Impacts of Climate Change on Carbon and Nitrogen Cycles in Boreal Forest Ecosystems

Research output: Other contribution

Abstract

It is well known that soil carbon stocks decrease considerably in response to soil warming,
but experimental data have shown that the loss of carbon declines within decades in
apparent acclimation. An explanation to such findings is offered under the theoretical
framework of ecosystem models in this thesis. Simulations of forest ecosystem responses to
increased soil temperatures showed that the labile carbon in soil was reduced considerably
within years after warming, although the structure and function of decomposer organisms
remained intact.
Simulations of increased CO2 also confirmed positive growth response in the short term.
The response of soil carbon was similar, however predicted to be less than the increase of
biomass. Nitrogen availability and negative feedback mechanisms of the plant soil system
were critical to the results, indicating that nitrogen progressively limited the growth
response.
Assumptions concerning the response of decomposing organisms to changes in soil nitrogen
are crucial to the interpretation of the above. Positive nitrogen feedback was therefore
implemented to test consequences of nitrogen additions, allowing for improved decomposer
efficiency when inorganic nitrogen becomes available in the soil. Responses compared well
with experimental results. Simulations of moderate inputs of slowly increasing inorganic
nitrogen loads in the long term revealed counteracting feedback responses: the positive
nitrogen feedback resulted in increased decomposer efficiency and biomass growth also
increased as expected; negative nitrogen feedback appeared in the sense that the growth
response was reduced due to decreased mineralisation.
An economic estimation of the net value of carbon sink capacity was also performed. The
value of the carbon sink was given in relation to conservative estimates of total net values of
important stocks and flows of forest natural capital – factors such as recreational values or
hydrological services omitted. The net value of the carbon sink was suggested to amount to
3-50% of the net value of Swedish forests.
Original languageEnglish
TypeDoctoral Thesis
Number of pages43
Place of PublicationGuilford and King’s Lynn, UK
Publication statusPublished - 2007

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