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Published in Soil Sci. Soc. Am. J. 68:588-595 (2004).
© 2004 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA

DIVISION S-7—FOREST & RANGE SOILS

Calcium Loss in Central European Forest Soils

Robert Jandl*,a, Christine Alewellb and Jörg Prietzelc

a Institute of Forest Ecology, Austrian Federal Office and Research Centre for Forests (BFW), Seckendorff Gudent Weg 8, A-1131 Vienna, Austria
b Umweltgeowissenschaften, Bernoullistrasse 30, 4056 Basel, Switzerland
c Chair of Soil Science, Technische Universität München, D-85350 Freising-Weihenstephan, Germany

* Corresponding author (robert.jandl{at}bfw.gv.at).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The Ca concentration in the soil of many Central European forest ecosystems is declining. The evidence for the extent of Ca loss in Norway spruce (Picea abies L. [Karst.]) forests was investigated from changes in exchangeable Ca between 1985 and 2000 at Weilhartsforst/Upper Austria and from soil solution chemistry between 1992 and 1999 at Coulissenhieb/NE Bavaria. The temporal trend of exchangeable Ca in the soil and the Ca concentration in the soil solution were compared with the change in the Ca concentration in spruce needles. The decline of the pool of exchangeable Ca in the soil within 15 yr was not reflected by the Ca concentration of needles in Austria. Analysis of a large regional database revealed that soil exchangeable Ca was only loosely correlated with the Ca level in needles and entirely unrelated to the rate of forest growth. At the Bavarian site a decline in soil solution Ca concentration and Ca/Al and a decline in needle Ca concentrations were observed; however, changes in foliar Ca concentrations were not statistically correlated with soil solution chemistry. This would suggest that trees access Ca from sources that are not evident from soil chemical data. Despite ongoing Ca losses, we did not identify an immediate stress for the forest ecosystems.

Abbreviations: BS, base saturation • CEC, cation-exchange capacity • ICP-AES, inductively coupled plasma analysis


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
CENTRAL EUROPEAN FORESTS embrace a diverse mosaic of site conditions, ranging from the calcareous and silicatic bedrock to quaternary and tertiary sediments. The boundaries between geological zones are blurred where glacial, fluvial, and eolian processes formed overburdens over the autochthonous bedrock. The natural soil acidification, driven by CO2 in the precipitation as well as by internal system processes, has decalcified many soils in the time domain of thousands of years. Besides, clear evidence for the anthropogenic acidification of European forest soils has been given (Hallbäcken and Tamm, 1986; von Wilpert and Hildebrand, 1994). More recently, a decline in the pool of exchangeable Ca had been reported (Meesenburg et al., 1999; Prietzel et al., 1997; Thimonier et al., 2000). It was most obvious in the uppermost part of the mineral soils that carry the largest load of anthropogenic and internal system acidity. Soils on calcareous bedrock were often unaffected, because Ca loss is quickly replenished by CaCO3 weathering.

Central European forests already have a long history of Ca loss. Commodities that are now provided by the chemical industry, historically used forest products as raw material (Glatzel, 1999). Exploitative land use had taken a heavy toll on site productivity and led to a rather uniform coniferous forest cover and to soil degradation. Formerly fertile sites with mixed-species and deciduous stands were turned into poor sites with open coniferous stands (Fiedler et al., 1962; Kreutzer, 1972). In the last century, secondary Norway spruce monocultures have contributed to a decline in soil Ca. Acidification of the upper horizons of the mineral soil and an increased susceptibility to storm damage and pest infestations was shown for certain sites, but the evidence remained controversial (Rehfuess, 1990; Stone, 1975).

In the early 1980s soil acidification and cation loss due to air pollution were established in field experiments (e.g., Abrahamsen et al., 1987). The link between the high rates of sulfate, nitrate, and proton deposition and soil acidification was quickly established (Singh et al., 1980; Reuss and Johnson, 1986). Large amounts of S are still bound in soils that formerly received high loads of atmospheric S deposition. Sulfate is gradually released until a new equilibrium between soil pools and S input rates is established (Harrison et al., 1989; Alewell, 1998). Nitrogen deposition adds nitrate as a mobile anion that leads to cation loss, but also eases the N limitation to forest growth. Nitrate became increasingly available and many forests approached N saturation (Farrell et al., 1994; Gundersen et al., 1998). Although forests are growing better than in the past, there is evidence of a decline in Ca pools of Central European and North American forest soils (von Wilpert and Hildebrand, 1994; Wesselink et al., 1995; Lawrence et al., 1997; Prietzel et al., 1997; Huntington, 2000; Raben et al., 2000).

Soils in Norway spruce stands are acidified and lose Ca by three simultaneous processes: (1) the nutrient uptake of the shallow rooting tree exploits the upper-most part of the soil profile (Glatzel et al., 2000), (2) the nutrient return from the acidic needle litter is slow, and (3) the interception of air pollutants in the canopy is higher than by deciduous trees (Ulrich, 1987; Rothe et al., 2002).

