Influence of tree species on acidification and mineral pools in deciduous forest soils of South Sweden

The influence of tree species on chemical properties of the soil profile (0 to 70 cm), especially acidity and cation pools, was studied below canopies of 100 to 150 yr old individuals of Fagus sylvatica L., Quercus robur L., Carpinus betulus L., Tilia cordata Mill, and Acer platanoides L., in three mixed deciduous forests. The pH(H₂O) range in the topsoil (0 to 5 cm) was 4.2 to 5.3 at the different sites and increased for all species by about 0.2 pH units to the upper C-horizon (50 to 70 cm). Carpinus had higher pH and base saturation, and the total exchangeable store of Ca (0 to 70 cm) at the ‘poorest’ site was ca 1.5 times greater than for Fagus and Quercus. Soils were less acid under crowns of Quercus than under Fagus and Carpinus in the upper 20 cm of the soil profile in the ‘richest’ site, but more acid at the deeper levels. The total exchangeable pools (0 to 70 cm) of K and Zn were 2 and 1.6 times greater under Quercus at the ‘richest’ site. Tilia had 10 to 20% units higher base saturation values and twice as much exchangeable Ca and Mg than the other species. It was concluded that out of all tree species studied, Tilia acidified the soil the least. The current annual total proton load (TPL) on the soil was 1.3 to 3.0 kEq ha^?1 yr^?1. The annual acid load due to cation excess accumulation in biomass was 30 to 50% of TPL. The remainder originated from atmospheric deposition. Quercus had the highest annual TPL at all sites, mainly because of greater input of atmospherically derived acidity, but also by a greater cation excess accumulation in biomass. Carpinus, compared to Fagus and Quercus, tended to have the lowest TPL at all sites, and Tilia had the lowest TPL at the intermediate site.     

Monitoring fish stocks in relation to acidification in Norwegian watersheds

The Norwegian Monitoring Programme for Long-Range Transported Air Pollutants started in 1980. The biological part of this programme includes besides invertebrate studies in streams, (i) fish community status in lakes by means of interviews, test-fishing in lakes by using standard gill-net series, recruitment studies of brown trout in inland streams, and juvenile stock assess and monitoring of fish kills in salmon rivers. Damaged fish stocks are recognized within a land area of 51,500 km² in southern Norway and 30 km² in northern Norway. At least 6,000 lake-dwelling fish stocks have either been lost or are at various stages of reduction. Brown trout (Salmo trutta) is the most widespread and abundant species of fish in Norwegian watersheds, and is also most severe affected by acidification. More recently, there are some indications of an increase in the abundance of brown trout in some areas. However, analysis of age structure in lakes, and fry densities in streams in such areas revealed large annual variations in recruitment rate, which indicates unstable water chemical conditions. Atlantic salmon (Salmo salar) is virtually extinct in 25 rivers in southernmost, southwestern and western Norway.     

Episodic acidification of a coastal plain stream in Virginia

This study investigates the episodic acidification of Reedy Creek, a wetland-influenced coastal plain stream near Richmond, Virginia. Primary objectives of the study were to quantify the episodic variability of acid-base chemistry in Reedy Creek, to examine the seasonal variability in episodic response and to explain the hydrological and geochemical factors that contribute to episodic acidification. Chemical response was similar in each of the seven storms examined, however, the ranges in concentrations observed were commonly greater in summer/fall storms than in winter/spring storms. An increase in SO _inf4 ^sup2? concentration with discharge was observed during all storms and peak concentration occurred at or near peak flow. Small increases in Mg²⁺, Ca²⁺, K⁺ concentrations and dissolved organic carbon (DOC) were observed during most storms. At the same time, ANC, Na⁺ and Cl^? concentrations usually decreased with increasing discharge. In summer/fall storms, the absolute increase in SO _inf4 ^sup2? concentration was one-third to 15 times the increase observed in winter/spring storms; the decrease in ANC during summer/fall storms was usually within the range of the decrease observed in winter/spring storms. In contrast, the decrease in Na⁺ and Cl^? concentrations during winter/spring storms was much greater than that observed during summer/fall storms. Data show that while base flow anion deficit was higher in summer/fall than in winter/spring, anion deficit decreased during most summer/fall storms. In contrast, base flow anion deficit was lower in spring and winter, but increased during winter/spring storms. Increased SO _inf4 ^sup2? concentration was the main cause of episodic acidification during storms at Reedy Creek, but increased anion deficit indicates organic acids may contribute to episodic acidification during winter/spring storms. Changes in SO _inf4 ^sup2? concentration coincident with the hydrograph rise indicate quick routing of water through the watershed. Saturation overland flow appears to be the likely mechanism by which solutes are transported to the stream during storm flow.     

