On the relationship between fire regime and vegetation structure in the tropics
Veenendaal, Elmar M. ; Torello-Raventos, Mireia ; Miranda, Heloisa S. ; Sato, Naomi Margarete ; Oliveras, Imma ; Langevelde, Frank van; Asner, Gregory P. ; Lloyd, Jon - \ 2018
New Phytologist 218 (2018)1. - ISSN 0028-646X - p. 153 - 166.
alternative stable states - feedbacks - fire ecology - forest - savannah
We assessed data from 11 experiments examining the effects of the timing and/or frequency of fire on tropical forest and/or savanna vegetation structure over one decade or more. The initial ‘control treatment’ in many such cases consisted of previously cleared land. This is as opposed to natural vegetation subject to some sort of endogenous fire regime before the imposition of fire treatments. Effects of fire on fractional foliar cover are up to 10-fold greater when clearing pre-treatments are imposed. Moreover, because many of the ‘classic’ fire trials were initialised with applied management questions in mind, most have also used burning regimes much more frequent and/or severe than those occurring in the absence of human activity. Once these factors are taken into account, our modelling analysis shows that nonanthropogenic fire regimes serve to reduce canopy vegetative cover to a much lower extent than has previously been argued to be the case. These results call into question the notion that fire effects on tropical vegetation can be of a sufficient magnitude to maintain open-type savanna ecosystems under climatic/soil regimes otherwise sufficient to give rise to a more luxurious forest-type vegetation cover.
Plant functional type classification for earth system models: results from the European Space Agency's Land Cover Climate Change Initiative
Poulter, B. ; MacBean, N. ; Hartley, A. ; Khlystova, I. ; Arino, O. ; Betts, R. ; Bontemps, S. ; Boettcher, M. ; Brockmann, C. ; Defourny, P. ; Hagemann, S. ; Herold, M. ; Kirches, C. ; Lamarche, C. ; Lederer, D. ; Ottlé, C. ; Peters, M. ; Peylin, P. - \ 2015
Geoscientific Model Development 8 (2015). - ISSN 1991-959X - p. 2315 - 2328.
global vegetation model - world map - ecosystems - forests - cycle - uncertainties - resolution - feedbacks - phenology - database
Global land cover is a key variable in the earth system with feedbacks on climate, biodiversity and natural resources. However, global land cover data sets presently fall short of user needs in providing detailed spatial and thematic information that is consistently mapped over time and easily transferable to the requirements of earth system models. In 2009, the European Space Agency launched the Climate Change Initiative (CCI), with land cover (LC_CCI) as 1 of 13 essential climate variables targeted for research development. The LC_CCI was implemented in three phases: first responding to a survey of user needs; developing a global, moderate-resolution land cover data set for three time periods, or epochs (2000, 2005, and 2010); and the last phase resulting in a user tool for converting land cover to plant functional type equivalents. Here we present the results of the LC_CCI project with a focus on the mapping approach used to convert the United Nations Land Cover Classification System to plant functional types (PFTs). The translation was performed as part of consultative process among map producers and users, and resulted in an open-source conversion tool. A comparison with existing PFT maps used by three earth system modeling teams shows significant differences between the LC_CCI PFT data set and those currently used in earth system models with likely consequences for modeling terrestrial biogeochemistry and land–atmosphere interactions. The main difference between the new LC_CCI product and PFT data sets used currently by three different dynamic global vegetation modeling teams is a reduction in high-latitude grassland cover, a reduction in tropical tree cover and an expansion in temperate forest cover in Europe. The LC_CCI tool is flexible for users to modify land cover to PFT conversions and will evolve as phase 2 of the European Space Agency CCI program continues.
