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Andrew D. Friend BSc PhD

Reader in Earth Systems Science and Fellow of Clare College


Andrew Friend's research interests concern controls on terrestrial vegetation type, structure, and productivity over a wide range of time and space scales and the effects of vegetation on atmospheric processes through land surface energy partitioning and carbon fluxes. He develops numerical models in order to test our understanding of processes through the ability of these models to faithfully simulate real-world phenomena, as well as address concerns regarding the effects of global change on terrestrial ecosystems and potential future atmospheric feedbacks. He continues to develop an individual-based model of vegetation dynamics, HYBRID, with the aim of producing processed-based representations of land surface processes for coupling to global-scale atmospheric models. His current work is particularly concerned with the representation of physiological differences between plant types and species, the representation of competition, and the global-scale dynamics of biogeochemistry-climate interactions.

PhD supervision

I welcome the opportunity to supervise PhD students who wish to work on modelling and observations in the areas of plant physiology, ecosystem dynamics, global biogeochemical cycles (especially the global carbon cycle), and/or climate systems, especially where one or more of these elements are coupled.

An example of a possible topic is shown at the end of this page, but many other topics are of equal interest.


(Google scholar)

Peer-reviewed publications

[51] Huber, V, Schellnhuber, HJ, Arnell, NW, Frieler, K, Friend, AD, Gerten, D, Haddeland, I, Kabat, P, Lotze-Campen, H, Lucht, W, Parry, M, Piontek, F, Rosenzweig, C, Schewe, J, and Warszawski, L: Climate impacts research: beyond patchwork, Earth Syst. Dynam. Discuss., 5, 721-746, doi:10.5194/esdd-5-721-2014, 2014.

[50] O'Shea, SJ, Allen G, Gallagher, MW, Bower K, Illingworth, SM, Muller, JBA, Jones B, Percival, CJ, Bauguitte SJ-B, Cain M, Warwick N, Quiquet A, Skiba U, Drewer J, Dinsmore K, Nisbet EG, Lowry D, Fisher RE, France JL, Aurela M, Lohila A, Hayman G, George C, Clark D, Manning AJ, Friend AD, Pyle J. Methane and carbon dioxide fluxes and their regional scalability for the European Arctic wetlands during the MAMM project in summer 2012. 2014. Atmospheric Chemistry and Physics Discussions, 14, 8455-8494, doi:10.5194/acpd-14-8455-2014

[49] Nishina K, Ito A, Beerling DJ, Cadule P, Ciais P, Clark DB, Falloon P, Friend AD, Kahana R, Kato E, Keribin R, Lucht W, Lomas M, Rademacher TT, Pavlick R, Schaphoff S, Vuichard N, Warszawaski L, Yokohata T. 2014. Quantifying uncertainties in soil carbon responses to changes in global mean temperature and precipitation. Earth System Dynamics 5, 197-209, doi:10.5194/esd-5-197-2014

[48] Foley AM, Willeit M, Brovkin V, Feulner G, Friend AD. 2014. Quantifying the global carbon response to volcanic stratospheric aerosol radiative forcing using Earth System Models. Journal of Geophysical Research: Atmospheres 119, 1-11, doi:10.1002/2013JD019724

[47] Friend AD, Lucht W, Rademacher TT, Keribin R, Betts R, Cadule P, Ciais P, Clark DB, Dankers R, Falloon PD, Ito A, Kahana R, Kleidon A, Lomas MR, Nishina K, Sebastian Ostberg S, RPavlick R, Peylin P, Schaphoff S, Vuichard N, Warszawski L, Wiltshire A, Woodward FI. 2013. Carbon residence time dominates uncertainty in terrestrial vegetation responses to future climate and atmospheric CO2. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1222477110

[46] Foley AM, Dalmonech D, Friend AD, Aires F, Archibald A, Bartlein P, Bopp L, Chappellaz J, Cox P, Edwards NR, Feulner G, Friedlingstein P, Harrison SP, Hopcroft PO, Jones CD, Kolassa J, Levine JG, Prentice IC, Pyle J, Vázquez Riveiros N, Wolff EW, Zaehle S. 2013. Evaluation of biospheric components in Earth system models using modern and palaeo observations: the state-of-the-art. Biogeosciences 10, 8305-8328, doi:10.5194/bg-10-8305-2013

