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Carbon dynamics in spruce forest ecosystems - modelling pools and trends for Swedish conditions
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.ORCID iD: 0000-0002-0926-3304
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Carbon (C) pools and fluxes in northern hemisphere forest ecosystems are attracting increasing attention concerning predicted climate change. This thesis studied C fluxes, particularly soil C dynamics, in spruce forest ecosystems in relation to interactions between physical/biological processes using a process-based ecosystem model (CoupModel) with data for Swedish conditions. The model successfully described general patterns of C and N dynamics in managed spruce forest ecosystems with both tree and field layers. Using regional soil and plant data, the change in current soil C pools was -3 g C m-2 yr-1 in northern Sweden and +24 g C m-2 yr-1 in southern Sweden. Simulated climate change scenarios resulted in increased inflows of 16-38 g C m-2 yr-1 to forest ecosystems throughout Sweden, with the highest increase in the south and the lowest in the north. Along a north-south transect, this increased C sequestration mainly related to increased tree growth, as there were only minor decreases in soil C pools. Measurements at one northern site during 2001-2002 indicated large soil C losses (-96 g C m-2 yr-1), which the model successfully described. However, the discrepancy between these large losses and substantially smaller losses obtained in regional simulations was not explained. A simulation based on Bayesian calibration successfully reproduced measured C, water and energy fluxes, with estimated uncertainties for major components of the simulated C budget. Site-specific measurements indicated a large contribution from field layer fine roots to total litter production, particularly in northern Sweden. Mean annual tree litter production was 66% higher at the most southerly site (240 g C m-2 yr-1 compared with 145 g C m-2 yr-1 in the north), but when field and bottom layers were included the difference decreased to 16% (total litter production 276 g C m-2 yr-1 and 239 g C m-2 yr-1 respectively). Regional simulations showed that decomposition rate for the stable soil C fraction was three times higher in northern regions compared with southern, providing a possible explanation why soil C pools in southern Sweden are roughly twice as large as those in the north.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , viii, 25 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1029
Keyword [en]
boreal, climate, CoupModel, net ecosystem production, nitrogen, process-based model, soil carbon
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4240ISBN: 978-91-7178-544-2 (print)OAI: oai:DiVA.org:kth-4240DiVA: diva2:11418
Public defence
2006-12-19, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100922Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2010-09-22Bibliographically approved
List of papers
1. Modelling soil C sequestration in spruce forest ecosystems along a Swedish transect based on current conditions
Open this publication in new window or tab >>Modelling soil C sequestration in spruce forest ecosystems along a Swedish transect based on current conditions
2008 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, 95-119 p.Article in journal (Refereed) Published
Abstract [en]

The change of current pools of soil C in Norway spruce ecosystems in Sweden were studied using a process-based model (CoupModel). Simulations were conducted for four sites representing different regions covering most of the forested area in Sweden and representing annual mean temperatures from 0.7 degrees C to 7.1 degrees C. The development of both tree layer and field layer (understory) was simulated during a 100-year period using data on standing stock volumes from the Swedish Forest Inventory to calibrate tree growth using different assumptions regarding N supply to the plants. The model successfully described the general patterns of forest stand dynamics along the Swedish climatic transect, with decreasing tree growth rates and increasing field layer biomass from south to north. However, the current tree growth pattern for the northern parts of Sweden could not be explained without organic N uptake and/or enhanced mineralisation rates compared to the southern parts. Depending on the assumption made regarding N supply to the tree, different soil C sequestration rates were obtained. The approach to supply trees with both mineralised N and organic N, keeping the soil C:N ratio constant during the simulation period was found to be the most realistic alternative. With this approach the soils in the northern region of Sweden lost 5 g C m(-2) year(-1), the soils in the central region lost 2 g C m(-2) year(-1), and the soils in the two southern regions sequestered 9 and 23 g C m(-2) year(-1), respectively. In addition to climatic effects, the feedback between C and N turnover plays an important role that needs to be more clearly understood to improve estimates of C sequestration in boreal forest ecosystems.

Keyword
boreal, carbon, CoupModel, climate, nitrogen, organic nitrogen uptake
National Category
Agricultural Sciences
Identifiers
urn:nbn:se:kth:diva-6648 (URN)10.1007/s10533-007-9134-y (DOI)000257201300008 ()2-s2.0-46249102136 (Scopus ID)
Note
Uppdaterad från manusript till artikel: 20100922 Tidigare titel: Soil C in spruce forest ecosystems in Sweden – modelling current pools and trends using different assumptions on N supply. QC 20100922Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
2. Pools and fluxes of carbon in three Norway spruce ecosystems along a climatic gradient in Sweden.
Open this publication in new window or tab >>Pools and fluxes of carbon in three Norway spruce ecosystems along a climatic gradient in Sweden.
Show others...
2008 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, 7-25 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an integrated analysis of organic carbon (C) pools in soils and vegetation, within-ecosystem fluxes and net ecosystem exchange (NEE) in three 40-year old Norway spruce stands along a north-south climatic gradient in Sweden, measured 2001-2004. A process-orientated ecosystem model (CoupModel), previously parameterised on a regional dataset, was used for the analysis. Pools of soil organic carbon (SOC) and tree growth rates were highest at the southernmost site (1.6 and 2.0-fold, respectively). Tree litter production (litterfall and root litter) was also highest in the south, with about half coming from fine roots (< 1 mm) at all sites. However, when the litter input from the forest floor vegetation was included, the difference in total litter input rate between the sites almost disappeared (190-233 g C m(-2) year(-1)). We propose that a higher N deposition and N availability in the south result in a slower turnover of soil organic matter than in the north. This effect seems to overshadow the effect of temperature. At the southern site, 19% of the total litter input to the O horizon was leached to the mineral soil as dissolved organic carbon, while at the two northern sites the corresponding figure was approx. 9%. The CoupModel accurately described general C cycling behaviour in these ecosystems, reproducing the differences between north and south. The simulated changes in SOC pools during the measurement period were small, ranging from -8 g C m(-2) year(-1) in the north to +9 g C m(-2) year(-1) in the south. In contrast, NEE and tree growth measurements at the northernmost site suggest that the soil lost about 90 g C m(-2) year(-1).

