Dan Aamlid

Avdelingsleder

(+47) 915 21 025
dan.aamlid@nibio.no

Sted
Ås - Bygg H7

Besøksadresse
Høgskoleveien 7, 1433 Ås

Sammendrag

Utstillingen «Det fantastiske treet» forteller om hvordan treet blir til, og at fotosyntesen er grunnlaget for alt liv. Bladene er verdens beste solfangere, og vi forteller hvordan fotosyntesen skjer i bladet. Trærnes magiske evne til å forvandle luft til sukker forklares på en ny og spennende måte. For å vise hvor spektakulær fotosyntesen er har vi lagd en 9 meter lang lysende akrylvegg som viser snittet av et blad. Midt i utstillingen står en 7,5 meter høy treskulptur laget av 10 km aluminiumsrør – selve Det fantastiske treet. Det fantastiske treeter et godt eksempel på forskningsformidling og et fruktbart samarbeid mellom to institusjoner. Norsk institutt for bioøkonomi (NIBIO) ved Skog og utmarksdivisjonen (tidligere Skog og landskap) har gjort et stort og omfattende arbeid med å tilgjengeliggjøre forskning og kvalitetssikre innholdet i utstillingen. NIBIO har vært en uvurdelig støttespiller i den faglige kvalitetssikringen. Vi har lagd en utstilling som skal overbevise publikum om hvilken spektakulær prosess fotosyntesen er og at det ikke er «bare bare» å bli et stort tre. Publikum skal både fascineres, og de skal få ny kunnskap. Den skal også vekke nysgjerrigheten for spennende forskning og alle ubesvarte spørsmål vi har rundt skogen og treet – det er fremdeles mye vi ikke vet!

Sammendrag

The Pasvik River valley is the easternmost part of Norway, and borders to Finland and Russia. In Norway it is known for its wilderness and taiga forests. During the 1960-1970s most of the mature pine forests were harvested, and large areas of pine stands have been naturally regenerated. In addition, large areas are covered with birch. The Pasvik River valley and the adjoining areas are therefore important both as an area for growing timber resources and for recreation. However, these areas have also been exposed to air pollution from Russian smelting industry since the 1930s. In addition to sulphur dioxide, emissions consist of various heavy metals which contaminate the surroundings. The main pollution source is the huge nickel plant in the Russian city Nikel, located only 10 km from the Norwegian border. For a long time there was general concern for the quality of the forest ecosystems in these areas. This concern accelerated in the mid-1980s.

Sammendrag

The chapter reviews the available literature about the adverse effects of excess nickel on plants and their adaptation mechanisms. The study is focused on forest ecosystems exposed to extreme air pollution from the nickel-processing industry in Northern Fennoscandia. Long-term deposition of heavy metals and sulphur has caused strong soil contamination and severe damage to trees and ground vegetation, their structure, composition and chemistry. Tree leaves, branches and bark as well as dwarf shrubs, mosses and lichens show clearly elevated concentrations of nickel and copper in the surroundings of the smelters. Multivariate analyses show that changes in the element composition of plants depend both on air pollution and on natural factors. Besides direct input of pollutants from atmosphere, soil contamination and nutritional disturbance contribute significantly to the observed changes. Despite decline in emissions, extreme pool of heavy metals accumulated in surface soils is expected to influence plant metabolism and chemistry over a long period of time.

Til dokument

Sammendrag

Kronevurdering av trærne på observasjonsflatene i 2007 viste at tilstanden fortsatt var god og som forventet ut fra vekstforholdene, og bekrefter de foregående års undersøkelser. Vi kan ikke tilskrive variasjon og forskjeller fra år til år i kronetilstanden til utslippene fra Kårstø gassprosesseringsanlegg. På lang sikt kan man likevel ikke se bort fra at enkelte av økosystemene kan være følsomme med hensyn på tilførsel av nitrogen, på grunn av områdets langvarige mottak av stort nedfall av langtransporterte luftforurensninger. Det er derfor fornuftig å følge med i økosystemenes skoglige tilstand.

Sammendrag

The joint network of tree crown condition monitoring under the EU and ICP Forests operates at two levels, a systematic extensive approach (Level I) based on a 16 km x 16 km trans-national grid of sample plots (>6000 plots) and an intensive approach (Level II) on more than 800 plots across continental Europe. Three ongoing projects embrace the different levels of monitoring, the above mentioned Level I and Level II systems, and the National Forest Inventories (NFIs). All of the three projects are based on a stand structure approach that assumes an increased potential for species diversity with increasing complexity of stand structure. An intensive test-phase of forest biodiversity assessment at more than 100 Level II plots, known as ForestBIOTA is underway during 2005. This project aims to test standardized methods of forest biodiversity assessment in the field and examine the relationship between stand structure, forest deadwood, ground vegetation and epiphytic lichens. A forest classification of the plots is also included. A separate approach, known as BioSoil (due to its combination with a detailed chemical inventory of the soils) is a demonstration project which aims to record indicators of forest biodiversity at the extensive Level I plots. Practical measures of stand structure, including records of tree species, lists of vascular plant species, and simple measures of forest deadwood are included for field assessment during 2006. A pan-European forest type classification elaborating on the EUNIS system and including the Natura 2000 habitat types is proposed. These initiatives are linked to a third project, COMON, operating at the level of the National Forest Inventories aiming to test the same core variables at national levels.