Synergistic effects of drought and deforestation on the resilience of the south-eastern Amazon rainforest
Staal, A. ; Dekkers, S. ; Hirota Magalhaes, M. ; Nes, E.H. van - \ 2015
Ecological Complexity 22 (2015). - ISSN 1476-945X - p. 65 - 75.
tropical tree cover - critical transitions - global resilience - african savannas - tipping points - linking theory - climate-change - woody cover - fire - feedbacks
The south-eastern Amazon rainforest is subject to ongoing deforestation and is expected to become drier due to climate change. Recent analyses of the distribution of tree cover in the tropics show three modes that have been interpreted as representing alternative stable states: forest, savanna and treeless states. This situation implies that a change in environmental conditions, such as in the climate, could cause critical transitions from a forest towards a savanna ecosystem. Shifts to savanna might also occur if perturbations such as deforestation exceed a critical threshold. Recovering the forest would be difficult as the savanna will be stabilized by a feedback between tree cover and fire. Here we explore how environmental changes and perturbations affect the forest by using a simple model with alternative tree-cover states. We focus on the synergistic effects of precipitation reduction and deforestation on the probability of regime shifts in the south-eastern Amazon rainforest. The analysis indicated that in a large part of the south-eastern Amazon basin rainforest and savanna could be two alternative states, although massive forest dieback caused by mean-precipitation reduction alone is unlikely. However, combinations of deforestation and climate change triggered up to 6.6 times as many local regime shifts than the two did separately, causing large permanent forest losses in the studied region. The results emphasize the importance of reducing deforestation rates in order to prevent a climate-induced dieback of the south-eastern Amazon rainforest.
No growth stimulation of tropical trees by 150 years of CO2 fertilization but water-use efficiency increased
Sleen, J.P. van der; Groenendijk, P. ; Vlam, M. ; Anten, N.P.R. ; Boom, A. ; Bongers, F. ; Pons, T.L. ; Terburg, G. ; Zuidema, P.A. - \ 2015
Nature Geoscience 8 (2015). - ISSN 1752-0894 - p. 24 - 28.
rising atmospheric co2 - carbon-dioxide - climate-change - elevated co2 - forest trees - responses - ecosystems - vegetation - feedbacks - lessons
The biomass of undisturbed tropical forests has likely increased in the past few decades (1, 2), probably as a result of accelerated tree growth. Higher CO2 levels are expected to raise plant photosynthetic rates (3) and enhance water-use efficiency (4), that is, the ratio of carbon assimilation through photosynthesis to water loss through transpiration. However, there is no evidence that these physiological responses do indeed stimulate tree growth in tropical forests. Here we present measurements of stable carbon isotopes and growth rings in the wood of 1,100 trees from Bolivia, Cameroon and Thailand. Measurements of carbon isotope fractions in the wood indicate that intrinsic water-use efficiency in both understorey and canopy trees increased by 30–35% over the past 150 years as atmospheric CO2 concentrations increased. However, we found no evidence for the suggested concurrent acceleration of individual tree growth when analysing the width of growth rings. We conclude that the widespread assumption of a CO2-induced stimulation of tropical tree growth may not be valid.
Introduced tree species released from negative soil biota
Putten, W.H. van der - \ 2014
New Phytologist 202 (2014)2. - ISSN 0028-646X - p. 341 - 343.
plant - feedbacks - ecology
Data-based perfect-deficit approach to understanding climate extremes and forest carbon assimilation capacity
Wei, S. ; Yi, C. ; Hendrey, G. ; Eaton, T. ; Rustic, G. ; Wang, S. ; Liu, H. ; Krakauer, N.Y. ; Wang, W. ; Desai, A.R. ; Moors, E.J. - \ 2014
Environmental Research Letters 9 (2014). - ISSN 1748-9326
net ecosystem exchange - drought - respiration - algorithm - heat - reduction - feedbacks - model
Several lines of evidence suggest that the warming climate plays a vital role in driving certain types of extreme weather. The impact of warming and of extreme weather on forest carbon assimilation capacity is poorly known. Filling this knowledge gap is critical towards understanding the amount of carbon that forests can hold. Here, we used a perfect-deficit approach to identify forest canopy photosynthetic capacity (CPC) deficits and analyze how they correlate to climate extremes, based on observational data measured by the eddy covariance method at 27 forest sites over 146 site-years. We found that droughts severely affect the carbon assimilation capacities of evergreen broadleaf forest (EBF) and deciduous broadleaf forest. The carbon assimilation capacities of Mediterranean forests were highly sensitive to climate extremes, while marine forest climates tended to be insensitive to climate extremes. Our estimates suggest an average global reduction of forest CPC due to unfavorable climate extremes of 6.3 Pg C (~5.2% of global gross primary production) per growing season over 2001–2010, with EBFs contributing 52% of the total reduction.
