling of other elements and water, usually as a snap shot at the current time; the origins of dinitrogen are rarely considered, for example. The authors suggest that Lovelock's Gaia hypothesis provides a useful and stimulating framework for consideration of the terrestrial nitrogen cycle. If it is used, it suggests that urbanization and management of sewage, and intensive animal rearing are probably bigger global issues than nitrogen deposition from fossil fuel combustion, and that plant evolution may be driven by the requirement of locally sustainable and near optimal soil mineral N supply dynamics. This may, in turn, be partially regulating global carbon and oxygen cycles. It is suggested that pollutant N deposition may disrupt this essential natural plant and terrestrial ecosystem evolutionary process, causing biodiversity change. Interactions between the Earth and other bodies in the solar system, and possibly beyond, also need to be considered in the context of the global N cycle over geological time scales. This is because of direct potential impacts on the nitrogen content of the atmosphere, potential long-term impacts of past boloid collisions on plate tectonics and thus on global N cycling via subduction and volcanic emissions, and indirect effects upon C, O and water cycling that all may impact upon the N cycle in the long term.

Do we ecologically model what we economically value?

For the period 1991–2005 inclusive we categorise peer-reviewed journal output depending on whether it pertains to case-studies in a) cropland or b) aggregate semi-natural and natural terrestrial (ASNNT) ecosystems for three applications in ecological modelling: 1) modelling of terrestrial carbon and nitrogen fluxes; 2) modelling of terrestrial root systems; 3) geographic information systems. Next we compare these research output magnitudes for case-studies in cropland and ASNNT ecosystems with estimates of the total economic value (TEV) of either system. For applications 1) and 3) the magnitude of research output for ASNNT ecosystems between 1991–2005 is greater than for cropland and research into the former is increasing at a faster rate over time compared to the latter. Given that the TEV of ASNNT ecosystems is 82 times greater than the TEV of cropland we deem these trends in research output as desirable under the assumption that value and research should be interdependent. However for application 2), although research into ASNNT ecosystems is increasing at a faster rate compared to cropland, total research output between 1991–2005 is greater for cropland. We conclude that increased research output which focuses on ASNNT ecosystems in this particular application should be a priority, given the high TEV of ASNNT ecosystems relative to cropland.

Air quality in natural areas: Interface between the public, science and regulation

Natural areas are important interfaces between air quality, the public, science and regulation. In the United States and Canada, national parks received over 315 million visits during 2004. Many natural areas have been experiencing decreased visibility, increased ozone (O 3) levels and elevated nitrogen deposition. Ozone is the most pervasive air pollutant in North American natural areas. There is an extensive scientific literature on O 3 exposure–tree response in chambered environments and, lately, free-air exposure systems. Yet, less is known about O 3 impacts on natural terrestrial ecosystems. To advance scientifically defensible O 3 risk assessment for natural forest areas, species-level measurement endpoints must be socially, economically and ecologically relevant. Exposure-based indices, based on appropriate final endpoints, present an underused opportunity to meet this need. Exposure–plant indices should have a high degree of statistical significance, have high goodness of fit, be biologically plausible and include confidence intervals to define uncertainty. They must be supported by exposure–response functions and be easy to use within an air quality regulation context. Ozone exposure–response indices developed within an ambient air context have great potential for improving risk assessment in natural forest areas and enhancing scientific literacy.