Alberta油砂地区在两种水文流域森林土壤酸化敏感性研究

Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta. We evaluated the sensitivity of forest soils to acidification in two watersheds （Lake 287 and Lake 185） with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems. Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine （Pinus banksiana） or aspen （Populus tremuloides）. Soils in the two watersheds were extremely to moderately acidic with pH （CaCl2） ranging from 2.83 to 4.91. Soil acid-base chemistry variables such as pH, base saturation, Al saturation, and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor 〉 subsurface mineral soil 〉 surface mineral soil. The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon. Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%, respectively; the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification. Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.     

Interspecific variation of bark water storage capacity of three deciduous tree species in relation to stemflow yield and solute flux to forest soils

The purpose of the study was to: (1) test if normative bark water storage capacities differed significantly among three co-occurring deciduous tree species; and (2) examine the extent to which stemflow production and resulting solute inputs in temperate deciduous forests are affected by bark water storage capacity. Normative bark water storage capacities were determined for: Betula lenta L. (sweet birch), Carya glabra Mill. (pignut hickory), and Quercus rubra L. (northern red oak). Using the computed normative bark water storage capacities, previously published allometric equations relating tree diameter to aboveground woody surface area, and stemflow yield and chemistry data from ten precipitation events, the influence of bark water storage capacity on stemflow production and solute inputs was examined. Results demonstrated normative bark water storage capacities differed significantly among the tree species examined. Quercus rubra was found to hold the most water and B. lenta the least. For a 30 cm diameter tree, normative bark water storage capacities ranged from approximately 100 l for B. lenta to 250 l for Q. rubra. Despite a higher normative bark water storage capacity, Q. rubra was computed to have the largest stemflow solute inputs. Differences in stemflow quantities as well as solute inputs were attributable to interspecific variation in bark morphology and branching architecture, characteristics that affect amount of storage and detention times. Bark water storage capacity is linked with the geoecology of temperate deciduous forests because stemflow volume and solute inputs are partly determined by bark water storage capacity.     

Decomposition rates and feeding activities of soil fauna in deciduous forest soils in relation to soil chemical parameters following liming and fertilization

 This study investigated the influence of liming and P/K fertilization on the feeding activities of soil fauna and leaf litter decomposition rates in deciduous forest soils. The parameters examined were correlated to soil chemical characteristics. In 1994, we established a field experiment with six plots in an oak-beech forest and added different amounts of dolomite, partly combined with P/K fertilization. Two years thereafter a bait-lamina test was used to examine the feeding activity of soil fauna and a minicontainer test to study beech-leaf decomposition. In 1996, the feeding activity in the Ah horizon was lower in the plots left untreated in 1994 than in the plots which had been fertilized in 1994. The highest feeding activity was found in the treatment with 6 t dolomite ha^–1 plus P/K. In all plots, the feeding activity decreased with increasing soil depth. The decomposition rates varied from 0.49% to 0.78% week^–1 in the period April–October 1996. In 1996, the plots treated with 6 t dolomite ha^–1 had the highest decomposition rates and differed significantly from those treated with 9 t or 15 t dolomite ha^–1. No significant differences were found between the untreated plots and those treated with 9 t or 15 t dolomite ha^–1. These results were confirmed by those obtained in 1997. The C/N ratio of litter also decreased, mostly in the treatment with 6 t dolomite ha^–1. Feeding activities in the Ah horizon correlated positively with pH and concentrations of mobile Ca, Mg, K, and negatively with concentrations of mobile Al and heavy metals. We concluded that an increased supply of mobile nutrients and a decrease in mobile Al and heavy metals in these forest soils, as well as a balanced ratio between macro- and micronutrients, led to increased biological activity. Received: 26 June 1998     