Sammendrag

Gjennomsnittlig kronetetthet for landet økte for gran og furu, mens den gikk svakt tilbake for bjørk sammenliknet med året før. Det ble imidlertid observert avtagende kronetetthet for gran på Østlandet. Utviklingen av kronefarge for gran fulgte stort sett det samme regionale mønsteret som ble observert for kronetetthet, med økende misfarging på Østlandet. I resten av landet var det ingen klare tendenser for gran. Totalt for landet økte andelen gule misfargede bjørketrær, mens andelen gul furu var på samme nivå som året før. Det er de eldste trærne som har mest misfarging. Avdøingen var i gjennomsnitt omtrent som i tidligere år. For gran var det en liten økning på Østlandet i antall nye døde trær. Skogens helsetilstand, registrert ved kronetetthet, misfarging og avdøing, påvirkes i stor grad av klimatiske forhold, enten direkte som ved tørke, frost og vind, eller indirekte ved at det påvirker omfanget av soppsykdommer og insektangrep. Det ble registrert få sopp- og insektangrep i løpet av registreringsperioden. I skogovervåkingen med permanente felt vil også økt alder bidra til negative trender over tid. Langtransporterte luftforurensninger kan komme i tillegg til eller virke sammen med klimatiske forhold. I 2004 ble det ikke registrert noe unormalt skadeomfang i skogen.

Sammendrag

Intensive monitoring plots of the ICP Forests gathered an amount of data about the ground vegetation in forest ecosystems throughout Europe. Each Country, applying different field techniques, conform to common rules of procedure, under the suggestions of a dedicated Expert Panel which implemented a Unified Coded Flora and comparability targets. Data series are foreseen to contribute to: definition of the forest ecosystem state and changes evaluation; assessment of the specific plant diversity at the ecosystems level. The contribution to scientific knowledge and to Global and Pan-European biodiversity initiatives and networks (ICP-IM, MCPFE, CBD, Forest BIOTA, ALTER-net, etc.) are also underlined. In spite of site-related data, first results (more than 670 plots, with large differences in plant diversity) depict the linkages with temperature, precipitation, dominant tree species and actual soil acidity. Nitrogen deposition seems to have some significant influence, which claims to further studies. Plant data series from ICP Forest’s plot, can be used for on-site confirmation of models including biodiversity k-factors and environment relations.

Sammendrag

Areas near the Norwegian-Russian border are being strongly contaminated by heavy metal emissions from copper-nickel smelters in the Kola peninsula. The present report presents data for the four elements arsenic, chromium, cobalt, and selenium in vegetation sampled in eastern Finmark, obtained by neutron activation analysis. It is no doubt that the smelters in Nikel and Zapolyarny, constitute the main source of these elements in this area. Some chromium comes from local domestic sources. Still, however, the concentration of these elements in soil and vegetation are probably too low as such to represent any harm to the ecosystem.

Sammendrag

Extended summary and conclusions The Pechenganikel combine in the Nikel-Zapolyarny area was established in 1933. During the first 30 years of production, 100 000 tons of sulphur dioxide (SO2) were emitted annually. Since 1971, nickel from the Norilsk ores in Siberia have been processed in the smelters. The Norilsk ore contains more sulphur than the Nikel ore. As a result of the processing of this sulphur-rich ore, emissions of SO2 increased rapidly, reaching 400 000 tons in 1979. Current annual emissions are much lower, about 150 000 tons. However, the present emission is still above the critical level for sensitive biota in the Nikel-Pasvik area. Investigations of soils show that the soil layers are contaminated by heavy metals (nickel and copper). The results also indicate an influence on soil fertility expressed as changes in base saturation (BS), cation exchange capacity (CEC) and soil acidity. According to the calculations (critical loads) future sulphur deposition has to be reduced to very low levels in order to stop the ongoing soil acidification. Air pollution influence has had severe effects on forest vegetation in the Nikel-Pasvik area. Trees, vascular plants, mosses and lichens are all affected. In the close vicinity of the smelters forests are dead or severely damaged. Visible injuries to vegetation caused by SO2 have some years been frequent. Symptoms are recognised on Scots pine (Pinus sylvestris) and downy birch (Betula pubescens), which are the dominant tree species in the region, and on other plants, e.g. dwarf birch (Betula nana) and bilberry (Vaccinium myrtillus). The species composition of the ground vegetation in the forest has been influenced, and epiphytic lichen vegetation has been severely influenced over large areas. Critical levels are exceeded on more than 3200 square kilometres of Russian and Norwegian territory. Air pollution has reduced invertebrate and animal diversity due to lack of forest vegetation and contamination of surface soils in the vicinity of the nickel smelters. Small vertebrates are impacted by an increased heavy metal content in the liver. However, no negative health effects to reindeer are foreseen. Long-term monitoring of water chemistry in lakes and rivers has revealed that extensive surface water acidification has taken place, particularly on the Norwegian side of the border. Critical loads are exceeded in large areas of Sør-Varanger municipality, especially in the Jarfjord area, and in areas situated around Nikel and Zapolyarny. However, on the Russian side, the contamination of lakes by the heavy metals (nickel and copper) is more severe than acidification, especially in the vicinity of the smelters, where damage to fish populations as well as phytoplankton and invertebrate communities are observed. Studies of human health in the Nikel-Pasvik area revealed no major health effects that can be ascribed to the air pollution by nickel and sulphur dioxide in the Nikel-Zapolyarny area or in the Pasvik valley. The most severe effects of air pollution in the border areas between Norway and Russia, caused by sulphur dioxide emission from Nikel and Zapolyarny, on the terrestrial and aquatic ecosystems seem to be on vegetation, surface water and soils, and thus also on other compartments of the ecosystem.

Sammendrag

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 for S and N deposition were calculated using the MAGIC and PROFILE models for more than 100 monitoring plots in Norway spruce forest in 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 these plots 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 positively to foliar N concentrations and crown density.

Sammendrag

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 of was sampled at distances 0-100 km from the coastline between 59¢ª and 65¢ª N, 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% of the needles sea salt content could be removed by 2 minutes washing in distilled water, and still much less of 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 variation in salt deposition and damage will occur at a rugged coast. 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.