Land Management and Land-Cover Change Have Impacts of Similar Magnitude on Surface Temperature
Luyssaert, S. ; Jammet, M. ; Stoy, P.C. ; Estel, S. ; Pongratz, J. ; Ceschia, E. ; Churkina, G. ; Don, A. ; Erb, K.H. ; Ferlicoq, M. ; Moors, E.J. - \ 2014
Nature Climate Change 4 (2014). - ISSN 1758-678X - p. 389 - 393.
climate-change - vegetation - feedbacks - forests - energy - carbon - earth
Anthropogenic changes to land cover (LCC) remain common, but continuing land scarcity promotes the widespread intensification of land management changes (LMC) to better satisfy societal demand for food, fibre, fuel and shelter1. The biophysical effects of LCC on surface climate are largely understood2, 3, 4, 5, particularly for the boreal6 and tropical zones7, but fewer studies have investigated the biophysical consequences of LMC; that is, anthropogenic modification without a change in land cover type. Harmonized analysis of ground measurements and remote sensing observations of both LCC and LMC revealed that, in the temperate zone, potential surface cooling from increased albedo is typically offset by warming from decreased sensible heat fluxes, with the net effect being a warming of the surface. Temperature changes from LMC and LCC were of the same magnitude, and averaged 2 K at the vegetation surface and were estimated at 1.7 K in the planetary boundary layer. Given the spatial extent of land management (42–58% of the land surface) this calls for increasing the efforts to integrate land management in Earth System Science to better take into account the human impact on the climate
Selective alteration of soil food web components by invasive Giant goldenrod (Solidago gigantea) in two distinct habitat types
Quist, C.W. ; Vervoort, M.T.W. ; Megen, H.H.B. van; Gort, G. ; Bakker, J. ; Putten, W.H. van der; Helder, J. - \ 2014
Oikos 123 (2014)7. - ISSN 0030-1299 - p. 837 - 845.
exotic plant invasions - nematode communities - alien plants - ergosterol - biota - diversity - biodiversity - extraction - canadensis - feedbacks
Apart from relatively well-studied aboveground effects, invasive plant species will also impact the soil food web. So far, most research has been focusing on primary decomposers, while studies on effects at higher trophic levels are relatively scarce. Giant goldenrod Solidago gigantea, native to North America, is a widespread and common invasive species in most European countries. We investigated its impact on plant communities and on multiple trophic levels of the soil food web in two contrasting habitats: riparian zones and semi-natural grasslands. In 30 pairs of invaded and uninvaded plots, floristic composition, pH, fungal biomass and the densities of 11 nematode taxa were determined by using a quantitative PCR-based method. In the two habitats, the invader outcompeted both rare and dominant plant species. Belowground, S. gigantea invasion reduced pH, increased overall fungal biomass as well as the density of a single lineage of fungivorous nematodes, the family Aphelenchoididae. The densities of two other, phylogenetically distinct lineages of fungivorous nematodes, Aphelenchidae and Diphtherophoridae, were unaffected by the local increase in fungal biomass. Apparently this plant species induces a local asymmetric boost of the fungal community, and only Aphelenchoididae were able to benefit from this invader-induced change. The alternative explanation – the results are explained by a subtle, S. gigantea-induced 0.1–0.2 units decrease of pH – seems unlikely, as pH optima for nematode taxa are relatively broad. Thus, apart from readily observable aboveground effects, the invasive plant species S. gigantea affects fungal biomass as well as a specific part of the fungivorous nematode community in a soil type-independent manner.
