Analyses of a time-series of needlefall data showed enhanced needlefall due to unusually warm and dry weather in southeastern Norway during 1986-2000. Needlefall was sampled routinely in ten stands of older Picea abies as part of long-term forest monitoring. Mixed linear models were developed for brown and green needlefall separately. Both the brown and the green needlefall had clear seasonal variations, peaking in October and May, respectively. In addition, the needlefall was correlated with weather conditions. Unusually dry summers were followed by increased brown needlefall in the autumns and winters, and unusually high temperatures were accompanied by increased amounts of green needlefall, in particular in the winter. Using the models, we found that unusually warm and dry weather during these 15 years likely caused an overall surplus of needlefall. Even though the brown needlefall was the dominant fraction of the needlefall, the surplus of green needlefall was of larger magnitude. The results suggest that unusually warm winters and dry summers were the main cause of increased crown defoliation during these years.

Concentrations of dissolved organic carbon (DOC) in soil water from the base of the soil organic layer were determined at three forest plots along an altitudinal gradient in eastern Norway. The lowest plot, at 830 m above sea level (a.s.l.), was in Norway spruce forest and there were additional plots at the ecotone between Norway spruce and mountain birch at 925 m a.s.l. and at the forest line (1000 m a.s.l.). DOC concentrations in soil water did not decrease uniformly with altitude although tree biomass, above-ground litterfall and the soil C pool all did so. Significant correlations between DOC and {H+} or electrical conductivity may reflect the contribution of DOC to solution acidity and the anionic charge, respectively. If mean temperature during the growing season increases, tree growth at any given altitude will tend to increase and the spruce-birch ecotone may move to a higher altitude than at present. Increased C inputs as litter to the soil might then lead to increasing DOC concentrations and fluxes in surface waters.

Several strong westerly storms hit western Norway during the winter of 1986/87. We studied the uptake, loss and visible effects of sea salt aerosols in Scots pine and Norway spruce. Foliage was sampled at distances 0-100 km from the coastline between 59degrees and 65degreesN, and analysed for chloride, sodium and other elements. The range of chloride and sodium concentrations in needles was 0.5-5.0, and 0.1-3.0 mg g(-1), respectively. The local variation was very large close to the coast. The relation to distance from the sea was improved by using distance from the nearest fjord rather than from the outer coastline. Other elements were less variable and not related to distance from the sea, or to sea salt concentrations. Only 1-10 per cent of the needles' sea salt content could be removed by 2 min washing in distilled water, and even less for other elements. The amount of sea salt removed by washing was less related to distance from the sea than was the total content. Visible damage to the foliage occurred at chloride concentrations above 1 mg g(-1) in the needles. Our conclusions are that analysis of the needles' chloride or sodium content is a robust method for confirming damage to tree foliage by sea salt aerosols. Fjords as well as the ocean are significant sources of sea salt aerosols. Large local variations in salt deposition and damage will occur near a rugged coastline. Nutrients and other elements are not significantly affected by the sea salt deposition. The use of chloride or sodium as a tracer for dry deposition should take into account not only the enrichment of these elements in canopy throughfall, but also the accumulation in the needles.

This study shows that it is questionable if critical load modelling can contribute in the search for harmful effects of acid deposition on forest health at present. Critical loads forS and N deposition were calculated using the MAGIC and PROFILE models for more than 100 monitoring plots in Norway spruce forestin south-east Norway. The two models gave different results, likely due to differences in the models, including differences in the time spans applied. The PROFILE model gave considerably more plots with exceedance than the MAGIC model.At plots where the CL was exceeded, calcium/aluminium (Ca/Al) ratios in the soil solutions were low. However, very few of theseplots had possible harmful values of the Ca/Al-ratio. More than 50 yr seems in most cases to be needed to bring Ca/Al ratios below 1.0. Present deposition was better correlated with measured forest condition variables such as crown condition and needle chemistry,than with modelled exceedance according to any of the two methods. The deposition of S and N was weakly, negatively correlated to foliar concentrations of P and Ca, and positivelyto foliar N concentrations and crown density.

Aluminium (Al) is a key element in critical loadcalculations for forest. Here, we argue for re-evaluating theimportance of Al. Effects of two levels of enhanced Alconcentrations and lowered Ca:Al ratios in the soil solutionin a field manipulation experiment in a mature spruce stand(1996–1999) on tree vitality parameters were tested. Inaddition, Al solubility controls were tested. Various loads ofAl were added to forest plots by means of an irrigationsystem. Potentially toxic Al concentrations and criticalratios of Ca to inorganic Al were established. The ratio of Cato total Al was not a suitable indicator for unfavourableconditions for plant growth. No significant effects on crowncondition, tree growth and fine root production were observedafter three years of treatment. In 1999, foliar Mg content inthe highest Al addition treatment had declined significantly.This agreed with the known response to Al stress of seedlingsin nutrient solution experiments. No support was found forusing the chemical criterion Ca:Al ratio in soil solution,foliar and root tissue as an indicator for forest damage dueto acidification. Al solubility was considerably lower thanimplied by the assumption of equilibrium with gibbsite,particularly in the root zone. The gibbsite equilibrium iscommonly used in critical load models. Substitution of thegibbsite equilibrium with an Al-organic matter complexationmodel to describe Al solubility in soil water may have largeconsequences for calculation of critical loads. The resultsindicate that critical load maps for forests should bereconsidered.