Sammendrag

Aluminium (Al) is a key element in critical load calculations for forest. Here, we argue for re-evaluating the importance of Al. Effects of two levels of enhanced Al concentrations and lowered Ca:Al ratios in the soil solution in a field manipulation experiment in a mature spruce stand (1996-1999) on tree vitality parameters were tested. In addition, Al solubility controls were tested. Various loads of Al were added to forest plots by means of an irrigation system. Potentially toxic Al concentrations and critical ratios of Ca to inorganic Al were established.The ratio of Ca to total Al was not a suitable indicator for unfavourable conditions for plant growth. No significant effects on crown condition, tree growth and fine root production were observed after three years of treatment. In 1999, foliar Mg content in the highest Al addition treatment had declined significantly. This agreed with the known response to Al stress of seedlings in nutrient solution experiments. No support was found for using the chemical criterion Ca:Al ratio in soil solution, foliar and root tissue as an indicator for forest damage due to acidification. Al solubility was considerably lower than implied by the assumption of equilibrium with gibbsite, particularly in the root zone.The gibbsite equilibrium is commonly used in critical load models. Substitution of the gibbsite equilibrium with an Al-organic matter complexation model to describe Al solubility in soil water may have large consequences for calculation of critical loads. The results indicate that critical load maps for forests should be reconsidered.

Sammendrag

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.

Sammendrag

Within the framework of the Programme for Terrestrial Monitoring (TOV), soil water has been collected from four monitoring plots in 2000 (Fig. 1). Three of the plots were located in birch forest, and one (Solhomfjell) in spruce forest. Height above sea level, annual precipitation and growing season temperature showed significant variation between plots. Bilberry and bilberry-crowberry were the main forest vegetation types on the plots. Results from the monitoring in 2000 are reported and compared with results from previous years. On all plots soil water has been sampled from three soil depths; the organic layer, the upper and the lower part of the mineral soil (5, 15 and 40 cm soil depth, respectively). The chemical composition of the soil water depended largely on the chemistry of the soil and the amount and quality of the precipitation. Concentrations of key chemical parameters in the organic layer and from 5-15 cm depth in the mineral soil are shown in Tables 1 and 2, respectively. The concentrations of some of the main elements in soil water from 2000 are shown in Table 3. pH in soil water usually increased with soil depth. The annual variations in pH from 1991 to 2000 are shown in Fig. 2. In Lund there has been a slight decrease in pH in these years, although continuous measurements were lacking at 5 cm. However, there was indication of improvement in pH during the last two years. Fig. 2 also shows similar long-term tendencies for Ca 2+ as for pH in Lund. There was greater annual variation in concentrations of Ca 2+ and other elements in the humic layer than in the mineral layers. Also other nutrients, such as Mg 2+ and K + , were found with the highest concentrations in the organic soil layer and decreased with increasing soil depth ...

Sammendrag

Epiphytic lichen vegetation on birch stems was studied in the border areas between Norway and Russia. The area is heavily influenced by sulphur dioxide pollution emitted from Russian nickel smelters.Hypogymnia physodes and Melanelia olivacea were the two most abundant lichen species on birch stems in the investigated area. However, the coverage of H. physodes and M. olivacea was clearly reduced in parts of the investigated area. The lichen vegetation increased with increasing distance from the pollution source, i.e. from a lichen desert to normal background levels. A different pattern of occurrence of the two lichen species was observed.

Sammendrag

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 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 provided a very distinct contamination, presumably mainly with smaller particles.Significant but less distinct effects leading to enhanced concentration levels were observed for P, S, V, Cr, Fe, 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 silvestris 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.

Sammendrag

Two fungi, V. heterodoxa and P. vaccinii, are found to have impact on the leaf coverage of bilberry plants. When studying vegetation or forest ecosystems, assessors should, therefore, be aware of the biotic impact of pathogens on plants.

Sammendrag

På 17 skogfelter, spredt over hele landet, foregår intensiv overvåking av tilstanden i skogøkosystemet. Disse flatene inngår i Overvåkingsprogram for skogskader, og i det europeiske nettverket av intensive skogovervåkingsflater. Denne overvåkingen har i Norge foregått siden 1986. Formålet er å beskrive skogtilstanden og belyse virkninger av langtransportert forurensing. Siden 1988 er antall felt redusert til 17, etter at granfeltet i Kårvatn (KV) er nedlagt etter omfattende snøbrekk i 1998. Furufeltet i Kårvatn går videre som tidligere. Tilførslene av de langtransporterte luftforurensningene svovel og sterk syre (H+) har avtatt gjennom de siste 20 år for, mens for nitrogen og ozon har det vært årlige variasjoner uten noen trend over tid. De sørvestligste delene av landet har hatt de største tilførslene. Resultatene tyder på at vi ikke har direkte eller indirekte skader av langtransporterte luftforurensninger på skog i Norge. Konsentrasjoner av luftforurensninger i luft og av mulig toksisk aluminium i jordvann på de intensive flatene er generelt klart lavere enn grenseverdier for skadelige effekter. Men noe usikkerhet er det omkring dette. Når det gjelder skogtilstanden (vitalitet, nålekjemi, tilvekst og strøfall), så er det verken tydelige trender over tid, eller tydelige regionale mønstre. Generelt er det betydelige variasjoner fra år til år. Det var en gjennomgående forbedring av vitaliteten til trærne fra 1998 til 1999, med tettere og grønnere trekroner. Bunn- og feltvegetasjonen har også vært stabil, kun med enkelte endringer som kan ha hatt med klimatiske forhold å gjøre. Generelt er det forøvrig er det som i tidligere år en del forskjeller mellom felter, som både kan tilskrives naturlige forskjeller i geologi, klima og skoglige forhold, og også langtransporterte luftforurensninger kan bidra.

