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W dniach 15–17 marca 2022 r. w Instytucie Badawczym Leśnictwa odbyła się XII Sesja Zimowej Szkoły Leśnej, której tematem był „Wpływ zmian klimatu na środowisko leśne”. Spośród licznych propozycji, o wyborze powyższego tematu przesądziło obserwowane od wielu lat systematyczne pogorszanie się stanu zdrowotnego drzewostanów na skutek synergicznego oddziaływania wielu czynników abiotycznych i biotycznych w warunkach zmian klimatu. Współorganizatorem Sesji była Dyrekcja Generalna Lasów Państwowych. Merytoryczne aspekty XII Sesji zostały przygotowane i opracowane przez Radę Programową Zimowej Szkoły Leśnej w składzie: dr hab. Krzysztof Stereńczak, prof. IBL (przewodniczący), prof. dr hab. Bogdan Brzeziecki, mgr inż. Michał Graczyk, prof. dr hab. Andrzej Grzywacz, prof. dr hab. Andrzej Jagodziński, prof. dr hab. Janusz Olejnik, mgr inż. Jan Tabor, mgr inż. Krzysztof Rostek, prof. dr hab. Iwona Skrzecz, dr inż. Klaudia Ziemblińska. Rada Programowa określiła nie tylko zakres problematyki XII Sesji, ale także propozycje tematyczne referatów zamawianych oraz ich autorów. W trakcie trzech dni obrad prelegenci przedstawili 33 referaty. Referaty wygłosili również zaproszeni goście zagraniczni reprezentujący: Uniwersytet w Helsinkach, Czeski Uniwersytet Przyrodniczy w Pradze, Instytut Badań nad Zmianami Globalnymi (Czechy), Uniwersytet Wspólnoty Wirginii, Łotewski Państwowy Instytut Badawczy Leśnictwa oraz Integrated Carbon Observation System. W XII Sesji, która odbyła się w wersji online, wzięło udział niemal 200 osób reprezentujących m.in.: Ministerstwo Klimatu i Środowiska, jednostki organizacyjne Lasów Państwowych, ośrodki uniwersyteckie i instytuty badawcze. Liczne grono stanowili również przedstawiciele ośrodków naukowych oraz polskich uczelni leśnych.

The ongoing debate on global climate change has polarized societies since ever. The attitude of an individual towards its anthropogenic nature as well as the need and extent to which human beings should mitigate climate warming can result from a number of factors. Also, since the consequences of such alteration in global climate have no borders and became much more severe in the last decades, it is worth it to shed some more light on a current state of an interplay between scientific findings and climate policies. In this paper, we examine a low-dimensional space of possible attitudes toward climate change, its impact, attribution, and mitigation. Insights into those attitudes and evidence-based interpretations are offered. We review a range of inconvenient truths and convenient untruths, respectively, related to fundamental climate-change issues and derive a systematic taxonomy of climate-change skepticism. In addition, the media track related to climate change is reconstructed by examining a range of cover stories of important magazines and the development of those stories with global warming. In a second major step, we span a low-dimensional space of outcomes of the combined climate science-policy system, where each of the sub-systems may either succeed or fail. We conclude that the most probable outcome from today’s perspective is still the same as it was 12 years ago: a tragic triumph, i.e., the success of climate science and the simultaneous failure of climate policy.

The accurate estimation of an increase in forest stand biomass has remained a challenge. Traditionally, in situ measurements are done by inventorying a number of trees and their biometric parameters such as diameter at the breast height (DBH) and height, sometimes these are complemented by carbon (C) content studies. Here we present the estimation of net primary productivity (NPP) over a two years period (2019–2020) at a 25-year-old Scots pine stand. Research was based on allometric equations made by direct biomass analysis (tree extraction) and carbon content estimations in individual components of sampled trees, combined with a series of stem diameter increments recorded by a network of band dendrometers. Site-specific allometric equations were obtained using two different approaches: using the whole tree biomass vs DBH (M1), and total dry biomass-derived as a sum of the results from individual tree components’ biomass vs DBH (M2). Moreover, equations for similar forest stands from the literature were used for comparison. Gross primary productivity (GPP) estimated from the eddy-covariance measurements allowed the calculation of carbon use efficiency (CUE = NPP/GPP). The two investigated years differed in terms of the sum and patterns of precipitation distribution, with a moderately dry year of 2019 that followed the extremely dry 2018, and the relatively average year of 2020. As expected, a higher increase in biomass was recorded in 2020 compared to 2019, as determined by both allometric equations based on in situ and literature data. For the former approach, annual NPP estimates reached ca. 2.0–2.1 t C ha−1 in 2019 and 2.6–2.7 t C ha−1 in 2020 depending on the “in situ equations” (M1-M2) used, while literature-derived equations for the same site resulted in NPP values ca. 20–30% lower. CUE was higher in 2020, which resulted from a higher NPP total than in 2019, with lower summer and spring GPP in 2020. However, the CUE values were lower than those reported in the literature for comparable temperate forest stands. A thorough analysis of the low CUE value would require a full interpretation of interrelated physiological responses to extreme conditions.

Solar-induced chlorophyll fluorescence (SIF) has been shown as a promising approach for the estimation of gross primary productivity (GPP), but whether SIF is merely a function of canopy structure or also contains precious physiological information, is presently heavily discussed. In this study, the SIF-GPP relationship was quantified at a Pinus sylvestris forest (Mezyk, Poland) during a series of short-term cold spells throughout the spring awakening to investigate the potential of SIF as a proxy for GPP during this period characterized by cold stress. GPP was inferred from the net ecosystem CO2 exchange measured by the eddy covariance technique. Canopy-scale SIF was measured using a high-resolution spectrometer system and retrieved via spectral fitting (SFM) algorithms. Active leaf-scale chlorophyll fluorescence measurements were conducted on seven branches using an automated field-deployable fluorometer system. Our results demonstrate a clear difference in GPP and the utilization of chlorophyll-absorbed energy between cold spell and warm days. At short, sub-daily time scales, the correlation between SIF and GPP was minor, but increased significantly when observed over extended temporal periods, when SIF exhibited a seasonal pattern that was more closely aligned with the GPP. Furthermore, the strong relationship between non-photochemical quenching (NPQ) and the photochemical reflectance index (PRI) shows good potential to better estimate GPP when integrated in the SIF-GPP model, as the integration of PRI overall increased the relation between SIF and GPP.