Attributing the impacts of land-cover changes in temperate regions on surface temperature and heat fluxes to specific causes: Results from the first LUCID set of simulations
Boisier, J.P. ; Noblet-Ducoudré, N. de; Pitman, A.J. ; Cruz, F.T. ; Delire, C. ; Hurk, B.J.J.M. van den; Molen, M.K. van der; Müller, C. ; Voldoire, A. - \ 2012
Journal of Geophysical Research: Atmospheres 117 (2012)D12. - ISSN 2169-897X
climate system model - soil-moisture - sensitivity - feedbacks - forcings - exchange - forest - energy - biomes - albedo
Surface cooling in temperate regions is a common biogeophysical response to historical Land-Use induced Land Cover Change (LULCC). The climate models involved in LUCID show, however, significant differences in the magnitude and the seasonal partitioning of the temperature change. The LULCC-induced cooling is directed by decreases in absorbed solar radiation, but its amplitude is 30 to 50% smaller than the one that would be expected from the sole radiative changes. This results from direct impacts on the total turbulent energy flux (related to changes in land-cover properties other than albedo, such as evapotranspiration efficiency or surface roughness) that decreases at all seasons, and thereby induces a relative warming in all models. The magnitude of those processes varies significantly from model to model, resulting on different climate responses to LULCC. To address this uncertainty, we analyzed the LULCC impacts on surface albedo, latent heat and total turbulent energy flux, using a multivariate statistical analysis to mimic the models' responses. The differences are explained by two major ‘features’ varying from one model to another: the land-cover distribution and the simulated sensitivity to LULCC. The latter explains more than half of the inter-model spread and resides in how the land-surface functioning is parameterized, in particular regarding the evapotranspiration partitioning within the different land-cover types, as well as the role of leaf area index in the flux calculations. This uncertainty has to be narrowed through a more rigorous evaluation of our land-surface models.
Determining robust impacts of land-use induced land-cover changes on surface climate over North America and Eurasia; Results from the first set of LUCID experiments
Noblet-Ducoudré, N. de; Boisier, J.P. ; Pitman, A. ; Bonan, G.B. ; Brovkin, V. ; Cruz, F. ; Delire, C. ; Gayler, V. ; Hurk, B.J.J.M. van den; Lawrence, P.J. ; Molen, M.K. van der; Müller, C. ; Reick, C.H. ; Strengers, B.J. ; Voldoire, A. - \ 2012
Journal of Climate 25 (2012)9. - ISSN 0894-8755 - p. 3261 - 3281.
tropical deforestation - temperature trends - secondary lands - use transitions - use/land cover - system model - wood-harvest - biosphere - database - feedbacks
The project Land-Use and Climate, Identification of Robust Impacts (LUCID) was conceived to address the robustness of biogeophysical impacts of historical land use–land cover change (LULCC). LUCID used seven atmosphere–land models with a common experimental design to explore those impacts of LULCC that are robust and consistent across the climate models. The biogeophysical impacts of LULCC were also compared to the impact of elevated greenhouse gases and resulting changes in sea surface temperatures and sea ice extent (CO2SST). Focusing the analys is on Eurasia and North America, this study shows that for a number of variables LULCC has an impact of similar magnitude but of an opposite sign, to increased greenhouse gases and warmer oceans. However, the variability among the individual models’ response to LULCC is larger than that found from the increase in CO2SST. The results of the study show that although the dispersion among the models’ response to LULCC is large, there are a number of robust common features shared by all models: the amount of available energy used for turbulent fluxes is consistent between the models and the changes in response to LULCC depend almost linearly on the amount of trees removed. However, less encouraging is the conclusion that there is no consistency among the various models regarding how LULCC affects the partitioning of available energy between latent and sensible heat fluxes at a specific time. The results therefore highlight the urgent need to evaluate land surface models more thoroughly, particularly how they respond to a perturbation in addition to how they simulate an observed average state.