Aluminium (Al) has been considered to be a central element for risk evaluation of forest damage due to acidification. It has been hypothesized that Al reduces root growth, nutrient uptake and forest vitality. However, forest monitoring studies fail to show correlations between soil acidification and forest health. In general, no direct relation between Al concentration and forest health has been established. Here, Al concentrations in soil solution were manipulated by weekly additions of dilute AlCl3 to levels that are believed to be unfavorable for plant growth. Four treatments (in triplicate), including a reference and three Al addition levels, were established. Effects of enhanced Al concentrations on fine root growth, nutrient uptake and crown condition in a mature Norway spruce forest in Norway were tested (1996–1999). After three years of manipulation, crown condition, tree growth and fine root growth were not affected by potentially toxic Al concentrations. However, the Mg content in current year's needles decreased at the highest Al addition treatment. The Mg/Al ratio of fine roots of the same treatment had declined too, which suggests that Al blocked Mg uptake at the root surface. The manipulation will be continued for two more years.

Air pollution induced changes in pine needle chemistry were observed at sample sites in the surroundings of the Pechenganikel smelter. Close to the smelter, elevated concentrations of Ni, Cu and S were found (Ni: 0.7–1 mmol/kg, Cu: 0.4–0.5, and S 40–60 mmol/kg). Close to the pollution source, needles were enriched in Ni and Cu by needle age. Correlation and principal component analyses show that changes in the element composition of pine needles depended on air pollution and on natural factors as well. The contribution from air pollution increased with needle age. Besides direct input of pollutants from atmosphere, soil contamination and nutritional disturbance contributed significantly to the observed changes.

Six sites for forest ecosystem monitoring were established to perform a long-term study of effects of air pollution on pine forest ecosystems along a pollution gradient in the border areas between Norway and Russia. The main pollution source is a nickel smelter. Several methods and analyses were used to investigate different compartments of this northern boreal forest ecosystem. The differences in ecological condition and diversity observed among the research sites are probably due to the air pollution load in the area. The elevated concentrations of Ni and Cu detected in plant tissues, the reduced lichen vegetation on stems and on the forest floor, and the reduced or absent moss vegetation are the most obvious impacts in the investigated area.

Measurement data on air, precipitation and canopy throughfall chemistry from a network of sites have been combined to study scavenging and deposition processes, with particular emphasis on the oxidised nitrogen species. High deposition rates of oxidised nitrogen occur in coastal areas of SW Norway. These are partly caused by high precipitation rates, partly also because a large fraction of the oxidised nitrogen is present as nitrate in large particles, which are rapidly removed by both wet and dry deposition processes. High wind speeds near the coast result in high concentrations of sea-salt particles in the air and high deposition rates of both nitrate and sea-salt particles, particularly in coniferous forest stands. HNO3 contributes on average only about 10–20% to the sum of aerosol nitrate and HNO3 (sNO3). Still, the combined dry deposition velocity of sNO3 to these forest stands may be between 4 and 6cms−1 on average.

The Norwegian Monitoring Programme for Forest Damage has now been running since 1984. Its main objective has been monitoring the boreal forest conditions in relation to air pollution. Surveys of forests are performed on plots in a nation-wide representative grid network, in a network of local countywise plots, and in a network of intensively monitored plots within the framework of the internationally co-ordinated UN/ECE ICP Forests. At intensively monitored plots, a number of measurements were performed, for example tree crown-condition assessments, foliar chemistry, air pollution, precipitation chemistry (open area and stand throughfall), soil and soil-water chemistry. Vitality criteria have shown a declining trend, expressed as reduced crown density and more of discoloured trees, particularly in spruce forests. These results are similar to findings in other Scandinavian countries and coincide with the general trend in Europe. Forest yield has increased in later years in most parts of Norway. Tree mortality in excess of normal is not recorded.Considering these results, it is reasonable to presume that most Norwegian forest ecosystems are generally in a good condition. Areas in the south-eastern part of the country, however, may have shown indications of a slightly reduced crown condition. These areas are located in a region with a relatively high load of air pollution and low buffering capacity against acidification. Although forest conditions generally depend on soil, tree age, climate, pests and diseases, and other natural stressors; air pollution loads add to, or may interact with, these factors. Most likely inciting factors (e.g. summer drought) have occurred and produced visual symptoms. The actual effect of the air pollution component is, therefore, difficult to estimate; however, its importance is not discounted. (C) 2000 Elsevier Science B.V. All rights reserved.

Concentrations of 34 elements determined by ICP mass spectrometry were studied in surface soil and vegetation along a north–south gradient through the ‘Pechenganickel’ smelter complex in Kola peninsula, northern Russia. Strong influence from the smelter was evident for Fe, Co, Ni, and Cu, mainly associated with dry deposition of large particles. Also for As, Se, Mo, Sb, Te, Bi, and Pb the smelter or associated sources appeared to be distinct contributors of contamination consisting presumably of smaller particles. Significant but less distinct effects leading to enhanced concentration levels were observed for P, S, V, Cr, Zn, and Tl. In the case of Mn, Rb, Sr, Cs, and Ba the concentrations in vegetation were generally lower near the source, which may be due to cation exchange with protons or heavy metal cations in the soil and subsequent leaching from the root zone. For Li, Be, B, Na, Mg, Al, Ca, Y, Cd, La, Th, and U no particular influence from the smelter complex was observed. Some characteristic differences observed in element concentrations in different plant species and between different years of Pinus sylvestris needles are discussed. The high concentrations observed for many trace elements in the humus horizon indicates that it acts as an active biogeochemical barrier against downward transport of these elements.

The complex character of variations in acidity and cation exchange properties of forest podzols under the impact of atmospheric emissions from the Pechenganikel' plant in the Kola Peninsula was revealed using correlation and regression analyses. The high level of acidity and the depletion of the upper horizons in exchangeable bases attest for the anthropogenic acidification of podzols in the affected zone of the plant.