There is evidence of increasing severity of extreme meteorological events, which due to climate warming are also more frequent than in the past few decades. Any disturbances (either natural or anthropogenic) exert a significant influence on the forest’s functioning. In Canada and the USA, fires and insect outbreaks cause the greatest damage while in Europe wind disturbances are the main threat. Since in Poland the majority of forests are managed by the State Forests, after such events disturbed areas are almost immediately designated for reforestation. While natural regeneration still contributes the least to forest restoration, the most common practices in our country include harvesting, soil preparation (ploughing) and manual seedlings introduction, which in this sense is similar to clear-cut’s management. Once such an event happened in Poland two EC stations were set up in the area of an 80-year old pine forest, which had been wiped out by a tornado in July 2012, to asses the impact of forest management. To date, there have been more than 5 full years of continuous carbon and energy fluxes measurement, allowing insight into forest regeneration patterns due to manual reforestation, as well as differences in CO2 losses connected to chosen treatments. The two sites (Tlen I and Tlen II) differ mostly in terms of soil preparation – at Tlen I site soil was ploughed before replanting and at Tlen II soil cover remained almost intact. Additionally, at the second location, only trunks and main branches were harvested, while all uprooted stumps were left to decompose. Both meteorological and soil conditions have been investigated, with most of them not being significantly different, which allowed drawing the conclusion that observed differences in GHGs balance are most likely related to chosen forest management practices. Thorough analysis of quality checked EC data revealed that in 5-year perspective the application of traditional method (Tlen I site), mainly due to soil ploughing, resulted in much less total CO2 loss to the atmosphere, reaching C-neutrality point in only 6 years after the damage as well as better seedling growth in general in comparison to the technique, where the soil cover was not disrupted. Moreover, it seems that furrows created at the conventionally managed forest site (“double” organic layer) serve as crucial water reservoirs during water shortage periods, preventing from the pine plantation damage caused by prolonged droughts.This work advances our understanding of how different forest management practices can help to sustain the least CO2 losses on the example of wind-disturbed forests. Although, it has to be remembered that long-term studies are needed to point the best option from the perspective of climate change mitigation.

Peatlands play a key role in the global carbon cycle and the greenhouse gas balance of the biosphere, due to the amount of stored organic carbon and rather big methane (CH4) emissions. Climate change can make these very valuable and vulnerable ecosystems a net emitter of greenhouse gases to the atmosphere. The question is however, how the anticipated climate changes may impact the methane emission. Will it decrease due to expected drier conditions, or other processes and factors may play a role leading to higher emissions? To answer this question we carried out a field climate manipulation experiment at Rzecin peatland in Poland to assess how, increased temperature and reduced precipitation may impact the CH4 emission. The field site consists of three times replicated treatments [control (CO); simulated warming (W); reduced precipitation (RP), and warming & RP (WRP)]. Temperature (T) was increased year around with infrared heaters (400Wx4 per site), while precipitation was reduced with an automatic curtain working during growth seasons at night. The average yearly peat (at 5 cm depth) and air temperatures (at 30 cm) increased at manipulated plots by ca. 1.0oC and 0.4oC, respectively, while the precipitation was reduced from 24% in 2017 to 38% in 2016. Methane and carbon dioxide fluxes were measured with an automated prototyped mobile chamber system equipped with LGR and Picarro gas analyzers. Here we present data from three years; very dry and warm 2015 (417 mm, 9.5°C), more wet and colder 2016 (678 mm, 8.9°C) ad very wet and warm 2017 (929 mm, 9.3°C). The net CH4 emissions at the control site were at the same rate of 25 gC·m-2yr-1 for both 2015 and 2016 years, and significantly higher (by 55%) in the very wet 2017 (39 gCH4-C·m2·yr-1). This may indicate that 1) temperature and precipitation play a role in driving the methane emissions from peatland, 2) increase of methane emissions due to higher precipitation can be compensated by lower temperature leading to smaller emission, 3) at more wet and warm years methane emissions may be higher than presently. However, our manipulation clearly indicated that at manipulated sites (W, WRP and RP) methane fluxes were significantly higher (by 28%) than on control plots for both 2015 and 2016 years, while no significant differences between sites exposed for manipulation were found for wet and warm 2017 (although peat temperatures at W, WRD and RD were higher than on CO). This can indicate that in conditions of a high level of groundwater in peatland (due to high rainfall) the sensitivity of methane production processes to temperature changes caused by manipulations may be lower. On the other hand, we found that higher methane fluxes at the manipulated plots are significantly correlated to a higher biomass of vascular plants. This may indicate how important might be the plant species composition on peatland in defining the transport pathways of methane to the atmosphere and overall methane emissions with respect to anticipated climate change.Research was funded within the NCN projects (017/25/N/ST10/02212, 72016/21/B/ST10/02271) and WETMAN project.

Since January 2008 the first eddy covariance (EC) ecosystem station in Polish forests was set up in a 54-year-old homogenous Scots pine stand near Tuczno (north-western part of the country). Almost 40-m tall steal scaffold tower ensures obtaining CO2 and H2O fluxes from the area extending to 500 m in the prevailing wind direction most of the time. Until now measurements carried out in Tuczno forest are the only direct, real-time and long-term studies of this type in the Poland. In comparison with other European pine forests, investigated using the same technique, this site is very productive, annually sequestering about 16 t of CO2 per hectare. There were many other comprehensive studies done nearby the main EC tower, which were the part of the common project founded by the State Forests since the very beginning e.g.: dendrometry and typical forest biometrics, hydrological and soil investigations, etc.The results of EC measurements of CO2 fluxes from Tuczno site together with data from two others pine forest sites: Tlen I (5-year-old forest, 6 years of data) and Mezyk (25-year-old forest, 2 years of data) allowed to create the cumulative NEP over the chronosequence. This is the first chronosequence curve for one tree species in this part of Europe. Since the climate and soil conditions at all three sites are very similar (there is no significant statistical difference), the current research at all site will be continued until 2025 and we do expect a full chronosequence curve very soon. These results were also compared with models (mainly CBM) and we would like to extend our results to the whole territory of Poland where it is a dominant species (about 60% of total forest area is covered by Pinus Silvestris).

