ALBERT

Notes: The effects of elevated CO2 and temperature on the resource allocation pattern and resistance against mammalian herbivores of silver birch (Betula pendula Roth) were studied. Birch seedlings were grown through two growing seasons in closed-top chambers exposed to four different treatments: ambient CO2 and temperature, elevated atmospheric CO2 (700 ppm) and ambient temperature, elevated temperature (+3°C above ambient) and ambient CO2, and a combination of elevated CO2 and temperature. After winter hardening of the seedlings, the growth of the seedlings was measured and the concentration of secondary compounds such as phenolics and papyriferic acid determined. The top parts of the stem were fed to hares, and the basal parts of the same stems were offered to voles.Elevated CO2 increased the height and basal diameter of the shoots, shoot biomass and total biomass of the seedlings but did not have any effect on secondary chemistry. Elevated temperature increased the height and shoot biomass, but did not have a significant effect on the total biomass of the seedlings. Elevated temperature decreased the concentration of condensed tannins and their precursor, (+)-catechin, in the top part of the stems, but only the concentration of (+)-catechin in the basal part of the stems. There were no significant interactive effects between CO2 and temperature on phenolics in the stems, while the concentration of papyriferic acid showed significant interaction in the top part of the stems. This indicates high accumulation of papyriferic acid in ambient CO2 under increased temperature. Consequently, elevated temperature increased the resistance of birch against hares, but did not affect the resistance of the basal parts of the same birches to voles. Our results indicate that the predicted climatic change will not necessarily lead to increased browsing damage by the mountain hare and the field vole to silver birch.

Notes: Reliable models are required to assess the impacts of climate change on forest ecosystems. Precise and independent data are essential to assess this accuracy. The flux measurements collected by the EUROFLUX project over a wide range of forest types and climatic regions in Europe allow a critical testing of the process-based models which were developed in the LTEEF project. The ECOCRAFT project complements this with a wealth of independent plant physiological measurements. Thus, it was aimed in this study to test six process-based forest growth models against the flux measurements of six European forest types, taking advantage of a large database with plant physiological parameters.The reliability of both the flux data and parameter values itself was not under discussion in this study. The data provided by the researchers of the EUROFLUX sites, possibly with local corrections, were used with a minor gap-filling procedure to avoid the loss of many days with observations.The model performance is discussed based on their accuracy, generality and realism. Accuracy was evaluated based on the goodness-of-fit with observed values of daily net ecosystem exchange, gross primary production and ecosystem respiration (gC m−2 d−1), and transpiration (kg H2O m−2 d−1). Moreover, accuracy was also evaluated based on systematic and unsystematic errors. Generality was characterized by the applicability of the models to different European forest ecosystems. Reality was evaluated by comparing the modelled and observed responses of gross primary production, ecosystem respiration to radiation and temperature. The results indicated that: Accuracy. All models showed similar high correlation with the measured carbon flux data, and also low systematic and unsystematic prediction errors at one or more sites of flux measurements. The results were similar in the case of several models when the water fluxes were considered. Most models fulfilled the criteria of sufficient accuracy for the ability to predict the carbon and water exchange between forests and the atmosphere. Generality. Three models of six could be applied for both deciduous and coniferous forests. Furthermore, four models were applied both for boreal and temperate conditions. However, no severe water-limited conditions were encountered, and no year-to-year variability could be tested. Realism. Most models fulfil the criterion of realism that the relationships between the modelled phenomena (carbon and water exchange) and environment are described causally. Again several of the models were able to reproduce the responses of measurable variables such as gross primary production (GPP), ecosystem respiration and transpiration to environmental driving factors such as radiation and temperature. Stomatalconductance appears to be the most critical process causing differences in predicted fluxes of carbon and water between those models that accurately describe the annual totals of GPP, ecosystem respiration and transpiration.As a conclusion, several process-based models are available that produce accurate estimates of carbon and water fluxes at several forest sites of Europe. This considerable accuracy fulfils one requirement of models to be able to predict the impacts of climate change on the carbon balance of European forests. However, the generality of the models should be further evaluated by expanding the range of testing over both time and space. In addition, differences in behaviour between models at the process level indicate requirement of further model testing, with special emphasis on modelling stomatal conductance realistically.

