Publications
433 results found
Kelley DI, Harrison SP, Prentice IC, 2014, Improved simulation of fire-vegetation interactions in the Land surface Processes and eXchanges dynamic global vegetation model (LPX-Mv1), Geoscientific Model Development, Vol: 7, Pages: 2411-2433, ISSN: 1991-959X
The Land surface Processes and eXchanges (LPX) model is a fire-enabled dynamic global vegetation model that performs well globally but has problems representing fire regimes and vegetative mix in savannas. Here we focus on improving the fire module. To improve the representation of ignitions, we introduced a reatment of lightning that allows the fraction of ground strikes to vary spatially and seasonally, realistically partitions strike distribution between wet and dry days, and varies the number of dry days with strikes. Fuel availability and moisture content were improved by implementing decomposition rates specific to individual plant functional types and litter classes, and litter drying rates driven by atmospheric water content. To improve water extraction by grasses, we use realistic plant-specific treatments of deep roots. To improve fire responses, we introduced adaptive bark thickness and post-fire resprouting for tropical and temperate broadleaf trees. All improvements are based on extensive analyses of relevant observational data sets. We test model performance for Australia, first evaluating parameterisations separately and then measuring overall behaviour against standard benchmarks. Changes to the lightning parameterisation produce a more realistic simulation of fires in southeastern and central Australia. Implementation of PFT-specific decomposition rates enhances performance in central Australia. Changes in fuel drying improve fire in northern Australia, while changes in rooting depth produce a more realistic simulation of fuel availability and structure in central and northern Australia. The introduction of adaptive bark thickness and resprouting produces more realistic fire regimes in Australian savannas. We also show that the model simulates biomass recovery rates consistent with observations from several different regions of the world characterised by resprouting vegetation. The new model (LPX-Mv1) produces an improved simulation of observed vege
Zhou S, Medlyn B, Sabate S, et al., 2014, Short-term water stress impacts on stomatal, mesophyll and biochemical limitations to photosynthesis differ consistently among tree species from contrasting climates, Tree Physiology, Vol: 34, Pages: 1035-1046, ISSN: 1758-4469
Predicting the large-scale consequences of drought in contrasting environments requires that we understand how drought effects differ among species originating from those environments. A previous meta-analysis of published experiments suggested that the effects of drought on both stomatal and non-stomatal limitations to photosynthesis may vary consistently among species from different hydroclimates. Here, we explicitly tested this hypothesis with two short-term water stress experiments on congeneric mesic and xeric species. One experiment was run in Australia using Eucalyptus species and the second was run in Spain using Quercus species as well as two more mesic species. In each experiment, plants were grown under moist conditions in a glasshouse, then deprived of water, and gas exchange was monitored. The stomatal response was analysed with a recently developed stomatal model, whose single parameter g1 represents the slope of the relationship between stomatal conductance and photosynthesis. The non-stomatal response was partitioned into effects on mesophyll conductance (gm), the maximum Rubisco activity (Vcmax) and the maximum electron transport rate (Jmax). We found consistency among the drought responses of g1, gm, Vcmax and Jmax, suggesting that drought imposes limitations on Rubisco activity and RuBP regeneration capacity concurrently with declines in stomatal and mesophyll conductance. Within each experiment, the more xeric species showed relatively high g1 under moist conditions, low drought sensitivity of g1, gm, Vcmax and Jmax, and more negative values of the critical pre-dawn water potential at which Vcmax declines most steeply, compared with the more mesic species. These results indicate adaptive interspecific differences in drought responses that allow xeric tree species to continue transpiration and photosynthesis for longer during periods without rain.
