Comparable regional scale estimates for the carbon balance of forests are needed for scientific and political purposes. We developed a method for deriving these estimates from readily available forest inventory data by using statistical biomass models and dynamic modelling of litter and soil. Here, we demonstrate this method and apply it to Finland's forests between 1922 and 2004. The method was reliable, since the results obtained were comparable to independent data. The amount of carbon stored in the forests increased by 29%, 79% of which was found in the biomass and 21% in the litter and soil. The carbon balance varied annually, depending on the climate and level of harvesting, with each of these factors having effects on the biomass differing from those on the litter and soil. Our results demonstrate the importance of accounting for all forest carbon pools to avoid misleading pictures of short-and long-term forest carbon balance. carbon inventory / forest biomass / greenhouse gas inventory / litter / soil modelling Résumé-Accumulation de carbone dans les forêts finlandaises entre 1922 et 2004, une estimation obtenue en combinant les données de l'inventaire forestier avec une modélisation de la biomasse de la litière et du sol. Une estimation comparable à l'échelle régionale du bilan de carbone des forêts était nécessaire pour des objectifs scientifiques et politiques. Nous avons développé une méthode pour déduire ces estimations de données facilement disponibles de l'inventaire forestier en utilisant des modèles statistique de la biomasse et une modélisation dynamique de la litière et du sol. Ici nous présentons cette méthode et l'appliquons aux forêts de Finlande entre 1922 et 2004. La méthode a été fiable, puisque les résultats obtenus ont été comparables à des données indépendantes. La quantité de carbone accumulée dans les forêts s'est accrue de 29 %,79 % de ce qui a été trouvé dans la biomasse et 21 % dans la litière et le sol. Le bilan de carbone varie annuellement, selon le climat et l'importance de la récolte, chacun de ces facteurs ayant des effets sur la biomasse différents de ceux qui agissent sur la litière et sur le sol. Nos résultats démontrent l'importance de comptabiliser tous les réservoirs de carbone en forêt pour éviter des images trompeuses du bilan de carbone des forêts à court et moyen terme. inventaire du carbone / biomasse forestière / inventaire des gaz à effet de serre / litière / sol

Decomposition of plant litter is a key process for the transfer of carbon and nutrients in ecosystems. Carbon contained in the decaying biomass is released to the atmosphere as respired CO₂, and may contribute to global warming. Litterbag studies have been used to improve our knowledge of the drivers of litter decomposition, but they lack comparability because litter quality is plant species-specific. The use of commercial tea bags as a standard substrate was suggested in order to harmonize studies, where green tea and rooibos represent more labile and more recalcitrant C compounds as surrogates of local litter. Here we examine the potential of the use of standardized material for improving our understanding of litter decomposition across climate regions, and to further develop pertinent models. We measured the decomposition of incubated local and standard litters over two years along an elevation gradient in the Austrian Limestone Alps. The similar response to changes in temperature and precipitation of the pairs of local and standard litter—i.e., Fagus sylvatica and green tea, and Pinus nigra and rooibos tea, respectively—suggests the suitability of the standard litters for further examining the role of environmental drivers of decomposition. Harmonized data obtained from standardized litter experiments would provide a key prerequisite for further developing simulation models for the estimation of the C balance of ecosystem litter pools.

Feedback to climate warming from the carbon balance of terrestrial ecosystems depends critically on the temperature sensitivity of soil organic carbon (SOC) decomposition. Still, the temperature sensitivity is not known for the majority of the SOC, which is tens or hundreds of years old. This old fraction is paradoxically concluded to be more, less, or equally sensitive compared to the younger fraction. Here, we present results that explain these inconsistencies. We show that the temperature sensitivity of decomposition increases remarkably from the youngest annually cycling fraction (Q₁₀ < 2) to a decadally cycling one (Q₁₀ = 4.2–6.9) but decreases again to a centennially cycling fraction (Q₁₀ = 2.4–2.8) in boreal forest soil. Compared to the method used for current global estimates (temperature sensitivity of all SOC equal to that of the total heterotrophic soil respiration), the soils studied will lose 30–45% more carbon in response to climate warming during the next few decades, if there is no change in carbon input. Carbon input, derivative of plant productivity, would have to increase by 100–120%, as compared to the earlier estimated 70–80%, in order to compensate for the accelerated decomposition.

We present a new application of terrestrial laser scanning and mathematical modelling for the quantitative change detection of tree biomass, volume, and structure. We investigate the feasibility of the approach with two case studies on trees, assess the accuracy with laboratory reference measurements, and identify the main sources of error, and the ways to mitigate their effect on the results. We show that the changes in the tree branching structure can be reproduced with about ±10% accuracy. As the current biomass detection is based on destructive sampling, and the change detection is based on empirical models, our approach provides a non-destructive tool for monitoring important forest characteristics without laborious biomass sampling. The efficiency of the approach enables the repeating of these measurements over time for a large number of samples, providing a fast and effective means for monitoring forest growth, mortality, and biomass in 3D.

The accurate characterization of three-dimensional (3D) root architecture, volume, and biomass is important for a wide variety of applications in forest ecology and to better understand tree and soil stability. Technological advancements have led to increasingly more digitized and automated procedures, which have been used to more accurately and quickly describe the 3D structure of root systems. Terrestrial laser scanners (TLS) have successfully been used to describe aboveground structures of individual trees and stand structure, but have only recently been applied to the 3D characterization of whole root systems. In this study, 13 recently harvested Norway spruce root systems were mechanically pulled from the soil, cleaned, and their volumes were measured by displacement. The root systems were suspended, scanned with TLS from three different angles, and the root surfaces from the co-registered point clouds were modeled with the 3D Quantitative Structure Model to determine root architecture and volume. The modeling procedure facilitated the rapid derivation of root volume, diameters, break point diameters, linear root length, cumulative percentages, and root fraction counts. The modeled root systems underestimated root system volume by 4.4%. The modeling procedure is widely applicable and easily adapted to derive other important topological and volumetric root variables.