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Impact of cold climate on boreal ecosystem processes: exploring data and model uncertainties
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
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 [en]
net ecosystem exchange; sensible and latent heat fluxes; soil temperature; soil moisture; CoupModel; GLUE
National Category
Forest Science
Identifiers
URN: urn:nbn:se:kth:diva-40451ISBN: 978-91-7501-104-2 (print)OAI: oai:DiVA.org:kth-40451DiVA: diva2:441319
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
List of papers
1. Modelling temperature, moisture and surface heat balance in the bare soil under seasonal frost conditions in China
Open this publication in new window or tab >>Modelling temperature, moisture and surface heat balance in the bare soil under seasonal frost conditions in China
2011 (English)In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 62, no 6, 780-796 p.Article in journal (Refereed) Published
Abstract [en]

Soil heat and moisture processes are interconnected, especially during low temperatures. To examine the interaction between soil temperature and moisture under freeze-thaw cycles, a physical process-based model (CoupModel) coupled with uncertainty analysis was applied to 3-year measurements under seasonal frost conditions from a site in the black soil belt of northeast China. The uncertainty in parameters and measurements was described by general likelihood uncertainty estimation (GLUE). To identify the degree of linkage between soil temperature and moisture, three criteria were applied to them separately or together. The most sensitive parameters among 26 site-specific parameters were closely related to soil heat, soil evaporation and freeze-thaw processes. Soil temperature was simulated with less uncertainty than soil moisture. Soil temperature measurements had the potential to improve model performance for soil water content, whereas soil moisture measurements demonstrated a trade-off effect when finding a model with good performance for both temperature and moisture. During winter conditions the uncertainty ranges of soil temperature were most pronounced, probably because of the greater complexity of soil properties during the freeze-thaw process and the uncertainty caused by snow properties. The largest uncertainty ranges of both soil water content and soil water storage were found mainly in the deep soil layers. The simulated surface heat fluxes are an important output of the model and it is of great value to compare them with the results from regional climate models and micrometeorological measurements.

Keyword
FROZEN SOIL; WATER-CONTENT; CALIBRATION; FREEZE; LAND; THAW; FOREST; SCALE; FLOW
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-27036 (URN)10.1111/j.1365-2389.2011.01397.x (DOI)000297206100002 ()2-s2.0-81855228878 (Scopus ID)
Note
QC 20101206. Updated from submitted to published, 20120316. Previous title: Model for temperature, moisture and surface heat balance in the bare soil with seasonal frost conditions in ChinaAvailable from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-12Bibliographically approved
2. Modeling seasonal courses of carbon fluxes and evaportranspiration in response to low temperature and moisture in a boreal scots pine ecosystem
Open this publication in new window or tab >>Modeling seasonal courses of carbon fluxes and evaportranspiration in response to low temperature and moisture in a boreal scots pine ecosystem
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.

Keyword
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:nbn:se:kth:diva-27038 (URN)10.1016/j.ecolmodel.2011.05.023 (DOI)000295071400010 ()2-s2.0-80051939835 (Scopus ID)
Note
QC 20101206 Uppdaterad från submitted till published 20110921Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-12Bibliographically approved
3. The role of air and soil temperature in the seasonality of photosynthesis and transpiration in a boreal Scots pine ecosystem
Open this publication in new window or tab >>The role of air and soil temperature in the seasonality of photosynthesis and transpiration in a boreal Scots pine ecosystem
2012 (English)In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 156, 85-103 p.Article in journal (Refereed) Published
Abstract [en]

Photosynthesis and transpiration in boreal forests are restricted by air temperature (T a) and soil temperature (T s), especially in spring after the dormant period, but the extent to which the recovery process is regulated these factors is still uncertain. To examine the role of air temperature and soil temperature, years with three types of typical patterns of temperature rises were identified from 13 years of continuous flux measurements for a Scots pine ecosystem in Hyytiälä, southern Finland. By combining a process-based ecosystem model (CoupModel) with an uncertainty estimation procedure (GLUE), the role of regulating factors was explored and 45 of 51 parameters were found to have reduced uncertainty after calibration. 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. Especially during warm spring with a large delay of soil temperature rise both water uptake and photosynthesis was strongly reduced due to low soil temperature. Soil moisture and nitrogen showed indications of being more important for regulating photosynthesis in the summer period. It proved possible to replace the soil temperature acclimation function on photosynthesis and transpiration with a corresponding air temperature function only during warm years with a small delay between T a and T s. Fluxes of photosynthesis and transpiration showed a sensitivity to the carbon footprint representation, as expected from the high spatial variability in soil temperature during the spring of a warm year with a large delay between T a and T s.

Keyword
Carbon and water balance, CoupModel, Generalised likelihood uncertainty estimation (GLUE), Gross primary productivity (GPP), Net ecosystem exchange (NEE), Sensible and latent heat fluxes, Total ecosystem respiration (TER)
National Category
Other Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-40699 (URN)10.1016/j.agrformet.2012.01.006 (DOI)000302670500008 ()2-s2.0-84862809362 (Scopus ID)
Note

QC 20120328

Available from: 2011-09-20 Created: 2011-09-20 Last updated: 2017-12-08Bibliographically approved
4. Modelling soil temperature and moisture and corresponding seasonality of photosynthesis and transpiration in a boreal spruce ecosystem
Open this publication in new window or tab >>Modelling soil temperature and moisture and corresponding seasonality of photosynthesis and transpiration in a boreal spruce ecosystem
(English)Manuscript (preprint) (Other academic)
National Category
Other Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-40700 (URN)
Note
QS 2011Available from: 2011-09-20 Created: 2011-09-20 Last updated: 2011-09-21Bibliographically approved

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