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Modeling seasonal courses of carbon fluxes and evaportranspiration in response to low temperature and moisture in a boreal scots pine ecosystem
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
Department of Forest Ecology, University of Helsinki, Finland.
2011 (English)In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 222, 3103-3119 p.Article in journal (Refereed) Published
Abstract [en]

Environmental conditions act above and below ground, and regulate carbon fluxes and evapotranspiration. The productivity of boreal forest ecosystems is strongly governed by low temperature and moisture conditions, but the understanding of various feedbacks between vegetation and environmental conditions is still unclear. In order to quantify the seasonal responses of vegetation to environmental factors, the seasonality of carbon and heat fluxes and the corresponding responses for temperature and moisture in air and soil were simulated by merging a process-based model (CoupModel) with detailed measurements representing various components of a forest ecosystem in Hyytiälä, southern Finland. The uncertainties in parameters, model assumptions, and measurements were identified by generalized likelihood uncertainty estimation (GLUE). Seasonal and diurnal courses of sensible and latent heat fluxes and net ecosystem exchange (NEE) of CO2 were successfully simulated for two contrasting years. Moreover, systematic increases in efficiency of photosynthesis, water uptake, and decomposition occurred from spring to summer, demonstrating the strong coupling between processes. Evapotranspiration and NEE flux both showed a strong response to soil temperature conditions via different direct and indirect ecosystem mechanisms. The rate of photosynthesis was strongly correlated with the corresponding water uptake response and the light use efficiency. With the present data and model assumptions, it was not possible to precisely distinguish the various regulating ecosystem mechanisms. Our approach proved robust for modeling the seasonal course of carbon fluxes and evapotranspiration by combining different independent measurements. It will be highly interesting to continue using long-term series data and to make additional tests of optional stomatal conductance models in order to improve our understanding of the boreal forest ecosystem in response to climate variability and environmental conditions.

Place, publisher, year, edition, pages
2011. Vol. 222, 3103-3119 p.
Keyword [en]
Net ecosystem exchange (NEE), Sensible and latent heat fluxes, Photosynthesis, Respiration, Scots pine forest, CoupModel, Generalized likelihood uncertainty estimation (GLUE)
National Category
Other Natural Sciences
Identifiers
URN: urn:nbn:se:kth:diva-27038DOI: 10.1016/j.ecolmodel.2011.05.023ISI: 000295071400010Scopus ID: 2-s2.0-80051939835OAI: oai:DiVA.org:kth-27038DiVA: diva2:374664
Note
QC 20101206 Uppdaterad från submitted till published 20110921Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Modeling the Seasonality of Carbon, Evapotranspiration and Heat Processes for Cold Climate Conditions
Open this publication in new window or tab >>Modeling the Seasonality of Carbon, Evapotranspiration and Heat Processes for Cold Climate Conditions
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The productivity of agricultural and forest ecosystems in regions at higher latitudes is to a large extent governed by low temperature and moisture conditions. Environmental conditions are acting both above- and below-ground and regulating carbon fluxes and evapotranspiration. However, the understanding of various feedbacks between vegetation and environmental conditions is still unclear. In this thesis, two studies were conducted to understand the physical and biological processes. In the first study, the aim was to simulate soil temperature and moisture dynamics in the bare soil with seasonal frost conditions in China. In the second study, the aims were to model seasonal courses of carbon and evapotranspiration and to examine the responses of photosynthesis, transpiration and respiration on environmental conditions in a boreal Scots pine ecosystem in Finland. In both studies the CoupModel was applied to simulate the dynamic responses of the systems. Both sites represented investigations from which a high number of measurements were available. To understand to what extent the data could be used to increase the understanding of the systems, the Generalized Likelihood Uncertainty Estimation (GLUE) was applied. The GLUE method was useful to reduce basic uncertainties with respect to parameter ranges, model structures and measurements.

The strong interactions between soil temperature and moisture processes have indicated by a few behavioral models obtained when constrained by combined temperature and moisture criteria. Model performance on sensible and latent heat fluxes and net ecosystem exchange (NEE) also indicated the coupled processes within the system. Seasonal and diurnal courses were reproduced successfully with reduced parameter ranges. However, uncertainties on what is the most general regulation for transpiration and NEE are still unclear and need further systematic investigations.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. x, 13 p.
Series
Trita-LWR. LIC, ISSN 1650-8629 ; 2045
Keyword
net ecosystem exchange (NEE), sensible and latent heat fluxes, photosynthesis, respiration, nitrogen turnover, Scots pine forest, bare soil, cold climate, soil physical characteristics, CoupModel, GLUE
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-26918 (URN)978-91-7415-826-7 (ISBN)
Presentation
2010-12-17, V3, KTH, Teknikringen 76, Stockholm, 13:15 (English)
Opponent
Supervisors
Note
QC 20101206Available from: 2010-12-06 Created: 2010-11-29 Last updated: 2010-12-06Bibliographically approved
2. Impact of cold climate on boreal ecosystem processes: exploring data and model uncertainties
Open this publication in new window or tab >>Impact of cold climate on boreal ecosystem processes: exploring data and model uncertainties
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The impact of cold climate on physical and biological processes, especially the role of air and soil temperature in recovering photosynthesis and transpiration in boreal forests, was investigated in a series of studies. A process-based ecosystem model (CoupModel) considering atmospheric, soil and plant components was evaluated and developed using Generalized Likelihood Uncertainty Estimation (GLUE) and detailed measurements from three different sites. The model accurately described the variability in measurements within days, within years and between years. The forcing environmental conditions were shown to govern both aboveground and belowground processes and regulating carbon, water and heat fluxes. However, the various feedback mechanisms between vegetation and environmental conditions are still unclear, since simulations with one model assumption could not be rejected when compared with another.

The strong interactions between soil temperature and moisture processes were indicated by the few behavioural models obtained when constrained by combined temperature and moisture criteria. Model performance on sensible and latent heat fluxes and net ecosystem exchange (NEE) also indicated the coupled processes within the system. Diurnal and seasonal courses of eddy flux data in boreal conifer ecosystems were reproduced successfully within defined ranges of parameter values. Air temperature was the major limiting factor for photosynthesis in early spring, autumn and winter, but soil temperature was a rather important limiting factor in late spring. Soil moisture and nitrogen showed indications of being more important for regulating photosynthesis in the summer period. The need for systematic monitoring of the entire system, covering both soil and plant components, was identified as a subject for future studies. The results from this modelling work could be applied to suggest improvements in management of forest and agriculture ecosystems in order to reduce greenhouse gas emissions and to find adaptations to future climate conditions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. x, 31 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1061
Keyword
net ecosystem exchange; sensible and latent heat fluxes; soil temperature; soil moisture; CoupModel; GLUE
National Category
Forest Science
Identifiers
urn:nbn:se:kth:diva-40451 (URN)978-91-7501-104-2 (ISBN)
Public defence
2011-10-07, V1, Teknikringen 76, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
the Nitro-Europe project
Note
QC 20110921Available from: 2011-09-21 Created: 2011-09-15 Last updated: 2011-09-21Bibliographically approved

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