Notes: The frost hardiness of 20 to 25-year-old Scots pine (Pinus sylvestris L.) saplings was followed for 2 years in an experiment that attempted to simulate the predicted climatic conditions of the future, i.e. increased atmospheric CO2 concentration and/or elevated air temperature. Frost hardiness was determined by an electrolyte leakage method and visual damage scoring on needles. Elevated temperatures caused needles to harden later and deharden earlier than the controls. In the first year, elevated CO2 enhanced hardening at elevated temperatures, but this effect disappeared the next year. Dehardening was hastened by elevating CO2 in both springs. The frost hardiness was high (〈−40 °C), even at elevated temperatures, in midwinter, at which time the electrolyte leakage method underestimated the frost hardiness compared with the visual scoring. In addition to the significant differences between treatments, there was also significant variation between trees in frost hardiness within treatments. These results suggest that the risks of frost damage are marked in the predicted climatic conditions in Finland, and, more specifically, they depend on how the occurrence of the frost episodes changes with respect to climatic warming during the annual cycle, especially in the autumn and spring. We also conclude that the conditions in midwinter are not critical for frost injury to trees in the future.

Notes: Starting in rrrr, individual trees of Scots pine (Pinus sylvestris L.) aged 30 years were grown in closed-top chambers and exposed to normal ambient conditions (CON), elevated CO2 (Elev. C), elevated temperature (Elev. T) and a combination of elevated CO2 and temperature (Elev. C + T). Using the constant-power heat balance method, sap flow was monitored simultaneously in a total of 16 trees, four for each treatment, over a 32 d period (after the completion of needle expansion and branch elongation in 1997). An overall variation in diurnal sap flow totals (Ft) was evident during the period of measurement (days 167–198, 1997) regardless of the treatments, with a range from 0·15 to 2·82 kg tree–1 d–1. Elev. C reduced Ft by 4·1–13·7% compared with CON on most days (P varies from 0·042 to 0·108), but slightly increased it on some days (P≥ 0·131), depending on the weather conditions. Although the decrease in Ft caused by Elev. C was statistically significant on only a few days (P≤ 0·042), the cumulative Ft for the 32 d decreased by 14·4% (P = 0·047), indicating that Elev. C may have an important influence on seasonal water use of the Scots pine. Analysis of the diurnal courses of sap flow combined with corresponding weather factors indicated that the CO2-induced decrease in Ft could be largely attributed to an increase in stomatal sensitivity to vapour pressure deficit (VPD), whereas the CO2-induced increase in Ft related to an increase in stomatal sensitivity to low light levels. Elev. T increased Ft by 11·2–35·6% throughout the measuring period and the cumulative Ft for the 32 d by 32·5% (P = 0·019), which could be largely attributed to the temperature-induced increase in current-year needle area and decrease in stomatal sensitivity to high levels of VPD. There were no significant interactive effects of CO2 and temperature on sap flow, so that Elev. C + T had approximately the same Ft as Elev. T and similar diurnal patterns of sap flow, suggesting that the temperature factor played a dominant role in the case of Elev. C + T.

Notes: The effects of elevated atmospheric CO2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, process-based computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO2] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (Amax), the potential electron transport rate (Jmax), the maximum Rubisco activity (Vcmax) and leaf nitrogen concentration on mass (Nm) and area (Na) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO2]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO2 concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters Jmax and Vcmax of the order of 10%. This reduction in Jmax and Vcmax was linked to the effects of elevated [CO2] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO2]. Tables of model parameter values for different European forest species are given.