Relating bat species presence to simple habitat measures in a central Appalachian forest

We actively sampled the bat community at 63 sites using detection and non-detection metrics on the Fernow Experimental Forest (FEF) in the central Appalachians of West Virginia using Anabat acoustical equipment May-June 2001-2003 to relate species presence to simple habitat measures such as proximity to riparian areas, forest canopy cover, forest canopy gap width, and forest canopy height. We acoustically detected eight species on the FEF, including the endangered Myotis sodalis. The presence of Lasiurus cinereus, M. lucifugus, M. sodalis, and Pipistrellus subflavus was associated more with riparian areas than upland areas. Both univariate comparisons and multiple logistic regression modeling showed that the probability that clutter-adapted foraging species such as M. septentrionalis and M. sodalis would be detected was greater as forest canopy cover increased or forest canopy gap size decreased, whereas the opposite was true for open-adapted foraging species such as Eptesicus fuscus and L. cinereus. The overall proportion of unidentifiable bat echolocation sequences to those identified to species was related to upland sites with increasing forest canopy cover indicating some sampling bias between cluttered and uncluttered habitats. However, given sufficient sample points, bat community surveys using acoustical detection show the ability to quickly develop generalized habitat associations for rugged areas such as the central Appalachians where traditional mist-net survey efforts often are logistically difficult and are lacking in scope. Moreover, these acoustical surveys also could lend themselves to species-specific predictive mapping of foraging habitat as well as allowing researchers to formulate testable hypotheses about detailed bat habitat relationships to be definitively tested with radio-telemetry techniques.     

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.     

Variation in methanotrophic bacterial population along an altitude gradient at two slopes in tropical dry deciduous forest

Soil samples were collected from Panchamarhi dry deciduous forest in Satpuda Biosphere Reserve, India to determine the effect of hill slopes and altitude on the population size of methanotrophic bacteria. Population size, in range of 4×10⁵-3.6×10⁷ g⁻¹ dry soil, was negatively correlated with altitude and increased exponentially (r²=0.97, P<0.001) at steep slope (60°) while logarithmically (r²=0.97, P<0.001) at low slope (45°). Soil organic C, total N, and soil moisture increased while C/N ratio and temperature decreased down the hill slope. The results indicated that nutritional status of the soil across the slopes determines the methanotrophic bacterial population size.     

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.     

Uncertainties in long-term predictions of forest soil acidification due to neglecting seasonal variability

Soil and soil solution response simulated with a site-scale soil acidification model (NUCSAM) was compared with results obtained by a regional soil acidification model (RESAM). RESAM is a multi-layer model with a temporal resolution of one year. In addition to RESAM, NUCSAM takes seasonal variability into account since it simulates solute transport and biogeochemical processes on a daily basis. Consequently, NUCSAM accounts for seasonal variation in deposition, precipitation, transpiration, litterfall, mineralization and root uptake. Uncertainty caused by the neglect of seasonal variability in long-term predictions was investigated by a comparison of long-term simulations with RESAM and NUCSAM. Two deposition scenarios for the period 1990–2090 were evaluated. The models were parameterized and validated by using data from an intensively monitored spruce site at Solling, Germany. Although both the seasonal and the interannual variation in soil solution parameters were large, the trends in soil solution parameters of RESAM and NUCSAM corresponded quite well. The leaching fluxes were almost similar. Generally it appeared that the uncertainty due to time resolution in long-term predictions was relatively small.     

