Summary Attempts to combine biometric and eddy‐covariance (EC) quantifications of carbon allocation to different storage pools in forests have been inconsistent and variably successful in the past. We assessed above‐ground biomass changes at five long‐term EC forest stations based on tree‐ring width and wood density measurements, together with multiple allometric models. Measurements were validated with site‐specific biomass estimates and compared with the sum of monthly CO2 fluxes between 1997 and 2009. Biometric measurements and seasonal net ecosystem productivity (NEP) proved largely compatible and suggested that carbon sequestered between January and July is mainly used for volume increase, whereas that taken up between August and September supports a combination of cell wall thickening and storage. The inter‐annual variability in above‐ground woody carbon uptake was significantly linked with wood production at the sites, ranging between 110 and 370 g C m−2 yr−1, thereby accounting for 10–25% of gross primary productivity (GPP), 15–32% of terrestrial ecosystem respiration (TER) and 25–80% of NEP. The observed seasonal partitioning of carbon used to support different wood formation processes refines our knowledge on the dynamics and magnitude of carbon allocation in forests across the major European climatic zones. It may thus contribute, for example, to improved vegetation model parameterization and provides an enhanced framework to link tree‐ring parameters with EC measurements.

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The net ecosystem exchange of CO₂ (NEE) between the atmosphere and a beech forest (Sorø, Denmark) showed significant interannual variation (IAV) over 13 years (1997–2009) of observations. The forest sequestered, on average, 157 g C m⁻² yr⁻¹, ranging from a source of 32 to a sink of 344 g C m⁻² yr⁻¹ in 1998 and 2008, respectively. The objectives of this study were to evaluate to what extent and at which temporal scale, climatic variability (through direct response) and changes in ecosystem functional properties (through biotic response) regulated the IAV in the ecosystem carbon balance. To address this question, we performed correlation analysis between the carbon fluxes and climate variables at different time scales. The response of CO₂ exchange to climatic variability was significantly higher at short time scales and the limiting factors changed intra-annually. Combinations of climate anomalies in different periods of the year either intensified or attenuated the aggregated ecosystem responses, implying that the changing distribution of climate anomalies, in addition to the average climate change, could have stronger impacts on the ecosystem carbon balance in the future. A semi empirical model was used to estimate a set of parameter time series for each of the 13 years, which was considered to represent the functional properties of the ecosystem. The climate and parameter time series were applied factorially by year to quantify their relative importance for the IAV in carbon flux. At an annual time scale, as much as 77 % of the IAV in NEE could be attributed to the variation in both photosynthesis and respiration related model parameters, indicating a strong influence of functional change. The possible causes for the observed functional change could not be addressed with the available dataset. This demonstrates the need for more targeted experiments, such as long-term measurements of leaf nitrogen content. Our approach incorporated seasonal variation in the ecosystem status and demonstrated a significant role of biotic factors on the carbon dynamics in a typical temperate deciduous forest. The method can be applied at other sites to explore ecosystem behaviour across different plant functional types and climate gradients. Further, this approach showed how important it is to incorporate functional change in process based models, which could guide model development and consequently reduce the uncertainties in long-term projection of global ecosystem carbon balance

Seasonal and spatial variations in foliar nitrogen (N) parameters were investigated in three European forests with different tree species, viz. beech (Fagus sylvatica L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and Scots pine (Pinus sylvestris L.) growing in Denmark, the Netherlands and Finland, respectively. The objectives were to investigate the distribution of N pools within the canopies of the different forests and to relate this distribution to factors and plant strategies controlling leaf development throughout the seasonal course of a vegetation period. Leaf N pools generally showed much higher seasonal and vertical variability in beech than in the coniferous canopies. However, also the two coniferous tree species behaved very differently with respect to peak summer canopy N content and N retranslocation efficiency, showing that generalisations on tree internal vs. ecosystem internal N cycling cannot be made on the basis of the leaf duration alone. During phases of intensive N turnover in spring and autumn, the NH+ 4 concentration in beech leaves rose considerably, while fully developed green beech leaves had relatively low tissue NH+ 4 , similar to the steadily low levels in Douglas fir and, particularly, in Scots pine. The ratio between bulk foliar concentrations of NH+ 4 and H+, which is an indicator of the NH3 emission potential, reflected differences in foliage N concentration, with beech having the highest values followed by Douglas fir and Scots pine. Irrespectively of the leaf habit, i.e. deciduous versus evergreen, the majority of the canopy foliage N was retained within the trees. This was accomplished through an effective N re-translocation (beech), higher foliage longevity (fir) or both (boreal pine forest). In combination with data from a literature review, a general relationship of decreasing N re-translocation efficiency with the time needed for canopy renewal was deduced, showing that leaves which live longer re-translocate relatively less N during senescence. The Douglas fir stand, exposed to relatively high atmospheric N deposition, had by far the largest peak summer canopy N content and also returned the largest amount of N in foliage litter, suggesting that higher N fertility leads to increased turnover in the ecosystem N cycle with higher risks of losses such as leaching and gas emissions

Changbaishan/Paektu volcano straddles the border between the Democratic People's Republic of Korea and China. It was responsible for one of the largest eruptions in history, the "Millennium Eruption' of 946 CE. An episode of unrest between 2002 and 2005, characterized by inflation and seismicity, refocused attention on this volcano. While satellite remote sensing has provided synoptic observations, ground-based surveillance has hitherto supported only disparate analyses and geophysical interpretations on either side of the border. Here, we derive receiver functions using seismic records from both Democratic People's Republic of Korea and China. H-stacking indicates thick crust (up to 40 km) and high average crustal V P ∕V S (up to 1.93) beneath the volcano. Grid search inversions constrain a significant velocity reduction at 4-8 km depth (below sea level), and harmonic analysis suggests this dips away from the volcano, with shallowest depths centered beneath the volcano. Common conversion point migrations show that this anomaly extends ∼30 km from the volcano summit and possibly as far as neighboring volcanoes. The colocation of the velocity reduction with a zone of high-conductivity, low-velocity, and low-density material at the depth of the inflation source implicated in the 2002-2005 unrest indicates that partial melt is present directly beneath Changbaishan/Paektu, likely recharged during the episode of unrest. Our study highlights the importance of continued surveillance of the volcano and the need for further geophysical studies to constrain more fully the triggers for unrest and controls on its evolution.