Assessment of the Exposure and Loads of Acidifying and Eutrophying Pollutants and Ozone,as well as their Harmful Influence on the Vitality of the Trees and the Speulder Forest Ecosystem as a Whole

Within the framework of the Dutch Priority Program on Acidification, 10 yr of research was conducted in a Douglas fir stand at Speulder forest. Research was conducted to establish the loads and levels of acidifying and eutrophying pollutants and ozone, to determine forest vitality characteristics and follow growth parameters and nutrient status in time and to determine the effects of reduction of loads and levels by manipulation experiments. Results indicate that during the last 20 yr critical levels for air pollutants have hardly been exceeded except for ozone, which slightly affected assimilation. Elevated nitrogen deposition has caused several adverse effects including (i) inhibited mycorrhizal development, leading to a decreased base cation and phosphorus uptake; (ii) elevated foliage/root (fine and coarse) ratios, making the forest more sensitive to drought and windthrow; (iii) elevated nitrogen and arginine concentrations in the foliage, associated with relative base cation and phosphorus deficiency, and (iv) elevated nitrate leaching polluting the groundwater. High inputs of acidity have caused elevated ratios of Al to base cations, affecting fine root (uptake) and depletion of the readily available Al pool, thus affecting the long-term sustainability. Despite these effects, forest vitality, in terms of defoliation/discoloration, is reasonable and forest growth even increased in response to nitrogen. The exceedances of critical loads for nitrogen and acidity, however, implies a (large) risk for the long-term sustainability of the Speulder forest.     

A model for the impact of soil solution Ca: Al ratio,soil moisture and temperature on tree base cation uptake

A model for tree base cation uptake has been developed, dependent on the soil solution concentration of Al³⁺, divalent base cations such as Ca²⁺, Mg²⁺ and H⁺ ions, modelled with a Mikaelis-Menten type of expression based on the molar BC∶Al ratio, where BC is the sum of the divalent non-toxic base cations Ca²⁺ and Mg²⁺. The expression has the form of counteracting adsorption isoterms for BC and Al to the tree root. The effect of toxic levels of Hg and Pb is incorporated into the model, using root adsorption as the mechanism, and parameterization against experimental data. The expression is modified with an expression accounting for the effect of heavy metal toxicity and soil water content. The dependence of the uptake rate on soil moisture content can be shown to have the form of a Freundlich adsorption isotherm for water. The available data indicate an activation energy of 47 kJ^?1 mol for base cation uptake to trees. Data from the literature was used to estimate the rate coefficients and ion selectivity coefficients for typical coniferous and decideous trees in Sweden and Germany. The model indicates that Ca²⁺ and Mg²⁺ is effective in mitigating Al³⁺ toxicity to tree roots, and that increasing the Ca²⁺+Mg²⁺ soil solution concentration has a promotive effect on base cation uptake. Above a certain limit base cation uptake becomes independent of the solution base cation concentration. This is consistent with field observations, and may be developed to become a tool for assessing the impact of soil chemistry changes on forest growth rate and health status. Field data from the Swedish Forest Survey indicate that uptake depend on the square root of the soil solution base cation availability originating from weathering and deposition input, which is consistent with the BC∶Al expression of the model.     

Effects of fertilization with MgSO4 and (NH4)2SO4 on soil solution chemistry,mycorrhiza and nutrient content of fine roots in a norway spruce stand

This paper focuses on the short-term reaction of fine root and mycorrhiza on changes in soil solution chemistry following application of MgSO₄ (Kieserite) and (NH₄)₂SO₄ (ammonium sulfate). The experiments were conducted within the ARINUS Experimental Watershed Area near Schluchsee in the Black Forest (SW Germany). Yellowing of the older needles as related to Mg deficiency was the typical symptom observed within this 45 yr old Norway spruce stand. On the N treated plot the relative mycorrhiza frequency declined and the percentage of nonmycorrhizal root tips increased, whereas in the Mg fertilized plot these parameters did not differ from the control. The observed changes cannot be caused by Al, because elevated concentrations of potentially toxic Al species and extremely low Ca/A1 molar ratios appeared in the soil solution of both treatments and did not result in reduced growth of long roots as reported from solution culture experiments. Moreover, the Al content of fine roots did not increase. Therefore, it is concluded that the thresholds for Al toxicity derived from solution culture experiments with nonmycorrhizal seedlings cannot be transferred to forest stands. A direct toxic effect of elevated NH₄ ⁺ concentrations on mycorrhiza is unlikely, but cannot be excluded. Enhanced root growth due to a higher uptake of NH₄ ⁺ from soil solution may provide a more plausible explanation for the observed increase in the percentage of nonmycorrhizal root tips after N application. Even though the N content of fine roots did not increase, the diminished K content gives some indirect indication for NH₄ ⁺ uptake by the roots. This is also consistent with reduced Mg content due to NH ₄ ⁺ /Mg²⁺ antagonism. On the MgSO₄ treated plot, Mg contents of the fine roots increased thus reflecting Mg uptake by the deficient stand.     