Keyword
soil carbon, boreal ecosystems, climatic gradient, CoupModel, root litter, dissolved organic carbon
National Category
Agricultural Sciences
Identifiers
urn:nbn:se:kth:diva-6649 (URN)10.1007/s10533-007-9136-9 (DOI)000257201300002 ()2-s2.0-46249089502 (Scopus ID)
Note
Uppdaterad från manuskript till artikel: 20100922 QC 20100922Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
3. Simulated climate change impacts on fluxes of carbon in Norway spruce ecosystems along a climatic transect in Sweden
Open this publication in new window or tab >>Simulated climate change impacts on fluxes of carbon in Norway spruce ecosystems along a climatic transect in Sweden
2008 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, 81-94 p.Article in journal (Refereed) Published
Abstract [en]

A simulation study based on recent regional climate scenarios for Sweden investigated possible changes in carbon (C) dynamics and net ecosystem exchange (NEE) of Swedish Norway spruce forest ecosystems. Four sites, representative of well-drained soils in four regions, were included. Stand development was simulated for a 100-year rotation period using a coupled model describing abiotic and biotic processes in the soil-plant-atmosphere system. Two IPCC climate change scenarios, corresponding to a mean annual temperature increase of about 2 degrees C (A2) or 3 degrees C (B2) from the reference period 1961-1990 to a new period 2061-2090, were considered. Annual maximum snow depth decreased with the increase in air temperature, whereas maximum soil frost depth and mean annual soil temperature showed only small changes, especially for the sites in northern Sweden. Simulations suggested that in the warmer climate, gross primary production (GPP) increased by 24-32% in northern Sweden and by 32-43% in the south. In the north, the increase was related to the combined effect of air and soil temperature extending the growing season, whereas in the south it was mainly governed by increased N availability due to increased soil temperature. NEE increased by about 20% (A2) or 25% (B2) at all sites, more or less solely due to increased accumulation of C in the tree biomass (including harvest residues), since changes in soil C were small compared with the current climate. Both light use efficiency and water use efficiency were improved in the future climate scenarios, despite increases in atmospheric CO2 not being considered.

Keyword
air temperature, boreal, CoupModel, net ecosystem exchange, nitrogen, soil temperature, soil frost, soil respiration
National Category
Agricultural Sciences
Identifiers
urn:nbn:se:kth:diva-6650 (URN)10.1007/s10533-007-9147-6 (DOI)000257201300007 ()2-s2.0-46249117260 (Scopus ID)
Note
Uppdaterad från manuskript till artikel: 20100922 Tidigare titel: Climate change impacts on fluxes of carbon in Norway spruce ecosystems along a climatic transect in Sweden. QC 20100922Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved
4. Bayesian calibration of a model describing carbon, water and heat fluxes for a Swedish boreal forest stand.
Open this publication in new window or tab >>Bayesian calibration of a model describing carbon, water and heat fluxes for a Swedish boreal forest stand.
Show others...
2008 (English)In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 213, no 3-4, 331-344 p.Article in journal (Other academic) Published
Abstract [en]

This study quantified major fluxes of carbon (C), heat and water, including uncertainty estimates, in a boreal forest in northern Sweden, using a process-based model (Coup-Model) and Bayesian calibration methodology. Coupled C, water and heat fluxes were described together with estimated uncertainties for all major components of the simulated C budget. Simulated mean gross primary production was 641 +/- 74 gC m(-2) yr(-1), total ecosystem respiration 570 +/- 55 gC m(-2)yr(-1) and net ecosystem productivity 71 +/- 37gCm(-2)yr(-1). Most high-resolution measurements were well described but some interesting exceptions arose between model and measurements, e.g. latent heat flux was overestimated and field layer (understory) root litter production underestimated. Bayesian calibration reduced the assumed prior parameter ranges in 30 of 33 parameters, thus reducing the uncertainty in the estimates. There was a high degree of couplings between different sub-models and processes in the model, highlighting the importance of considering parameters not as singularities but in clusters

Keyword
carbon budget, CoupModel, Markov chain Monte Carlo simulation, process-based model, uncertainty estimate
National Category
Agricultural Sciences
Identifiers
urn:nbn:se:kth:diva-6651 (URN)10.1016/j.ecolmodel.2008.01.001 (DOI)000255624900006 ()2-s2.0-41149133225 (Scopus ID)
Note
Uppdaterad från manuskript till artikel: 20100922. QC 20100922 Available from: 2006-12-15 Created: 2006-12-15 Last updated: 2017-12-14Bibliographically approved

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