[45] Piontek, F, Müller C, Pugh TAM, Clark DB, Deryng D, Elliott J, Colón-González FJ, Flörke M, Folberth C, Franssen W, Frieler K, Friend AD, Gosling SN, Hemming D, Khabarov N, Kim H, Lomas MR, Masaki Y, Mengel M, Morse A, Neumann K, Nishina K, Ostberg S, Pavlick R, Ruane AC, Schewe J, Schmid E, Stacke T, Tang Q, Tessler ZD, Tompkins AM, Warszawski L, Wisser D, Schellnhuber HJ. 2013. Multi-sectoral climate impact hotspots in a warming world. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1222471110

[44] Warszawski L, Friend A, Ostberg S, Frieler K, Lucht W, Schaphoff S, Beerling D, Cadule P, Ciais P, Clark DB, Kahana R, Ito A, Keribin R, Kleidon A, Lomas M, Nishina K, Pavlick R, Rademacher TT, Buechner M, Piontek F, Schewe J, Serdeczny O, Schellnhuber HJ. 2013. A multi-model analysis of risk of ecosystem shifts under climate change. Environmental Research Letters 8, 044018 doi:10.1088/1748-9326/8/4/044018

[43] Eriksson A, Betti L, Friend AD, Lycett SJ, Singarayer JS, von Cramon-Taubadel N, Valdes PJ, Balloux F, Manica A. Late Pleistocene climate change and the global expansion of anatomically modern humans. Proceedings of the National Academy of Sciences, published ahead of print September 17, 2012, doi:10.1073/pnas.1209494109

[42] Marthews TR, Malhi Y, Girardin CAJ, Silva Espejo JE, Aragão LEO, Metcalfe DB, Rapp JM, Mercado LM, Fisher RA, Galbraith DR, Fisher JB, Salinas-Revilla N, Friend AD, Restrepo-Coupe N, Williams RJ. 2012. Simulating forest productivity along a neotropical elevational transect: temperature variation and carbon use efficiency. Global Change Biology 18, 2882-2898, doi:10.1111/j.1365-2486.2012.02728.x

[41] Gerken T, Babel W, Hoffmann A, Biermann T, Herzog M, Friend AD, Li M, Ma Y, Foken T, Graf H-F. 2012 Turbulent flux modelling with a simple 2-layer soil model and extrapolated surface temperature applied at Nam Co Lake basin on the Tibetan Plateau. Hydrology and Earth System Sciences, 16, 1095-1110, doi:10.5194/hess-16-1095-2012

[40] Friend AD. 2011. Response of Earth's surface temperature to radiative forcing over AD 1-2009. Journal of Geophysical Research - Atmospheres 116, D13112, doi:10.1029/2010JD015143

[39] Zaehle S, Ciais P, Friend AD, Prieur V. 2011. Carbon benefits of anthropogenic reactive nitrogen offset by nitrous oxide emissions. Nature Geoscience 4, 601-605, doi:10.1038/ngeo1207

[38] Durant A, Le Quéré C, Hope C, Friend AD. 2011. Economic value of improved quantification in global sources and sinks of carbon dioxide. Philosophical Transactions of The Royal Society A 369, 1967-1979, doi:10.1098/rsta.2011.0002

[37] Friend AD. 2010. Terrestrial plant production and climate change. Journal of Experimental Botany 61, 1293-1309, doi:10.1093/jxb/erq019

[36] Zaehle S, Friend AD. 2010. Carbon and nitrogen cycle dynamics in the O-CN land surface model: 1. Model description, site-scale evaluation, and sensitivity to parameter estimates. Global Biogeochemical Cycles, 24, GB1005, doi:10.1029/2009GB003521

[35] Zaehle S, Friedlingstein P, Friend AD. 2010. Terrestrial nitrogen feedbacks may accelerate future climate change. Geophysical Research Letters, 37, L01401, doi:10.1029/2009GL041345 ; see also Editor's Highlight

[34] Zaehle S, Friend AD, Friedlingstein P, Dentener F, Peylin P, Schulz M. 2010. Carbon and nitrogen cycle dynamics in the O-CN land surface model: 2. Role of the nitrogen cycle in the historical terrestrial carbon balance. Global Biogeochemical Cycles, 24, GB1006, doi:10.1029/2009GB003522

[33] Keenan T, García R, Friend AD, Zaehle S, Gracia C, Sabate S. 2009. Improved understanding of drought controls on seasonal variation in Mediterranean forest canopy CO2 and water fluxes through combined in situ measurements and ecosystem modelling. Biogeosciences 6, 1423-1444.

