Vantaa, Finland
Vantaa, Finland
Time filter
Source Type

Naudts K.,CEA Saclay Nuclear Research Center | Ryder J.,CEA Saclay Nuclear Research Center | McGrath M.J.,CEA Saclay Nuclear Research Center | Otto J.,CEA Saclay Nuclear Research Center | And 24 more authors.
Geoscientific Model Development | Year: 2015

Since 70% of global forests are managed and forests impact the global carbon cycle and the energy exchange with the overlying atmosphere, forest management has the potential to mitigate climate change. Yet, none of the land-surface models used in Earth system models, and therefore none of today's predictions of future climate, accounts for the interactions between climate and forest management. We addressed this gap in modelling capability by developing and parametrising a version of the ORCHIDEE land-surface model to simulate the biogeochemical and biophysical effects of forest management. The most significant changes between the new branch called ORCHIDEE-CAN (SVN r2290) and the trunk version of ORCHIDEE (SVN r2243) are the allometric-based allocation of carbon to leaf, root, wood, fruit and reserve pools; the transmittance, absorbance and reflectance of radiation within the canopy; and the vertical discretisation of the energy budget calculations. In addition, conceptual changes were introduced towards a better process representation for the interaction of radiation with snow, the hydraulic architecture of plants, the representation of forest management and a numerical solution for the photosynthesis formalism of Farquhar, von Caemmerer and Berry. For consistency reasons, these changes were extensively linked throughout the code. Parametrisation was revisited after introducing 12 new parameter sets that represent specific tree species or genera rather than a group of often distantly related or even unrelated species, as is the case in widely used plant functional types. Performance of the new model was compared against the trunk and validated against independent spatially explicit data for basal area, tree height, canopy structure, gross primary production (GPP), albedo and evapotranspiration over Europe. For all tested variables, ORCHIDEE-CAN outperformed the trunk regarding its ability to reproduce large-scale spatial patterns as well as their inter-annual variability over Europe. Depending on the data stream, ORCHIDEE-CAN had a 67 to 92% chance to reproduce the spatial and temporal variability of the validation data. © Author(s) 2015.

Ogurtsov M.G.,RAS Ioffe Physical - Technical Institute | Jungner H.,University of Helsinki | Helama S.,University of Lapland | Lindholm M.,Metla | Oinonen M.,University of Helsinki
Geografiska Annaler, Series A: Physical Geography | Year: 2011

Eight, millennial-scale proxy reconstructions of temperature of the Northern Hemisphere were compared to instrumentally measured temperatures. The effect of anomalous reduction in sensitivity over the last decades (divergence) in the tree-ring based records was taken into account. Statistical analyses showed that in the extratropical part of the Northern Hemisphere the time period 1988-2008 was the warmest two decades within the last 1000 years and had a probability of more than 0.70. The established exceptional level of current temperature changes over those areas that were the least disturbed by local anthropogenic impact indicates that over the last two decades the climatic system was perturbed by an additional global-scale forcing factor, which had not operated in the past. © The authors 2011. Geografiska Annaler: Series A © 2011 Swedish Society for Anthropology and Geography.

Ogurtsov M.G.,RAS Ioffe Physical - Technical Institute | Jungner H.,University of Helsinki | Lindholm M.,Metla | Helama S.,University of Helsinki | Dergachev V.A.,RAS Ioffe Physical - Technical Institute
Geomagnetism and Aeronomy | Year: 2010

Paleoclimatological reconstructions of temperature of the Earth's Northern Hemisphere for the last thousand years have been studied using the up-to-date methods of statistical analysis. It has bee indicated that the quasisecular (a period of 60-130 years) cyclicity, which is observed in the climate of the Earth's Northern Hemisphere, has a bimodal structure, i.e., being composed of the 60-85 and 85-130 year periodicities. The possible relation of the quasisecular climatic rhythm to the corresponding Gleissberg solar cycle has been studied using the solar activity reconstructions performed with the help of the solar paleoastrophysics methods. © Pleiades Publishing, Ltd., 2009.

Ogurtsov M.G.,RAS Ioffe Physical - Technical Institute | Raspopov O.M.,Russian Academy of Sciences | Oinonen M.,University of Helsinki | Jungner H.,University of Helsinki | Lindholm M.,Metla
Geomagnetism and Aeronomy | Year: 2010

The response of the nonlinear oscillatory system to an insignificant external disturbance has been considered as applied to the effect of solar activity on climatic processes. Based on a simplified model, it has been indicated that the response of a nonlinear oscillator to a weak disturbing impact can be substantial. The oscillator fluctuation spectrum can decrease under the action of a disturbing factor. This means that the effect of an even weak solar or cosmophysical signal to the Earth's climatic system can lead to significant climate variations if this system is nonlinear. However, it will be rather difficult to identify the solar-climatic nature of these variations because a linear relation between the cause and response is absent. © Pleiades Publishing, Ltd., 2010.