Notes: Naturally regenerated Scots pines (Pinus sylvestris L.), aged 28–30 years old, were grown in open-top chambers and subjected in situ to three ozone (O3) regimes, two concentrations of CO2, and a combination of O3 and CO2 treatments From 15 April to 15 September for two growing seasons (1994 and 1995). The gas exchanges of current-year and 1-year-old shoots were measured, along with the nitrogen content of needles. In order to investigate the factors underlying modifications in photosynthesis, five parameters linked to photosynthetic performance and three to stomatal conductance were determined. Elevated O3 concentrations led to a significant decline in the CO2 compensation point (Г*), maximum RuP2-saturated rate of carboxylation (Vcmax), maximum rate of electron transport (Jmax), maximum stomatal conductance (gsmax), and sensitivity of stomatal conductance to changes in leaf-to-air vapour pressure difference (∂gs/∂Dv) in both shoot-age classes. However, the effect of elevated O3 concentrations on the respiration rate in light (Rd) was dependent on shoot age. Elevated CO2(700 μmol mol−1) significantly decreased Jmax and gsmax but increased Rd in 1-year-old shoots and the ∂gs/∂Dv in both shoot-age classes. The interactive effects of O3 and CO2 on some key parameters (e.g. Vcmax and Jmax) were significant. This may be closely related to regulation of the maximum stomatal conductance and stomatal sensitivity induced by elevated CO2. As a consequence, the injury induced by O3 was reduced through decreased ozone uptake in 1-year-old shoots, but not in the current-year shoots. Compared to ambient O3 concentration, reduced O3 concentrations (charcoal-filtered air) did not lead to significant changes in any of the measured parameters. Compared to the control treatment, calculations showed that elevated O3 concentrations decreased the apparent quantum yield by 15% and by 18%, and the maximum rate of photosynthesis by 21% and by 29% in the current-year and 1-year-old shoots, respectively. Changes in the nitrogen content of needles resulting from the various treatments were associated with modifications in photosynthetic components.

Notes: In this experiment, the photosynthetic acclimation of successive needle cohorts of Scots pine were studied during 3 years of growth at elevated CO2 and temperature. Naturally regenerated Scots pine (Pinus sylvestris L.) trees were subjected to elevated CO2 concentration (+CO2, 700 p.p.m), elevated temperature (+T, ambient +2 to +6 °C) and to a combination of elevated CO2 and temperature (+CO2 + T) in closed-top chambers, starting in August 1996. Trees growing in chambers with ambient CO2 and ambient temperature served as controls (AmbC). Elevated CO2 influenced the dark reactions more than the light reactions of photosynthesis, as in the 1996 and 1997 cohorts the carboxylation capacity of Rubisco was reduced in the first and second year of exposure, but there was no consistent change in chlorophyll fluorescence. Net photosynthesis measured at growth concentration of CO2 was higher at +CO2 than at AmbC on only one measuring occasion, was generally lower at +T and was not changed at +CO2 + T. However, trees grown at +T tended to invest more nitrogen (N) in Rubisco, as Rubisco/chlorophyll and the proportion of the total needle N bound to Rubisco occasionally increased. The interaction of +CO2 and +T on Rubisco was mostly negative; consequently, in the second and third year of the experiment the carboxylation capacity decreased at +CO2 + T. In the 1996, 1997 and 1998 cohorts, the structural N concentration of needles was lower at +CO2 than at AmbC. Elevated CO2 and elevated temperature generally had a positive interaction on N concentration; consequently, N concentration in needles decreased less at +CO2 + T than at +CO2. At +CO2 + T, the acclimation response of needles varied between years and was more pronounced in the 1-year-old needles of the 1997 cohort than in those of the 1998 cohort. Thus, acclimation was not always greater in 1-year-old needles than in current-year needles. In the +CO2 + T treatment, elevated temperature had a greater effect on acclimation of needles than elevated CO2.