[32] Demarty J, Chevallier F, Friend AD, Viovy N, Piao S, Ciais P 2007. Assimilation of global MODIS leaf area index retrievals within a terrestrial biosphere model. Geophysical Research Letters 34, L15402, doi:10.1029/2007GL030014

[31] Friend, A.D., Arneth, A., Kiang, N.Y., Lomas, M., Ogée, J., Rödenbeck, C., Running, S.W., Santaren, D., Sitch, S., Viovy, N., Woodward, F.I., and Zaehle, S. 2007. FLUXNET and modelling the global carbon cycle. Global Change Biology 13, 610-633, doi:10.1111/j.1365-2486.2006.01223.x.

[30] Hansen, J., Sato, Mki., Ruedy, R., Kharecha, P., Lacis, A., Miller, R.L., Nazarenko, K., Lo, K., Schmidt, G.A., Russell, G., Aleinov, I., Bauer, S., Baum, E., Cairns, B., Canuto, V., Chandler, M., Cheng, Y., Cohen, A., Del Genio, A., Faluvegi, G., Fleming, E., Friend, A., and 25 co-authors. 2007. Climate simulations for 1880-2003 with GISS modelE. Climate Dynamics 29, 661-696. doi:10.1007/s00382-007-0255-8.

[29] Hansen, J., Sato, Mki., Ruedy, R., Kharecha, P., Lacis, A., Miller, R.L., Nazarenko, L., Lo, K., Schmidt, G.A., Russell, G., Aleinov, I., Bauer, S., Baum, E., Cairns, B., Canuto, V., Chandler, M., Cheng, Y., Cohen, A., Del Genio, A., Faluvegi, G., Fleming, E., Friend, A., and 25 co-authors. 2007. Dangerous human-made interference with climate: A GISS modelE study. Atmospheric Chemistry and Physics 7, 2287-2312,

[28] Schmidt, G. A., Ruedy, R., Hansen, J. E., Aleinov, I., Bell, N., Bauer, M., Bauer, S., Cairns, B., Cheng, Y., DelGenio, A., Faluvegi, G., Friend, A.D., and 23 co-authors. 2006. Present day atmospheric simulations using GISS ModelE: Comparison to in-situ, satellite and reanalysis data. Journal of Climate 19, 153-192, doi:10.1175/JCLI3612.1.

[27] Ciais, P., Reichstein, M, Viovy, N., Granier, A., Ogée, J., Allard, V., Aubinet, M., Buchmann, N., Bernhofer, Chr., Carrara, A., Chevallier, F., De Noblet, N., Friend, A.D., and 20 co-authors. 2005. European-wide reduction in primary productivity caused by heat and drought in 2003. Nature 437, 529-533. doi:10.1038/nature03972.

[26] Friend, A.D. and Kiang, N.Y. 2005. Land-surface model development for the GISS GCM: Effects of improved canopy physiology on simulated climate. Journal of Climate 18, 2883-2902, doi:10.1175/JCLI3425.1.

[25] Hansen, J., Sato, Mki., Ruedy, R., Nazarenko, L., Lacis, A., Schmidt, G.A., Russell, G., Aleinov, A., Bauer, M., Bauer, S., Bell, N., Cairns, B., Canuto, V., Chandler, M., Cheng, Y., Del Genio, T., Faluvegi, G., Fleming, E., Friend, A., and 26 co-authors. 2005. Efficacy of climate forcings. Journal of Geophysical Research 110, D18104, doi:1029/2005JD005776.

[24] Lathière, J., Hauglustaine, D.A., Friend, A.D., De Noblet-Ducoudré, N., Viovy, N., Folberth, G. 2005. Impact of climate variability and land use change on global biogenic volatile organic compounds emissions. Atmospheric Chemistry and Physics 6, 2129-2146,

[23] Levy, P.E., Friend, A.D., White, A., and Cannell, M.G.R. 2004. The influence of land use change on global-scale fluxes of carbon from terrestrial ecosystems. Climatic Change 67(2-3), 185-209, doi:10.1007/s10584-004-2849-z.

