Interactions between nitrogen deposition, land cover conversion, and climate change determine the contemporary carbon balance of Europe

Abstract. European ecosystems are thought to take up large amounts of carbon, but neither the rate nor the contributions of the underlying processes are well known. In the second half of the 20th century, carbon dioxide concentrations have risen by more that 100 ppm, atmospheric nitrogen deposition has more than doubled, and European mean temperatures were increasing by 0.02 °C yr−1. The extents of forest and grasslands have increased with the respective rates of 5800 km2 yr−1 and 1100 km2 yr−1 as agricultural land has been abandoned at a rate of 7000 km2 yr−1. In this study, we analyze the responses of European land ecosystems to the aforementioned environmental changes using results from four process-based ecosystem models: BIOME-BGC, JULES, ORCHIDEE, and O-CN. The models suggest that European ecosystems sequester carbon at a rate of 56 TgC yr−1 (mean of four models for 1951–2000) with strong interannual variability (±88 TgC yr−1, average across models) and substantial inter-model uncertainty (±39 TgC yr−1). Decadal budgets suggest that there has been a continuous increase in the mean net carbon storage of ecosystems from 85 TgC yr−1 in 1980s to 108 TgC yr−1 in 1990s, and to 114 TgC yr−1 in 2000–2007. The physiological effect of rising CO2 in combination with nitrogen deposition and forest re-growth have been identified as the important explanatory factors for this net carbon storage. Changes in the growth of woody vegetation are suggested as an important contributor to the European carbon sink. Simulated ecosystem responses were more consistent for the two models accounting for terrestrial carbon-nitrogen dynamics than for the two models which only accounted for carbon cycling and the effects of land cover change. Studies of the interactions of carbon-nitrogen dynamics with land use changes are needed to further improve the quantitative understanding of the driving forces of the European land carbon balance.

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Interactions between nitrogen deposition, land cover conversion, and climate change determine the contemporary carbon balance of Europe

Biogeosciences Discussions ◽

10.5194/bgd-7-2227-2010 ◽

2010 ◽

Vol 7 (2) ◽

pp. 2227-2265 ◽

Cited By ~ 4

Author(s):

G. Churkina ◽

S. Zaehle ◽

J. Hughes ◽

N. Viovy ◽

Y. Chen ◽

...

Keyword(s):

Land Cover ◽

Nitrogen Deposition ◽

Carbon Storage ◽

Carbon Balance ◽

Agricultural Land ◽

Environmental Changes ◽

Driving Forces ◽

Carbon Sink ◽

Terrestrial Ecosystems ◽

Nitrogen Dynamics

Abstract. European ecosystems are thought to uptake significant amounts of carbon, but neither the rate nor the contributions of the underlying processes are well known. In the second half of the 20th century, carbon dioxide concentrations have risen by more than 100 ppm, atmospheric nitrogen deposition has more than doubled, and European mean temperatures were increasing by 0.02 °C per year. The extents of forest and grasslands have increase with the respective rates of 5800 km2 yr-1 and 1100 km2 yr-1 as agricultural land has been abandoned at a rate of 7000 km2 yr-1. In this study, we analyze the responses of European land ecosystems to the aforementioned environmental changes using results from four process-based ecosystem models: BIOME-BGC, JULES, ORCHIDEE, and O-CN. All four models suggest that European terrestrial ecosystems sequester carbon at a rate of 100 TgC yr-1 (1980–2007 mean) with strong interannual variability (± 85 TgC yr-1) and a substantial inter-model uncertainty (± 45 TgC yr-1). Decadal budgets suggest that there has been a slight increase in terrestrial net carbon storage from 85 TgC yr-1 in 1980–1989 to 114 TgC yr-1 in 2000–2007. The physiological effect of rising CO2 in combination with nitrogen deposition and forest re-growth have been identified as the important explanatory factors for this net carbon storage. Changes in the growth of woody vegetation are an important contributor to the European carbon sink. Simulated ecosystem responses were more consistent for the two models accounting for terrestrial carbon-nitrogen dynamics than for the two models which only accounted for carbon cycling and the effects of land cover change. Studies of the interactions of carbon-nitrogen dynamics with land use changes are needed to further improve the quantitative understanding of the driving forces of the European land carbon balance.