Sammendrag

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 (sNO(3)). Still, the combined dry deposition velocity of sNO(3) to these forest stands may be between 4 and 6 cm s(-1) on average.

Sammendrag

Within the framework of the Programme for Terrestrial Monitoring (TOV), soil water has been collected from four monitoring plots in 1999 (Fig. 1). Three of the plots are located in birch forest, and one (Solhomfjell) is located in spruce forest. Height above sea level, annual precipitation and growing season temperature show significant variation between plots. Bilberry and bilberry-crowberry are the main forest vegetation types on the plots. Results from 1999 are reported and compared with results from previous years. On all plots soil water has been sampled from three soil depths; the organic layer, the upper and the lower part of the mineral soil (5, 15 and 40 cm soil depth, respectively). The chemical composition of the soil water depends largely on the chemistry of the soil and the amount and quality of the precipitation. The soil chemistry in the organic layer and from 5-15 cm depth in the mineral soil is shown in Table 1 and 2, respectively. The concentrations of some of the main elements in soil water from 1999 are shown in Table 3. The pH in soil water increases usually with soil depth. The annual variations in pH from 1991 to 1999 are shown in Fig. 2. In Lund there has been a slight decrease in pH in these years, although continuous measurements are lacking at 5 cm. Fig. 2 also show the same tendencies for Ca2+ as for pH in Lund. There is greater annual variation in concentrations of Ca2+ and other element in the humic layer than mineral layers. Also other nutrients, such as Mg2+ and K+, were found with the highest concentrations in the organic soil layer and decreased with increasing soil depth. The concentrations of SO42- were in 1999 below 1 mg/l and only with a few exceptions larger than 1 from 1991 to 1999 (Fig.3). SO42- generally show a decreasing trend in that period. Total Al were lower than 1.0 mg/l for most of the samples. The amount of inorganic Al, which is known to be toxic for plant roots at certain concentrations was first time measured on the plots in 1999. However, the values were small, well below 1.0 mg/l. That were similar to results from Monitoring Programme for Forest Damage (OPS) in Norway which shows that the concentration of inorganic Al varies between plots and soil depths. Here, however, at some plots there were concentrations of inorganic Al up to 1,77 mg/l (Solberg et al.1999). Results from experiments with Norway spruce seedlings (Picea abies) in nutrient solution show slight decline of the roots at concentrations of inorganic Al at 2.0 mg/l (Nygaard & Eldhuset 1999). This may suggest that even if the concentration of inorganic Al at the TOV-plots were below 1.0 mg/l, there could be periods with higher concentrations that could have effected the plant roots. The concentration of Cl- varied greatly between the plots (Fig. 3), due to the deposition of sea salts. The plot in Gutulia had minimal variation between years and here the Cl- concentrations were always below 1.0 mg/l. In contrast, the plot in Lund had the highest concentrations of Cl- and the highest seasonal and annual variation. The between layer differences were usually small each year. Analyses of precipitation show that Lund had the highest supply Cl- of all plots (Tørseth & Manø 1997). Canonical discriminant analysis of soil water chemistry of a number of variables group the plot centroides along an acidification gradient at one axis, with Lund and Solhomfjell in the ”polluted part”. Even if the supply of N also is highest in Lund, soil water from all plots has shown low amounts of N (mostly at detection levels for NH4+ and NO3-, Table 3) throughout the monitoring period. This may be explained by the low content of plant available nitrogen in Norwegian soils, and plant uptake would minimize any leaching. At present these results give no indication of forest decline in Lund despite decreased pH and concentration of Ca2+ in the soil water, nor that these results are caused by acid deposition. They may be due to natural variations in the chemical composition of soil water. It is therefore recommended to continue the soil water monitoring.

Sammendrag

The Norwegian Monitoring Programme for Forest Damage has run since 1995. Its main objective has been to monitor forest condition in relation to air pollution. Surveys of forests are performed on plots in a nation-wide representative grid network (Level 1 in the UN/ECE ICP Forests system), in a network of local county-wise plots, and in a network of intensively monitored plots (Level 2 in the UN/ECE ICP Forests system). Vitality indicators have shown a declining trend as reported earlier, expressed as reduced crown density and more of discoloured trees, particularly in spruce forests. However, results from last two years have shown a slight improvement in tree crown condition. Tree mortality in excess of normal is not recorded. Forest condition generally depends upon soil, tree age, climate, pests and diseases, and other natural impact. The observed decreased crown density since 1989 is likely a caused by a harsh climate, poor soil conditions and forest diseases. Air pollution loads, add to and interact with these factors. Most likely initiating factors are needed to produce visual symptoms. Summer drought is possibly such a factor of relevance to Norway. The actual effect of the air pollution component is therefore difficult to estimate; however, its importance is not excluded. In future, possible effects of a changed global climate should also be considered. Considerin g these results it is reasonable to presume that most Norwegian forest ecosystems generally are still in a satisfactory condition

Sammendrag

Aluminium (Al) has been considered to be a central element for risk evaluation of forest damage due to acidification. It has been hypothesised 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.

Sammendrag

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.