Merila P.,Finnish Forest Research Institute | Malmivaara-Lamsa M.,Metla | Spetz P.,Metla | Stark S.,Metla | And 3 more authors.
Applied Soil Ecology | Year: 2010

In this study we hypothesized that a change in the composition of vegetation communities is closely linked to a concurrent change in the structure of microbial communities through the decisive role of plant residues in regulating the quality of carbon sources for soil microbes. The study was carried out in a boreal forest along an 80-m-long successional transect (willow, alder, birch, spruce) located on the land-uplift coast of the Gulf of Bothnia, western Finland. The field and ground layer vegetation were recorded by species percentage cover on 2m2 sample plots located at 10m intervals. Organic layer samples were taken from around each vegetation sample plot for the determination of phospholipid fatty acid (PLFA) profiles and chemical composition of the organic layer, as characterized by the concentrations of neutral and acidic sugar units in non-cellulosic polysaccharides, cellulose, the acid-soluble lignin (ASL), and acid-insoluble residue (AIR). The organic layer along the transect showed a decrease in pH (from 5.2 to 4.4), moisture content and concentrations of ASL and the hemicellulosic sugars arabinose, rhamnose, xylose, galactose, and glucuronic acid, while the AIR concentration increased. These organic matter fractions and pH also showed a strong positive or negative correlation with the vegetation and the PLFA ordination. The percentage cover of grasses significantly correlated with the PLFA data, as well as with that of herbs and field layer species. However, PLFA ordination showed a higher correlation with the organic layer properties than with the coverage of plant species groups. In conclusion, our data showed a strong directional relationship between the organic matter characteristics and structure of the vegetation and microbial communities along the study transect. This study is, to our knowledge, the first investigation to apply acid methanolysis in the characterization of non-cellulosic polysaccharides in the organic layer. © 2010 Elsevier B.V.

Merila P.,Finnish Forest Research Institute | Mustajarvi K.,Metla | Helmisaari H.-S.,Metla | Helmisaari H.-S.,University of Helsinki | And 7 more authors.
Forest Ecology and Management | Year: 2014

Nitrogen (N) is typically the growth-limiting factor in boreal forest ecosystems. Therefore, knowledge on forest N stocks and fluxes is crucial in order to predict and evaluate the effects of different anthropogenic factors (e.g. climate change, air pollutant deposition, forest management practices) on the condition, development and sustainability of boreal forests. In this study, we evaluated the amount and distribution of N and biomass in different compartments of forest ecosystem, including not only tree stand and soil, but also such rarely reported N stocks as litter layer, ground vegetation and fine and small roots. We also calculated the theoretical export of N in three forest harvest regimes of different intensity (stem-only harvest, whole-tree harvest, whole-tree harvest and stump uplifting) and assessed the time required for N deposition to compensate the N losses occurring in them. The study included seven Scots pine and eight Norway spruce dominated stands belonging to the UN-ECE ICP Forests Level II programme in Finland. The average effective temperature sum and stand age of the sites ranged 658-1351 d.d. and 55-200 yrs, respectively. Among the study sites, the total biomass (needles, living and dead branches, stems, bark, stumps, coarse roots, fine and small roots, understory, litter, humus and mineral soil layers) ranged from 178Mg ha-1 to 541Mg ha-1, the respective range for N stock being 1890-7530kg ha-1. The two largest pools of N in forest ecosystem were mineral soil (depth 0-40cm; mean=70%) and humus layer (mean=16%). The largest living biomass N stock was in stems in pine stands (88kg ha-1) and in needles in spruce stands (134kg ha-1). Nstored in tree biomass accounted for 7-19% of the total ecosystem N stock. The proportion of N stored in potential logging residues or biofuel (needles, living and dead branches, stumps and coarse roots) was 67±4% and 53±5% of the tree N stock in northern spruce stands and in southern pine stands, respectively. The understory vegetation N stock was the largest in northern spruce stands, and the lowest in southern spruce stands. Our results supported the hypothesis that in boreal coniferous forests, inputs of N by deposition accumulating during the following rotation period will be able to replenish the export of N caused by conventional stem-only-harvest in final cutting, but the sustainability of the site productivity will be challenged when more intense whole tree harvest regimes are practiced, especially in Norway spruce stands. © 2013 Elsevier B.V.

Rantala J.,METLA | Saarinen V.-M.,METLA | Hallongren H.,METLA
Scandinavian Journal of Forest Research | Year: 2010

In Nordic countries, the harvesting of slash and stumps from regeneration areas for energy purposes has rapidly increased, and will increase further in the future. This development has unknown technoeconomic effects on soil scarification. This study investigated three spot mounding methods and factors affecting their quality, productivity and costs in regeneration areas after slash and stump removal. The methods were integrated stump lifting and spot mounding (INTE), separate excavator-based spot mounding (BLADE), and separate spot mounding by a continuously working mounding unit (CONT). The average quality of work was worst in INTE, while CONT was the most sensitive to stoniness. Average work times per spot mound were 4.1 and 3.1 times higher in INTE and BLADE, respectively, than in CONT. Altogether, the costquality ratio of CONT was better than that of the other methods, except in very small areas. © 2010 Taylor & Francis.

Loading Metla collaborators
Loading Metla collaborators