Application of lime and wood ash to decrease acidification of forest soils

Liming and wood ash application are measures to decrease acidification of forests soils. The assessment of lime requirement can be based on that base saturation, which indicates a low risk of acid toxicity. Because of a wide spread Mg deficiency in Central European forests, Mg containing lime is normally applied. Ash from untreated wood is applied to decrease soil acidity as well as to improve K and P nutrition. In wood ash, K is the most soluble nutrient, follwed by Ca and Mg. The overall dissolution rate of lime applied to the forest floor is about 1t ha^?1 a^?1. After liming, soil solution alkalinity and Mg concentrations increase markedly, while changes of Ca, H ions and Al concentrations are less pronounced. After the application of wood ash, K concentrations increase due to the high K content and the high solubility of K in wood ash. After the application of a sufficiently high dosage of lime to the forest floor, the decrease of acidity in deeper soil layers may need decades because of the low solubility of lime. Nitrification and nitrate leaching induced by lime or wood ash may reduce their acid buffering efficiency.     

Oxidant effects on forest tree seedling growth in the Appalachian mountains

Long range transport of episodic concentrations of O₃ into the Appalachian Mountains of Virginia was recorded in the summer season of 1979 and 1980. Continuous monitoring of O₃ indicated monthly averages of ? 0.05 ppm O₃ and several periods averaged ? 0.08 ppm O₃. Open-top chambers were used to test the effect of ambient doses of the pollutant on the growth of 8 planted forest tree species native to the area. Height growth was suppressed for all species at the end of the second growing season when grown in open plots (no chamber) and ambient chambers compared to those grown in charcoal-filtered air supplied chambers. Height growth trends of open < ambient chamber < filtered air chamber were consistent. Virginia pine and green ash were significantly taller (p=0.10) when grown within filtered air chambers. Tulip poplar and green ash manifested purple stippling on the adaxial leaf surface and sweetgum developed purple coloration under open or ambient chamber conditions; other species exhibited no visible injury.     

Effects of experimental acidification on macroinvertebrate drift diversity in a mountain stream

A small stream (Norris Brook) within the Hubbard Brook Experimental Forest was acidified to determine what effect elevated H⁺ stress may have on the ecology of a mountain stream. The experiment was designed to simulate a pH level (4.0) that can occur during initial snowmelt (acute period) and during longer term (chronic period) acidification. Daily macroinvertebrate drift samples were collected from treatment and reference areas of Norris Brook. Drift diversity at the generic level was calculated using Brillouin's formula and partitioned hierarchically following macroinvertebrate classifications based on taxonomy (orders) and feeding strategies (functional groups or guilds). The rate of movement of individuals and genera was significantly greater for those organisms leaving the acid-stressed area during the first five days than for those entering, whereas no difference between the rate of macroinvertebrates entering or leaving the acid-stressed area was apparent for either numbers or genera over the remaining 25-day study period. For the acute period (first five days), the increased macroinvertebrate drift leaving the acidified area was significantly more diverse at the levels of aquatic insect orders and functional groups but less diverse at the generic level than the drift entering. For the chronic period (25-day period) no significant differences were detected in either major taxa, functional group (with the exception of collectors), or generic diversity between the drift entering and leaving the treatment reach. Mayflies and probably chironomids leaving the acid-stressed area during the acute period were generically more diverse than those entering, whereas stoneflies drifting out of the acidified reach were generically less diverse than those drifting in. The overall change in the normal pattern of spatial and temporal variation in drift rate and diversity provides quantitative evidence that H⁺ stress significantly altered the structure and function of the macrobenthic community.     

