Abstract As part of the EUROFLUX network a long-term monitoring station for fluxes of CO 2 and water vapour has been established in an 80-year old beech forest in Denmark. The station has been in continuous operation since June 1996 and will be so at least to the end of 2002. A primary goal of EUROFLUX is to combine flux measurements on a continuous multi-year time basis with ecological processes interpretation and modeling. The station consists of a 57 m high mast with conventional meteorological profile instrumentation and one level of eddy-flux measurements. Ancillary measurements such as soil respiration, soil moisture, soil temperature, leaf surface temperature and leaf area index are also made. Results from the first 2 years of measurements are described. The observed diurnal and seasonal variation in the fluxes are discussed and the monthly and annual sums of ecosystem exchange are contrasted between the 2 years. The first year (1 June 1996–31 May 1997) had a net uptake of 223 g C m −2 whereas the net uptake during the second year (1 June 1997–31 May 1998) was only 144 g C m −2 . It was found that the difference was mainly the result of higher respiration in the second year caused by a very warm summer of 1997 and an average soil and air temperature, respectively, 1.2 and 1.6°C higher than the first year. The ecosystem photosynthetic assimilation was slightly higher during the second year, mainly caused by increased incoming radiation.

Six years of continuous CO 2 eddy-flux measurements over a Danish beech forest

. Strong winds may uproot and break trees and represent a major natural disturbance for European forests. Wind disturbances have intensified over the last decades globally and are expected to further
rise in view of the effects of climate change. Despite the importance of such natural disturbances, there are currently no spatially explicit databases of wind-related impact at a pan-European scale. Here, we present a new database of wind disturbances in European forests (FORWIND). FORWIND is comprised of more than 80 000 spatially delineated areas in Europe that were disturbed by wind in the period 2000–2018 and describes them in a harmonized and consistent geographical vector format. The database includes all major windstorms that occurred over the observational period (e.g. Gudrun, Kyrill, Klaus, Xynthia and Vaia) and represents approximately 30 % of the reported damaging wind events in Europe. Correlation analyses between the areas in FORWIND and land cover changes retrieved from the Landsat-based Global Forest Change dataset and the MODIS Global Disturbance Index corroborate the robustness of FORWIND. Spearman rank coefficients range between 0.27 and 0.48 ( p  value   0.05). When recorded forest areas are rescaled based on their damage degree, correlation increases to 0.54. Wind-damaged growing stock volumes reported in national inventories (FORESTORM dataset) are generally higher than analogous metrics provided by FORWIND in combination with satellite-based biomass and country-scale statistics of growing stock volume. The potential of FORWIND is explored for a range of challenging topics and scientific fields, including scaling relations of wind damage, forest vulnerability modelling, remote sensing monitoring of forest disturbance, representation of uprooting and breakage of trees in large-scale land surface models, and hydrogeological risks following wind damage. Overall, FORWIND represents an essential and open-access spatial source that can be used to improve the understanding, detection and prediction of wind disturbances and the consequent impacts on forest ecosystems and the land–atmosphere system. Data sharing is encouraged in order to continuously update and improve FORWIND. The dataset is available at https://doi.org/10.6084/m9.figshare.9555008 
(Forzieri et al., 2019).

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A spatially explicit database of wind disturbances in European forests over the period 2000–2018

CO2 fluxes before and after partial deforestation of a Central European spruce forest

Sensitivity analysis of the typhoon disturbance effect on forest dynamics and carbon balance in the future in a cool-temperate forest in northern Japan by using SEIB-DGVM

. To better understand the distributions and sources of
low-molecular-weight (LMW) monocarboxylic acids (monoacids) in the forest
atmosphere, we conducted simultaneous collection of gaseous and particulate
samples at a deciduous broadleaf forest site in northern Japan. LMW normal
(C 1 –C 10 ), branched (iC 4 –iC 6 ), hydroxyl (glycolic and
lactic) and aromatic (benzoic) monoacids were detected in the gas and
particle phases. The dominant LMW monoacids in gas phase were formic (mean:
953 ng m −3 ) and acetic (528 ng m −3 ) acids followed by propionic
(37 ng m −3 ) or isopentanoic (42 ng m −3 ) acid. In the particle
phase, isopentanoic (159 ng m −3 ) was dominant, followed by acetic
(104 ng m −3 ) and formic (71 ng m −3 ) or lactic
(65 ng m −3 ) acids. Concentrations of LMW monoacids did not show
correlations with anthropogenic tracers such as nss- SO 4 2 - and
 NO 3 - , indicating that anthropogenic contribution is not important.
Concentrations of C 1 –C 6 monoacids in the gas phase showed positive
correlations ( r2=0.21 –0.91) with isobutyric acid (iC 4 ), which
may be produced by microbial activity in soil. The forest soil may be a
source of gaseous C 1 –C 6 monoacids in the forest atmosphere. Acetic
acid in the particle phase positively correlated with nonanoic acid (C 9 )
( r2=0.63 ), suggesting that formation of acetic and nonanoic acids is
associated with the oxidation of biogenic unsaturated fatty acids in the
aerosol phase, in addition to photochemical oxidation of biogenic volatile
organic compounds. The particle-phase fractions ( Fp ) of formic
and acetic acids showed negative correlation with ambient temperature
(C 1 : r2=0.49 , C 2 : r2=0.60 ) but showed positive
correlation with relative humidity (C 1 : r2=0.30 , C 2 : r2=0.55 ) in daytime, suggesting that these meteorological parameters are
important for the gas and particle portioning of monoacids in the forest
atmosphere.

/pdf/distributions-and-sources-of-low-molecular-weight-2u1rn3csnm.pdf

Distributions and sources of low-molecular-weight monocarboxylic acids in gas and particles from a deciduous broadleaf forest in northern Japan

. Forests play an important role in the terrestrial carbon balance, with most being in a carbon sequestration stage. The net carbon releases that occur result from forest disturbance, and windthrow is a typical disturbance event affecting the forest carbon balance in eastern Asia. The CO2 flux has been measured using the eddy covariance method in a deciduous broadleaf forest (Japanese white birch, Japanese oak, and castor aralia) in Hokkaido, where incidental damage by the strong Typhoon Songda in 2004 occurred. We also used the biometrical method to demonstrate the CO2 flux within the forest in detail. Damaged trees amounted to 40 % of all trees, and they remained on site where they were not extracted by forest management. Gross primary production (GPP), ecosystem respiration (Re), and net ecosystem production were 1350, 975, and 375 g C m−2 yr−1 before the disturbance and 1262, 1359, and −97 g C m−2 yr−1 2 years after the disturbance, respectively. Before the disturbance, the forest was an evident carbon sink, and it subsequently transformed into a net carbon source. Because of increased light intensity at the forest floor, the leaf area index and biomass of the undergrowth (Sasa kurilensis and S. senanensis) increased by factors of 2.4 and 1.7, respectively, in 3 years subsequent to the disturbance. The photosynthesis of Sasa increased rapidly and contributed to the total GPP after the disturbance. The annual GPP only decreased by 6 % just after the disturbance. On the other hand, the annual Re increased by 39 % mainly because of the decomposition of residual coarse-wood debris. The carbon balance after the disturbance was controlled by the new growth and the decomposition of residues. The forest management, which resulted in the dead trees remaining at the study site, strongly affected the carbon balance over the years. When comparing the carbon uptake efficiency at the study site with that at others, including those with various kinds of disturbances, we emphasized the importance of forest management as well as disturbance type in the carbon balance.

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H. Utsugi

Papers

Effects of a windthrow disturbance on the carbon balance of a broadleaf deciduous forest in Hokkaido, Japan