Dani KGS, Jamie IM, Prentice IC, et al., 2014, Increased Ratio of Electron Transport to Net Assimilation Rate Supports Elevated Isoprenoid Emission Rate in Eucalypts under Drought, PLANT PHYSIOLOGY, Vol: 166, Pages: 1059-1072, ISSN: 0032-0889
- Author Web Link
- Cite
- Citations: 22
Prentice IC, Liang X, Medlyn BE, et al., 2014, Reliable, robust and realistic: The three R's of next-generation land surface modelling, Atmospheric Chemistry and Physics Discussions, Vol: 14, Pages: 24811-24861, ISSN: 1680-7367
Land surface models (LSMs) are increasingly called upon to represent not only the exchanges of energy, water and momentum across the land-atmosphere interface (their original purpose in climate models), but also how ecosystems and water resources respond to climate and atmospheric environment, and how these responses in turn influence land-atmosphere fluxes of carbon dioxide (CO2), trace gases and other species that affect the composition and chemistry of the atmosphere. However, the LSMs embedded in state-of-the-art climate models differ in how they represent fundamental aspects of the hydrological and carbon cycles, resulting in large inter-model differences and sometimes faulty predictions. These "third-generation" LSMs respect the close coupling of the carbon and water cycles through plants, but otherwise tend to be under-constrained, and have not taken full advantage of robust hydrological parameterizations that were independently developed in offline models. Benchmarking, combining multiple sources of atmospheric, biospheric and hydrological data, should be a required component of LSM development, but this field has been relatively poorly supported and intermittently pursued. Moreover, benchmarking alone is not sufficient to ensure that models improve. Increasing complexity may increase realism but decrease reliability and robustness, by increasing the number of poorly known model parameters. In contrast, simplifying the representation of complex processes by stochastic parameterization (the representation of unresolved processes by statistical distributions of values) has been shown to improve model reliability and realism in both atmospheric and land-surface modelling contexts. We provide examples for important processes in hydrology (the generation of runoff and flow routing in heterogeneous catchments) and biology (carbon uptake by species-diverse ecosystems). We propose that the way forward for next-generation complex LSMs will include: (a) repr
Bistinas I, Harrison SP, Prentice IC, et al., 2014, Causal relationships versus emergent patterns in the global controls of fire frequency, Biogeosciences, Vol: 11, Pages: 5087-5101, ISSN: 1726-4170
Global controls on month-by-month fractional burnt area (2000–2005) were investigated by fitting a generalised linear model (GLM) to Global Fire Emissions Database (GFED) data, with 11 predictor variables representing vegetation, climate, land use and potential ignition sources. Burnt area is shown to increase with annual net primary production (NPP), number of dry days, maximum temperature, grazing-land area, grass/shrub cover and diurnal temperature range, and to decrease with soil moisture, cropland area and population density. Lightning showed an apparent (weak) negative influence, but this disappeared when pure seasonal-cycle effects were taken into account. The model predicts observed geographic and seasonal patterns, as well as the emergent relationships seen when burnt area is plotted against each variable separately. Unimodal relationships with mean annual temperature and precipitation, population density and gross domestic product (GDP) are reproduced too, and are thus shown to be secondary consequences of correlations between different controls (e.g. high NPP with high precipitation; low NPP with low population density and GDP). These findings have major implications for the design of global fire models, as several assumptions in current models – most notably, the widely assumed dependence of fire frequency on ignition rates – are evidently incorrect.
Harrison SP, Bartlein PJ, Brewer S, et al., 2014, Climate model benchmarking with glacial and mid-Holocene climates, CLIMATE DYNAMICS, Vol: 43, Pages: 671-688, ISSN: 0930-7575
- Author Web Link
- Cite
- Citations: 149
Morfopoulos C, Sperlich D, Penuelas J, et al., 2014, A model of plant isoprene emission based on available reducing power captures responses to atmospheric CO2, New Phytologist, Vol: 203, Pages: 125-139, ISSN: 0028-646X
We present a unifying model for isoprene emission by photosynthesizing leaves based on the hypothesis that isoprene biosynthesis depends on a balance between the supply of photosynthetic reducing power and the demands of carbon fixation.We compared the predictions from our model, as well as from two other widely used models, with measurements of isoprene emission from leaves of Populus nigra and hybrid aspen (Populus tremula × P. tremuloides) in response to changes in leaf internal CO2 concentration (Ci) and photosynthetic photon flux density (PPFD) under diverse ambient CO2 concentrations (Ca).Our model reproduces the observed changes in isoprene emissions with Ci and PPFD, and also reproduces the tendency for the fraction of fixed carbon allocated to isoprene to increase with increasing PPFD. It also provides a simple mechanism for the previously unexplained decrease in the quantum efficiency of isoprene emission with increasing Ca.Experimental and modelled results support our hypothesis. Our model can reproduce the key features of the observations and has the potential to improve process‐based modelling of isoprene emissions by land vegetation at the ecosystem and global scales.
