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The ability of a quadrupole-based ICP-MS with an octopole collision cell to obtain precise and accurate measurements of isotope ratios of magnesium, calcium and potassium was evaluated. Hydrogen and helium were used as collision/reaction gases for ICP-MS isotope ratio measurements of calcium and potassium in order to avoid isobaric interference with the analyte ions from (mainly) argon ions 40Ar+ and argon hydride ions 40Ar1H+. Mass discrimination factors determined for the isotope ratios 25Mg/24Mg, 40Ca/44Ca and 39K/41K under optimized experimental conditions varied between 0.044 and 0.075. The measurement precisions for 25Mg/24Mg, 40Ca/44Ca and 39K/41K were found to be 0.09%, 0.43% and 1.4%, respectively. This analytical method that uses ICP-QMS with a collision cell to obtain isotope ratio measurements of magnesium, calcium and potassium was used in routine mode to characterize biological samples (nutrient solution and small amounts of digested plant samples). The mass spectrometric technique was employed to study the dynamics of nutrient uptake and translocation in barley plants at different root temperatures (10 degrees C and 20 degrees C) using enriched stable isotopes (25Mg, 44Ca and 41K) as tracers. For instance, the mass spectrometric results of tracer experiments demonstrated enhanced 25Mg and 44Ca uptake and translocation into shoots at a root temperature of 20 degrees C 24 h after isotope spiking. In contrast, results obtained from 41K tracer experiments showed the highest 41K contents in plants spiked at a root temperature of 10 degrees C.

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-The shape of red heartwood in beech was studied on 16 trees, based on the mean red heart radius at about every 2 m along the stem axis up to the crown base. The longitudinal red heart shape was modelled by sections of bell-shaped curves, given by an exponential function with a fourth order polynomial term. Using individual tree parameters for the red heart width, length and height, the observed red heart shapes were closely described by the model. An approach of a predictive model at the standing tree level was developed for estimating these parameters from the diameter at breast height, height of the crown base related to total tree height and height of a possible red heart initiation point. Remaining issues concerning the model structure should be analysed on a higher number of samples. An application of the model at the log level could be developed. red heart / model / beech / Fagus sylvatica / shape Résumé -Modélisation de la forme du coeur rouge du hêtre (Fagus sylvatica L.) à partir de caractéristiques externes de l'arbre. La forme du coeur rouge du hêtre a été décrite sur 16 arbres par des mesures du rayon moyen du coeur rouge effectuées tous les 2 m de hauteur environ jusqu'à la base du houppier. La forme longitudinale du coeur rouge a été modélisée par des sections de courbe en cloche données par une fonction exponentielle avec un terme polynomial d'ordre quatre. Le modèle comprenant des paramètres arbres individuels pour les largeur, longueur et hauteur du coeur rouge décrit bien les formes de coeur rouge observées. Un modèle prédictif expérimental au niveau de l'arbre sur pied est proposé pour estimer ces paramètres à partir du diamètre à 1 m 30, de la hauteur relative de la base du houppier et de la hauteur d'un point d'initiation potentiel du coeur rouge. Pour élaborer un modèle plus robuste, il serait nécessaire d'analyser un échantillon plus important. Une application du modèle au niveau de la grume pourrait être développée.coeur rouge / modèle / hêtre / Fagus sylvatica / forme

Modern forestry is increasingly confronted with challenges that appear with intensive forest management and the progression of the effects of climate change. The forestry sector is able to react to the changing conditions by adapting management plans, forest structure or planting tree species with a higher stress resistance. However, during stand management activities, silvicultural treatments and harvesting operations can have an impact on the further development of the remaining forest ecosystem. In Germany, the most widely used harvesting system for thinning operations is a single-grip harvester used for felling and processing trees followed by a forwarder for timber extraction from the machine operating trails to roadside. In this research project, debarking rollers and other modifications designed for Eucalyptus harvesting heads were tested on conventional harvesting heads for the first time to assess the possibility of adding debarking to mechanized forest operations under Central European conditions. Seven field tests with varying tree species, diameters and age classes, were established within German state forests in Lower Saxony and in Bavaria. These tests were repeated in both summer and winter seasons to evaluate the influence of associated tree sap flows on debarking quality. Three different harvesting heads were modified to assess the altered mechanical characteristics and setups. To assess debarking ability originating from head modifications, a photo-optical measurement system developed within the scope of the project was used. The results demonstrate that especially for summertime operations, simple modifications to currently used harvesting heads are able to provide an average debarking efficiency up to 90% depending on the modifications. Another key finding is that a negatively affected sap flow, experienced during wintertime operations, resulted in 46% lower debarking efficiency, while spruce bark beetle infestations only resulted in a wider spread of the variation. Additionally, the vertical position of the log within the tree proved to have an influence on debarking efficiency, resulting in 15% lower average debarking for butt logs and 9% for top logs as compared to middle logs. Since a debarking process requires the stem to be fed through the harvesting head on multiple occasions to remove bark, average harvesting productivity might be reduced by approx. 10% compared to productivity measured with conventional harvesting heads. Considering the results and the extent of the modifications, the system proved to be a potential addition to existing harvesting methods facing changing challenges in future forestry.