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Peat Carbon Vulnerability to Projected Climate Warming in the Hudson Bay Lowlands, Canada: A Decision Support Tool for Land Use Planning in Peatland Dominated Landscapes

Frontiers in Earth Science ◽

10.3389/feart.2021.650662 ◽

2021 ◽

Vol 9 ◽

Author(s):

James W. McLaughlin ◽

Maara S. Packalen

Keyword(s):

Land Cover ◽

Carbon Storage ◽

Carbon Sink ◽

Bayesian Belief Network ◽

Bayesian Belief Networks ◽

Sink Strength ◽

Hudson Bay ◽

Climate Scenarios ◽

Belief Network ◽

Hudson Bay Lowlands

Peatlands help regulate climate by sequestering (net removal) carbon from the atmosphere and storing it in plants and soils. However, as mean annual air temperature (MAAT) increases, peat carbon stocks may decrease. We conducted an in-depth synthesis of current knowledge about ecosystem controls on peatland carbon storage and fluxes to constrain the most influential parameters in probabilistic modelling of peat carbon sinks, such as Bayesian belief networks. Evaluated parameters included climate, carbon flux and mass, land cover, landscape position (defined here as elevation), fire records, and current and future climate scenarios for a 74,300 km2 landscape in the Hudson Bay Lowlands, Canada. The Bayesian belief network was constructed with four tiers: 1) exposure, expressed as MAAT, and the state variables of elevation and land cover; 2) sensitivity, expressed as ecosystem conditions relevant to peat carbon mass and its quality for decomposition, peat wetness, and fire; 3) carbon dioxide and methane fluxes and peat combustion; and 4) vulnerability of peat carbon sink strength under warmer MAAT. Simulations were conducted using current (−3.0 to 0.0°C), moderately warmer (0.1–4.0°C), and severely warmer (4.1–9.0°C) climate scenarios. Results from the severely warmer climate scenario projected an overall drying of peat, with approximately 20% reduction in the strong sink categories of net ecosystem exchange and peat carbon sink strength for the severely and, to a lesser degree, the moderately warmer climate scenarios relative to current MAAT. In the warmest temperature simulation, probability of methane emission decreased slightly and the probability of the strong peat carbon sink strength was 27% lower due to peat combustion. Our Bayesian belief network can assist land planners in decision-making for peatland-dominated landscapes, such as identifying high carbon storage areas and those projected to be at greatest risk of carbon loss due to climate change. Such areas may be designated, for example, as protected or reduced management intensity. The Bayesian belief network presented here is built on an in-depth knowledge synthesis to construct conditional probability tables, so is expected to apply to other peatland-dense jurisdictions by changing only elevation, peatland types, and MAAT.

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Intensity and Driving Forces of Land Abandonment in Eastern Poland

Applied Sciences ◽

10.3390/app10103500 ◽

2020 ◽

Vol 10 (10) ◽

pp. 3500 ◽

Cited By ~ 1

Author(s):

Wojciech Zgłobicki ◽

Kamil Karczmarczuk ◽

Bogusława Baran-Zgłobicka

Keyword(s):

Land Use ◽

Rural Areas ◽

Agricultural Production ◽

Agricultural Land ◽

Environmental Changes ◽

Driving Forces ◽

Arable Land ◽

Land Abandonment ◽

Farm Size ◽

Study Objective

Agricultural land is an important natural resource and forms the basis for food production. Global and local socio-economic and environmental changes are often the driving forces of changes in land cover and land use. Land abandonment in rural areas is one of the processes observed in Europe today and usually leads to increased afforestation. The intensity of this process in Central Europe is linked to the political and economic changes that took place at the end of the 20th century. The study objective was to identify the natural and socio-economic factors of this process in Lublin Province—a major region of agricultural production in Poland. From 1990 to 2018, over 130,000 ha were excluded from agricultural use, which represents 7% of the arable land in 1990. Land abandonment showed considerable spatial differences when comparing different counties: its magnitude ranged from 4% to 13% of the county area. At the same time, due to the specific type of land use in the province (small farm holdings divided into several fields), the intensity of land abandonment was underestimated when based on overview data (CORINE). It was observed that the intensity of this process was correlated with the natural conditions (topography, soils) for agricultural production and the socio-economic characteristics (area of arable land, forest cover changes, farm size) of the counties as well as the absorption of Common Agricultural Policy funds.