Testing the Aluminium Toxicity Hypothesis: A Field Manipulation Experiment in Mature Spruce Forest in Norway

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.     

Water‐Soluble and Exchangeable Aluminum in Some Forest Soils of the Czech Republic Affected by Acid Precipitation

Abstract

The high contents of soluble and exchangeable aluminum (Al) in soils are believed to be main factors of forest damage in large areas. Krkono?e National Park, in the Czech Republic, is one of the most damaged areas in Central Europe, although the industrial emissions have declined in the past years. The purpose of this work was to evaluate the present concentration of soluble and exchangeable Al in some soils of that area, with different degrees of forest decline. The total Al concentration in water extracts was found to range within the limits 0.022–0.102 mM. According to the commonly used criteria, these values do not exceed the limit of toxicity for most plant species. Aluminum compounds in water extracts are represented predominantly by Al organic complexes and Al polymers. The percentage of the most toxic for plants, Al monomeric hydroxocomplex, ranges within the limits 0–52% of the total Al concentration and is higher in water extracts from the upper parts of the solum as compared with those from the subsoils, in compliance with the increase in pH values down the profile. The molar ratios of calcium (Ca)/Al and (Ca+Mg+K)/Al in water extracts exceed 1, but no clear relation with the forest status is found. The content of exchangeable Al is instead very high, especially in mineral horizons, and the lowest ratios between Ca or the sum of base cations and Al in the exchange complex occurs under the most degraded forest stands.     

Soil base saturation affects root growth of European beech seedlings§

To assess the potential effects of Al toxicity on the roots of young European beech (Fagus sylvatica L.), seeds were sown in soil monoliths taken from the Ah and B horizons of forest soils with very low base saturation (BS) and placed in the greenhouse. The Ah horizons offered a larger supply of exchangeable cation nutrients than the B horizons. After 8 weeks of growth under optimal moisture conditions, the seedlings were further grown for 14 d under drought conditions. Root‐growth dynamics were observed in rhizoboxes containing soils from the Ah and B horizons. The concentrations of Al³⁺, base cations, and nitrate in the soil solution and element concentrations in the root tissue were compared with above‐ and belowground growth parameters and root physiological parameters. There was no strong evidence that seedling roots suffered from high soil‐solution Al³⁺ concentrations. Within the tested range of BS (1.2%–6.5%) our results indicated that root physiological parameters such as O₂ consumption decreased and callose concentration increased in soils with a BS < 3%. In contrast to the B horizons, seedlings in the Ah horizons had higher relative shoot‐growth rates, specific root lengths, and lengths and branching increments, but a lower root‐to‐shoot ratio and root‐branching frequency. In conclusion, these differences in growth patterns were most likely due to differences in nutrient availability and to the drought application and not attributable to differences in Al³⁺ concentrations in the soil solution.     

The Impact of Nitrogen on Forest Soils and Feedbacks on tree Growth

The effects of pollutant nitrogen on forest soils and the potential feedbacks on tree growth are discussed using data from recent plot and catchment manipulation studies. Results indicate that N applied to the soil affects both soil N transformations and base cation status in some forest soils. Whilst reductions in tree growth are infrequently reported, a greater understanding of the effect of increased N deposition on soil N transformations, and associated changes in soil acidification and nutritional balance, is essential if sensitive stands are to identified. In particular, the factors controlling soil N accumulation rates and thus the onset of nitrate leaching are not clearly understood with increased nitrogen availability potentially increasing nitrogen accumulation due to abiotic fixation and lignolytic enzyme suppression, whilst the onset of nitrification as the C/N ratio of forest floor material declines, may reduce N retention efficiency. The switch from increased to decreased tree growth rate in response to N additions in some experiments highlights the need for long-term studies as a necessary component of future research.     