Sammendrag

Potential response of forest soils to sulphur deposition in the Norwegian-Russian border area in the surroundings of the Pechenganikel smelters, the major sulphur emitters in the northern Europe, has been assessed with the PROFILE model. The release rate of base cations due to weathering range from 0.05 to 0.28 kmol(c)/ha/yr in the 0 - 50 cm soil layer, thus demonstrating the high sensitivity of the coarse and thin podzols studied. Calculated steady-state BC/Al values are significantly lower than the presumed critical value of 1, which indicate possible negative effect on vegetation through soil acidification. According to the model calculations future sulphur deposition have to be very low in order to stop the ongoing acidification and prevent vegetation damage. However, model assumptions, uncertainty in input data and critical chemical values applied implies that modelling results must be interpreted carefully

Sammendrag

Contamination of atmosphere and soils was found to be accompanied by the active participation of S, Ni, Cu and Fe in the biological cycle in the area adjacent to \"Petchenganickel\" group of smelting works. The content of Ni, Cu and S in pine needles near the works is as high as 0,7-1; 0,4-0,5 and 40-60 mmol/kg respectively, these values for metals being by an order of magnitude higher than those in unpolluted areas. With increase in the age of trees the content of N, P, K, Mg and S in pine needles decreases and the content of Ca, Al, Fe and Mn increases; accumulation of Ni and Cu in pine needles is usually observed near the smelting works.

Sammendrag

The objective structure of parameters of soil acidity and cation exchange properties of podzols affected by the emission of the Pechenganikel factory (the Kola Peninsula) is revealed. The multiparametric analysis of soil properties and the traditional correlation analysis complement one another. They point to the complex character of interrelations between soil properties in conditions of progressing human-induced acisification.

Sammendrag

Within the framework of the Programme for Terrestrial Monitoring (TOV), soil water has been collected from four monitoring plots in 1998 (Fig. 1). Three of the plots are located in birch forest, and one (Solhomfjell) is located in spruce forest. Height above sea level, annual precipitation and growing season temperature show significant variation between plots. Bilberry or bilberry-crowberry are the main vegetation types.Results from 1998 are reported and compared with results from preceeding years. On all plots soil water has been sampled from three soil depths (except Gutulia); the organic layer, the upper and the lower part of the mineral soil (5, 15 and 40 cm soil depth, respectively).The chemical composition of the soil water depends largely on the chemistry of the soil and the amount and quality of the precipitation. The soil chemistry in humic layer and from 5-15 cm depth in the mineral soil is shown in Table 1 and 2, respectively. The concentrations of some of the main elements in soil water from 1998 are shown in Table 3.The pH in soil water increases usually with soil depth. The annual variations in pH from 1991 to 1998, are shown in Figure 2. In Lund there has been a slight decrease in pH in these years, although continous measurements are lacking at 5 cm. Figure 2 also show the same tendencies for Ca2 as for pH in Lund.There is greater annual variation in concentrations of Ca2 and other element in the humic layer than mineral layers. Also other nutrients, such as Mg2 and K, were found with the highest concentrations in the organic soil layer and decreased with increasing soil depth.The concentrations of SO42- were in 1998 below 1 mg/l and only with a few exceptions larger than 1 from 1991 to 1998 (Fig.3). SO42- generally show a decreasing trend in that period. Total Al were lower than 1.0 mg/l for most of the samples. The amount of inorganic Al, which is known to be toxic for plant roots at certain concentrations was first time measuered on the plots in 1998. However, the values were small, well below 1.0 mg/l.That were simular to results from The Forest Monitoring Programme in Norway (OPS) which shows that the concentration of inorganic Al varies between plots and soil depths. Here, however, at some plots there were concentrations of inorganic Al up to 2.0-3.4 mg/l. Results from experiments with Norway spruce seedlings (Picea abies) in nutrient solution show slight decline of the roots at concentrations of unorganic Al at 2.0 mg/l (Eldhuset pers. comm.). This may suggest that even if the concentration of unorganic Al at the TOV-plots were below 1.0 mg/l, there could be periods with higher concentrations that could have effected the plant roots.The concentration of Cl- varied greatly between the plots (Fig. 3), due to the deposition of sea salts. The plot in Gutulia had minimal variation between years and Cl- concentrations were always below 1.0 mg/l. In contrast, the plot in Lund had both the highest concentrations of Cl- and the highest seasonal and annual variation. The between layer differences were usually small each year.Analyses of precipitation show that Lund has the highest supply of acidity, Mg2, SO42-, Na and Cl- of all plots (Trseth og Man 1997). Even if the supply of N also is highest in Lund, soil water from all plots has shown low amounts of N (mostly at detection levels for NH4 and NO3, Table 3) throughout the monitoring period. This may be explained by the low content of plant available nitrogen in Norwegian soils, and plant uptake would minimize any leaching.At present these results give no indication of forest decline in Lund despite decreasing pH and concentration of Ca2 in the soil water. At present it is not possible to confirm that the changes observed in pH and Ca2 are caused by long range air pollution. They may also be due to natural variations in the chemical composition of soil water. It is recommended to continue the soil water monitoring.

Sammendrag

The Norwegian Monitoring Programme for Forest Damage has now been running for more than 10 years. Its main objective has been to monitor forest condition in relation to air pollution. Surveys of forests are performed on plots in a nation-wide representative grid network (Level 1 in the UN/ECE ICP Forests system), in a network of local county-wise plots, and in a network of intensively monitored plots (Level 2 in the UN/ECE ICP Forests system). Vitality indicators have shown a declining trend as reported earlier, expressed as reduced crown density and more of discoloured trees, particularly in spruce forests. However, results from last year have shown a slight improvement in tree crown condition. Tree mortality in excess of normal is not recorded. Forest condition generally depends upon soil, tree age, climate, pests and diseases, and other natural impact. The observed decreased crown density since 1989 is likely caused by a harsh climate, poor soil conditions and forest diseases. Air pollution loads, add to and interact with these factors. Most likely initiating factors are needed to produce visual symptoms. Summer drought is possibly such a factor of relevance to Norway. The actual effect of the air pollution component is therefore difficult to estimate; however, its importance is not excluded. In future, possible effects of a changed global climate should also be considered. Considering these results it is reasonable to presume that most Norwegian forest ecosystems generally are still in a satisfactory condition.