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Monitoring and Projecting Land Use/Land Cover Changes of Eleven Large Deltaic Areas in Greece from 1945 Onwards

Remote Sensing ◽

10.3390/rs12081241 ◽

2020 ◽

Vol 12 (8) ◽

pp. 1241

Author(s):

Anastasia Krina ◽

Fotios Xystrakis ◽

Kostas Karantininis ◽

Nikos Koutsias

Keyword(s):

Land Use ◽

Land Cover ◽

Urban Areas ◽

Agricultural Land ◽

Driving Forces ◽

Arable Land ◽

Land Use Land Cover ◽

Anthropogenic Pressures ◽

Composition And Structure ◽

Economic Developments

Wetlands are areas of high biodiversity and provide many ecosystem services of high value. However, they are under constant threat from intense anthropogenic pressures, mainly agriculture intensification, urbanization, pollution, and climate change. The temporal and spatial patterns of land use/land cover (LULC) changes within eleven large wetlands in Greece were analyzed based on thematic maps generated from aerial orthophotos taken in 1945, 1975, and 2007. Socio-economic developments and the consequent need for more arable land and utilization of water resources are among the factors that mainly determine their evolution. In 2007, LULC classes related to wetland vegetation were reduced to one third as compared to 1945 and they were mainly replaced with croplands and urban infrastructures. Each of the different sub-periods that was considered (1945–1975 and 1975–2007) was distinguished by characteristic patterns of change. Agricultural land increased up to 42% from 1945 to 1975 and became the dominant LULC class in all deltaic areas but Evros. A considerable stability was observed for the period 1975–2007 for all LULC classed but it is remarkable the extent of urban areas that doubled. There is a tendency of landscape simplification and homogenization among the deltaic areas and the output of Markov chain analysis indicates that future composition of deltaic landscapes will be similar to the current one if the main driving forces remain constant. Changes in LULC composition and structure are also combined with coastal erosion in all deltaic areas. This is attributed to the modification of sedimentary deposits due to dam construction. The results summarize the change trajectories of the major deltaic areas in Greece from 1945 to 2007 thus offering a great outlook of changes that allows managers to understand how policies and socio-economic requirements affect the deltaic ecosystems and what decisions should be made to protect and enhance them.

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Modelled land use and land cover change emissions – A spatio-temporal comparison of different approaches

10.5194/esd-2020-93 ◽

2021 ◽

Author(s):

Wolfgang A. Obermeier ◽

Julia E. M. S. Nabel ◽

Tammas Loughran ◽

Kerstin Hartung ◽

Ana Bastos ◽

...

Keyword(s):

Land Use ◽

Land Cover ◽

Environmental Conditions ◽

Agricultural Land ◽

Environmental Changes ◽

Land Cover Changes ◽

Legacy Effects ◽

Spatio Temporal ◽

The Impact ◽

Global Carbon

Abstract. Quantifying the net carbon flux from land use and land cover changes (fLULCC) is critical for understanding the global carbon cycle, and hence, to support climate change mitigation. However, large-scale fLULCC is not directly measurable, but has to be inferred from models instead, such as semi-empirical bookkeeping models, and process-based dynamic global vegetation models (DGVMs). By definition, fLULCC estimates are not directly comparable between these two different model types. As an example, DGVM-based fLULCC in the annual global carbon budgets is estimated under transient environmental forcing and includes the so-called Loss of Additional Sink Capacity (LASC). The LASC accounts for the impact of environmental changes on land carbon storage potential of managed land compared to potential vegetation which is not represented in bookkeeping models. In addition, fLULCC from transient DGVM simulations differs depending on the arbitrary chosen simulation time period and the historical timing of land use and land cover changes (including different accumulation periods for legacy effects). An approximation of fLULCC by DGVMs that is independent of the timing of land use and land cover changes and their legacy effects requires simulations assuming constant pre-industrial or present-day environmental forcings. Here, we analyze three DGVM-derived fLULCC estimations for twelve models within 18 regions and quantify their differences as well as climate- and CO2-induced components. The three estimations stem from the commonly performed simulation with transiently changing environmental conditions and two simulations that keep environmental conditions fixed, at pre-industrial and present-day conditions. Averaged across the models, we find a global fLULCC (under transient conditions) of 2.0 ± 0.6 PgC yr-1 for 2009–2018, of which ∼40 % are attributable to the LASC (0.8 ± 0.3 PgC yr-1). From 1850 onward, fLULCC accumulated to 189 ± 56 PgC with 40 ± 15 PgC from the LASC. Regional hotspots of high cumulative and annual LASC values are found in the USA, China, Brazil, Equatorial Africa and Southeast Asia, mainly due to deforestation for cropland. Distinct negative LASC estimates, in Europe (early reforestation) and from 2000 onward in the Ukraine (recultivation of post-Soviet abandoned agricultural land), indicate that fLULCC estimates in these regions are lower in transient DGVM- compared to bookkeeping-approaches. By unraveling spatio-temporal variability in three alternative DGVM-derived fLULCC estimates, our results call for a harmonized attribution of model-derived fLULCC. We propose an approach that bridges bookkeeping and DGVM approaches for fLULCC estimation by adopting a mean DGVM-ensemble LASC for a defined reference period.

