We modelled the combined effects of past and expected future changes in climate and nitrogen deposition on tree carbon sequestration by European forests for the period 1900–2050. Two scenarios for deposition (current legislation and maximum technically feasible reductions) and two climate scenarios (no change and SRES A1 scenario) were used. Furthermore, the possible limitation of forest growth by calcium, magnesium, potassium and phosphorus is investigated. The area and age structure of the forests was assumed to stay constant to observations during the period 1970–1990. Under these assumptions, the simulations show that the change in forest growth and carbon sequestration in the past is dominated by changes in nitrogen deposition, while climate change is the major driver for future carbon sequestration. However, its impact is reduced by nitrogen availability. Furthermore, limitations in base cations, especially magnesium, and in phosphorus may significantly affect predicted growth in the future.

The estimate of growth losses by ozone exposure of forest trees is a significant part in current C sequestration calculations and will also be important in future modeling. It is therefore important to know if the relationship between ozone flux and growth reduction of young trees, used to derive a Critical Level for ozone, is also valid for mature trees. Epidemiological analysis of stem increment data from Fagus sylvatica L. and Picea abies Karst. observed in Swiss forest plots was used to test this hypothesis. The results confirm the validity of the flux-response relationship at least for beech and therefore enable estimating forest growth losses by ozone on a country-wide scale. For Switzerland, these estimates amount to 19.5% growth reduction for deciduous forests, 6.6% for coniferous forests and 11.0% for all forested areas based on annual ozone stomatal uptake during the time period 1991–2011.

A dramatic increase in winter (December–February) temperature by 7.2 K (1.1 K per decade) since 1950 has occurred in the Ulan Bator basin, Mongolia. This increase in temperature strongly exceeds the global average of late twentieth century warming and even exceeds warming in most of the polar regions with pronounced increases in temperature. The exceptional warming is restricted to Ulan Bator within the Mongolian forest-steppe region and to wintertime. This suggests that the observed warming could result from radiative forcing by black carbon aerosols. In winter, Ulan Bator’s air is heavily polluted by particulate matter, including black carbon, originating from the combustion of low-quality fuel at low temperature. Winter smog has strongly increased in recent decades, concomitant to the increase in winter temperature, as the result of a strong increase in the city’s population. Exponential growth of Ulan Bator’s population started in the mid-twentieth century, but since 1990, altered socioeconomic frame conditions and a warming climate have driven more than 700,000 pastoralists from rural Mongolia to Ulan Bator where people live in provisional dwellings and cause Ulan Bator’s heavy air pollution. Tree-ring analysis from larch trees growing at the edge of the Ulan Bator basin shows negative correlation of stem increment with December temperature. This result suggests that milder winters promote herbivores and, thus, reduce the tree’s productivity. The negative impact of winter warming on the larch forests adds to adverse effects of summer drought and the impact of high sulfur dioxide emissions. Winter warming putatively associated with high atmospheric concentrations of black carbon aerosols in the Ulan Bator basin is an interesting example of a case where greenhouse gas-mediated climate warming in an area where people themselves hardly contribute to global greenhouse gas emissions affects both humans and ecosystems and causes additional local climate warming.

The effect of chronic high groundwater nitrate loading on riparian forests is poorly understood. The growth patterns of northern white cedar (Thuja occidentalis) and related plant–soil processes were examined at four riparian sites in southern Ontario, Canada which have similar vegetation, soils, and hydrology but have differed in adjacent land use for >60 years. Fertilized cropland at two riparian sites produced groundwater-fed surface flows with high mean NO3–N concentrations of 9 and 31 mg l−1, whereas mean concentrations were <0.5 mg l−1 at two control sites down slope from forest. Tree-ring analysis at the two nitrate-rich sites indicated a positive growth trend in 1980–2004 and an absence of a positive growth trend in the 1945–1970 period that preceded high rates of synthetic nitrogen fertilizer use on cropland. However, a significant increase in growth also occurred in 1980–2004 at the two control riparian sites suggesting that high groundwater nitrate inputs did not influence tree growth. Cedar foliar and litter N content did not differ significantly between the high nitrate and control sites. Litter decomposition rates measured by the litterbag technique at a nitrate-enriched and control site were similar. Litter from a high nitrate and a control site produced a similar rate of potential denitrification in lab incubations of riparian surface peat. This study indicates that prolonged nitrate inputs in groundwater did not increase nitrogen uptake and growth of white cedar or stimulate decomposition and denitrification as a result of changes in the quality of plant material. In the absence of anthropogenic nitrate inputs, riparian wetland soils are typically high in ammonium and low in nitrate, and as a consequence, white cedar may have a limited ability to utilize nitrate.