Assessment of soil acidification effects on forest growth in Sweden

The results of mapping critical loads, areas where they have been exceeded and steady state (Ca+Mg+K)/Al ratios of soils in Sweden, has been used to assess the order of magnitude of the ecological and economic risks involved with acid deposition for Swedish forests. The results of the calculations indicate that 81% of the Swedish forested area receive acid deposition in excess of the critical load at present. Under continued deposition at 1990 level, forest die-back is predicted to occur on approximately 1% of the forested area, and significant growth rate reductions are predicted for 80% of the Swedish forested area. For Sweden, growth losses in the order of 17.5 million m^?3 yr^?1 is predicted, equivalent to approximately 19% of current growth. Comparable losses can be predicted for other Nordic countries. The soil acidification situation is predicted to deteriorate significantly during the next 5–15 years, unless rapid emission reductions can be achieved. A minimum deposition reduction over Sweden of 85% on sulphur deposition and 30% on the N deposition in relation to 1990 level is required in order to protect 95% of the Swedish forest ecosystems from adverse effects of acidification. A minimum reduction of 60% on sulphur deposition and 30% on the N deposition is required to keep forest harvest at planned levels.     

Principal geographic variation in the acidification of Swedish forest soils

The principal geographic variation in acid-base status of 25 deep soil profiles (maximum 2.6 m deep) was investigated along three transects across Sweden. The transects represent gradients in the atmospheric deposition of acidifying compounds. A latent variable describing the acidity of the profile was extracted by Principal Component Analysis (PCA) and found to contain information that could be geographically interpreted. The variable was correlated more strongly with the atmospheric deposition of S (r=?0.86) than with groundwater recharge (r=?0.30) or base mineral index (r=0.45). It was concluded that variation in the deposition of S, in the form of H₂SO₄, is the main factor responsible for the large geographical differences in acidity in forest soils along transects from west to east in southern and middle parts of Sweden.     

A greenhouse study of northern red oak seedling growth on two forest soils at different stages of acidification

The objective of this study was to determine whether or not Ca and P in soils from two forested sites at two different stages of acidification were limiting growth of red oak seedlings. The A and E horizons of a Berks soil from Watershed 4 at the Fernow Experimental Forest (cation exchange buffer range) and a Hazelton/Dekalb soil from Pea Vine Hill in Southwestern Pennsylvania (Al buffer range) were placed in pots and utilized as the growth medium for northern red oak seedlings in a greenhouse environment. Soil water NO₃-N, Ca, Mg, and K concentrations were significantly higher (α≤0.05) on the Berks soil. Soil exchangeable P and soil solution TP (total phosphorus) were significantly higher (α≤0.10) on the Hazelton/Dekalb soil. Both soils were amended with bone meal (CaPO₄) to determine the effects of Ca and P addition on the growth and nutrient uptake of the seedlings. Height growth of the control red oak seedlings was significantly (α≤0.05) greater on the Berks soil after 45 d, but amendment of Hazelton/Dekalb soil with bone meal eliminated this difference. Bone meal addition to the Hazelton/Dekalb soil resulted in significantly greater (α≤0.05) height growth of red oak seedlings when compared to red oak seedlings grown on unamended Hazelton/Dekalb soil, but did not have a similar effect for red oak seedlings grown on Berks soil. Bone meal addition to Hazelton/Dekalb soil resulted in greater (α≤0.05) concentrations of Ca and Mg in red oak leaves. Unfertilized Berks red oak seedling leaves had significantly higher (α≤0.05) concentrations of Ca and K than their Hazelton/Dekalb counterparts. Al/Ca molar ratios were significantly lower on the Berks soil. Red oak height growth was increased significantly by Ca addition to the Hazelton/Dekalb soil.     

Analysis of summertime cloud water measurements made in a Southern Appalachian spruce forest