Even though windthrows are the main disturbance type in European forests, their impact on forest carbon balance is generally understudied. In order to close this knowledge gap, we took advantage of a tornado event, which occurred in July 2012 in Trzebciny Forest District in northwest Poland. The main objective of this study was to determine how two completely different reforestation techniques in windthrow areas impact net ecosystem production (NEP) of this Scots pine forest ecosystem under similar meteorological conditions. The two techniques were: conventional (“Tlen I” site): uprooted stumps pulled out and removed from the site followed by ploughing, and non-conventional (“Tlen II” site): all stumps left on the site to decompose with no ploughing. Therefore, we measured carbon dioxide (CO2) fluxes using the eddy covariance (EC) technique for four continuous years. Our results indicate that both sites became significant carbon (C) sources after the windthrow (up to 575 ± 56 g C m−2 y-1 in the first year, Tlen I). However, the Tlen I (conventional technique) lost over 30% less C than Tlen II during the 2015–2016 observation period. In contrast to existing knowledge, ploughing as done at Tlen I, did not substantially increase CO2 emission, as compared to local soil ripping (non-conventional technique). The decrease in net C emission, estimated on the basis of linear model parameters, was almost five times greater at Tlen I than at Tlen II. We thus hypothesize that the annual NEP at conventionally reforested windthrow site will reach C neutrality (NEP = 0) six years after windthrow at most, while at the non-conventionally managed area it will probably take ca. 18 years. So far then, the currently widely applied conventional reforestation technique in wind-disturbed Polish forest appeared to be more effective in decreasing C losses than a technique that leaves stumps to decompose and avoids ploughing.

Although most studies find temperature, soil moisture and water table to be important environmental factors that affect peatland carbon dynamics, the role of vegetation communities has been investigated less. Therefore, this study investigates whether peatland ecosystems produce heterogeneous CO2 fluxes due to differences in vegetation community. In addition, the study also examines which major environmental factors influence this vegetation. To achieve the aims of this study, four sites with different vegetation communities were established in a semi-natural peatland ecosystem in Poland. CO2 flux measurements were carried out using a closed dynamic chamber system. Measurement campaigns were carried out from April until December 2008, every 2–3 weeks. Measured ecosystem respiration (Reco) and net ecosystem exchange (NEE) rates showed daily and seasonal variation at all investigated sites. Reco presented a strong dependence on soil temperature at the 5 cm depth, while NEE showed a strong dependence on solar radiation. The mean temperature sensitivity (Q10) for the four sites ranged between 3.17 and 8.3. The highest NEE and Reco values were obtained at the site represented by Caricetum elatae and the lowest NEE and Reco at the site represented by Calamagrostietum neglectae.

Accurate predictions of net ecosystem productivity (NEPc) of forest ecosystems are essential for climate change decisions and requirements in the context of national forest growth and greenhouse gas inventories. However, drivers and underlying mechanisms determining NEPc (e.g., climate and nutrients) are not entirely understood yet, particularly when considering the influence of past periods. Here we explored the explanatory power of the compensation day (cDOY)-defined as the day of year when winter net carbon losses are compensated by spring assimilation-for NEPc in 26 forests in Europe, North America, and Australia, using different NEPc integration methods. We found cDOY to be a particularly powerful predictor for NEPc of temperate evergreen needleleaf forests (R2=0.58) and deciduous broadleaf forests (R2=0.68). In general, the latest cDOY correlated with the lowest NEPc. The explanatory power of cDOY depended on the integration method for NEPc, forest type, and whether the site had a distinct winter net respiratory carbon loss or not. The integration methods starting in autumn led to better predictions of NEPc from cDOY then the classical calendar method starting 1 January. Limited explanatory power of cDOY for NEPc was found for warmer sites with no distinct winter respiratory loss period. Our findings highlight the importance of the influence of winter processes and the delayed responses of previous seasons' climatic conditions on current year's NEPc. Such carry-over effects may contain information from climatic conditions, carbon storage levels, and hydraulic traits of several years back in time. (Less)

The effects of atmospheric nitrogen deposition (Ndep) on carbon (C) sequestration in forests have often been assessed by relating differences in productivity to spatial variations of Ndep across a large geographic domain. These correlations generally suffer from covariation of other confounding variables related to climate and other growth-limiting factors, as well as large uncertainties in total (dry + wet) reactive nitrogen (Nr) deposition. We propose a methodology for untangling the effects of Ndep from those of meteorological variables, soil water retention capacity and stand age, using a mechanistic forest growth model in combination with eddy covariance CO2 exchange fluxes from a Europe-wide network of forest flux towers. Total Nr deposition rates were estimated from local measurements as far as possible. The forest data were compared with data from natural or semi-natural, non-woody vegetation sites. The carbon sequestration response of forests to nitrogen deposition (dC / dN) was estimated after accounting for the effects of the co-correlates by means of a meta-modelling standardization procedure, which resulted in a reduction by a factor of about 2 of the uncorrected, apparent dC / dN value. This model-enhanced analysis of the C and Ndep flux observations at the scale of the European network suggests a mean overall dC / dN response of forest lifetime C sequestration to Ndep of the order of 40–50 g (C) g−1 (N), which is slightly larger but not significantly different from the range of estimates published in the most recent reviews. Importantly, patterns of gross primary and net ecosystem productivity versus Ndep were non-linear, with no further responses at high Ndep levels (Ndep > 2.5–3 g (N) m−2 yr−1) partly due to large ecosystem N losses by leaching and gaseous emissions. The reduced increase in productivity per unit N deposited at high Ndep levels implies that the forecast increased Nr emissions and increased Ndep levels in large areas of Asia may not positively impact the continent's forest CO2 sink. The large level of unexplained variability in observed carbon sequestration efficiency (CSE) across sites further adds to the uncertainty in the dC / dN response.

