Carl-Fredrik Johannesson defends his thesis,<\/p>\n
Forest management effects on soil carbon storage and soil CO2\u00a0and CH4\u00a0fluxes in high latitude forests<\/p>\n <\/strong>Supervisors<\/strong>: Assessment<\/strong> Committee<\/strong>: Abstract<\/strong> (shortened)<\/strong>: Soil CO2\u00a0and CH4\u00a0fluxes were site dependent, with lower CO2\u00a0efflux at the clear-cut, mature-unthinned and mature-thinned sites than at the thinned and old-unmanaged sites. Possible\u00a0explanations for these patterns include C input limitations at the clear-cut site and high soil\u00a0moisture levels limiting oxygen availability at the mature-unthinned and mature-thinned sites. Net\u00a0soil CH4\u00a0consumption was highest at the clear-cut site and lowest at the mature-thinned site which\u00a0we hypothesize is due to differences in soil moisture levels which regulate O2\u00a0availability and\u00a0diffusion of atmospheric CH4\u00a0into the soil. Application of nitrogen\u00a0 fertilizer led to decreased soil\u00a0CO2\u00a0efflux only at the mature-unthinned site, and while it led to a decreased mean net soil CH4\u00a0consumption at all sites, this effect was associated with large uncertainties. The effect of biochar\u00a0was site dependent,\u00a0 resulting in decreased soil CO2\u00a0efflux at the clear-cut and thinned sites and\u00a0positive effect sizes at the mature-unthinned and mature-thinned sites. The mean net soil CH4\u00a0consumption increased in response to biochar addition at the mature-unthinned and mature-thinned\u00a0sites and decreased at the clear-cut and thinned sites, yet these effects were associated with large\u00a0 uncertainties. The largest reductions in the net soil CO2\u00a0and CH4\u00a0budgets in response to biochar\u00a0were achieved at the sites believed to be the driest, and likely due to exacerbated soil moisture\u00a0limitations. Such increased moisture limitations may have negative effects also on tree growth.\u00a0Thus, trade-offs between the effects on soil greenhouse gas budgets and C sequestration by trees\u00a0need to be carefully considered before conclusions on the climate change mitigation potential of\u00a0biochar can be drawn. Our results suggest that application of nitrogen fertilizer and biochar has\u00a0limited potential for reducing soil CO2\u00a0and CH4\u00a0budgets in boreal forests dominated by Norway\u00a0spruce (Picea abies).<\/p>\n In short, this thesis provides evidence of the magnitude and persistence of soil C stock declines\u00a0after clear-cut harvesting, it provides guidance on how to improve the accuracy of greenhouse gas\u00a0flux rate estimates and shows that the effects of biochar and nitrogen fertilizer on soil CO2\u00a0and\u00a0CH4\u00a0fluxes depend on the site-specific soil environment.<\/p>\n A digital version of the PhD thesis can be obtained from the PhD secretary at\u00a0phd@ign.ku.dk\u00a0before the defence. After the defence the thesis will become available from the Royal Danish Libary at\u00a0kb@kb.dk.<\/p>\n","protected":false},"excerpt":{"rendered":" Carl-Fredrik Johannesson defends his thesis, Forest management effects on soil carbon storage and soil CO2\u00a0and CH4\u00a0fluxes in high latitude forests Supervisors: Associate Professor Klaus Steenberg Larsen, IGN Senior Research Scientist Jenni Nord\u00e9n, NINA, Norway Senior Research Scientist Hanna M. Silvennoinen, NINA, Norway Assessment Committee: Professor Mari Pihlatie, University of Helsinki, Finland Professor Tobias R\u00fctting, University […]<\/p>\n","protected":false},"author":0,"featured_media":171727,"template":"","class_list":["post-171726","event","type-event","status-publish","has-post-thumbnail","hentry","event_category-phd"],"acf":[],"yoast_head":"\n
\nAssociate Professor Klaus Steenberg Larsen, IGN
\nSenior Research Scientist Jenni Nord\u00e9n, NINA, Norway
\nSenior Research Scientist Hanna M. Silvennoinen, NINA, Norway<\/p>\n
\nProfessor Mari Pihlatie, University of Helsinki, Finland Professor
\nTobias R\u00fctting, University of Gothenburg, Sweden
\nAssociate Professor Jesper Riis Christiansen (chair), IGN<\/p>\n
\nForests are important storages and sinks of carbon (C) and high latitude forests specifically store\u00a0the majority of total ecosystem C in soils, and still accumulate C. Thus, when aiming to preserve\u00a0or enhance the forest C sink in boreal or northern temperature forests, it is vital that soils are not\u00a0neglected. The forests of the Nordics and Canada are to a large extent managed, but whether soil\u00a0C storage and accumulation is affected positively or negatively depends on the specific\u00a0management practice. Forest harvesting is one of the management practices that has the largest\u00a0impact on soil C storage and accumulation, but application of biochar and nitrogen fertilizer have\u00a0also been found to affect the soil C cycle. In Paper I of this thesis the effect of clear-cut harvesting\u00a0on soil C storage is investigated based on a chronosequence approach using National Forest Soil\u00a0Inventory data from Sweden, Denmark, Norway, Finland and Canada.<\/p>\n