[22] Levy, P.E., Cannell, M.G.R., and Friend, A.D. 2004. Modelling the impact of future changes in climate, CO2 concentration and land use on natural ecosystems and the terrestrial carbon sink. Global Environmental Change 14(1), 21-30, doi:10.1016/j.gloenvcha.2003.10.005.

[21] Cramer, W., Bondeau, A., Woodward, F.I., Prentice, I.C., Betts, R.A., Brovkin, V., Cox, P.M., Fisher, V., Foley, J., Friend, A.D., and 7 co-authors. 2001. Global response of terrestrial ecosystem structure and function to CO2 and climate change: results from six dynamic global vegetation models. Global Change Biology 7, 357-373, doi:10.1046/j.1365-2486.2001.00383.x

[20] Friend, A.D. 2001. Modelling canopy CO2 fluxes: are 'big-leaf' simplifications justified? Global Ecology and Biogeography 10, 603-619, 10.1046/j.1466-822x.2001.00268.x

[19] Wullschleger, S.D., Jackson, R.B., Currie, W.S., Friend, A.D., Luo, Y., Mouillot, F., Pan, Y., Shao, G. 2001. Below-ground processes in gap models for simulating forest response to global change. Climatic Change 51, 449-473, 10.1023/A:1012570821241.

[18] Friend, A.D. and White, A. 2000. Evaluation and analysis of a dynamic terrestrial ecosystem model under preindustrial conditions at the global scale. Global Biogeochemical Cycles 14(4), 1173-1190.

[17] Murray, M.B., Smith, R.I., Friend, A., and Jarvis, P.G. 2000. Effect of elevated [CO2] and varying nutrient application rates on physiology and biomass accumulation of Sitka spruce (Picea sitchensis). Tree Physiology 20(7), 421-434.

[16] White, A., Cannell, M.G.R., and Friend, A.D. 2000. CO2 stabilization, climate change and the terrestrial carbon sink. Global Change Biology 6, 817-833, doi:10.1046/j.1365-2486.2000.00358.x

[15] White, A., Cannell, M.G.R., and Friend, A.D. 2000. The high-latitude terrestrial carbon sink: a model analysis. Global Change Biology 6, 227-245, doi:10.1046/j.1365-2486.2000.00302.x

[14] White, A., Cannell, M.G.R., and Friend, A.D. 1999. Climate change impacts on ecosystems and the terrestrial carbon sink: a new assessment. Global Environmental Change 9, S21-S30.

[13] Cannell, M.G.R., Thornley, J.H.M., Mobbs, D.C., Friend, A.D. 1998. UK conifer forests may be growing faster in response to increased N deposition, atmospheric CO2 and temperature. Forestry 71, 277-296.

[12] Friend, A.D. 1998. Parameterisation of a global daily weather generator for terrestrial ecosystem and biogeochemical modelling. Ecological Modelling 109, 121-140.

[11] Mobbs, D.C., Cannell, M.G.R., Crout, N.M.J., Lawson, G.J., Friend, A.D., and Arah, J. 1998. Complementarity of light and water use in tropical agroforests. I. Theoretical model outline, performance and sensitivity. Forest Ecology and Management, 102, 259-274.

[10] Friend, A.D., Stevens, A. K., Knox, R. G., and Cannell, M. G. R. 1997. A process-based, terrestrial biosphere model of ecosystem dynamics (Hybrid v3.0). Ecological Modelling 95, 249-287.

[9] Kramer, K., Friend, A.D. and Leinonen, I. 1996. Modelling comparison to evaluate the importance of phenology and spring frost damage for the effects of climate change on growth of mixed temperate zone deciduous forests. Climate Research, 7, 31-41.

[8] Friend, A.D. 1995. PGEN - an integrated model of leaf photosynthesis, transpiration, and conductance. Ecological Modelling 77, 233-255.

[7] Friend, A.D. and Cox, P.M. 1995. Modelling the effects of atmospheric CO2 on vegetation-atmosphere interactions. Agricultural and Forest Meteorology 73, 285-295.

