Towards an integrated ecology through mechanistic modelling of ecosystem structure and functioning

Abstract

Plant physiology, population dynamics and the structure and functioning of ecosystems are closely interrelated. However, these processes are often investigated independently within different subdisciplines of ecology. Mechanistic models of ecosystem structure and functioning combine representations of processes operating at a range of scales and levels of organisation, providing a tool for the description and study of ecosystems as integrated entities.



This thesis is based on the development and application of LPJ-GUESS, a modelling framework which integrates processes such as leaf-level photosynthesis, the dynamics of populations competing for resources, and the fluxes of carbon and water between soil layers, vegetation and the atmosphere. LPJ-GUESS currently includes as alternative configurations the Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM) and the General Ecosystem Simulator (GUESS).



The results from a study of potential future ecosystem dynamics on the continental scale projected by two DGVMs (LPJ and MC1) suggest that changes in climate and atmospheric CO2 concentrations may severely impact North American ecosystems within the next century (e.g. through vegetation dieback caused by drought), but simulation results depended heavily on the climate scenario and alternative assumptions as to the effects of increasing atmospheric CO2 on carbon assimilation and ecosystem water balance. LPJ-DGVM simulated similar effects of elevated CO2 on forest productivity as observed during four years of CO2 fumigation at a free air CO2 enrichment (FACE) experiment, but it remains uncertain if a CO2 effect of the magnitude commonly simulated by ecosystem models is realistic in the longer term.



A comparison of the structure and composition of pristine forests simulated by a number of forest gap models revealed that most of the models have restricted generality because the empirical relationships used to calculate growth are usually not applicable beyond the climatic region for which each particular model was developed. More generally applicable gap models should incorporate process representations derived from generalised plant-physiological mechanisms. The physiology-based gap-type model GUESS was demonstrated to reproduce observed patterns of vegetation dynamics at the plant-type as well as the species level.



Finally, a comprehensive hypothesis on the effects of plant hydraulic architecture on water uptake in different types of plants was implemented within the LPJ-DGVM. The hypothesis was validated through a comparison of simulated ecosystem structural and functional features with available data.



Comparing the predictions from a number of models that have been applied under standardised conditions has been useful for identifying major drivers and uncertainties in mechanistic ecosystem models, but the future development of the field will crucially depend on evaluation of individual process formulations by field and experimental scientists in close collaboration with modellers. Such approaches could benefit ecology through integration of knowledge from different subdisciplines and by tightening the coupling between empirical studies and models.

Abstract (Swedish)

Popular Abstract in Swedish

Traditionellt har olika aspekter av ett ekosystem studerats var för sig inom olika ekologiska discipliner såsom växtfysiologi, forskning om hur organismer interagerar med varandra och forskning om hur ekosystem som helhet beter sig. Denna avhandling innehåller exempel på att simulationsmodeller gör det möjligt att undersöka hur de olika processerna samverkar för att forma ekosystemet. Det simulerade ekosystemets utveckling blir följden av bland annat fysiologiska processer som fotosyntesen i bladen och av hur olika trädslag förökar sig och konkurrerar om ljus och vatten. Syftet med modellerna är bland annat att med hjälp av prognoser om klimatförändringar till följd av växthuseffekten kunna förutse hur olika ekosystem på jorden kan komma att utvecklas till följd av detta.



Arbetet har inneburit en vidareutveckling av några befintliga simulationsmodeller, utvärdering av deras tillförlitlighet genom att jämföra simulationsresultat med verklig data samt jämförelse mellan olika simulationsmodellers resultat och funktion. Resultaten visar att de undersökta modellerna tämligen väl kan simulera befintlig vegetation och ekosystem. Genom att utgå från data om jordartsförhållanden, nederbörd, temperatur m.m. kan modellerna visa t.ex. vilka trädslag som dominerar i en skog, hur hög produktionen av biomassa är i olika ekosystem, och hur stor vattenavdunstningen är. Simulationsresultat för framtida utveckling av ekosystem varierar däremot mycket beroende av hur särskilda processer representeras i de olika modellerna och antaganden om hur klimatet kommer att förändras. Stor osäkerhet råder också ännu om hur en ökad CO2-halt i atmosfären påverkar växternas fysiologi, något som i sin tur påverkar hela ekosystemet. Dessutom behövs mer kunskap om hur olika växter tar upp vatten. Detta innebär att det inte är möjligt att förutsäga framtida utveckling av ekosystem innan kunskapen om klimatförändringar och särskilda ekologiska processer förbättrats. För detta krävs intensivt samarbete mellan forskare från olika ekologiska discipliner, forskare som jobbar empirisk och de som utvecklar simulationsmodeller, vilket i sin tur skulle leda till en mer integrerande ekologisk vetenskap.

• author: Hickler, Thomas
• supervisor: [unknown] [unknown]
• opponent: Prof Grace, John, University of Edinburgh
• organization: Dept of Physical Geography and Ecosystem Science
• publishing date: 2004
• type: Thesis
• publication status: published
• subject: Physical Geography
• keywords: pedology, cartography, climatology, Fysisk geografi, geomorfologi, marklära, kartografi, klimatologi, geomorphology, Physical geography, integrated ecology, plant hydraulic architecture, climate change, CO2 fertilisation effect, biogeography, biogeochemistry, vegetation dynamics, ecosystem modelling
• pages: 170 pages
• defense location: room 111, Geocentrum I, Sölvegatan 10, Lund
• defense date: 2004-03-12 10:00:00
• external identifiers: scopus:77953886527
• ISBN: 91-973857-8-6
• language: English
• LU publication?: yes
• additional info: Article: Bachelet, D., R. P. Neilson, T. Hickler, R. J. Drapek, J. M. Lenihan, M. T. Sykes, B. Smith, S. Sitch, and K. Thonicke. 2003. Simulating past and future dynamics of natural ecosystems in the United States. Global Biochemical Cycles 17:1045 doi:1010.1029/2001GB001508. Article: Hickler, T., I. C. Prentice, B. Smith and M. T. Sykes. 2004. Simulating the effects of elevated CO2 on productivity at the Duke Forest FACE experiment: a test of the dynamic global vegetation model LPJ. Manuscript. Article: Badeck, F. W., H. K. Lischke, H. Bugmann, T. Hickler, K. Hönninger, P. Lasch, M. J. Lexer, F. Mouillot, J. Schaber, and B. Smith. 2001. Tree species composition in European pristine forests. Comparison of stand data to model predictions. Climatic Change 51:307-347. Article: Hickler, T., B. Smith, M.T. Sykes, M. Davis, S. Sugita and K. Walker. 2004. Using a generalized vegetation model to simulate vegetation dynamics in northeastern USA. Ecology. In press. Article: Hickler, T., I. C. Prentice, B. Smith, M. T. Sykes, and S. Zaehle. 2004. Using a global vegetation model to test a comprehensive hypothesis on the effects of plant hydraulic architecture on water uptake in different types of plants. Manuscript.
• id: 169e6b1e-bfea-438c-b67b-dfb213634399 (old id 466709)
• date added to LUP: 2016-04-01 16:54:23
• date last changed: 2022-01-28 23:01:08