The impact of atmospheric reactive nitrogen (Nr) deposition on carbon (C) sequestration in soils and biomass of unfertilised, natural, semi-natural and forest ecosystems has been much debated. Many previous results of this dC / dN response were based on changes in carbon stocks from periodical soil and ecosystem inventories, associated with estimates of Nr deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2019) strive to reduce uncertainties of N effects on C sequestration by linking multi-annual gross and net ecosystem productivity estimates from 40 eddy covariance flux towers across Europe to local measurement-based estimates of dry and wet Nr deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and Nr inputs and losses, these data were also combined with in situ flux measurements of NO, N2O and CH4 fluxes, soil NO3− leaching sampling, as well as results of soil incubation experiments for N and greenhouse gas (GHG) emissions, surveys of available data from online databases and from the literature, together with forest ecosystem (BASFOR) modelling. Multi-year averages of net ecosystem productivity (NEP) in forests ranged from −70 to 826 g (C) m−2 yr−1 at total wet + dry inorganic Nr deposition rates (Ndep) of 0.3 to 4.3 g (N) m−2 yr−1; and from −4 to 361 g (C) m−2 yr−1 at Ndep rates of 0.1 to 3.1 g (N) m−2 yr−1 in short semi-natural vegetation (moorlands, wetlands and unfertilised extensively managed grasslands). The GHG budgets of the forests were strongly dominated by CO2 exchange, while CH4 and N2O exchange comprised a larger proportion of the GHG balance in short semi-natural vegetation. Nitrogen losses in the form of NO, N2O and especially NO3− were of the order of 10–20 % of Ndep at sites with Ndep 3 g (N) m−2 yr−1, indicating that perhaps one third of the sites were in a state of early to advanced N saturation. Net ecosystem productivity increased with Nr deposition up to 2–2.5 g (N) m−2 yr−1, with large scatter associated with a wide range in carbon sequestration efficiency (CSE, defined as the NEP / GPP ratio). At elevated Ndep levels (> 2.5 g (N) m−2 yr−1), where inorganic Nr losses were also increasingly large, NEP levelled off and then decreased. The apparent increase in NEP at low to intermediate Ndep levels was partly the result of geographical cross-correlations between Ndep and climate, indicating that the actual mean dC / dN response at individual sites was significantly lower than would be suggested by a simple, straightforward regression of NEP vs. Ndep.

This protocol is an example of utilizing the eddy covariance (EC) technique to investigate spatially and temporally averaged net CO2 fluxes (net ecosystem production, NEP), in non-typical ecosystems, on a currently reforested windthrow area in Poland. After a tornado event, a relatively narrow "corridor" was created within surviving forest stands, which complicates such kind of experiments. The application of other measuring techniques, such as the chamber method, is even more difficult under these circumstances, because especially at the beginning, fallen trees and in general great heterogeneity of the site provide a challenging platform to perform flux measurements and then to properly upscale obtained results. In comparison with standard EC measurements carried out in untouched forests, the case of windthrow areas requires special consideration when it comes to the site location and data analysis in order to ensure their representativeness. Therefore, here we present a protocol of real-time, continuous CO2 flux measurements at a dynamically changing, non-ideal EC site, which includes (1) site location and instrumentation setup, (2) flux computation, (3) rigorous data filtering and quality control, and (4) gap filling and net fluxes partitioning into CO2 respiration and absorption. The main advantage of the described methodology is that it provides a detailed description of the experimental setup and measurement performance from scratch, which can be applied to other spatially limited ecosystems. It can also be viewed as a list of recommendations on how to deal with unconventional site operation, providing a description for non-specialists. Obtained quality-checked, gap filled, half-hour values of net CO2, as well as absorption and respiration fluxes, can be finally aggregated into daily, monthly, seasonal or annual totals.

This protocol is an example of utilizing the eddy covariance (EC) technique to investigate spatially and temporally averaged net CO2 fluxes (net ecosystem production, NEP), in non-typical ecosystems, on a currently reforested windthrow area in Poland. After a tornado event, a relatively narrow "corridor" was created within surviving forest stands, which complicates such kind of experiments. The application of other measuring techniques, such as the chamber method, is even more difficult under these circumstances, because especially at the beginning, fallen trees and in general great heterogeneity of the site provide a challenging platform to perform flux measurements and then to properly upscale obtained results. In comparison with standard EC measurements carried out in untouched forests, the case of windthrow areas requires special consideration when it comes to the site location and data analysis in order to ensure their representativeness. Therefore, here we present a protocol of real-time, continuous CO2 flux measurements at a dynamically changing, non-ideal EC site, which includes (1) site location and instrumentation setup, (2) flux computation, (3) rigorous data filtering and quality control, and (4) gap filling and net fluxes partitioning into CO2 respiration and absorption. The main advantage of the described methodology is that it provides a detailed description of the experimental setup and measurement performance from scratch, which can be applied to other spatially limited ecosystems. It can also be viewed as a list of recommendations on how to deal with unconventional site operation, providing a description for non-specialists. Obtained quality-checked, gap filled, half-hour values of net CO2, as well as absorption and respiration fluxes, can be finally aggregated into daily, monthly, seasonal or annual totals.

Temperate forest soils of Europe are regarded as an important sink of carbon and thought to have potential to sequester CO2 from atmosphere. However, there are insufficient data not only on organic carbon (OC) content in forest soils and its temporal changes but also on microbiological activity and especially their relationship to carbon turnover. In this study seven research plots were located on afforested land in the north-western part of Poland in Tuczno Forest District (Western Pomerania) in order to examine seasonal variation in OC content and dehydrogenases activity (DHA) during 2012–2016. Based on the studies conducted, statistically significant seasonal variation of the OC content was observed. Higher amounts of OC in the A horizon were observed during spring and autumn seasons and lower in summer. However, no seasonal variation on OC content was observed in the organic horizon (O horizon). Although DHA is thought to exhibit strong seasonal variability, no seasonal variation on DHA was observed. However, a statistically significant difference was observed among studied years (2012–2016), a sharp drop of DHA was noted from spring 2014. Statistical analyses revealed that OC content in soils was a function of forest stand age and progressing acidification of soil. Moreover, OC content in O horizon was negatively correlated with soil moisture and DHA, suggesting that periods with higher microbial activity lead to lower accumulation of carbon in the O horizon. During 2012–2016 only for the O horizon was an increase in OC content was observed.

Although there have been many studies of the net ecosystem productivity (NEP) of different types of forests around the world, the CO 2 dynamics in afforested pine stands of Central Europe are poorly understood. To fill this gap, continuous eddy-covariance (EC) measurements of net ecosystem exchange (NEE) were made from January 2008 to December 2013 in a 62-year-old temperate afforested Scots pine stand near Tuczno. The site is located in north-western Poland, where forests account for almost 30% of the land area and are dominated by Scots pine. Weather conditions during this 5-year period were mostly warm and wet. In all 5 years, air temperature ( T a ) was higher than the 30-year (1983–2013) mean and by 3.3 °C during winter 2008, while precipitation ( P ) was noticeably higher only in summer months. The high productivity of the forest, which sequestered 118 Mg of CO 2 per ha over the 5-year period, is likely because it was planted on fertile meadowland. Annual net ecosystem productivity (NEP = −NEE) ranged from 494 g C m −2 in 2012 to 765 g C m −2 in 2009, with an average of 645 g C m −2 . The interannual variation in NEP was attributed more to the interannual variation in gross ecosystem photosynthesis (GEP) than to ecosystem respiration ( R ). Moreover, both annual NEP and GEP significantly decreased over the 5 years. This was the result of increasingly drier springs and wetter summers as time progressed during the 5-year period, as compared to the 30-year averages, which resulted in a gradual reduction in the growing season NEP and consequently the annual values. Seasonal values of NEP were highly correlated with T a , photosynthetic photon flux density and vapor pressure deficit. The sensitivity of NEP to T a was largely due to the much higher sensitivity of GEP to T a compared to that of R . Although the interannual variability in NEP for separate seasons could not be explained using seasonal values of individual meteorological variables, a hygrothermal index, defined as P /10 T a , explained a large proportion of the interannual variability in NEP in spring and summer.