[6] Murray, M.B., Smith, R.I., Leith, I.D., Fowler, D., Lee, H.S.J., Friend, A.D., and Jarvis, P. 1994. Effects of elevated CO2, nutrition and climatic warming on bud phenology in Sitka spruce (Picea sitchensis (Bong.) Carr) and its impact on frost tolerance. Tree Physiology 14, 691-706.

[5] Friend, A.D., Shugart, H.H., and Running, S.W. 1993. A physiology-based gap model of forest dynamics. Ecology 74, 792-797.

[4] Friend, A.D. 1991. Use of a model of photosynthesis and leaf microenvironment to predict optimal stomatal conductance and leaf nitrogen partitioning. Plant, Cell and Environment 14, 895-905.

[3] Friend, A.D. and Woodward, F.I. 1990. Evolutionary and ecophysiological responses of mountain plants to the growing season environment. Advances in Ecological Research 20, 59-124.

[2] Friend, A.D., Woodward, F.I. and Switsur, V.R. 1989. Field measurements of photosynthesis, stomatal conductance, leaf nitrogen and δ13C along altitudinal gradients in Scotland. Functional Ecology 3, 117-122.

[1] Woodward, F.I. and Friend, A.D. 1988. Controlled environment studies on the temperature responses of leaf extension in species of Poa with diverse altitudinal ranges. Journal of Experimental Botany 39, 411-420.

Other publications

  • Friend AD, Geider RJ, Behrenfeld MJ, Still CJ. 2009. Photosynthesis in Global-Scale Models. In: Photosynthesis in silico: Understanding Complexity from Molecules to Ecosystems. Laisk A, Nedbal L, Govindjee (Eds). Springer Series "Advances in Photosynthesis and Respiration". Vol 29. Springer (Dordrecht, The Netherlands). pp. 465-497.
  • Ciais, P., Friedlingstein, P., Friend, A., and Schimel, D.S. 2001. Integrating global models of terrestrial primary productivity. In: Terrestrial Global Productivity. Roy, J. et al. (Eds). Academic Press, San Diego. pp. 449-478.
  • Cannell, M.G.R., Mobbs, D.C., Friend, A.D., and Ågren, G.I. 1999. Air chemistry and effects on tree growth as indicated by preliminary modelling results. In: Relationships Between Recent Changes of Growth and Nutrition of Norway Spruce, Scots Pine, and European Beech Forests in Europe - RECOGNITION - . EFI Working Paper 19. Rehfuess, K.-E., Ågren, G.I., Andersson, F., Cannell, M.G.R., Friend, A., Hunter, I., Kahle, H.-P., Prietzel, J., and Spiecker, H. pp. 27-53.
  • Friend, A.D. 1998. Biochemical modelling of leaf photosynthesis. In: European forests and global change: the likely impact of rising CO2 and temperature. P. G. Jarvis (Ed). Cambridge, Cambridge University Press. pp. 335-346.
  • Friend, A., Kellomäki, S., and Kruijt, B. 1998. Modelling leaf, tree and forest responses to increasing CO2 and temperature. In: European forests and global change: the likely impacts of rising CO2 and temperature. P. G. Jarvis (Ed). Cambridge, Cambridge University Press. pp. 293-334.
  • White, A., Friend, A.D., and Cannell, M.G.R. 1997. The impact of climate change on natural vegetation. In: Climate Change and its Impacts: a Global Perspective. UK Department of the Environment, Transport and Regions, UK Met. Office, Bracknell, 16 pp.
  • Melillo, J.M., et al., (inc. Friend, A.D.) 1996. Terrestrial biotic responses to environmental change and feedbacks to climate. In: Climate change 1995: the science of climate change. J.T. Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg, and K. Maskell (Eds). Cambridge: Cambridge University Press. pp. 445-481.
  • Ryan, M.G., Hunt, E.R., McMurtrie, R.E., Ågren, G.I., Aber, J.D., Friend, A.D., Rastetter, E.B., Pulliam, W.M., Raison, R.J., and Linder, S. 1996. Comparing models of ecosystem function for coniferous forests. I. Model description and validation. In: Global Change: Effects on Coniferous Forests and Grasslands. SCOPE 56. J.M. Melillo, G.I. Ågren, and A. Breymeyer (Eds). John Wiley and Sons, New York. pp. 313-362.
  • Ryan, M.G., McMurtrie, R.E., Hunt, E.R., Friend, A.D., Pulliam, W.M., Ågren, G.I., Aber, J.D., and Rastetter, E.B. 1996. Comparing models of ecosystem function for coniferous forests. II. Simulations of the effect of climate change. In: Global Change: Effects on Coniferous Forests and Grasslands. SCOPE 56. J.M. Melillo, G.I. Ågren, and A. Breymeyer (Eds). John Wiley and Sons, New York. pp. 363-387.
  • Murray, M.B., Friend, A.D., and Leith, I.D. 1994. Effects of elevated CO2 on Sitka spruce (Picea sitchensis (Bong.) Carr). March 1994. In: Carbon sequestration by vegetation in the UK. UK Department of the Environment. 23 pp.
  • Friend, A.D. 1993. Final report on modelling in the EPOC-13 Project. In: An investigation of the impact of elevated CO2 on the responses of European forests. Commission of the European Communities.
  • Friend, A.D. 1993. The prediction and physiological significance of tree height. In: Vegetation Dynamics and Global Change. A.M. Solomon and H.H. Shugart (Eds). New York: Chapman and Hall. pp. 101-115.
  • Friend, A.D., Cox, P. and Dewar, R.C. 1992. Modelling the fluxes of water and carbon from plant canopies. In: Proceedings of the Scientific Conference on Biospheric Aspects of the Hydrological Cycle, Toulouse.
  • Friend, A.D., Murray, M.B., and Leith, I.D. 1992. Effects of elevated CO2 on the growth, phenology, and physiology of Picea sitchensis. In: Carbon sequestration by vegetation in the UK. Department of the Environment.