Intercomparison of modis albedo retievals and in situ measurements across the global fluxnet network
Cescatti, A. ; Marcolla, B. ; Santhana Vannan, S.K. ; Roman, J.Y. ; Moors, E.J. - \ 2012
Remote Sensing of Environment 121 (2012). - ISSN 0034-4257 - p. 323 - 334.
reflectance distribution function - broad-band albedo - surface albedo - boreal forests - climate-change - vegetation - products - feedbacks - validation - instrument
Surface albedo is a key parameter in the Earth's energy balance since it affects the amount of solar radiation directly absorbed at the planet surface. Its variability in time and space can be globally retrieved through the use of remote sensing products. To evaluate and improve the quality of satellite retrievals, careful intercomparisons with in situ measurements of surface albedo are crucial. For this purpose we compared MODIS albedo retrievals with surface measurements taken at 53 FLUXNET sites that met strict conditions of land cover homogeneity. A good agreement between mean yearly values of satellite retrievals and in situ measurements was found (r2 = 0.82). The mismatch is correlated with the spatial heterogeneity of surface albedo, stressing the relevance of land cover homogeneity when comparing point to pixel data. When the seasonal patterns of MODIS albedo are considered for different plant functional types, the match with surface observations is extremely good at all forest sites. On the contrary, satellite retrievals at non-forested sites (grasslands, savannas, croplands) underestimate in situ measurements across the seasonal cycle. The mismatch observed at grassland and cropland sites is likely due to the extreme fragmentation of these landscapes, as confirmed by geostatistical attributes derived from high resolution scenes.
A comprehensive view on climate change: coupling of Earth system and integrated assessment models
Vuuren, D.P. van; Batlle Bayer, L. ; Chuwah, C. ; Ganzeveld, L.N. ; Hazeleger, W. ; Hurk, B. van den; Noije, T. van; O'Neill, B. ; Strengers, B.J. - \ 2012
Environmental Research Letters 7 (2012)2. - ISSN 1748-9326
carbon-cycle models - land-cover change - environmental-change - atmosphere-ocean - simpler model - scenarios - emissions - impact - feedbacks - dynamics
There are several reasons to strengthen the cooperation between the integrated assessment (IA) and earth system (ES) modeling teams in order to better understand the joint development of environmental and human systems. This cooperation can take many different forms, ranging from information exchange between research communities to fully coupled modeling approaches. Here, we discuss the strengths and weaknesses of different approaches and try to establish some guidelines for their applicability, based mainly on the type of interaction between the model components (including the role of feedback), possibilities for simplification and the importance of uncertainty. We also discuss several important areas of joint IA–ES research, such as land use/land cover dynamics and the interaction between climate change and air pollution, and indicate the type of collaboration that seems to be most appropriate in each case. We find that full coupling of IA–ES models might not always be the most desirable form of cooperation, since in some cases the direct feedbacks between IA and ES may be too weak or subject to considerable process or scenario uncertainty. However, when local processes are important, it could be important to consider full integration. By encouraging cooperation between the IA and ES communities in the future more consistent insights can be developed.
Modelled suppression of boundary-layer clouds by plants in a CO2-rich atmosphere
Vilà-Guerau de Arellano, J. ; Heerwaarden, C.C. van; Lelieveld, J. - \ 2012
Nature Geoscience 5 (2012). - ISSN 1752-0894 - p. 701 - 704.
soil-moisture - co2 - climate - feedbacks
Cumulus clouds in the atmospheric boundary layer play a key role in the hydrologic cycle, in the onset of severe weather by thunderstorms and in modulating Earth’s reflectivity and climate1. How these clouds respond to climate change, in particular over land, and how they interact with the carbon cycle are poorly understood2,3. It is expected that as a consequence of rising atmospheric CO2 concentrations the plant stomata will close4,5, leading to lower latent heat fluxes and higher sensible heat fluxes. Here we show that this causes a decline in boundary-layer cloud formation in middle latitudes. This could be partly counteracted by the greater ability of a warmer atmosphere to take up water and by a growth in biomass due to CO2 fertilization6. Our results are based on a new soil–water–atmosphere–plant model supported by comprehensive observational evidence, from which we identify the dominant atmospheric responses to plant physiological processes. They emphasize the intricate connection between biological and physical aspects of the climate system and the relevance of short-term and small-scale processes in establishing this connection.