The influence of acid soil factors on the growth of snapbeans in major appalachian soils

Abstract

Acid soil limitations to plant growth were assessed In 55 horizons of 14 major Appalachian hill land soils. Aluminum sensitive “Romano” and Al‐tolerant “Dade” snapbeans (Phaseolus vulgaris L.) were grown for 5 weeks in limed and unlimed treatments of the 55 horizons. Shoot and root growth was depressed >20% in unlimed relative to limed treatments in approximately 2/3 of the horizons. Dade snapbeans were generally more tolerant of the acid soil conditions and had higher Ca concentrations in the shoots than Romano snapbeans. However, the sensitive‐tolerant snapbean pair could not consistently be used to identify horizons with soil Al problems. Growth of both snapbeans was generally best in A horizons and worst in E horizons. The E horizons in this study were characterized by low Ca saturation (exchangeable Ca x 100/cation exchange capacity) and high Al saturation (exchangeable Al x 100/cation exchange capacity). Exchangeable Ca, soil Ca saturation and total soil solution Ca were positively correlated (p<0.01) with snapbean root and shoot growth. Soil Al saturation, total soil solution Al and soil solution Al reacting in 15 seconds with 8‐hydroxyquinoline were negatively correlated (p<0.01) with growth. The ratio of Ca/Al in soil solution was more closely related to snapbean growth than the soil solution concentration of any individual element. Soil and soil solution Mn were, in general, not significantly correlated with snapbean growth. Many of the horizons in this study had both Al toxicity and Ca deficiency problems and interaction between Ca and Al affected both snapbean growth and Ca uptake. These findings confirm the importance of considering Ca as well as Al when investigating Al phytotoxicity.     

Role of air pollution in forest decline in Eastern North America

Evidence for and against three general mechanisms by which air pollution stress may cause or contribute to forest decline in eastern North America is examined. These mechanisms are (1) soil acidification, cation nutrient depletion, and subsequent Al toxicity, (2) direct and indirect effects of gaseous pollutants on the physiology and growth of forest trees; and (3) excess nitrogen deposition and subsequent soil acidification or physiological injury. Recent studies have revealed reductions in base saturation in some sites (both polluted and pristine), but the consequences of these changes to forest health and nutrition are not resolved. Aluminum toxicity may contribute to forest decline in red spruce (Picearubens L.) in high-elevation sites, but the data are contradictory. In forested landscapes in which regional decline (reduced tree growth and/or dieback) is reported, O₃ is the only gaseous pollutant documented as a contributing factor in the eastern North America. Whereas this secondary pollutant exhibits a regional distribution and occurs at potentially phytotoxic levels, a linkage between O₃ and forest decline is substantive only for loblolly pine (Pinustaeda Sarg.) in the southeast. Studies in high elevations do not support the hypothesis that O₃ or hydrogen peroxide directly affects the growth of red spruce or fraser fir (Abiesfraseri Poir.).However, preliminary data link chronic-level O₃ exposure with indirect effects, principally changes in drought tolerance in low-elevations (e.g., P. taeda) nd winter hardiness in high elevations (e.g., P. rubens).The emerging data on the role of air pollution as an environmental stress indicate that indirect effects (i.e., responses in which pollution alters the plant's ability to compete for limited resources or withstand other environmental stresses) are more important than direct effects (e.g., foliar necrotic lesions). Nitrogen saturation has been offered as an hypothesis for P. rubens decline, but no experimental data exist supporting this hypothesis.     