The Global Atmospheric Environment for the Next Generation

Air quality, ecosystem exposure to nitrogen deposition, and climate change are intimately coupled problems: we assess changes in the global atmospheric environment between 2000 and 2030 using 26 state-of-the-art global atmospheric chemistry models and three different emissions scenarios. The first (CLE) scenario reflects implementation of current air quality legislation around the world, while the second (MFR) represents a more optimistic case in which all currently feasible technologies are applied to achieve maximum emission reductions. We contrast these scenarios with the more pessimistic IPCC SRES A2 scenario. Ensemble simulations for the year 2000 are consistent among models and show a reasonable agreement with surface ozone, wet deposition, and NO2 satellite observations. Large parts of the world are currently exposed to high ozone concentrations and high deposition of nitrogen to ecosystems. By 2030, global surface ozone is calculated to increase globally by 1.5 +/- 1.2 ppb (CLE) and 4.3 +/- 2.2 ppb (A2), using the ensemble mean model results and associated +/-1 sigma standard deviations. Only the progressive MFR scenario will reduce ozone, by -2.3 +/- 1.1 ppb. Climate change is expected to modify surface ozone by -0.8 +/- 0.6 ppb, with larger decreases over sea than over land. Radiative forcing by ozone increases by 63 +/- 15 and 155 +/- 37 mW m(-2) for CLE and A2, respectively, and decreases by -45 +/- 15 mW m(-2) for MFR. We compute that at present 10.1% of the global natural terrestrial ecosystems are exposed to nitrogen deposition above a critical load of 1 g N m(-2) yr(-1). These percentages increase by 2030 to 15.8% (CLE), 10.5% (MFR), and 25% (A2). This study shows the importance of enforcing current worldwide air quality legislation and the major benefits of going further. Nonattainment of these air quality policy objectives, such as expressed by the SRES-A2 scenario, would further degrade the global atmospheric environment.

Maasai Mara — an ecosystem under siege: an African case study on the societal dimension of rangeland conservation

'Let me assure you all that our commitment to the preservation of wildlife and the habitat in the Maasai Mara reserve is total. We do not deny that the reserve is of vital economic importance to us, but we also firmly believe, and proclaim, that wildlife deserves to be protected for its own sake. The animals are God's creatures and we affirm their right to live and survive as undisturbed as possible in this busy and over-populated world. The Mara can provide a relief from the commercial pressures of profit and survival. We must thus emphasize that in the Maasai Mara reserve interests of wildlife are paramount.' Samson Ole Tuya, Chairman Narok County Council — Maasai Mara Tourism Workshop, March 1991 'The chances of wildlife surviving when people are hungry and poor are becoming increasingly slim.' Samson Ole Tuya, Member of Parliament, Narok South. Workshop — Defining the framework for management and conservation planning for the Maasai Mara ecosystem, November 1996 The Maasai Mara ecosystem has one of the richest assemblages of wildlife in the world and supports about 237 herbivores per km2, making it one of the most productive natural terrestrial ecosystems. It maintains the greatest and most spectacular large mammal migration on earth and is the most highly visited tourist area in the East African region. Tourism generates millions of dollars annually while livestock and agriculture contribute significantly to the local and national economy. This paper examines the enormous threats facing the ecosystem and the efforts being made to keep the ecosystem open in order to support a vibrant tourist trade and a healthy livestock economy. These aspects are currently threatened by a burgeoning human population, land subdivision, changing land tenure systems, crop farming, poaching, habitat fragmentation, blockage of wildlife migratory corridors, habitat destruction, sedentarisation, environmental degradation and poverty. Wildlife conservation is in conflict with agriculture, while tourism has taken away the best grazing areas for livestock. The paper also reviews the ecological and socio-economic problems associated with tourism, land use changes and break down of traditional governance structures and how they have weakened the capacity of Maasai Mara to sustain a viable wildlife populations.

Ozone and natural systems: understanding exposure, response, and risk

Research aimed at understanding the response of plants to ozone has been conducted for over four decades but little of it has addressed intact natural systems. Even so, there is sufficient scientific information at this time to support air quality standards that will protect natural terrestrial ecosystems from ozone. What is unknown is the risk associated with continued exposure of natural systems, including both above- and below-ground components, in combination with other stresses including changing temperature and precipitation, elevated carbon dioxide, pests and pathogens, invasive species, and other activities that may fragment the landscape. Research to support an assessment of the ecological risk associated with ozone as it exists, in a milieu of stresses, must include endpoints beyond those addressed in the past, primarily productivity and species composition. To estimate the risk to society of ozone impacts on natural systems, endpoints such as the integrity of soil food webs, the quantity and quality of water supplied from terrestrial ecosystems, wildlife and recreational values, and the transfer and fate of carbon, nutrients, and water within the systems must be quantified. Not only will this research provide the basis for a sound estimate of risk, but also it will improve our understanding of fundamental ecosystem processes.