The response of Arctic vegetation to the summer climate: relation between shrub cover, NDVI, surface albedo and temperature
Blok, D. ; Schaepman-Strub, G. ; Bartholomeus, H. ; Heijmans, M.M.P.D. ; Maximov, T.C. ; Berendse, F. - \ 2011
Environmental Research Letters 6 (2011)3. - ISSN 1748-9326 - 9 p.
northern alaska - tundra vegetation - siberian tundra - feedbacks - ecosystems - expansion - exchange - trends - forest - map
Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming. However, it is unknown how albedo and NDVI are affected by shrub cover and inter-annual variations in the summer climate. Here, we examine the relationship between deciduous shrub fractional cover, NDVI and albedo using field data collected at a tundra site in NE Siberia. Field data showed that NDVI increased and albedo decreased with increasing deciduous shrub cover. We then selected four Arctic tundra study areas and compiled annual growing season maximum NDVI and minimum albedo maps from MODIS satellite data (2000–10) and related these satellite products to tundra vegetation types (shrub, graminoid, barren and wetland tundra) and regional summer temperature. We observed that maximum NDVI was greatest in shrub tundra and that inter-annual variation was negatively related to summer minimum albedo but showed no consistent relationship with summer temperature. Shrub tundra showed higher albedo than wetland and barren tundra in all four study areas. These results suggest that a northwards shift of shrub tundra might not lead to a decrease in summer minimum albedo during the snow-free season when replacing wetland tundra. A fully integrative study is however needed to link results from satellite data with in situ observations across the Arctic to test the effect of increasing shrub cover on summer albedo in different tundra vegetation types.
A Carbon Cycle Science Update Since IPCC AR-4
Dolman, A.J. ; Werf, G.R. van der; Molen, M.K. van der; Ganssen, G. ; Erisman, J.W. ; Strengers, B. - \ 2010
Ambio 39 (2010)5-6. - ISSN 0044-7447 - p. 402 - 412.
climate-change - co2 emissions - terrestrial plants - atmospheric co2 - forests - sinks - feedbacks - trends - ocean - exchange
We review important advances in our understanding of the global carbon cycle since the publication of the IPCC AR4. We conclude that: the anthropogenic emissions of CO2 due to fossil fuel burning have increased up through 2008 at a rate near to the high end of the IPCC emission scenarios; there are contradictory analyses whether an increase in atmospheric fraction, that might indicate a declining sink strength of ocean and/or land, exists; methane emissions are increasing, possibly through enhanced natural emission from northern wetland, methane emissions from dry plants are negligible; old-growth forest take up more carbon than expected from ecological equilibrium reasoning; tropical forest also take up more carbon than previously thought, however, for the global budget to balance, this would imply a smaller uptake in the northern forest; the exchange fluxes between the atmosphere and ocean are increasingly better understood and bottom up and observation-based top down estimates are getting closer to each other; the North Atlantic and Southern ocean take up less CO2, but it is unclear whether this is part of the ‘natural’ decadal scale variability; large-scale fires and droughts, for instance in Amazonia, but also at Northern latitudes, have lead to significant decreases in carbon uptake on annual timescales; the extra uptake of CO2 stimulated by increased N-deposition is, from a greenhouse gas forcing perspective, counterbalanced by the related additional N2O emissions; the amount of carbon stored in permafrost areas appears much (two times) larger than previously thought; preservation of existing marine ecosystems could require a CO2 stabilization as low as 450 ppm; Dynamic Vegetation Models show a wide divergence for future carbon trajectories, uncertainty in the process description, lack of understanding of the CO2 fertilization effect and nitrogen–carbon interaction are major uncertainties.