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Modelled land use and land cover change emissions – a spatio-temporal comparison of different approaches

Earth System Dynamics ◽

10.5194/esd-12-635-2021 ◽

2021 ◽

Vol 12 (2) ◽

pp. 635-670

Author(s):

Wolfgang A. Obermeier ◽

Julia E. M. S. Nabel ◽

Tammas Loughran ◽

Kerstin Hartung ◽

Ana Bastos ◽

...

Keyword(s):

Land Use ◽

Land Cover ◽

Land Cover Change ◽

Environmental Conditions ◽

Agricultural Land ◽

Environmental Changes ◽

Land Cover Changes ◽

Environmental Forcing ◽

The Impact ◽

Global Carbon

Abstract. Quantifying the net carbon flux from land use and land cover changes (fLULCC) is critical for understanding the global carbon cycle and, hence, to support climate change mitigation. However, large-scale fLULCC is not directly measurable and has to be inferred from models instead, such as semi-empirical bookkeeping models and process-based dynamic global vegetation models (DGVMs). By definition, fLULCC estimates are not directly comparable between these two different model types. As an important example, DGVM-based fLULCC in the annual global carbon budgets is estimated under transient environmental forcing and includes the so-called loss of additional sink capacity (LASC). The LASC results from the impact of environmental changes on land carbon storage potential of managed land compared to potential vegetation and accumulates over time, which is not captured in bookkeeping models. The fLULCC from transient DGVM simulations, thus, strongly depends on the timing of land use and land cover changes mainly because LASC accumulation is cut off at the end of the simulated period. To estimate the LASC, the fLULCC from pre-industrial DGVM simulations, which is independent of changing environmental conditions, can be used. Additionally, DGVMs using constant present-day environmental forcing enable an approximation of bookkeeping estimates. Here, we analyse these three DGVM-derived fLULCC estimations (under transient, pre-industrial, and present-day forcing) for 12 models within 18 regions and quantify their differences as well as climate- and CO2-induced components and compare them to bookkeeping estimates. Averaged across the models, we find a global fLULCC (under transient conditions) of 2.0±0.6 PgC yr−1 for 2009–2018, of which ∼40 % are attributable to the LASC (0.8±0.3 PgC yr−1). From 1850 onward, the fLULCC accumulated to 189±56 PgC with 40±15 PgC from the LASC. Around 1960, the accumulating nature of the LASC causes global transient fLULCC estimates to exceed estimates under present-day conditions, despite generally increased carbon stocks in the latter. Regional hotspots of high cumulative and annual LASC values are found in the USA, China, Brazil, equatorial Africa, and Southeast Asia, mainly due to deforestation for cropland. Distinct negative LASC estimates in Europe (early reforestation) and from 2000 onward in the Ukraine (recultivation of post-Soviet abandoned agricultural land), indicate that fLULCC estimates in these regions are lower in transient DGVM compared to bookkeeping approaches. Our study unravels the strong dependence of fLULCC estimates on the time a certain land use and land cover change event happened to occur and on the chosen time period for the forcing of environmental conditions in the underlying simulations. We argue for an approach that provides an accounting of the fLULCC that is more robust against these choices, for example by estimating a mean DGVM ensemble fLULCC and LASC for a defined reference period and homogeneous environmental changes (CO2 only).

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Analysis of land cover change and its driving forces in a desert oasis landscape of southern Xinjiang, China

Solid Earth Discussions ◽

10.5194/sed-6-1907-2014 ◽

2014 ◽

Vol 6 (2) ◽

pp. 1907-1947

Author(s):

T. Amuti ◽

G. Luo

Keyword(s):