The uncertainty in forecasting trends of forest soil acidification

A Regional Soil Acidification Model (RESAM) has been developed to gain insight in long-term impacts of deposition scenarios on forest soils in The Netherlands. Model predictions of such large-scale environmental effects of acid deposition require extrapolation of site specific data to large geographical regions. The major aim of this study is to quantify the uncertainty in model response to a given deposition scenario, due to uncertainty and spatial variability in data. Furthermore, the uncertainty analysis was performed to determine which additional data will most likely improve the reliability of predictions. An efficient Monte Carlo technique was used in combination with regression analysis. The analysis was restricted to one forest soil ecosystem: a leptic podzol with Douglas fir, subject to a reducing deposition scenario. The investigated output variables were pH, Al/Ca ratio and NH₄/K ratio in the root zone, which are generally used as indicators of forest soil acidification and of potential forest damage. Statistical analyses showed that in most cases the relation between the parameters and model output can be satisfactorily described by a linear regression model. The uncertainty contribution of various parameters depends on the considered output variable, soil compartment and time. The uncertainty, as measured by the coefficient of variation, appears to be high for the NH₄/K and Al/Ca ratios, whereas it was relatively low for the pH. Results show that the uncertainty in the depositions of SO_x, NO_x, and NH_x in a receptor area and the uncertainty in the parameters and variables determining the nitrogen and aluminium dynamics contribute most to the resulting uncertainty of the considered model output.     

华北山地6种天然次生林土壤氮素的空间异质性特征

 利用地统计学理论和方法研究华北山地次生林区6种天然次生林土壤氮素的空间异质性特征。结果表明:1)次生阔叶林土壤总氮质量分数相对较高（3 1004 500 mg/kg）,而针叶林相对较低（9001 300 mg/kg）,各森林类型土壤中有效NH4+-N质量分数均高于有效NO3--N,形成以NH4+-N占优势的氮营养生境;2)针阔混交林中,土壤全氮的变异强度最大,变异的空间相关性较差（随机性变异占总变异的42.7%）,针叶林中,全氮空间变异强度相对较弱,但以自相关变异为主（结构方差比为72.2%81.0%）,呈现弱的斑块分布特征;3)阔叶林中,NH4+-N具有很强的空间自相关变异,NO3--N异质性程度相对较弱,针叶林中,NH4+-N变异强度较小,而NO3--N空间变异却相对明显;4)不同森林类型对土壤全氮及各有效氮形态的空间异质性特征有影响;5)植被种类、植被组成、植被多样性等因素的差异及由此导致的树种空间分布格局是影响总氮量及氮矿化,进而导致氮素不同形态在林分间甚至林分内不同空间样点间异质性形成的重要原因。     

Modelling Impacts of Atmospheric Deposition,Nutrient Cycling and Soil Weathering on the Sustainability of Nine Forest Ecosystems

To assess the impact of acid deposition on the long-term sustainability of nine oak, pine and spruce stands on sandy to loamy sandy parent material in Sweden, Denmark and The Netherlands, a dynamic soil acidification model (ReSAM) was applied. Two deposition scenarios for the period 1990–2090 were used: a business as usual scenario (BAU) and a restrictive critical load scenario (CL). The BAU scenario leads to a strong decrease in both Al concentrations and pH in the topsoil of the Dutch and the Danish sites due to a decrease in the amount of amorphous Al compounds. The decline in pH leads to an enhanced release of base cations by silicate weathering. Despite the ongoing acidification, base saturation increases during the simulation period, due to both the increase in base cation weathering and an increased input from mineralization with the ageing of the tree stands. No change in Al concentration is predicted for northern Sweden as deposition levels are below critical loads. Soil chemistry at the recently replanted Swedish sites is dominated by changes in N cycling instead of by deposition. The CL scenario leads, especially after 2010, to a stronger decline in Al concentration compared with the BAU scenario, which is mainly caused by a reduction of the acid input. Up to 2010, a considerable acid input to the soil system is maintained as N supply is larger than the consumption of N by the trees. Despite the reduction of the deposition of S and N to critical loads, the readily available cation pools are still declining on the Danish and Dutch sites in 2090. It is concluded that deposition levels above critical loads lead to exhaustion of the pool of amorphous Al compounds and a decline in pH. Base saturation does not decline due to an increase in mineralization with stand age and an increase in weathering rate due to the decline in pH.     