Foster PN, Prentice IC, Morfopoulos C, et al., 2014, Isoprene emissions track the seasonal cycle of canopy temperature, not primary production: evidence from remote sensing, Biogeosciences, Vol: 11, Pages: 3437-3451, ISSN: 1726-4170
Isoprene is important in atmospheric chemistry, but its seasonal emission pattern – especially in the tropics, where most isoprene is emitted – is incompletely understood. We set out to discover generalized relationships applicable across many biomes between large-scale isoprene emission and a series of potential predictor variables, including both observed and model-estimated variables related to gross primary production (GPP) and canopy temperature. We used remotely sensed atmospheric concentrations of formaldehyde, an intermediate oxidation product of isoprene, as a proxy for isoprene emission in 22 regions selected to span high to low latitudes, to sample major biomes, and to minimize interference from pyrogenic sources of volatile organic compounds that could interfere with the isoprene signal. Formaldehyde concentrations showed the highest average seasonal correlations with remotely sensed (r = 0.85) and model-estimated (r = 0.80) canopy temperatures. Both variables predicted formaldehyde concentrations better than air temperature (r= 0.56) and a "reference" isoprene model that combines GPP and an exponential function of temperature (r = 0.49), and far better than either remotely sensed green vegetation cover, fPAR (r = 0.25) or model-estimated GPP (r = 0.14). Gross primary production in tropical regions was anti-correlated with formaldehyde concentration (r = −0.30), which peaks during the dry season. Our results were most reliable in the tropics, where formaldehyde observational errors were the least. The tropics are of particular interest because they are the greatest source of isoprene emission as well as the region where previous modelling attempts have been least successful. We conjecture that positive correlations of isoprene emission with GPP and air temperature (as found in temperate forests) may arise simply because both covary with canopy temperature, peaking during the relatively short growing season. The lack of a gener
Dani KGS, Jamie IM, Prentice IC, et al., 2014, Evolution of isoprene emission capacity in plants, TRENDS IN PLANT SCIENCE, Vol: 19, Pages: 439-446, ISSN: 1360-1385
- Author Web Link
- Cite
- Citations: 43
De Kauwe MG, Medlyn BE, Zaehle S, et al., 2014, Where does the carbon go? A model-data intercomparison of vegetation carbon allocation and turnover processes at two temperate forest free-air CO2 enrichment sites, NEW PHYTOLOGIST, Vol: 203, Pages: 883-899, ISSN: 0028-646X
Elevated atmospheric CO2concentration (eCO2) has the potential to increase vegetationcarbon storage if increased net primary production causes increased long-lived biomass.Model predictions of eCO2effects on vegetation carbon storage depend on how allocationand turnover processes are represented. We used data from two temperate forest free-air CO2enrichment (FACE) experiments toevaluate representations of allocation and turnover in 11 ecosystem models. Observed eCO2effects on allocation were dynamic. Allocation schemes based on func-tional relationships among biomass fractions that vary with resource availability were best ableto capture the general features of the observations. Allocation schemes based on constantfractions or resource limitations performed less well, with some models having unintendedoutcomes. Few models represent turnover processes mechanistically and there was wide vari-ation in predictions of tissue lifespan. Consequently, models did not perform well at predictingeCO2effects on vegetation carbon storage. Our recommendations to reduce uncertainty include: use of allocation schemes constrainedby biomass fractions; careful testing of allocation schemes; and synthesis of allocation andturnover data in terms of model parameters. Data from intensively studied ecosystem manip-ulation experiments are invaluable for constraining models and we recommend that suchexperiments should attempt to fully quantify carbon, water and nutrient budgets.