Sammendrag

Studies were undertaken in forest ecosystems of the northwestern Kola Peninsula, Russia and South-Varanger, Norway in the zone affected by the Pechenganikel smelter. The soils consist mainly of shallow sandy iron-humus-illuvial and iron-illuvial podzols on highly bouldery unsorted morainic deposits of course texture, fluvioglacial sands and bedrocks.Plant specimens were collected from 16 plots located at different distances from the source of emissions: Pinus sylvestris needles, bark and wood, dwarf shrub (Empetrum hermaphroditum, Vaccinium myrtillus and Vaccinium vitis-idaea ) leaves, wavy-hair grass (Deschampsia flexuosa), green mosses (Hylocomium splendens and Pleurozium schreberi) and lichens (Cladina rangifirina [Cladonia rangiferina], and Cladina stellaris [Physcia stellaris]) were collected at the end of the growing season.Results showed that the elemental composition of the dominants of the tree, grass-shrub, and moss layers was affected by the sulfur and heavy metals from the source of pollution. The content of nickel and copper in pine needles near the smelter exceeded control levels by an order of magnitude and the content of sulfur exceeded it twofold, reaching toxic levels.In addition to the direct input of pollutants from the atmosphere, soil contamination by nickel and copper within a 30 km radius of the smelter will have adverse effects on mineral nutrition of plants.It is concluded that the disturbance of biological cycles because of the active involvement of pollutants and the decreased availability of nutrients results in retardation of plant growth, a reduction in forest biomass and alterations in plant succession and species composition that leads to simplification and death of forest ecosystems.

Sammendrag

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

Sammendrag

The area along the Norwegian-Russian border is threatened by air pollution from emission sources on the Kola Peninsula. A permanent network of 78 systematically chosen monitoring sites has been established in eastern Finnmark, Norway. Species abundance data from the ground vegetation have been recorded from 1320 systematically chosen permanent plots inside 66 of these sites, using frequency in subplots and visual estimates of percentage cover. Environmental variables were obtained for the whole site. Multivariate data analysis has been used to describe the variation in the species composition and to study its relation to environmental variables and pollution impact. The analyses show that much of the variation in the species composition, based on average species abundance at the sites, is well explained by different soil and climatic conditions. However, estimated SO2 deposition, Ni, and Cu in the soil, and Ni in Cladina tissue have also been found to be statistically significantly correlated with the variation in the species data, but they explain only a minor part of the variation. The pollution impact over several years may have lead to a reduced lichen cover in the bottom-layer vegetation. Further development in an either negative or positive direction can be detected by re-investigations of the monitoring sites.

Sammendrag

I Program for terrestrisk naturovervåking (TOV) ble det samlet inn jordvann fra fire over-våkingsflater i 1997. Disse ligger på Lund (Rogaland), Solhomfjell (Aust-Agder), Møsvatn (Telemark) og Gutulia (Hedmark). Flatene ligger i områder med blåbærskog. Fra overvåkingen startet i 1991 og frem til 1997 har det blitt registrert en nedgang i jordvannets pH fra henholdsvis 4,96 til 4,26 (medianverdier) og konsentrasjon av Ca2+ i 15 cm sjiktet på Lund fra 1,53 til 0,26 (medianverdier). Nedbør og kronedrypp fra Lund hadde også lavere pH samt høgere konsentrasjon av SO42- og Cl- enn det som var tilfelle på de andre flatene. Det var imidlertid ingen tegn på dårligere skogvitalitet på Lund som følge av forholdene nevnt over. Generelt for alle flatene var det store årlige variasjoner i konsentrasjonen av Ca2+, Mg2+, K+ og tot-Al i jordvannet i 5 cm sjiktet, mens konsentrasjonen og variasjonen avtok nedover i jorda. Alle flatene hadde lave konsentrasjoner av NH4-N og NO3-N i jordvannet (nær deteksjonsgrensen på henholdsvis 0,05 og 0,02 mg/l) i hele overvåkings-perioden. Det er sannsynligvis flere årsaker til de endringene som observeres i jordvannet. Dette er forhold som bør følges nøye videre i TOV.

Sammendrag

Det norske Overvåkingsprogram for skogskader har vært i drift i 10 år. Formålet har generelt vært å overvåke skogtilstanden i relasjon til luftforurensninger. Registreringer av skogtilstanden er gjort i et landsrepresentativt flatenett, et nett av fylkesvise lokale flater og et nett av intensive forskningsflater. Resultater fremkommet siden 1992 rapporteres og sammenholdes tildels med resultater fra tidligere år. Vitaliteten beskrevet ved utvalgte kriterier har fortsatt vist en nedadgående tendens, med fortsatt redusert kronetetthet og flere misfargete trær, særlig for granskogen. De norske resultatene samsvarer med en generell utvikling ellers i Europa, og ligger stort sett nær de tilsvarende for de øvrige nordiske land. Tilveksten har økt i de senere år, men ikke i alle landsdeler. Det er ikke registrert noen unormal avdøing av trær i de norske skogene. Alle forhold tatt i betraktning synes det rimelig å anta at de fleste norske skogøkosystemene generelt har en relativt god status. Det er imidlertid områder i den sørøstlige del av landet som viser indikasjoner på en noe dårligere tilstand enn andre steder, og samtidig viser tildels negative endringer over siste femårsperiode. Dette er områder med høy belastning av luftforurensninger og lav naturlig tåleevne mot forsuring. Skogens helsetilstand avhenger i stor grad av jordsmonn, trealder, klima, skadegjørere og andre naturlige stressfaktorer. Tilførsler av luftforurensninger vil komme i tillegg til, og i samspill med disse faktorene. Trolig må det bestemte utløsende faktorer til, for at synlige ytringer skal bli dannet. Forurensningenes virkelige bidrag er derfor ytterst vanskelig å fastslå, men det betyr på ingen måte at deres betydning må nedvurderes.