Due to their unique flora, hydrology and environmental characteristics, peatlands are precious and specific habitats for microorganisms and microscopic animals. Their microbial network structure and their biomass are crucial for peatland carbon cycling, through primary production, as well as decomposition and mineralization of organic matter. Wetlands are one of the ecosystems most at risk from anthropogenic activities and climate change. Most recent scenarios of climate change for Central Europe predict an increase in air temperature and a decrease in annual precipitation. These changes may disturb the biodiversity of aquatic organisms, and the peat carbon sink. Considering the above climatic scenarios, we aimed to: i) assess the response of microbial community biomass to warming and reduced precipitation through the lens of a manipulative experiment in a peatland ecosystem ii) predict how global warming might affect microbial biodiversity on peatlands exposed to warmer temperatures and decreased precipitation conditions. Additionally, we wanted to identify ecological indicators of warming among microorganisms living in Sphagnum peatland. The result of a manipulative experiment carried out at Rzecin peatland (W Poland) suggested that the strongest reduction in microbial biomass was observed in heated plots and plots where heating was combined with a reduction of precipitation. The most pronounced changes were observed in the case of the very abundant mixotrophic testate amoeba Hyalosphenia papilio and cyanobacteria. Shifts in the Sphagnum microbial network can be used as an early warning indicator of peatland warming, especially a decrease in the biomass of important phototrophic microbes living on the Sphagnum capitula, e.g. Hyalosphenia papilio.

The Scots pine is one of the most important species in European and Asian forests. Due to a widespread occurrence of pine forests, their significance in the energy and mass exchange between the Earth surface and the atmosphere is also important, particularly in the context of climate change and greenhouse gases balance. The aim of this work is to present the relationship between the average annual net ecosystem productivity and growing season length, latitude and air temperature (tay) over Europe. Therefore, CO2 flux measurement data from eight European pine dominated forests were used. The observations suggest that there is a correlation between the intensity of CO2 uptake or emission by a forest stand and the above mentioned parameters. Based on the obtained results, all of the selected pine forest stands were CO2 sinks, except a site in northern Finland. The carbon dioxide uptake increased proportionally with the increase of growing season length (9.212 g C m-2 y-1 per day of growing season, R2 = 0.53, p = 0.0399). This dependency showed stronger correlation and higher statistical significance than both relationships between annual net ecosystem productivity and air temperature (R2 = 0.39, p = 0.096) and annual net ecosystem productivity and latitude (R2 = 0.47, p = 0.058). The CO2 emission surpassed assimilation in winter, early spring and late autumn. Moreover, the appearance of late, cold spring and early winter, reduced annual net ecosystem productivity. Therefore, the growing season length can be considered as one of the main factor affecting the annual carbon budget of pine forests.

Peatlands store substantial amount of carbon, are vulnerable to climate change. To predict the fate of carbon stored in peatlands, the complex interactions between water, peat and vegetations need more attention. This study describes a modified version of the ORCHIDEE land surface model for simulating the hydrology, surface energy and CO2 fluxes of peatlands on daily to annual time scales. The model, referred to as ORCHIDEE-PEAT, includes a separate soil tile in each 0.5° grid-cell, defined from a global peatland map and identified with peat-specific soil hydraulic properties. Runoff from non-peat vegetation with a grid-cell containing a fraction of peat is routed to this peat soil tile, which maintains shallow water tables. The water table position separates oxic from anoxic decomposition. The model is evaluated against eddy-covariance (EC) observations from 30 northern peatland sites, with the maximum rate of carboxylation (Vcmax) being optimized at each site to match the peak of growing season gross primary productivity (GPP), derived from direct EC measurements. Regarding short-term variations from day to day, the model performance was good for the variations in GPP (r2 = 0.76, Nash-Sutcliff modeling efficiency, MEF = 0.76), with lesser accuracy for latent heat fluxes (LE, r2 = 0.42, MEF = 0.14) and Net ecosystem CO2 exchange (NEE, r2 = 0.38, MEF = 0.26). Seasonal variations in GPP, NEE and energy fluxes on monthly scales showed moderate to high r2 values ranging from 0.57 to 0.86. For spatial across-sites gradients of annual mean GPP, NEE and LE, r2 of 0.93, 0.27, and 0.71, respectively, were achieved. The water table variations are not well predicted (r2 < 0.1), likely due to the uncertain water input to the peat from surrounding areas. However, when using the observed water table in the carbon module to define the fraction of oxic and anoxic decomposition instead of the modeled water table, ORCHIDEE-PEAT shows a small improvement in reproducing NEE. Moreover, we found a significant relationship between optimized Vcmax and the latitude (temperature), which can better reflect the spatial gradients of annual NEE than using an average Vcmax value. In a future version of ORCHIDEE-PEAT, the influences of water table on photosynthesis and depth-dependent influences of soil temperature on respiration may be included.

Aim of study: The main aim of the work was to summarize availability, quality and comparability of on-going European Research and Monitoring Networks (ERMN), based on the results of a COST FP0903 Action questionnaire carried out in September 2010 and May 2012.Area of study: The COST Action FP0903 involves 29 European countries and 4 non-COST institutions from USA, Morocco and Tunisia. In this study, the total of 22 replies to the questionnaire from 18 countries were included.Materials and methods: Based on the feedback from the Action FP0903 countries, the most popular European Networks were identified. Thereafter, the access to the network database, available quality assurance/quality control procedures and publication were described. Finally, the so-called “Supersites” concept, defined as a “highly instrumented research infrastructure, for both research and monitoring of soil-plant-atmosphere interactions” was discussed.Main results: The result of the survey indicate that the vast majority of the Action FP0903 countries participate in the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forest (ICP Forest). The multi-disciplinary International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICPIM) is the second most widespread forest programme. Research highlights: To fully understand biochemical cycles in forest ecosystems, long-term monitoring is needed. Hence, a network of “Supersites”, is proposed. The application of the above infrastructure can be an effective way to attain a better integration of research and monitoring networks at forest sites in Europe.Keywords: Supersites; European Research Monitoring Networks; Harmonization; Forest.