Walker AP, Hanson PJ, De Kauwe MG, et al., 2014, Comprehensive ecosystem model-data synthesis using multiple data sets at two temperate forest free-air CO2 enrichment experiments: Model performance at ambient CO2 concentration, Journal of Geophysical Research: Biogeosciences, Vol: 119, Pages: 937-964, ISSN: 2169-8961
Free‐air CO2 enrichment (FACE) experiments provide a remarkable wealth of data which can be used to evaluate and improve terrestrial ecosystem models (TEMs). In the FACE model‐data synthesis project, 11 TEMs were applied to two decadelong FACE experiments in temperate forests of the southeastern U.S.—the evergreen Duke Forest and the deciduous Oak Ridge Forest. In this baseline paper, we demonstrate our approach to model‐data synthesis by evaluating the models' ability to reproduce observed net primary productivity (NPP), transpiration, and leaf area index (LAI) in ambient CO2 treatments. Model outputs were compared against observations using a range of goodness‐of‐fit statistics. Many models simulated annual NPP and transpiration within observed uncertainty. We demonstrate, however, that high goodness‐of‐fit values do not necessarily indicate a successful model, because simulation accuracy may be achieved through compensating biases in component variables. For example, transpiration accuracy was sometimes achieved with compensating biases in leaf area index and transpiration per unit leaf area. Our approach to model‐data synthesis therefore goes beyond goodness‐of‐fit to investigate the success of alternative representations of component processes. Here we demonstrate this approach by comparing competing model hypotheses determining peak LAI. Of three alternative hypotheses—(1) optimization to maximize carbon export, (2) increasing specific leaf area with canopy depth, and (3) the pipe model—the pipe model produced peak LAI closest to the observations. This example illustrates how data sets from intensive field experiments such as FACE can be used to reduce model uncertainty despite compensating biases by evaluating individual model assumptions.
Zaehle S, Medlyn BE, De Kauwe MG, et al., 2014, Evaluation of 11 terrestrial carbon-nitrogen cycle models against observations from two temperate Free-Air CO<sub>2</sub> Enrichment studies, NEW PHYTOLOGIST, Vol: 202, Pages: 803-822, ISSN: 0028-646X
- Author Web Link
- Open Access Link
- Cite
- Citations: 290
Bistinas I, Oom D, Sa ACL, et al., 2013, Relationships between Human Population Density and Burned Area at Continental and Global Scales, PLOS ONE, Vol: 8, ISSN: 1932-6203
We explore the large spatial variation in the relationship between population density and burned area, usingcontinental-scale Geographically Weighted Regression (GWR) based on 13 years of satellite-derived burned areamaps from the global fire emissions database (GFED) and the human population density from the gridded populationof the world (GPW 2005). Significant relationships are observed over 51.5% of the global land area, and the areaaffected varies from continent to continent: population density has a significant impact on fire over most of Asia andAfrica but is important in explaining fire over < 22% of Europe and Australia. Increasing population density isassociated with both increased and decreased in fire. The nature of the relationship depends on land-use: increasingpopulation density is associated with increased burned are in rangelands but with decreased burned area incroplands. Overall, the relationship between population density and burned area is non-monotonic: burned areainitially increases with population density and then decreases when population density exceeds a threshold. Thesethresholds vary regionally. Our study contributes to improved understanding of how human activities relate to burnedarea, and should contribute to a better estimate of atmospheric emissions from biomass burning.
