The complex fluxes between standing and harvested carbon stocks, and the linkage between harvested biomass and fossil fuel substitution, call for a holistic, system-wide analysis in a life-cycle perspective to evaluate the impacts of forest management and forest product use on carbon balances. We have analysed the net carbon emission under alternative forest management strategies and product uses, considering the carbon fluxes and stocks associated with tree biomass, soils, and forest products. Simulations were made using three Norway spruce ( Picea abies (L.) Karst.) forest management regimes (traditional, intensive management, and intensive fertilization), three slash management practices (no removal, removal, and removal with stumps), two forest product uses (construction material and biofuel), and two reference fossil fuels (coal and natural gas). The greatest reduction of net carbon emission occurred when the forest was fertilized, slash and stumps were harvested, wood was used as construction material, and the reference fossil fuel was coal. The lowest reduction occurred with a traditional forest management, forest residues retained on site, and harvested biomass was used as biofuel to replace natural gas. Product use had the greatest impact on net carbon emission, whereas forest management regime, reference fossil fuel, and forest residue usage as biofuel were less significant.

Disturbance of ecosystems is a major factor in regional carbon budgets, and it is believed to be partly responsible for the large inter-annual variability of the terrestrial part of the carbon balance. Forest fires have so far been considered as the most important disturbance but also other forms of disturbance such as insect outbreaks or wind-throw might contribute significantly to the largely unexplained inter-annual variability, at least in specific regions. The effect of wind-throw has not yet been estimated because of lack of data on how carbon fluxes are affected. The Gudrun storm, which hit Sweden in January 2005, resulted in ca. 66 million m 3 of wind-thrown stem wood on an area of ca. 272 000 ha. Using a model (BIOME-BGC) calibrated to CO 2 flux measurements at two sites, the annual net ecosystem productivity during the first year after the storm was estimated to be in the range À897 to À1259 g C m À2 yr À1 . This is a much higher loss compared with harvested (clear-cut) forests in Europe, which ranged between ca. À420 and À100 g m À2 yr À1 . The reduction in the carbon sink scaled to the whole wind-thrown area was estimated at ca. 3 million tons C during the first year. By historical data on windthrow in Europe combined with modelling, we estimated that the large Lothar storm in 1999 reduced the European carbon balance by ca. 16 million tons C, this is ca. 30% of the net biome production in Europe. We conclude that the impact of increased forest damage by more frequent storms in future climate change scenarios must be considered and that intermittent large wind-throw events may explain a part of the large inter-annual variability in the terrestrial carbon sink.

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 2001Sweden, measured -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 À2 year À1 ). 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 À8 g C m À2 year À1 in the north to +9 g C m À2 year À1 in the south. In contrast, NEE and tree growth measurements at the northernmost site suggest that the soil lost about 90 g C m À2 year À1 .

No abstract

Human-induced salinization caused by the use of road deicing salts, agricultural practices, mining operations, and climate change is a major threat to the biodiversity and functioning of freshwater ecosystems. Yet, it is unclear if freshwater ecosystems are protected from salinization by current water quality guidelines. Leveraging an experimental network of land-based and in-lake mesocosms across North America and Europe, we tested how salinization—indicated as elevated chloride (Cl−) concentration—will affect lake food webs and if two of the lowest Cl− thresholds found globally are sufficient to protect these food webs. Our results indicated that salinization will cause substantial zooplankton mortality at the lowest Cl− thresholds established in Canada (120 mg Cl−/L) and the United States (230 mg Cl−/L) and throughout Europe where Cl− thresholds are generally higher. For instance, at 73% of our study sites, Cl− concentrations that caused a ≥50% reduction in cladoceran abundance were at or below Cl− thresholds in Canada, in the United States, and throughout Europe. Similar trends occurred for copepod and rotifer zooplankton. The loss of zooplankton triggered a cascading effect causing an increase in phytoplankton biomass at 47% of study sites. Such changes in lake food webs could alter nutrient cycling and water clarity and trigger declines in fish production. Current Cl− thresholds across North America and Europe clearly do not adequately protect lake food webs. Water quality guidelines should be developed where they do not exist, and there is an urgent need to reassess existing guidelines to protect lake ecosystems from human-induced salinization.