A b s t r a c t. Methane emission from a wetland was measured with the eddy covariance system. The location of the system allowed observation of methane efflux from areas that were covered by different vegetation types. The data presented in this paper were collected in the period between the13th of June and the 31st of August 2012. During the warmest months of the summer, there was no strong correlation between methane emissions and either the water table depth or peat temperature. The presence of reed and cattail contributed to a pronounced diurnal pattern of the flux and lower methane emission, while areas covered by sedges emitted higher amounts more with no clear diurnal pattern. K e y w o r d s: eddy covariance, methane emission, wetland

International audience; Light use efficiency (LUE) models are widely used to simulate gross primary production (GPP). However, the treatment of the plant canopy as a big leaf by these models can introduce large uncertainties in simulated GPP. Recently, a two-leaf light use efficiency (TL-LUE) model was developed to simulate GPP separately for sunlit and shaded leaves and has been shown to outperform the big-leaf MOD17 model at six FLUX sites in China. In this study we investigated the performance of the TL-LUE model for a wider range of biomes. For this we optimized the parameters and tested the TL-LUE model using data from 98 FLUXNET sites which are distributed across the globe. The results showed that the TL-LUE model performed in general better than the MOD17 model in simulating 8 day GPP. Optimized maximum light use efficiency of shaded leaves (epsilon(msh)) was 2.63 to 4.59 times that of sunlit leaves (epsilon(msu)). Generally, the relationships of epsilon(msh) and epsilon(msu) with epsilon(max) were well described by linear equations, indicating the existence of general patterns across biomes. GPP simulated by the TL-LUE model was much less sensitive to biases in the photosynthetically active radiation (PAR) input than the MOD17 model. The results of this study suggest that the proposed TL-LUE model has the potential for simulating regional and global GPP of terrestrial ecosystems, and it is more robust with regard to usual biases in input data than existing approaches which neglect the bimodal within-canopy distribution of PAR.

The main goal of this paper is to estimate how the observed and predicted climate changes may affect the development rates and emergence of the codling moth in the southern part of the Wielkopolska region in Poland. In order to simulate the future climate conditions one of the most frequently used A1B SRES scenarios and two different IPCC climate models (HadCM3 and GISS modelE) are considered. A daily weather generator (WGENK) was used to generate temperature values for present and future climate conditions (time horizons 2020-2040 and 2040-2060). Based on the generated data set, the degree-days values were then calculated and the emergence dates of the codling moth at key stages were estimated basing on the defined thresholds. Our analyses showed that the average air surface temperature in the Wielkopolska region may increase from 2.8°C (according to GISS modelE) even up to 3.3°C (HadCM3) in the period of 2040-2060. With the warming climate conditions the cumulated degree-days values may increase at a rate of about 142 DD per decade when the low temperature threshold (T(low)) of 0°C is considered and 91 DD per decade when T(low) = 10°C. The key developmental stages of the codling moth may occur much earlier in the future climate conditions than currently, at a rate of about 3.8-6.8 days per decade, depending on the considered GCM model and the pest developmental stage. The fastest changes may be observed in the emergence dates of 95% of larvae of the second codling moth generation. This could increase the emergence probability of the pest third generation that has not currently occurred in Poland.

In this paper some of aspects in modeling over sparse vegetation using the Land-Air Parameterization Scheme (LAPS), including an approach in calculating the turbulent transfer coefficient using “K-theory” inside a sparse vegetation canopy, were considered. For this purpose, the scheme was run for different sparse agricultural cultivars, i.e., apple orchard, winter wheat and soybean crops, at different sites. The modeled values for surface fluxes, canopy temperature and soil moisture content, were compared with observations. [Projekat Ministarstva nauke Republike Srbije, br. 43007: Studying climate change and its influence on the environment: Impacts, adaptation and mitigation]

The global warming potential of nitrous oxide (N2O) and its long atmospheric lifetime mean its presence in the atmosphere is of major concern, and that methods are required to measure and reduce emissions. Large spatial and temporal variations means, however, that simple extrapolation of measured data is inappropriate, and that other methods of quantification are required. Although process-based models have been developed to simulate these emissions, they often require a large amount of input data that is not available at a regional scale, making regional and global emission estimates difficult to achieve. The spatial extent of organic soils means that quantification of emissions from these soil types is also required, but will not be achievable using a process-based model that has not been developed to simulate soil water contents above field capacity or organic soils. The ECOSSE model was developed to overcome these limitations, and with a requirement for only input data that is readily available at a regional scale, it can be used to quantify regional emissions and directly inform land-use change decisions. ECOSSE includes the major processes of nitrogen (N) turnover, with material being exchanged between pools of SOM at rates modified by temperature, soil moisture, soil pH and crop cover. Evaluation of its performance at site-scale is presented to demonstrate its ability to adequately simulate soil N contents and N2O emissions from cropland soils in Europe. Mitigation scenarios and sensitivity analyses are also presented to demonstrate how ECOSSE can be used to estimate the impact of future climate and land-use change on N2O emissions.

Numerical simulations and tests with the recently redesigned land–air parameterization scheme (LAPS) are presented. In all experiments, supported either by one-point micrometeorological, 1D or 3D simulations, the attention has been directed to: (1) comparison of simulation outputs, expressing the energy transfer over and through heterogeneous and non-heterogeneous surfaces, versus observations and (2) analysis of uncertainties occurring in the solution of the energy balance equation at the land–air interface. To check the proposed method for aggregation of albedo, “propagating hole” sensitivity tests with LAPS over a sandstone rock grid cell have been performed with the forcing meteorological data for July 17, 1999 in Baxter site, Philadelphia (USA). Micrometeorological and biophysical measurements from the surface experiments conducted over crops and apple orchard in Serbia, Poland, Austria and France were used to test the operation of LAPS in calculating surface fluxes and canopy environment temperatures within and above plant covers of different densities. In addition, sensitivity tests with single canopy covers over the Central Europe region and comparison against the observations taken from SYNOP data using 3D simulations were made. Validation of LAPS performances over a solid surface has been done by comparison of 2 m air temperature observations against 5-day simulations over the Sahara Desert rocky ground using 3D model. To examine how realistically the LAPS simulates surface processes over a heterogeneous surface, we compared the air temperature measured at 2 m and that predicted by the 1D model with the LAPS as the surface scheme. Finally, the scheme behaviour over urban surface was tested by runs over different parts of a hypothetical urban area. The corresponding 1D simulations were carried out with an imposed meteorological dataset collected during HAPEX-MOBILHY experiment at Caumont (France). The quantities predicted by the LAPS compare well with the observations and the various subcomponents of the scheme appear to operate realistically.