Assessing the potential for forest effects due to soil acidification in Maryland

Calculations with the PROFILE model indicates that present acid deposition will lead to soil solution BC/Al molar ratios in the forest soils of Maryland far below the limits used for calculation of critical loads in Europe. Weathering rates and molar soil solution BC/Al ratios were calculated using measured mineralogy and texture. It has been assumed that the laboratory experiments on tree seedling response to soil solution Al concentration is applicable to field conditions as applied in the PROFILE model and that the observed connection between growth and needle loss for Sweden is also valid for North America. The assumptions were utilized to estimate the potential for forest damage due to soil acidification in Maryland. The results for Maryland was used to speculate over the possibilities for adverse effects due to soil acidity in Northeastern United States. A preliminary comparison with Maryland and European results, suggests that the threat of soil acidification to forest health in the Northeastern United States may have been underestimated.     

Timing,magnitude, and impact of acidic deposition on sensitive forest sites

Adverse effects of acidic deposition on forest health are most likely to occur in forests which develop a thick raw or “mor” humus layer in which the effective cation exchange capacity is highly sensitive to acid input. A study of the trend of exchangeable Ca and Mg ions in sensitive humus layers over the past six decades indicated that a downward shift in equilibrium has occurred that is consistent with theories of ion mobilization and coincident in time with increasing acidic deposition in the mid-1900's. Independent records of a base cation mobilization in wood supports the view of a change in the root zone in sensitive forest sites and in lake water chemistry. Induced nutrient deficiency in declining forest stands was indicated by a high Al∶Ca ratio in fine root tip tissue as a marker of altered uptake efficiency which leads to increased vulnerability to biotic factors and greater sensitivity to abiotic stresses. Evidence indicates that sensitive sites were damaged by acidic deposition 20 to 40 yr ago, long before the problem of “acid rain” was recognized.     

Modeling soil respiration based on carbon, nitrogen, and root mass across diverse Great Lake forests

The variability in the net ecosystem exchange of carbon (NEE) is a major source of uncertainty in quantifying global carbon budget and atmospheric CO₂. Soil respiration, which is a large component of NEE, could be strongly influential to NEE variability. Vegetation type, landscape position, and site history can influence soil properties and therefore drive the microbial and root production of soil CO₂. This study measured soil respiration and soil chemical, biological and physical properties on various types of temperate forest stands in Northern Wisconsin (USA), which included ash elm, aspen, northern hardwood, red pine forest types, clear-cuts, and wetland edges. Soil respiration at each of the 19 locations was measured six times during 1 year from early June to mid-November. These data were combined with two additional data sets from the same landscape that represent two smaller spatial scales. Large spatial variation of soil respiration occurred within and among each forest type, which appeared to be from differences in soil moisture, root mass and the ratio of soil carbon to soil nitrogen (C:N). A soil climate driven model was developed that contained quadratic functions for root mass and the ratio of soil carbon to soil nitrogen. The data from the large range of forest types and site conditions indicated that the range of root mass and C:N on the landscape was also large, and that trends between C:N, root mass, and soil respiration were not linear as previously reported, but rather curvilinear. It should be noted this function appeared to level off and decline at C:N larger than 25, approximately the value where microbial nitrogen immobilization limits free soil nitrogen. Weak but significant relationships between soil water and soil C:N, and between soil C:N and root mass were observed indicating an interrelatedness of (1) topographically induced hydrologic patterns and soil chemistry, and (2) soil chemistry and root production. Future models of soil respiration should address multiple spatial and temporal factors as well as their co-dependence.     

Spatial and Temporal Variation in Calcium and Aluminum in Northern Hardwood Forest Floors

Acid rain results in losses of exchangeable base cations from soils, but the mechanism of base cation displacement from the forest floor is not clear, and has been hypothesized to involve mobilization of aluminum from the mineral soil. We attempted to test the hypothesis that losses of calcium from the forest floor were balanced by increases in Al in NewHampshire northern hardwoods. We measured exchangeable (six stands) and acid extractable (13 stands) Ca and Al in horizons of the forest floor over an interval of 15 years. Our sampling scheme was quite intensive, involving 50 or 60 blocks per stand, composited in groups of 10 for chemical analysis. Even at this level of effort, few stands exhibited changes large enough to be significant. Because of high spatial variability, differences would have had to be greater than about 50% to be statistically detectable. Differences in Ca and Al concentrations between Oi, Oe, Oa, and A horizons, however, were readily detected. Acid-extractable Al increased with depth, while Ca concentrations decreased; Ca-to-Al ratios decreased from 8.3 (charge basis) in the Oi to 0.2 in the A horizon. Therefore, a small change in sampling depth, or the inclusion of more or less A horizon material in the forest floor, could cause large differences in measured Ca and Al concentrations. To detect small changes in exchangeable cations over time would require sampling very intensively with careful control for comparability of horizons.     