An agent-based approach to explore the effect of voluntary mechanisms on land use change: A case in rural Queensland, Australia
Valbuena, D.F. ; Bregt, A.K. ; McAlpine, C. ; Verburg, P.H. ; Seabrook, L. - \ 2010
Journal of Environmental Management 91 (2010)12. - ISSN 0301-4797 - p. 2615 - 2625.
cover change - stakeholder involvement - vegetation management - brigalow belt - farmers - participation - agriculture - information - simulation - feedbacks
In rural regions, land use changes (LUC) are often the result of the decision-making of individual farmers. To influence this decision-making, compulsory and voluntary mechanisms are implemented. However, farmers’ decision-making is a heterogeneous process that depends on their ability and willingness to take certain decisions. Discrepancies between farmers’ ability and willingness and the design of voluntary mechanisms occur frequently. This makes it necessary to understand how farmers’ participation in these mechanisms can affect LUC. The aim of this paper was to demonstrate an agent-based approach to analyse and explore how voluntary mechanisms can influence LUC processes in rural regions. This approach was applied to a rural region in Australia, where clearing of native vegetation has occurred for agricultural development. Historical land cover data and semi-structured interviews were used to parameterise an agent-based model. Factors that influence farmers’ ability and willingness to participate in these mechanisms were identified. Three scenarios were simulated with the model to explore how the implementation of different voluntary mechanisms can affect the landscape structure of the region. This paper identifies how the diversity of farmers’ decision-making can influence the landscape structure in the region. The advantages and limitations of an agent-based approach in relation to LUC research and policy are discussed.
The REFLEX project: Comparing different algorithms and implementations for the inversion of a terrestrial ecosystem model against eddy covariance data
Fox, A. ; Williams, M. ; Richardson, A.D. ; Cameron, D. ; Gove, J.H. ; Quaife, T. ; Ricciuto, D. ; Reichstein, M. ; Tomelleri, E. ; Trudinger, C.M. ; Wijk, M.T. van - \ 2009
Agricultural and Forest Meteorology 149 (2009)10. - ISSN 0168-1923 - p. 1597 - 1615.
parameter-estimation - data assimilation - carbon-dioxide - uncertainty - climate - forest - productivity - variability - simulation - feedbacks
We describe a model-data fusion (MDF) inter-comparison project (REFLEX), which compared various algorithms for estimating carbon (C) model parameters consistent with both measured carbon fluxes and states and a simple C model. Participants were provided with the model and with both synthetic net ecosystem exchange (NEE) of CO2 and leaf area index (LAI) data, generated from the model with added noise, and observed NEE and LAI data from two eddy covariance sites. Participants endeavoured to estimate model parameters and states consistent with the model for all cases over the two years for which data were provided, and generate predictions for one additional year without observations. Nine participants contributed results using Metropolis algorithms, Kalman filters and a genetic algorithm. For the synthetic data case, parameter estimates compared well with the true values. The results of the analyses indicated that parameters linked directly to gross primary production (GPP) and ecosystem respiration, such as those related to foliage allocation and turnover, or temperature sensitivity of heterotrophic respiration, were best constrained and characterised. Poorly estimated parameters were those related to the allocation to and turnover of fine root/wood pools. Estimates of confidence intervals varied among algorithms, but several algorithms successfully located the true values of annual fluxes from synthetic experiments within relatively narrow 90% confidence intervals, achieving >80% success rate and mean NEE confidence intervals
Uncertainties in climate responses to past land cover change: First results from the LUCID intercomparison study
Pitman, A.J. ; Noblet-Ducoudré, N. de; Cruz, F.T. ; Davin, E.L. ; Bonan, G.B. ; Brovkin, V. ; Claussen, M. ; Delire, C. ; Ganzeveld, L.N. ; Gayler, V. ; Hurk, B.J.J.M. van den; Lawrence, P.J. ; Molen, M.K. van der; Müller, C. ; Reick, C.H. ; Senevirantne, S.I. ; Strengers, B.J. ; Voldoire, A. - \ 2009
Geophysical Research Letters 36 (2009). - ISSN 0094-8276 - 6 p.