Land Cover ◽

Land Cover Change ◽

Land Degradation ◽

Agricultural Land ◽

Driving Forces ◽

Soil Salinization ◽

Land Cover Changes ◽

Detection Techniques ◽

Desert Oasis ◽

Southern Xinjiang

Abstract. The combined effects of drought, warming and the changes in land cover have caused severe land degradation for several decades in the extremely arid desert oases of Southern Xinjiang, Northwest China. This study examined land cover changes during 1990–2008 to characterize and quantify the transformations in the typical oasis of Hotan. Land cover classifications of these images were performed based on the supervised classification scheme integrated with conventional vegetation and soil indexes. Change-detection techniques in remote sensing (RS) and a geographic information system (GIS) were applied to quantify temporal and spatial dynamics of land cover changes. The overall accuracies, Kappa coefficients, and average annual increase rate or decrease rate of land cover classes were calculated to assess classification results and changing rate of land cover. The analysis revealed that major trends of the land cover changes were the notable growth of the oasis and the reduction of the desert–oasis ecotone, which led to accelerated soil salinization and plant deterioration within the oasis. These changes were mainly attributed to the intensified human activities. The results indicated that the newly created agricultural land along the margins of the Hotan oasis could result in more potential areas of land degradation. If no effective measures are taken against the deterioration of the oasis environment, soil erosion caused by land cover change may proceed. The trend of desert moving further inward and the shrinking of the ecotone may lead to potential risks to the eco-environment of the Hotan oasis over the next decades.

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Dynamics of Tree outside Forest Land Cover Development and Ecosystem Carbon Storage Change in Eastern Coastal Zone, Bangladesh

Land ◽

10.3390/land11010076 ◽

2022 ◽

Vol 11 (1) ◽

pp. 76

Author(s):

Imranul Islam ◽

Shenghui Cui ◽

Muhammad Ziaul Hoque ◽

Hasan Muhammad Abdullah ◽

Kaniz Fatima Tonny ◽

...

Keyword(s):

Land Cover ◽

Carbon Storage ◽

Coastal Zone ◽

Agricultural Land ◽

Automated Classification ◽

Rural Settlements ◽

Invest Model ◽

Ecosystem Carbon ◽

Spatio Temporal ◽

Storage Change

Tree outside forest (TOF) has immense potential in economic and environmental development by increasing the amount of tree vegetation in and around rural settlements. It is an important source of carbon stocks and a critical option for climate change regulation, especially in land-scarce, densely populated developing countries such as Bangladesh. Spatio-temporal changes of TOF in the eastern coastal zone of Bangladesh were analyzed and mapped over 1988–2018, using Landsat land use land cover (LULC) maps and associated ecosystem carbon storage change by linking the InVEST carbon model. Landsat TM and OLI-TIRS data were classified through the Maximum Likelihood Classifier (MLC) algorithm using Semi-Automated Classification (SAC). In the InVEST model, aboveground, belowground, dead organic matter, and soil carbon densities of different LULC types were used. The findings revealed that the studied landscapes have differential features and changing trends in LULC where TOF, mangrove forest, built-up land, and salt-aquaculture land have increased due to the loss of agricultural land, mudflats, water bodies, and hill vegetation. Among different land biomes, TOF experienced the largest increase (1453.9 km2), and it also increased carbon storage by 9.01 Tg C. However, agricultural land and hill vegetation decreased rapidly by 1285.8 km2 and 365.7 km2 and reduced carbon storage by 3.09 Tg C and 4.89 Tg C, respectively. The total regional carbon storage increased by 1.27 Tg C during 1988–2018. In addition to anthropogenic drivers, land erosion and accretion were observed to significantly alter LULC and regional carbon storage, necessitating effective river channel and coastal embankment management to minimize food and environmental security tradeoff in the studied landscape.

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Geospatial Analyses for Assessing the Driving Forces of Land Use/Land Cover Dynamics Around the Nile Delta Branches, Egypt

Journal of the Indian Society of Remote Sensing ◽

10.1007/s12524-020-01189-2 ◽

2020 ◽

Vol 48 (12) ◽

pp. 1661-1674

Author(s):

Hazem T. Abd El-Hamid

Keyword(s):