Changes in soil properties and site productivity caused by red alder

Red alder (Alnus rubra Bong.) is well recognized as an effective host plant for the symbiotic fixation of N. While this fixation process leads to the rapid accumulation of N within the ecosystem, it also enhances nutrient accumulation in biomass and soil organic matter and increases nitrification and cation leaching. We hypothesized that changes in soil properties resulting from these processes would decrease site productivity for second rotation red alder. Adjacent stands of 55 yr old alder and Douglas fir (Pseudotsuga menziesii (Mirb.] Franco) were studied at the Thompson Research Center on the Cedar River Watershed in western Washington, USA.The presence of red alder caused the following soil changes: decreased soil solution pH, increased CEC, increased exchangeable acidity accompanied by a decreased soil pH and base saturation. This decreased soil and soil solution pH resulted in increased A1 concentration in the soil solution and on exchange sites as well as decreased P availability. To determine the effect of these changes on the productivity of the 2nd rotation alder forest, a species conversion experiment was initiated 5 yr ago. Results from this conversion study clearly indicated that the first rotation red alder forest has caused a relative decrease in the productivity of the second rotation red alder plantation. Compared to the growth of red alder on the former Douglas fir site, the second rotation red alder on the former red alder site exhibited 339 less height growth and 759, less aboveground biomass accumulation after 5 yr. Future research will focus on identifying those factors causing this lower productivity including P availability, soil acidity and Al toxicity, cation availability, and competition with other vegetation.     

Changes in soil properties and site productivity caused by red alder

Red alder (Alnus rubra Bong.) is well recognized as an effective host plant for the symbiotic fixation of N. While this fixation process leads to the rapid accumulation of N within the ecosystem, it also enhances nutrient accumulation in biomass and soil organic matter and increases nitrification and cation leaching. We hypothesized that changes in soil properties resulting from these processes would decrease site productivity for second rotation red alder. Adjacent stands of 55 yr old alder and Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) were studied at the Thompson Research Center on the Cedar River Watershed in western Washington, USA. The presence of red alder oaused the following soil changes: decreased soil solution pH, increased CEC, increased exchangeable acidity accompanied by a decreased soil pH and base saturation. This decreased soil and soil solution pH resulted in increased A1 concentration in the soil solution and on exchange sites as well as decreased P availability. To determine the effect of these changes on the productivity of the 2nd rotation alder forest, a species conversion experiment was initiated 5 yr ago. Results from this conversion study clearly indicated that the first rotation red alder forest has caused a relative decrease in the productivity of the second rotation red alder plantation. Compared to the growth of red alder on the former Douglas fir site, the second rotation red alder on the former red alder site exhibited 33% less height growth and 75% less aboveground biomass accumulation after 5 yr. Future research will focus on identifying those factors causing this lower productivity including P availability, soil acidity and Al toxicity, cation availability, and competition with other vegetation.     

Modelling Acidification Effects on Coniferous Forest Soils

Two submodels for simulating the leaching of forest soils are described. SOILORG is used for O, E, and top B layers where Al(OH)₃ is absent and organic matter is the major base cation storage. SOILMIN cares for the rest of the profile where Al(OH)₃ control of Al is assumed and goethite provides most of the sulphate storage, clay mineral surfaces providing base cation storage. Results are presented from a test run for the period 1911 to 2030, based on data from a 260 cm deep soil profile in the SW of Sweden investigated 1990 and on a likely deposition scenario. Considering that the deposition of base cations exceeded the removal by stemwood in 1911 when the simulation started, the biologic acidification of the soil profile had reached a steady state before 1911 so that no additional acidification took place before 1930 and very little before 1950. After 1950 it was strongly enhanced by the increased acid deposition. In the mineral soil a considerable resistance against acidification is offered both by base cation exchange and sulphate adsorption, creating an acidification front which moved slowly down the B-horizon then accelerated, reaching the bottom of the profile in 1990. A deposition reduction by 2/3 during 1990–2010 will cause a partial recovery of pH, particularly in the deeper parts of the profile.