Forest is an important vegetation type on the globe, and clearcutting is the main forest management method. This paper presents a process-based model developed to project the impact of forest growth and clearcutting on dissolved organic carbon (DOC) and total mercury (THg) export from forest-dominated watersheds over two forest-growing cycles. The modelling of THg is based on the observation that THg export from terrestrial to aquatic ecosystems occurs with the binding and subsequent in-stream transport of THg by DOC. From the results generated with the integrated model, DOC and THg export follows two main trends; (i) a multiple-year trend, associated with forest harvesting and re-growth patterns over the lifetime of the forest, and (ii) an annual trend, associated with the seasonal dynamics in forest litter production and decomposition. During a forest rotation, DOC and THg concentration decreases following clearcutting, reaches a minimum at about 15 years after forest regeneration and then gradually increases with forest ageing. Large debris pools left on site following clearcutting can provide a significant pulse in DOC production and within-watershed THg export during the first 2–3 years after harvest. In a single year, the integrated model predicts that DOC- and THg-concentration peaks after leaf fall in autumn, decreases to a minimum in April, increases to another maximum in June and finally decreases to a second minimum just before leaf fall. This seasonal cycle is repeated every year. Conifer species and wetland-dominated watersheds are anticipated to release a greater amount of DOC and THg to aquatic ecosystems than deciduous and dryland-dominated watersheds. The long-term and seasonal DOC production is consistent with field measurements.

In recent years, there has been the phenomena of spruce dieback in Europe. Significant areas of spruce low mortality now cover both sides of the Polish southern border. We evaluated ecochemical parameters influencing the heavy dieback occurring in mature spruce stands in the Polish Carpathian Mountains. Dolomite, magnesite and serpentinite fertilizers were applied to experimental plots located in 100-year-old stands in the autumn of 2008. The experimental plots were located in the mid-elevational forest zone (900–950 m) on two nappes of the flysch Carpathians: Magura (Ujsoły Forest District) and Silesian (Wisła Forest District). The saturation of the studied soils demonstrates moderate resilience of soils in Wisła Forest District in relation to acid load and high flexibility of the Ujsoły soils. After application of the fertilizers, an increase of Mg, Ca and Mb was noted in the soil solution, determined in the overlaying highly acidic organic horizons through the ion-exchange buffering mechanism of highly protonated functional groups with high buffering capacity. Magnesium concentration increased following fertilization, presenting a potential improvement of forest growth capacity without the hazard of adverse side effects of liming. Aluminium stress in old spruce is unlikely, while trees in the control plots in Wisła Forest District may already be sensitive to aluminium stress. Serpentinite fertilization improved the supply of soils in magnesium without causing significant changes in the pH of the soil. Such changes in the pH were found in dolomite and magnesite fertilizer.

Within limited growth age in some regions, forest production, including gross primary production (GPP) and net primary production (NPP), was linearly correlated with leaf area index (LAI). However, over wide range of growth age in the global scale, LAI patterns of forest production are unclear. Here, we compiled a subset from the Global Soil Respiration Database (SRDB) for global temperate forest ecosystems. The subset database mainly included forest production, soil respiration, and LAI data in 493 study sites over wide range of forest growth age (0–500 years). The results showed that LAI initially increased rapidly, reached a peak at juvenility, decreased slowly until maturity, and again increased possibly with further forest aging (R² = 0.21, P < 0.001). We found that the dynamics of both GPP and NPP across global temperate forest ecosystems were driven by LAI. GPP initially increased and subsequently stabilized with increasing LAI. NPP peaked at LAI of about 5.6 m² m⁻², and subsequently decreased. The decrease in NPP resulted from the asymptotic increase in GPP and the continuing decrease in the NPP/GPP ratio with increasing LAI. The decline in the NPP/GPP ratio resulted from the significant increase in autotrophic respiration (Rₐ), and especially after canopy closure, Rₐ increased more quickly with increasing LAI than GPP. These results will improve our understanding of the control of LAI on ecosystem production.