Prentice IC, Dong N, Gleason SM, et al., 2013, Balancing the costs of carbon gain and water transport: testing a new theoretical framework for plant functional ecology, Ecology Letters, Vol: 17, Pages: 82-91, ISSN: 1461-023X
A novel framework is presented for the analysis of ecophysiological field measurements and modelling. The hypothesis ‘leaves minimise the summed unit costs of transpiration and carboxylation’ predicts leaf‐internal/ambient CO2 ratios (ci/ca) and slopes of maximum carboxylation rate (Vcmax) or leaf nitrogen (Narea) vs. stomatal conductance. Analysis of data on woody species from contrasting climates (cold‐hot, dry‐wet) yielded steeper slopes and lower mean ci/ca ratios at the dry or cold sites than at the wet or hot sites. High atmospheric vapour pressure deficit implies low ci/ca in dry climates. High water viscosity (more costly transport) and low photorespiration (less costly photosynthesis) imply low ci/ca in cold climates. Observed site‐mean ci/ca shifts are predicted quantitatively for temperature contrasts (by photorespiration plus viscosity effects) and approximately for aridity contrasts. The theory explains the dependency of ci/ca ratios on temperature and vapour pressure deficit, and observed relationships of leaf δ13C and Narea to aridity.
Zhou S, Duursma RA, Medlyn BE, et al., 2013, How should we model plant responses to drought? An analysis of stomatal and non-stomatal responses to water stress, AGRICULTURAL AND FOREST METEOROLOGY, Vol: 182, Pages: 204-214, ISSN: 0168-1923
- Author Web Link
- Cite
- Citations: 202
Medlyn BE, Duursma RA, De Kauwe MG, et al., 2013, The optimal stomatal response to atmospheric CO<sub>2</sub> concentration: Alternative solutions, alternative interpretations, AGRICULTURAL AND FOREST METEOROLOGY, Vol: 182, Pages: 200-203, ISSN: 0168-1923
- Author Web Link
- Cite
- Citations: 35
Morfopoulos C, Prentice IC, Keenan TF, et al., 2013, A unifying conceptual model for the environmental responses of isoprene emissions from plants, ANNALS OF BOTANY, Vol: 112, Pages: 1223-1238, ISSN: 0305-7364
Background and AimsIsoprene is the most important volatile organic compound emitted by land plants in terms ofabundance and environmental effects. Controls on isoprene emission rates include light, temperature, water supplyand CO2concentration. A need to quantify these controls has long been recognized. There are already models thatgive realistic results, but they are complex, highly empirical and require separate responses to different drivers.This study sets out to find a simpler, unifying principle.†MethodsA simple model is presented based on the idea of balancing demands for reducing power (derived fromphotosynthetic electron transport) in primary metabolism versus the secondary pathway that leads to the synthesisof isoprene. This model’s ability to account for key features in a variety of experimental data sets is assessed.†Key resultsThe model simultaneously predicts the fundamental responses observed in short-term experiments,namely: (1) the decoupling between carbon assimilation and isoprene emission; (2) a continued increase in isopreneemission with photosynthetically active radiation (PAR) at high PAR, after carbon assimilation has saturated; (3) amaximum of isoprene emission at low internal CO2concentration (ci) and an asymptotic decline thereafter with in-creasingci; (4) maintenance of high isoprene emissions when carbon assimilation is restricted by drought; and (5) atemperature optimum higher than that of photosynthesis, but lower than that of isoprene synthase activity.†ConclusionsA simple model was used to test the hypothesisthat reducing poweravailable to the synthesis pathwayfor isoprene varies according to the extent to which the needs of carbon assimilation are satisfied. Despite its simpli-city the model explains much in terms of the observed response of isoprene to external drivers as well asthe observeddecoupling between carbon assimilation and isoprene emission. The concept has the potential to improve global-scale
