1. General Model Information

Name: General Ecosystem Model

Acronym: HYBRID

Main medium: terrestrial
Main subject: biogeochemistry
Organization level: ecosystem
Type of model: ordinary differential equations, not specified
Main application: research
Keywords: generalized plant type, climate change, global, Farquhar type, pipe model, gap model


Andrew Friend
Institute of Terrestrial Ecology, NERC-ITE
Bush Estate, Penicuick, Midlothian EH26 0QB
United Kingdom
Tel.: +44-131-445-4343
Fax: +44-131-445-3943
Email: a.friend@ite.ac.uk



The main target of HYBRID is to describe the effect of environmental factors on the carbon, nitrogen, and water cycle of ecosystems in a generic way, such that the effects of changes in the environment can be predicted.
HYBRID is a general global ecosystem model driven by climate. Three generalized plant types are distinguished within the model - grass, broadleaf deciduous trees, and coniferous evergreen trees. Competition between plants is modelled with a gap model approach, while plant growth is based on physiological knowledge (hybrid approach).
HYBRID follows the classic gap model approach in that plants are one-dimensional entities competing on a small plot mainly to light, but also to nitrogen and water, dying when the carbon balance becomes negative, and a certain regeneration taking place.
HYBRID uses a Farquhar type of photosynthesis model based on  PGEN. Photosynthetic activity of leaves are affected by PAR radiation, air temperature, atmospheric CO2 concentration, foliage nitrogen content, and soil water potential. Crown photosynthesis is assumed to be proportional to the amount of light absorbed by the uppermost crown layer. This assumption is derived from an optimality hypothesis, implying that leaf nitrogen and other characteristics important for photosynthesis are distributed over the crown in the same way as PAR radiation.
The photosynthetically active period is calculated as a function of temperature and day length.
Maintenance respiration depends on temperature and in the case of foliage and fine roots also on nitrogen content.
Allocation of carbon follows structural constraints imposed by the pipe model theory and functional balance, and are combined with the priority principle.

Abstract author: CAMASE data base of agro-ecosystem models.

II. Technical Information

II.1 Executables:

Operating System(s):

II.2 Source-code:

Programming Language(s): Fortran

II.3 Manuals:

II.4 Data:

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

III.2.2 Output

IV. References

Friend, A.D., Stevens, A.K., Knox, R.G. and Cannell, M.G.R., 1997. A process-based, biogeochemical, terrestrial biosphere model of ecosystem dynamics (Hybrid v3.0). Ecological Modelling, 95: 249-287.
Friend, A.D., 1997. Parameterization of a global daily weather generator for terrestrial ecosystem and biogeochemical modelling. Ecol. Modelling (in press).
Friend, A.D., 1995. PGEN: an integrated model of leaf photosynthesis, transpiration and conductance. Ecol. Modelling 77: 233-255.
Friend, A.D.; Cox, P.M.; Becker, A. 1995. Modelling the effects of atmospheric CO2 on vegetation-atmosphere interactions. Special issue.Biospheric aspects of the hydrological cycle: a selection of presentations made primarily at the BAHC open meeting and scientific conference, 16-18 November 1992, Toulouse, France. Agricultural-and-Forest-Meteorology. 1995, 73: 3-4, 285-295; 27 ref..
Friend, A.D.; Schugart, H.H.; Running, S.W. 1993. A physiology-based gap model of forest dynamics. (HYBRID) Ecology.1993, 74: 3, 792-797; 14 ref..
Mohren, G.M.J., 1987.Simulation of forest growth, applied to douglas fir stands in the Netherlands. PhD thesis, Wageningen, the Netherlands. 184 pp.
Mohren, G.M.J., H.H. Bartelink, I.T.M. Jorritsma & K. Kramer, 1993.
A process-base growth model (ForGro) for analysis of forest dynamics in relation to environmental factors. In: Broekmeyer, M.E.A., W. Vos & H. Koop (Eds.). European Forest Reserves. Proceedings of the European Forest Reserves Workshop, 6-8 May 1992, The Netherlands. Pudoc-DLO, Wageningen, The Netherlands. 273-280.

V. Further information in the World-Wide-Web

VI. Additional remarks

FORGRO was recently successfully applicated in the EU-project LTEEF ("Long Term Effects of CO2 increase and climate change on European Forests", project-leader G.M.J. Mohren).
FORGRO was also applied in the modelling of a spruce stand at Solling, Germany with 15 other simulation models. A comparison and description of these models is to be found in the special issue: Ecological Modelling 83 (1995): Modelling water, carbon and nutrient cycles in forests: application of 16 simulation models to a spruce stand at Solling, Germany, Proceedings of a workshop held in Leusden, The Netherlands, 10-14 May 1993.

Last review of this document by: M. Sonntag : October, 18th 1997

Status of the document:
last modified by Joachim Benz Mon Jul 2 18:31:37 CEST 2007

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