Sammendrag

Nedbør ble samlet inn i skogbestand på de faste forskningsflatene til Overvåkingsprogram for skogskader, på ialt 20 steder i Norge i 1993. Det ble også samlet inn nedbør i åpent terreng i nærheten av flatene. Resultatene viste at det var stor forskjell i nedbørens mengde og kvalitet fra flate til flate. Skogflatene mottok 23% mindre nedbør enn åpen mark i samme område. Tilførselen av langtransporterte forurensninger var langt sterkere for skog enn for åpen mark. I alle flatene ble det registrert en utvasking av viktige plantenæringsstoffer fra trekronene. Flatene i sør og sørøst er de mest utsatte. Situasjonen for kystflatene er ikke så ugunstig som totaltilførselen alene indikerer, fordi tilførsel av sjøsaltene (f.eks. magnesium) bedrer forholdene i disse flatene. Minst langtransportert forurensning hadde skog fra Møre til Troms. Forurensningskilder på Kola medførte stor tilførsel av forurensninger til skogen i Pasvik. På de fleste flater faller det mindre nitrogen ned til bakken i skogbestand enn utenfor.

Sammendrag

Rapporten er en sammenstilling av de viktigste skader og sykdommer som ble registrert på skog i Norge i 1992 og 1993. Skogskadene er dokumentert ved beskrivelse av symptom, årsak og utbredelse. Skogskader som følge av spesielle værforhold har dominert skadebildet i 1992 og 1993. I vestlige kyststrøk førte storm og sjørokk til sterke skader i begge år. En nattefrost i juni 1992 gav sjeldent sterke skader på Østlandet, og tørken på Øst- og Sørlandet samme sommer førte også til ulike skader. Enkelte sopp- og insektangrep har ført til betydelige skader lokalt eller regionalt. Selv om materialets representativitet for skogskadesituasjonen i Norge er begrenset, har de beskrevne skadene høyst sannsynlig vært en del av årsakene til den negative trend som er registrert for kronetetthet og kronefarge i Overvåkingsprogram for skogskader.

Sammendrag

Nedbør ble samlet inn i skogbestand på de faste forskningsflatene til Overvåkingsprogram for skogskader på ialt 20 steder i Norge i 1992. Det ble også samlet inn nedbør i åpent terreng i nærheten av flatene. Resultatene viste at det var stor forskjell i nedbørens mengde og kvalitet fra flate til flate. Skogflatene mottok omtrent 22% mindre nedbør enn åpen mark i samme område. Belastningen av langtransporterte forurensninger var langt sterkere for skog enn for åpen mark. I alle flatene ble det registrert en utvasking av viktige plantenæringsstoffer fra trekronene. Flatene i sør og sørøst er de mest utsatte. Situasjonen for kystflatene er ikke så ugunstig som totaltilførselen alene indikerer, fordi tilførsel av sjøsaltene (f.eks. magnesium) bedrer ioneforholdene i disse flatene. Minst langtransportert forurensning hadde skog fra Møre til Troms. Forurensningskilder på Kola medførte stor belastning på skogen i Pasvik. Siden overvåkingen av forurensningsnedfall i skog startet (1986/89), har sulfat-svovel nedfallet økt noe i de kystnære flatene i nord, mens det har vært relativt stabilt i sør. På de fleste flater faller det mindre nitrogen ned til bakken i skogbestand enn utenfor.

Sammendrag

Innhold av nikkel, kopper, samt bly, kadmium, sink, kobolt, jern, mangan, arsen, vanadium og krom ble undersøkt i multer og blåbær fra Jarfjordområdet, et sterkt forurensningsbelastet område i Sør-Varanger, Finnmark, Norge. Forurensningene kommer fra tungmetallindustri på Kola, Russland. Undersøkelsen viste at konsentrasjonene av nikkel og kopper i multer og blåbær var mye høyere i det undersøkte området enn i kontrollområdene. Også konsentrasjonene av arsen var forhøyet. De lokalitetene som hadde de høyeste konsentrasjonene lå i det samme området der det tidligere har vært påvist høye metallkonsentrasjoner i andre planter og i humus. Kvaliteten i bærene kan være av betydning for konsumentene.

Sammendrag

Norwegian forests receive various amounts of air pollutants. Several of them are harmful to trees. The forest health situation is therefore monitored by regular surveys, in accordance with internationally recommended methods. Investigations so far have shown that the deposition of air pollutants is largest in southeastern Norway and in a limited area close to the Russian border, in northeastern Norway.Sulphur and nitrogen compounds are among the main pollutants that may lead to adverse effects. However, their airborne concentrations are not high enough to cause direct injury to trees in Norway, except for northeastern parts being affected by emissions from Russian industries. Indirect injury, by leaching of nutrients from trees and soils, and disturbances of the nutrient balance in various ways, is more likely. Ozone concentrations may reach harmful levels, and may affect vegetation directly, especially in the southern part of Norway.Monitoring is performed in order to reveal whether forest damage occurs from such causes, and if so, where, and whether the amount of damage will change with time. So far the results show that there is no extensive dieback of forests in Norway; the annual death rate of trees is low and appears normal.Based on the international criteria applied, the vitality of the forest appears to be low. Part of the reason for that may be the location of Norwegian forests towards the north, towards mountains, and towards the ocean, where forest growth is limited naturally.However, results indicate that forest conditions in the southern part of the country are affected by air pollution. Most cases of crown discolouration are found in that region, and the number of discoloured (yellow) trees has increased noticeably during the last few years. In the same region crown density has been low, and has been further reduced lately. According to a conservative estimate the average crown density is being reduced by 0.4% (units) annually.Crown density has been shown to be related to tree increment. However, the negative effect of reduced tree vitality is believed to be over-shadowed by the positive effect on growth of nitrogen deposition.Air pollutants are causing various effects in forest ecosystems. It appears that regions in southern Norway receiving large amounts of air pollutants have a high number of acidified lakes containing high concentrations of sulphate and nitrate. In this region the soil is shown to be low in base saturation and leachable phosphate, and high in nitrogen, sulphur and zinc.Those monitored plots showing the highest concentrations of Al and the lowest Ca:Al ratio in their soil water are also located here. The forest in this region receives a more acidic precipitation than elsewhere in Norway, which may contribute to increased leaching from needles. Higher nitrogen deposition is taking place here, causing a heavy cover of epiphytic algae on needles.It is noteworthy that this region contains more low vitality forests (of low crown density and yellowish discolouration) than other regions, and that the negative changes in vitality have been more pronounced than in other regions.More clearly we see that forests in southern, southeastern, and northeastern parts of Norway, next to Russia, are negatively affected. The causal factors may be several, and they may interact in complex processes. The symptoms are not specific, but their regional occurrence seems to indicate a causal relationship with deposition of air pollutants. This indication is now more pronounced than found earlier.