Mackey B, Prentice IC, Steffen W, et al., 2013, Untangling the confusion around land carbon science and climate change mitigation policy (vol 3, pg 552, 2013), NATURE CLIMATE CHANGE, Vol: 3, Pages: 847-847, ISSN: 1758-678X
Li G, Harrison SP, Bartlein PJ, et al., 2013, Precipitation scaling with temperature in warm and cold climates: An analysis of CMIP5 simulations, GEOPHYSICAL RESEARCH LETTERS, Vol: 40, Pages: 4018-4024, ISSN: 0094-8276
- Author Web Link
- Cite
- Citations: 42
Stocker BD, Roth R, Joos F, et al., 2013, Multiple greenhouse-gas feedbacks from the land biosphere under future climate change scenarios, NATURE CLIMATE CHANGE, Vol: 3, Pages: 666-672, ISSN: 1758-678X
- Author Web Link
- Cite
- Citations: 159
Mackey B, Prentice IC, Steffen W, et al., 2013, Untangling the confusion around land carbon science and climate change mitigation policy, NATURE CLIMATE CHANGE, Vol: 3, Pages: 552-557, ISSN: 1758-678X
- Author Web Link
- Cite
- Citations: 145
De Kauwe MG, Medlyn BE, Zaehle S, et al., 2013, Forest water use and water use efficiency at elevated CO2: a model-data intercomparison at two contrasting temperate forest FACE sites, GLOBAL CHANGE BIOLOGY, Vol: 19, Pages: 1759-1779, ISSN: 1354-1013
- Author Web Link
- Cite
- Citations: 267
Murray SJ, Watson IM, Prentice IC, 2013, The use of dynamic global vegetation models for simulating hydrology and the potential integration of satellite observations, PROGRESS IN PHYSICAL GEOGRAPHY-EARTH AND ENVIRONMENT, Vol: 37, Pages: 63-97, ISSN: 0309-1333
- Author Web Link
- Cite
- Citations: 34
Gallego-Sala AV, Prentice IC, 2013, Blanket peat biome endangered by climate change, NATURE CLIMATE CHANGE, Vol: 3, Pages: 152-155, ISSN: 1758-678X
- Author Web Link
- Cite
- Citations: 106
Prentice IC, Cowling SA, 2013, Dynamic Global Vegetation Models, Encyclopedia of Biodiversity: Second Edition, Pages: 670-689, ISBN: 9780123847201
Dynamic global vegetation models encapsulate our knowledge of plant and ecosystem function. They have many potential applications but not all of these are well developed, and large differences among model predictions are a concern. Fields of application include analysis of land-atmosphere biophysical interactions, carbon and water cycling, climate impacts on vegetation structure, fire, atmospheric trace gas composition, Quaternary vegetation and environmental changes, and ecosystem structure and function through Earth history. There is scope to improve models using a wider range of information from plant functional ecology, ecophysiology, environmental remote sensing, and atmospheric measurement, Quaternary paleoecology, and paleobotany.
Harrison SP, Morfopoulos C, Dani KGS, et al., 2013, Volatile isoprenoid emissions from plastid to planet, NEW PHYTOLOGIST, Vol: 197, Pages: 49-57, ISSN: 0028-646X
- Author Web Link
- Cite
- Citations: 121
Foley AM, Dalmonech D, Friend AD, et al., 2013, Evaluation of biospheric components in Earth system models using modern and palaeo-observations: the state-of-the-art, BIOGEOSCIENCES, Vol: 10, Pages: 8305-8328, ISSN: 1726-4170
- Author Web Link
- Cite
- Citations: 8
Ukkola AM, Prentice IC, 2013, A worldwide analysis of trends in water-balance evapotranspiration, HYDROLOGY AND EARTH SYSTEM SCIENCES, Vol: 17, Pages: 4177-4187, ISSN: 1027-5606
- Author Web Link
- Cite
- Citations: 53
Wang H, Prentice IC, Ni J, 2013, Data-based modelling and environmental sensitivity of vegetation in China, BIOGEOSCIENCES, Vol: 10, Pages: 5817-5830, ISSN: 1726-4170
- Author Web Link
- Cite
- Citations: 24
Kelley DI, Prentice IC, Harrison SP, et al., 2013, A comprehensive benchmarking system for evaluating global vegetation models, BIOGEOSCIENCES, Vol: 10, Pages: 3313-3340, ISSN: 1726-4170
- Author Web Link
- Cite
- Citations: 102
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.