Uncertainties in the fate of nitrogen: II. a quantitative assessment of the uncertainties in major nitrogen fluxes in the Netherlands

Enhanced levels of nitrogen in the environment may have several adverse effects, including decreased plant species diversity in (semi) natural terrestrial ecosystems, eutrophication of surface waters, pollution of groundwater due to nitrate leaching and global warming due to nitrous and nitrogen oxide (N2O and NOx) emissions. To determine the effectiveness of policies aimed at the reduction of emission of ammonia (NH3), N2O and NOx, nitrate (NO3) leaching and nitrogen (N) runoff, it is essential to have information on the fate of nitrogen in both agricultural and non-agricultural soils on a regional and national scale and its inherent uncertainties. In this paper, we quantified the uncertainties in the emission, uptake, accumulation, denitrification, leaching and runoff of nitrogen at a national scale and for specific land use–soil type combinations. Furthermore, we identified which parameters contribute most to the overall uncertainty in the emission of ammonia to the atmosphere and the leaching/runoff to groundwater and surface water. To gain quantitative insight into the propagation of the uncertainty, a model was developed representing all crucial processes in the N chain by simple process descriptions. Uncertainties were quantified for the Netherlands as a whole, including terrestrial systems, both agricultural and non-agricultural land, and aquatic systems. For agricultural and non-agricultural land, plots were distinguished, consisting of a multiple of 500 × 500 m2 and of 250 × 250 m2 grid cells, respectively, with unique combinations of soil use, soil type and groundwater table class that were derived from existing digital maps. Model parameters were assigned by using relationships with soil type, groundwater level class and land use. The uncertainty was quantified by means of a Monte Carlo analysis, whereas statistical approaches were used to identify which parameters contribute most to the overall uncertainty of the fate of nitrogen. The 90% confidence interval for the fluxes of N compounds to air, groundwater and surface water (in Gg N.yr−1) ranged between 102 and 194 for ammonia emission, between 18 and 51 for N2O emissions, between 32 and 108 for NO3 inflow to groundwater and between 2 and 38 for N inflow to surface water. The uncertainty in NH3 emission was mainly caused by the uncertainty in the NH3 emission fractions for animal manure, whereas the uncertainty in N2O emission was mainly due to the uncertainty in the fractions relating total nitrification and denitrification to N2O emissions. The uncertainty in inflow to groundwater and runoff to surface water was mainly caused by the uncertainty in denitrification in the soil and in upper groundwater and in non-agricultural soils also by the N accumulation in the soil. In view of the need to monitor and evaluate the impact of N reduction policies and measures, it is essential to put more effort in activities yielding a reduction of these large uncertainties, such as additional data gathering and process research under field circumstances.

Mapping burned surfaces in Sub-Saharan Africa based on multi-temporal neural classification

Biomass burning from vegetation fire is one of the major disturbances of natural terrestrial ecosystems and an increased understanding of its impact requires extensive documentation of the phenomenon at global scale. Satellite remote sensing has been demonstrated as the only tool able to cope with this global issue. Global daily coverage using the SPOT-VEGETATION instrument has been made for the year 2000 in the frame of the Global Burnt Area-2000 (GBA2000) initiative. This paper presents a new methodology for detecting burned areas from time series of coarse resolution satellite images. The proposed methodology is a supervised classification strategy based on hierarchical use of the Multi-Layer Perceptron neural network. The use of a neural network-based approach allows the exploitation of spatial and temporal dimensions within a unified scheme. The methodology has been applied to a series of daily SPOT-VEGETATION images covering the northern part of the African continent and daily burned area maps were produced for the dry season of the year 2000. Evaluation of the results has been done both in terms of the algorithm performance and of the final burned map accuracy using Landsat-7 Enhanced Thematic Mapper Plus (ETM+) data.