Oxidation of pyrite by nitrate (autotrophic denitrification) was identified as the main cause for sulfate increase in drinking water wells in an agriculturally used watershed, located in the north of Lower Saxony (Germany). Nitrate, which inducts this microbial catalyzed process, is drained into ground water predominantly from agricultural fertilization. The increase of sulfate in the ground water can only be stopped by reducing nitrate leaching into the ground water. To analyze the negative influence of agricultural fertilization on the quality of ground water different fertilization strategies were deducted for an investigated area of 890 ha. Calculated on the basis of nutrient balance of soil surface, the current average nitrogen balance in the investigated area amounts to 91 kg N ha-1 a−1. Farm-gate balance of nutrients is a strong indicator for assessing potential nutrient losses caused by leaching. This indicator shows comparable accuracy to the calculated nutrient balance of soil surface which demands, however, much more data input for calculations. Nitrate concentrations in seepage water in 2 m depth layer of the soil from agricultural fields were simulated with the model HERMES for the whole investigated area (agricultural land + forest). The nitrate concentration in seepage water was calculated for the whole area on the basis of farm-gate nutrient balance as an annual average, which amounts to 14.0 mg NO3–N l−1 (62 mg NO3 l−1). In order to keep the nitrate concentration of the ground water below the threshold value for drinking water (EU-water directive: 11.3 mg NO3–N l−1 (50 mg NO3 l−1) and to limit pyrite oxidation, different scenarios with simulation studies to optimize fertilization measures were developed. Only those scenarios which assured reduction of an average nitrate concentration in the drainage water below 11.3 mg NO3–N l−1 (50 mg NO3 l−1) without profit cuts for the farms were analyzed.

The carbon balance issue is directly related to global warming, since the presence of carbon dioxide and methane in the atmosphere is the key factor behind the greenhouse effect. As observing the exchange of carbon compounds between the ecosystem and the atmosphere has become important in ecological studies, several methods have been developed over recent decades in order to estimate carbon fluxes at different scales. The following text contains a description of the most commonly applied techniques, such as chambers, eddy covariance, and relaxed eddy accumulation. The authors of this chapter have gained experience in designing, building, and using the techniques described below over the past several decades. These systems have been successfully applied in wetlands, forests, and crop ecosystems and have been reliable sources of ecological data until now. The presented overview of the measurement methods is focused on providing an insight into the theoretical basis, as well as the advantages and limitations of all these techniques. This chapter is intended to help a potential user to decide what approach could be applied in their own investigations.

International audience; The turbulence within and immediately above a vegetation canopy is the driver of the exchange processes of heat, trace gases and particles between the soil, the plants and the atmosphere above.

Change in the number of ponds in the Wyskoć catchment basin in the years 1980-2003 and characteristics of the newly excavated pondsThe article presents the results of analyses of changes in the number of ponds in the Wyskoć catchment basin carried out in the years 1980-2003 and the characteristics of ponds excavated in that period. Only water reservoirs of an area less than 2 ha were considered. Analyses were based on topographic maps in the scale of 1:10 000 and aerial photographs taken in 1996. The results indicated that the number of filled ponds increased, especially those located in fields and grasslands. However, forest and wetland ponds were the most resistant to the processes of quantitative degradation because not even a single pond was filled during the analysed period. Over 70% newly excavated water bodies were made as an effect of exploitation of mineral and peat resources. However, nowadays ponds are more often created as a result of intentional human activities and are used for fish farming, recreation and as water retention reservoirs used in irrigation of small agricultural and gardening areas.

Intensive agricultural production leads to degradation of the environment and consequently to decrease of quality of agricultural products. Therefore, there is a need to develop a universal environmental index, which could give information about the ‘environmental quality’ of agricultural products. From the physical point of view environmental degradation can be linked with the concept of entropy and therefore the main goal of the project is: to develop a new method, based on thermodynamics theory of ecosystems, for evaluation of the environmental degradation caused by the intensification of agriculture and to support and ensure ecological and sustainable public policies for agricultural land use. In this project the Pimental theory of eco-energetic analysis of ecosystems will be used. For the analysis and balance of entropy of agricultural ecosystems in relation to the referenced (natural) ecosystem, the concept of ‘entropy pump’ will be used. The overproduction of entropy (not balanced by the ‘entropy p...

The study investigates the potential of a commercially available proximal sensing system – based on a 16-band multispectral sensor – for monitoring mean midday gross ecosystem production (GEPm) in a subalpine grassland of the Italian Alps equipped with an eddy covariance flux tower. Reflectance observations were collected for 5 consecutive years, characterized by different climatic conditions, together with turbulent carbon dioxide fluxes and their meteorological drivers. Different models based on linear regression (vegetation indices approach) and on multiple regression (reflectance approach) were tested to estimateGEPm from optical data. The overall performance of this relatively low-cost system was positive. Chlorophyll-related indices including the red-edge part of the spectrum in their formulation (red-edge normalized difference vegetation index, NDVIred-edge; chlorophyll index, CIred-edge) were the best predictors of GEPm, explaining most of its variability during the observation period. The use of the reflectance approach did not lead to considerably improved results in estimating GEPm: the adjusted R2 (adjR2) of the model based on linear regression – including all the 5 years – was 0.74, while the adjR2 for the multiple regression model was 0.79. Incorporating mean midday photosynthetically active radiation (PARm) into the model resulted in a general decrease in the accuracy of estimates, highlighting the complexity of the GEPm response to incident radiation. In fact, significantly higher photosynthesis rates were observed under diffuse as regards direct radiation conditions. The models which were observed to perform best were then used to test the potential of optical data for GEPm gap filling. Artificial gaps of three different lengths (1, 3 and 5 observation days) were introduced in the GEPm time series. The values of adjR2 for the three gap-filling scenarios showed that the accuracy of the gap filling slightly decreased with gap length. However, on average, the GEPm gaps were filled with an accuracy of 73% with the model fed with NDVIred-edge, and of 76% with the model using reflectance at 681, 720 and 781 nm and PARm data.