Land Use ◽

Land Cover ◽

Land Surface ◽

Driving Forces ◽

Nile Delta ◽

Annual Rate ◽

Land Use Land Cover ◽

Environmental Indices ◽

Continuous Increase ◽

Delta Branches

AbstractMajor driving forces can alter Land use/Land cover (LULC) dynamics and affect landscape sustainability around the Nile Delta of Egypt. The present study aims at evaluating and mapping changes in LULC and assessing the dynamics of LULC and Land Surface Temperature (LST) around the two branches of the Nile Delta, Egypt using Landsat data and GIS. Calibrated Landsat images were acquired on 2000, 2014 and 2019 and processed to produce LULC, environmental indices and LST, respectively, using ENVI 5.3. ArcGIS 10.1 was used to extract a transition map from 2000 to 2019 around the two branches. The results displayed that five classes of LULC were extracted around Damietta and Rosetta branches; water, urban, bare, dense and spare vegetation. A continuous increase in water was recorded around Damietta branch; 13.66 km2 (197%), 14.21 km2 (2.04%) and 16.54 km2 (2.30%) in 2000, 2014 and 2019, respectively. Also, urban area was increased around Damietta and Rosetta branch as follows: 53.6 km2 (7.72%), 58.34 (8.37%) and 90.37 km2 (13.70%) in 2000, 2014 and 2019, 59.55 km2 (6.809%), 104.16 (11.90%) and 149.77 km2 (17.11%) in 2000, 2014 and 2019, respectively. Urban achieved the highest gain of 24.807 and 85.70 km2 at the expense of dense vegetation around Damietta and Rosetta branch, respectively. The results showed that the decrease in vegetation and the increase in urban density lead to increasing LST of the study area. The changes in LST can be monitored depending on the construction materials such as the presence of green areas and topography. Urban and bare lands have the highest LST while the water bodies and vegetation temperature showed a tendency to decrease. It can be concluded that urban areas increased with annual rate 0.27 and 0.54 km2 and vegetation decreased with annual rate −0.57 and−0.55 km2 around Damietta and Rosetta branches from 2000 to 2019. Results showed that comprehensive index was 321.14 and 330.03 around Damietta and Rosetta branch, the higher the degree of development and exploitation. There has been a significant land use change which was due to an increase in population. Overall, this research provides valuable data about changes in LU/LC around the Nile Delta branches, it is very important for decision maker and stockholders for proper management.

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Sub-grid scale representation of vegetation in global land surface schemes: implications for estimation of the terrestrial carbon sink

Biogeosciences ◽

10.5194/bg-11-1021-2014 ◽

2014 ◽

Vol 11 (4) ◽

pp. 1021-1036 ◽

Cited By ~ 33

Author(s):

J. R. Melton ◽

V. K. Arora

Keyword(s):

Land Cover ◽

Water Balance ◽

Environmental Conditions ◽

Land Surface ◽

Carbon Balance ◽

Carbon Sink ◽

Terrestrial Ecosystem ◽

Terrestrial Carbon ◽

Global Land ◽

Terrestrial Carbon Sink

Abstract. Terrestrial ecosystem models commonly represent vegetation in terms of plant functional types (PFTs) and use their vegetation attributes in calculations of the energy and water balance as well as to investigate the terrestrial carbon cycle. Sub-grid scale variability of PFTs in these models is represented using different approaches with the "composite" and "mosaic" approaches being the two end-members. The impact of these two approaches on the global carbon balance has been investigated with the Canadian Terrestrial Ecosystem Model (CTEM v 1.2) coupled to the Canadian Land Surface Scheme (CLASS v 3.6). In the composite (single-tile) approach, the vegetation attributes of different PFTs present in a grid cell are aggregated and used in calculations to determine the resulting physical environmental conditions (soil moisture, soil temperature, etc.) that are common to all PFTs. In the mosaic (multi-tile) approach, energy and water balance calculations are performed separately for each PFT tile and each tile's physical land surface environmental conditions evolve independently. Pre-industrial equilibrium CLASS-CTEM simulations yield global totals of vegetation biomass, net primary productivity, and soil carbon that compare reasonably well with observation-based estimates and differ by less than 5% between the mosaic and composite configurations. However, on a regional scale the two approaches can differ by > 30%, especially in areas with high heterogeneity in land cover. Simulations over the historical period (1959–2005) show different responses to evolving climate and carbon dioxide concentrations from the two approaches. The cumulative global terrestrial carbon sink estimated over the 1959–2005 period (excluding land use change (LUC) effects) differs by around 5% between the two approaches (96.3 and 101.3 Pg, for the mosaic and composite approaches, respectively) and compares well with the observation-based estimate of 82.2 ± 35 Pg C over the same period. Inclusion of LUC causes the estimates of the terrestrial C sink to differ by 15.2 Pg C (16%) with values of 95.1 and 79.9 Pg C for the mosaic and composite approaches, respectively. Spatial differences in simulated vegetation and soil carbon and the manner in which terrestrial carbon balance evolves in response to LUC, in the two approaches, yields a substantially different estimate of the global land carbon sink. These results demonstrate that the spatial representation of vegetation has an important impact on the model response to changing climate, atmospheric CO2 concentrations, and land cover.

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