Notes: Abstract Guidelines of the Intergovernmental Panel on Climate Change (IPCC) were used to assess a greenhouse gas inventory for land use change and forestry in Finland. In 1952, managed forests represented a carbon (C) sink of 2.3 Tg yr-1 (Tg=teragram=1012g) in terms of total biomass growth and drain, converted into respective biomass. In 1960, forests were a carbon source of 0.1 Tg C yr-1, but since 1970 the size of the forest C sink has increased from 0.5 Tg yr-1 to 8.3 Tg yr-1 in 1990. If the future use of the forest resources remains at the level of late 1980s, the size of forest C sink could increase to 14.2 Tg yr-1 by 2010 and to 24.9 Tg yr-1 by 2030. The maximum use of the forest resources could result in a 2.2 Tg yr-1 C source by 2010, and in a 0.8 Tg yr-1 source by 2030. The average annual C balance for the period 1991–2030 could amount to −0.5−17.6 Tg yr-1, depending on the use of forest resources. Carbon emissions related to forest drainage and soil preparation seem to be extremely uncertain, although they seem to have a potential to decrease the sinks substantially. On the other hand, taking roundwood import, and wood products more precisely, into consideration would increase the C sink. Changing climate may increase carbon accumulation in forests and affect the sink.

Notes: Abstract Guidelines of the Intergovernmental Panel on Climate Change (IPCC) were used to assess a greenhouse gas inventory for land use change and forestry in Finland. In 1952, managed forests represented a carbon (C) sink of 2.3 Tg yr−1 (Tg = teragram = 1012g) in terms of total biomass growth and drain, converted into respective biomass. In 1960, forests were a carbon source of 0.1 Tg C yr−1, but since 1970 the size of the forest C sink has increased from 0.5 Tg yr−1 to 8.3 Tg yr−1 in 1990. If the future use of the forest resources remains at the level of late 1980s, the size of forest C sink could increase to 14.2 Tg yr−1 by 2010 and to 24.9 Tg yr−1 by 2030. The maximum use of the forest resources could result in a 2.2 Tg yr−1 C source by 2010, and in a 0.8 Tg yr−1 source by 2030. The average annual C balance for the period 1991–2030 could amount to −0.5–17.6 Tg yr−1, depending on the use of forest resources. Carbon emissions related to forest drainage and soil preparation seem to be extremely uncertain, although they seem to have a potential to decrease the sinks substantially. On the other hand, taking roundwood import, and wood products more precisely, into consideration would increase the C sink. Changing climate may increase carbon accumulation in forests and affect the sink.

Notes: Abstract Flows of carbon (C) in the forest ecosystem were simulated with a gap-phase dynamics type model, while flows of C in wood products were simulated using a model that processes raw material into final products. In southern Finland, the ratio between gross production and total storage for the 500 year period was 3052–3572 Mg C ha−1: 192–223 Mg C ha−1 under the current climate and 4257–5096 Mg C ha−1: 260–318 Mg C ha−1 under the predicted changing climate. In northern Finland, the respective ratios were 1721–2021 Mg C ha−1: 103–134 Mg C ha−1 and 3409–4475 Mg C ha−1: 212–244 Mg C ha−1. The average total C storage in southern Finland over the 500 year period was 174–181 Mg C ha−1 under the current climate, and 206–217 Mg C ha−1 under the changing climate. In northern Finland, average total storage was 101 Mg C ha−1 under the current climate, and 191–198 Mg C ha−1 under the changing climate. The average C storages in unmanaged forest ecosystems under the current climate and under changing climate were 200 and 191 Mg C ha−1 respectively in southern Finland, and 142 and 193 Mg C ha−1 in northern Finland. Approximately 27–43% of total C was stored in wood products over a 500 year period. Wood products contributed 15–22% of the total emissions to the atmosphere. Over short periods, C sequestration potentials are much greater than over longer periods.