Sammendrag

Nedbør ble samlet inn i skogbestand på de faste forskningsflatene til Overvåkingsprogram for skogskader på i alt 19 steder i Norge i 1991. Det ble også samlet inn nedbør i åpent terreng i tilknytning til flatene. Nedbøren ble målt og analysert. Resultatene viste at det var stor forskjell i nedbørsmengde og kvalitet fra flate til flate. Skogbunnen i flatene mottok omtrent 24% mindre nedbør enn åpen mark i samme område. Belastningen av langtransporterte forurensninger var langt sterkere for skog enn for åpen mark. Flatene i sør og sørøst var de mest belastete. Men situasjonen for kystflatene er ikke så ugunstig som totaltilførselen alene indikerer, fordi tilførsel av sjøsaltene bedrer ioneforholdene i disse flatene. Minst langtransportert forurensning hadde skog fra Møre til Troms. Forurensningskilder på Kola medførte stor belastning på skogen i Pasvik. Størst utvasking av næringsstoffer fra nåler er registrert i de mest belastede flatene. Denne utvaskingen kan føre til mangelsymptomer i nåler.

Sammendrag

Rapporten beskriver lavvegetasjonen på bjørkestammer i Sør-Varanger kommune, Finnmark, relatert til forurensningsutslipp fra Nikel. Resultatene er sammenholdt med kjemiske analyser. Tålegrensene for lavvegetasjon på bjørkestammer i de østligste delene av Sør-Varanger er overskredet. Liten dekningsgrad av lav, og en viss sammenheng mellom lavdekning og innhold av forurensningskomponenter i lav fra lokalitetene gir grunn til å anta at forurensningen fra Nikel er hovedårsaken til manglende lav på bjørkestammer i de østligste delene av Sør-Varanger. Samtidig som områdene er de mest forurensningsbelastede, vil imidlertid også en rekke andre naturlige økologiske forhold være medvirkende, eller dominerende årsak til at lavvegetasjonen på enkelte steder er svært sparsom eller manglende i disse områdene. Luftforurensningens betydning er derfor vanskelig å anslå kvantitativt, men den er klart en medvirkende årsak til lavens reduserte opptreden i området.

Sammendrag

Rapporten beskriver sammenhengen mellom viktige næringsstoffer i barnåler og noen viktige jordparametre på faste overvåkingsflater til Overvåkingsprogram for skogskader. Det er funnet signifikante sammenhenger mellom innholdet av flere plantenæringstoffer målt i nåler og i jordas humussjikt. For elementet kalium, et element som ved for lave konsentrasjoner forårsaker gulfarging av nåler, er det ikke en sammenheng mellom jordanalyser og planteanalyser. Kaliummangel er kanskje den mest hyppige årsak til gulfarging i norsk skog. Gulfarging av bar og blad er samtidig et viktig skogskadesymptom. Nåleprøver må derfor tas for å avdekke skogens kaliumstatus. Resultatene viser at jordanalyser ikke kan erstatte planteanalyser for å belyse skogens næringstilstand, og nåleanalyser kan heller ikke erstatte jordanalyser for å belyse skogsjordas tilstand. Ut fra en samlet vurdering ser det ut som elementinnholdet i nest siste nåleårgang best gjenspeiler næringsstatus i jorda. Forholdet mellom siste og nest siste nåleårgangs elementinnhold vil illustrere dynamikken i næringstilstanden.

Sammendrag

Stadige tilførsler av langtransporterte luftforurensninger vil kunne føre til en svekkelse av skogen og derigjennom økt omfang av vanlige skader og sykdommer. Arbeidet med diagnostisering av skogskader er derfor styrket gjennom det såkalte brannkorpset, for å kartlegge omfanget av skader og så langt som råd er å finne en årsakssammenheng. Denne rapporten gir hovedresultatene av dette arbeidet i 1991. Det har vært mange tilfeller av gulfarget barmasse, først og fremst på gran. Symptomene har variert, og årsakene er ikke fullstendig klarlagt. Næringsmangel er påvist i flere tilfeller. Klimapåkjenninger, særlig tørke, kan i mange tilfeller ha vært utløsende årsak til disse symptomene. Enkelte steder over hele landet var det klimaskader pga. unormalt høy og vekslende temperatur gjennom vinteren og våren 1990-91. Flere steder var det såkalte frostbelter.Skader ble observert på flere treslag, og på lyng. Almesjuke fikk et betydelig omfang i 1991, noe som trolig har sammenheng med mangelfullt saneringsarbeid. Luftforurensninger kan ha vært predisponerende for noen av skogskadene, men det er ikke mulig å si hvor stor betydning dette kan ha hatt.