Nitrogen fertilization (N) is commonly known as a main source of direct nitrous oxide (N2O) emission from agricultural soils. An area of 38 % of the total land surface of Poland was covered by agricultural soils in 2009. In this paper, we aimed at analyzing data regarding the land exploitation for 13 selected subareas of Poland between 1960 and 2009. Seven out of the 13 subareas studied are located in the West (area A), and six subareas are located in southeast of Poland (area B). The total area covered by large farms (>20 ha) differed largely, between area A (10.6 %) and area B (0.9 %) in 2009. Both areas varied in terms of the amount of fertilizers used annually, average crop yield and crop structure. Average direct emissions of N2O from agricultural soils were 1.66 ± 0.09 kg N2O–N ha−1 a−1 for area A, 1.39 ± 0.07 kg N2O–N ha−1 a−1 for area B and 1.46 ± 0.07 kg N2O–N ha−1 a−1 for the whole country between 1960 and 2009., Regional Environmental Change, 14 (3), ISSN:1436-3798, ISSN:1436-378X

Aims Recent studies revealed convergent temperature sensitivity of ecosystem respiration (R e) within aquatic ecosystems and between terrestrial and aquatic ecosystems. We do not know yet whether various terrestrial ecosystems have consistent or divergent temperature sensitivity. Here, we synthesized 163 eddy covariance flux sites across the world and examined the global variation of the apparent activation energy (Ea), which characterizes the apparent temperature sensitivity of R e, and its interannual variability (IAV) as well as their controlling factors.Methods We used carbon fluxes and meteorological data across FLUXNET sites to calculate mean annual temperature, temperature range, precipitation, global radiation, potential radiation, gross primary productivity and R e by averaging the daily values over the years in each site. Furthermore, we analyzed the sites with >8 years data to examine the IAV of Ea and calculated the standard deviation of Ea across years at each site to characterize IAV.Important Findings The results showed a widely global variation of Ea, with significantly lower values in the tropical and subtropical areas than in temperate and boreal areas, and significantly higher values in grasslands and wetlands than that in deciduous broadleaf forests and evergreen forests. Globally, spatial variations of Ea were explained by changes in temperature and an index of water availability with differing contribution of each explaining variable among climate zones and biomes. IAV and the corresponding coefficient of variation of Ea decreased with increasing latitude, but increased with radiation and corresponding mean annual temperature. The revealed patterns in the spatial and temporal variations of Ea and its controlling factors indicate divergent temperature sensitivity of R e, which could help to improve our predictive understanding of R e in response to climate change.

This paper compares the results of simulations and measurements of evapotranspiration from cultivated fields in Middle Europe. The modelling system THESEUS (i.e. toolbox for hydro-ecological simulation and evaluation utilities) from Wegehenkel (1997a, 2000) was used in this study. Evapotranspiration was also calculated from the latent heat flux density (LE) measured using a modified Bowen ratio method. The model, as well as the modification of the Bowen ratio procedure are described. Heat balance components for eight measurement periods (81 days) were used in the comparison. There was good agreement between model simulations and measurements. The average relative error in evapotranspiration estimation by the model was about 10% for time of integration of few days, and the error decreases with the increase of integration time. The error is smaller for higher daily rates of evapotranspiration.

During 2007-2009 the ADAGIO project (http://www.adagio-eu.org) is carried out to evaluate regional adaptation options in agriculture in most vulnerable European regions (mediterranean, central and eastern European regions). In this context a bottom-up approach is used beside the top-down approach of using scientific studies, involving regional experts and farmers in the evaluation of potential regional vulnerabilities and adaptation options. Preliminary results of the regional studies and gathered feedback from experts and farmers show in general that (increasing) drought and heat are the main factors having impact on agricultural vulnerability not only in the Mediterranean region, but also in the Central and southern Eastern European regions. Another important aspect is that the increasing risk of pest and diseases may play a more important role for agricultural vulnerability than assumed before, however, till now this field is only rarely investigated in Europe. Although dominating risks such as increasing drought and heat are similar in most regions, the vulnerabilities in the different regions are very much influenced by characteristics of the dominating agroecosystems and prevailing socio-economic conditions. This will be even be more significant for potential adaptation measures at the different levels, which have to reflect the regional conditions.

Of a wide variety of international forest research and monitoring networks, several networks are dedicated to the effects of climate change on forests, while the effects of anthropogenic pollutants on forests have been a major area for both monitoring and research for decades. The large amounts of data already obtained within existing monitoring programmes and large-scale international projects can be used to increase understanding of the state and potential of forest mitigation and adaptation to climate change in a polluted environment, and a major challenge now is to evaluate and integrate the presently available databases. We present a meta-database with the main goal to highlight available data and integrate the information about research and monitoring of selected European Research and Monitoring Networks (ERMNs). Depending on the selected ERMNs, the list of variables and the measurement units differ widely in the databases. As a result, activities related to the identification, evaluation and integration of the presently available databases are important for the scientific community. Furthermore, and equally important, the recognition of current knowledge gaps and future needed research is made easier. This analysis suggests that: ground-level ozone is under-investigated, although it is one of the pollutants of greatest concern to forests; in addition to CO2, long-term other greenhouse gasses (GHG) flux measurements should be carried out; there is still a need of improving links between monitoring of atmospheric changes and impacts on forests; research-oriented manipulative experiments in the forests are missing.

This paper reports the results of the analysis of CO2 exchange from a one-month experiment conducted at a mixed deciduous forest, Camp Borden (80°65′W, 44°19′ N), Canada, in the summer of 1993. The mid-day CO2 flux from the forest under clear sky conditions was around −1.0 mg m−2 s−1, the average light and water use efficiencies 13 mmol CO2(mol photon)−1 and 7.95 mg CO2(gH2O)−1 , and the average nocturnal respiration rate 0.21 mg CO2m−2s−1. We observed different flow features at heights of 34.5 (14.5 m above the canopy) and 22.4 m at night. Wavelike structures were frequently encountered at z = 34.5 m. Depending on the phase angle between the vertical velocity and CO2 concentration time series, they could act to enhance the co-gradient (upward) flux or to create counter-gradient (downward) flux of CO2. We speculate that the wave events were limited to isolated regions in the upwind direction. Near the tree-tops (z = 22.4 m), the strong wind shear was able to maintain turbulence. Inverse temperature ramp structures were very common and flux of sensible heat was well behaved (directed downward).