  • Undergraduate: Biogeography (second year Geography); Modelling Earth's Atmosphere (third year Geography); Ecology: Global Change (third year Natural Sciences); Atmospheric Chemistry and Global Change (fourth year Chemistry)
  • Postgraduate (all Geography): Research Design for Environmental Science; MPhil in Environmental Science; The PhD viva

External activities

  • American Geophysical Union (member)
  • European Geosciences Union (member)

Possible topic: The role of ecosytem physiological processes in the historical global carbon cycle on land

Terrestrial ecosystems plays a key role in the global carbon cycle, as well as providing humans and other ecosystem trophic levels with essential services. However, we only have a very poor understanding of the global behaviour of their interaction with the atmosphere, including the surface carbon balance. This is despite numerous observational systems collecting data on ecosystem state and behaviour. These observations include in situ fluxes, tree rings, and structural parameters such as height, as well as remote sensing estimates of surface light absorption, leaf area, and atmospheric CO2 dynamics (which can be used to estimate surface fluxes). It is essential that we improve our understanding of past fluxes and their controls in order to inform future projections of both impacts and feedbacks with the atmosphere. Examples of controls on temporal and spatial variability include seasonal drought, temperatures extremes, and storm damage (e.g. across the Amazon rainforest in 2005).

This PhD project will address this problem using a dynamic global vegetation model (see References below). The model will be further developed, tested, and used to better understand the role of climate and atmospheric CO2 on the historical global terrestrial carbon balance. The model exists in different forms that allow the analysis of controls on ecosystem state as a result of climate variability in space and time. The model will be extended to incorporate land use change over the 1880-2009 period , and simulations will be made of the global distribution of carbon sources and sinks over this period. Comparisons will be made with satellite data (e.g. MODIS), in situ data such as from flux towers, and the dynamics of atmospheric CO2. In addition, collaborations with other research groups will be exploited to compare different model and remote-sensing based estimates of historical carbon fluxes. This will enable the quantification and attribution of uncertainty, and establish methodologies for further improving our understanding of controls on terrestrial ecosystem states and behaviour, particularly their roles in the global carbon cycle.


  • Friend AD. 2010. Terrestrial plant production and climate change. Journal of Experimental Botany, doi:10.1093/jxb/erq019
  • Friend, A.D. and Kiang, N.Y. 2005. Land-surface model development for the GISS GCM: Effects of improved canopy physiology on simulated climate. Journal of Climate 18, 2883-2902, doi:10.1175/JCLI3425.1.
  • Friend, A.D. and White, A. 2000. Evaluation and analysis of a dynamic terrestrial ecosystem model under preindustrial conditions at the global scale. Global Biogeochemical Cycles 14(4), 1173-1190.