tropical deforestation - feedbacks - scale
Seven climate models were used to explore the biogeophysical impacts of human-induced land cover change (LCC) at regional and global scales. The imposed LCC led to statistically significant decreases in the northern hemisphere summer latent heat flux in three models, and increases in three models. Five models simulated statistically significant cooling in summer in near-surface temperature over regions of LCC and one simulated warming. There were few significant changes in precipitation. Our results show no common remote impacts of LCC. The lack of consistency among the seven models was due to: 1) the implementation of LCC despite agreed maps of agricultural land, 2) the representation of crop phenology, 3) the parameterisation of albedo, and 4) the representation of evapotranspiration for different land cover types. This study highlights a dilemma: LCC is regionally significant, but it is not feasible to impose a common LCC across multiple models for the next IPCC assessment
Interactions between dry-air entrainment, surface evaporation and convective boundary-layer development
Heerwaarden, C.C. van; Vilà-Guerau de Arellano, J. ; Moene, A.F. ; Holtslag, A.A.M. - \ 2009
Quarterly Journal of the Royal Meteorological Society 135 (2009)642. - ISSN 0035-9009 - p. 1277 - 1291.
equilibrium evaporation - land-surface - soil-moisture - feedbacks - dynamics - models - parameterization - sensitivity - simulations - heat
The influence of dry-air entrainment on surface heat fluxes and the convective boundary-layer (CBL) properties is studied for vegetated land surfaces, using a mixed-layer CBL model coupled to the Penman¿Monteith equation under a wide range of conditions. In order to address the complex behaviour of the system, the feedback mechanisms involved were put into a mathematical framework. Simple expressions for the evaporative fraction and the Priestley¿Taylor parameter were derived, based on the concept of equilibrium evaporation. Dry-air entrainment enhances the surface evaporation under all conditions, but the sensitivity of the evaporation rate to the moisture content of the free troposphere falls as temperature rises. Due to the evaporation enhancement, shallower CBLs develop beneath dry atmospheres. In all cases, dry-air entrainment reduces the relative humidity at the land surface and at the top of the CBL. However, because of dry-air entrainment-induced land¿atmosphere feedback mechanisms, relative humidity at the top of the CBL responds nonlinearly to temperature rise; it decreases as temperature rises beneath a moist free troposphere, whereas it increases beneath a dry free troposphere. Finally, it was found that in certain conditions the evolution of the surface fluxes, relative humidity and CBL height can be as sensitive to the free tropospheric moisture conditions as to the land-surface properties. Therefore, studies of the land surface and of convective clouds have to take into account the influence of dry-air entrainment through land¿atmosphere feedback mechanisms
Carbon and nitrogen cycles in European ecosystems respond differently to global warming
Beier, C. ; Emmett, B.A. ; Penuelas, J. ; Schmidt, I.K. ; Tietema, A. ; Estiarte, M. ; Gundersen, P. ; Llorens, L. ; Riis-Nielsen, T. ; Sowerby, A. ; Gorissen, A. - \ 2008
Science of the Total Environment 407 (2008)1. - ISSN 0048-9697 - p. 692 - 697.
climate-change - soil respiration - drought - temperature - forests - feedbacks - gradient - dioxide - impacts - plants
The global climate is predicted to become significantly warmer over the next century. This will affect ecosystem processes and the functioning of semi natural and natural ecosystems in many parts of the world. However, as various ecosystem processes may be affected to a different extent, balances between different ecosystem processes as well as between different ecosystems may shift and lead to major unpredicted changes. In this study four European shrubland ecosystems along a north¿south temperature gradient were experimentally warmed by a novel nighttime warming technique. Biogeochemical cycling of both carbon and nitrogen was affected at the colder sites with increased carbon uptake for plant growth as well as increased carbon loss through soil respiration. Carbon uptake by plant growth was more sensitive to warming than expected from the temperature response across the sites while carbon loss through soil respiration reacted to warming in agreement with the overall Q10 and response functions to temperature across the sites. Opposite to carbon, the nitrogen mineralization was relatively insensitive to the temperature increase and was mainly affected by changes in soil moisture. The results suggest that C and N cycles respond asymmetrically to warming, which may lead to progressive nitrogen limitation and thereby acclimation in plant production. This further suggests that in many temperate zones nitrogen deposition has to be accounted for, not only with respect to the impact on water quality through increased nitrogen leaching where N deposition is high, but also in predictions of carbon sequestration in terrestrial ecosystems under future climatic conditions. Finally the results indicate that on the short term the above-ground processes are more sensitive to temperature changes than the below ground processes