This paper presents an analysis of cloud water measurements made during the summers of 1986 and 1987 at Whitetop Mountain, Virginia (36.639° N, 81.605° W). Analysis of cloud water chemistry, cloud type, and air mass origin are made for each cloud event occurring during one 3 to 4 week measurement ‘intensive’ per year. Regional source/receptor relationships are also investigated. Cloud water concentrations of major ions (i.e., H⁺, SO₄ ^2?, NO₃ ?, and NH₄ ⁺) are consistently higher during orographically formed ‘cap’ cloud events. Differences in cloud liquid water content between cap and frontal cloud events explains most, but not all, of the cloud water ion concentration differences. The remaining difference can be explained by greater rainfall associated with frontal cloud events. Most of the cloud water sulfate measured at Whitetop Mountain is apparently due to nucleation of aerosol sulfate within cloud droplets and not to local in-cloud aqueous phase SO, oxidation. No strong source/ receptor relationships were evident from this analysis. Most 72 hr air trajectories arriving at Whitetop Mountain during the cloud events described in this paper originated in the southeastern United States. Few came from the Ohio River Valley or the northeastern United States.     

Outcomes of longterm deciduous forest restoration in southwestern Ontario, Canada

At present, forest cover in southwestern Ontario, Canada, remains at less than 5% due to intensive agricultural and urban land use. Although much of the extant forest is increasingly protected by legislation, remnants continue to be degraded by the spread of non-native plant species, overgrazing, and recreational use. Some parks in the region have adopted management programs aimed at mitigating this degradation. Over the last 35 years, cottages and roads at Point Pelée National Park have been removed and sites either passively restored (i.e. road or cottage eliminated and vegetation allowed to regenerate) or actively restored (i.e. road or cottage eliminated, exotic vegetation removed, and native species planted). In 1994 and 1995, we assessed the effectiveness of restoration by comparing the understorey plant communities in 28 restored sites with those in less disturbed reference sites. There was a significant increase (P<0.0001) in the similarity of understorey plant communities between restored and reference sites as time-since-restoration increased. Soil moisture, canopy cover, distance to continuous forest, and site-shape all significantly affected plant species composition. Former road sites recovered significantly (P<0.05) more rapidly than former cottage sites, and the former lawns of passively restored cottage sites were the slowest to recover. Five years following active restoration, non-native ruderal species continued to dominate restored sites. The observed recovery of understorey plant communities in restored sites is attributed to their proximity to natural vegetation, and its function as a seed source. In some sites, recovery is substantial and, assuming present trajectories of change are maintained, we predict that recovery could occur in many mesic sites within the next 20 years. Restoration activity facilitates forest recovery and would appear to have a valuable function in mitigating ongoing conflicts between conservation and human use in this region.     

The sensitivity of Swiss forest soils to acidification and the risk of aluminum toxicity

In the context of pollution‐control strategies to minimize the detrimental effects of soil acidification, there is a need to know how and to what extent soils respond to acidifying substances. The purposes of this study were to assess the sensitivity of soil to acidification, in particular to a decrease in pH and in base saturation (BS), and the risk of Al toxicity for vulnerable plants using chemical indicators. These indicators were derived from soil data (pH, exchangeable cations, amount of fine earth) measured in the mineral horizons of 257 soil profiles throughout Switzerland. Based on the analysis of the distribution of pH and BS values in the soil collective, we assessed the sensitivity of soils to a decrease in pH and in BS. Soils that were considered sensitive to a decrease in pH had pH values between 4.8 and 7.0. The degree of sensitivity was estimated with the proportion of fine earth in the critical pH range to a depth of 100 cm. Soils that were considered sensitive to a decrease in BS had pH values between 3.6 and 5.5 and a BS between 10% and 95%. Since the effective cation‐exchange capacity (CEC_eff) of the fine earth might dampen the decrease in BS when acidity is added, the disposition for a decrease in BS was related to the relative amount of fine earth in the sensitive BS and to the mean CEC_eff of this fine‐earth fraction. The risk of Al toxicity for vulnerable plants was estimated using the ratio of base cations to Al at the cation‐exchange sites (BC : Al_exc). A BC : Al_exc of 0.2 was taken as a threshold value below which the risk for sensitive plants increases. The degree of risk was based on the proportion of fine earth in the critical BC : Al range (≤0.2) in the soil profile. These indicators taking into account the various aspects of soil acidification are derived from usually available data and represent therefore a cost‐effective tool to assess the sensitivity of soils to an input of acidity.