We investigated whether studies of the mineral soil and the soil solution deliver consistent conclusions with respect to the temporal trend of Ca in the forest soils and the forest growth rate, and the extent to which the Ca concentration in needles relates to the observed Ca loss from soils. We present data from two regions in Central Europe where Ca loss during the last decades has been reported. A study at Weilhartsforst in Upper Austria, examined the decline in Ca saturation of the mineral soil. In 1982, the region was chosen for a monitoring project because symptoms of forest decline had been expected to develop rapidly. In addition to the high rates of Central European background deposition the Weilhartsforst received S from an industrial district in the vicinity. The study site Coulissenhieb in the NE-Bavarian catchment Lehstenbach examined, among other parameters, the temporal trend in the ion concentrations in the soil solution. The site is a member of a suite of watershed studies that were started to monitor the effects of acidic deposition. After the reduction in industrial emissions the monitoring was continued to follow the expected recovery of the forest.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Site Weilhartsforst/Upper Austria
Evidence for changes in the chemistry of Austrian forest soils was available from monitoring programs within the EU Level-I-project (ECDG VI, 1998) and its precursors, from control plots of fertilizer experiments, and from a number of individual studies. We analyzed data from an intensive monitoring program to represent the plot level. For the regional level, we used needle data of the growth region, where the plot is located. For the national level we analyzed soil and needle data from the Austrian Forest Monitoring Program.

The site chosen for a detailed soil chemical investigation was a plot of 0.5 ha in a 110-yr-old Norway spruce stand in the Weilhartsforst, Upper Austria (48° 10' N, 12°55' E). The Weilhartsforst is a continuous and homogeneous forest area of 9100 ha. The elevation is 450 m above sea level; soils are derived from a mixture of quaternary moraine sediments and silicatic gravel from fluvial transport. Soils are classified as Cambisols (FAO, 1998) and soil chemical characteristics are given in Table 1. The annual air temperature is 7.7°C and the precipitation is 800 mm. The stem density is approximately 630 per hectare and the height of dominant trees is 32 m. Litter had been raked over centuries. Soil degradation was evident from the herbaceous vegetation that suggests much poorer site conditions than one would expect based on elevation, bedrock, and climate. The site was classified as Mastigobryo-Piceetum with Vaccinium myrtillus L., Lycopodim clavatum, and Oxalis acetosella as dominant herbaceous species, although a Luzulo nemorosae-Fagetum had been the potential plant community (Starlinger, 2000).


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  		Table 1. Soil properties at the sites Weilhartsforst (status of 1990) and Coulissenhieb (data from Manderscheid and Göttlein, 1995); pH Weilhartsforst is pHCaCl2, pH Coulissenhieb is pHH2O.

 
Moreover, we evaluated a data set of Ca concentrations of spruce needles from the entire growth region, in which the Weilhartsforst is embedded. It comprised 59 trees from an area of 410 000 ha; needle samples are collected annually. The relationship between soil exchangeable Ca and yield class, and Ca concentration in needles, respectively, was evaluated from the 330 noncalcareous sites of the Austrian National Forest Monitoring Program, where samples have been collected between 1987 and 1990 (FBVA, 1992).

Soil Analysis
In the Weilhartsforst, soil samples were taken in 1985, 1990, 1995, and 2000 from four pits that are permanently marked in the field. In 1985 and 1990, soil samples were collected from fixed depths (0–10, 10–20, 20–30, 30–50, and 50–80 cm). In 1995 and 2000, the uppermost mineral soil horizon was further divided into 0 to 5 and 5 to 10 cm. The samples of the Austrian Monitoring Program were collected from fixed depths (0–10, 10–20, 20–30, 30–50, and 50–80 cm). Here we used the data of the depth 0 to 10 cm, because this soil layer contains the majority of the tree roots. We therefore expected that the data best reflect the relation between soil and plant. The concept of representing the local variability of soil properties changed with time: Before 1990 samples from all four soil pits were pooled in the field into one sample per site and horizon. Thereafter samples from all pits were analyzed separately. In the laboratory, soils were sieved through a mesh of 2 mm. The chemical analysis included pH in 0.01 M CaCl2 and extraction of exchangeable cations (Na, K, Ca, Mg, Mn, Al, and Fe) with an unbuffered 0.1 M BaCl2 solution. Cation-exchange capacity (CEC) was calculated as the sum of exchangeable cations; data are given in Table 1. Archived soil samples were used to establish a regression equation for correction of old data for exchangeable Ca. In cases where the correction seemed unreliable, a re-analysis of archived samples was performed.

Stand Growth and Tree Nutrition
Stands were characterized with a yield class system that uses the stand height–age relation (Marschall, 1975). The annual Ca uptake in the aboveground biomass at the experimental plot Weilharsforst was calculated from the tabulated annual stem increment and unpublished data on the Ca concentration in stem wood. The assumption was that the amount of Ca in the canopy and the belowground biomass of the mature spruce forest was in steady state. The Ca concentration of 6-mo-old needles was used as a measure of Ca nutrition. Needle samples were collected in the dormant period from the seventh whorl of dominant trees. At the experimental plot Weilhartsforst, samples were obtained from five trees and were analyzed individually. The 59 trees comprising the regional data set were sampled annually and were analyzed individually. The samples from the Austrian Forest Monitoring Program consisted of needles from three trees that were pooled to one representative sample per grid point. Needles were dried at 75°C, finely ground, digested in concentrated HNO3/HClO4, and analyzed for total Ca concentration.

Concentrations of cations were measured by means of atomic absorption spectroscopy (PerkinElmer, Norwalk, CT) before 1990 and by atomic emission spectroscopy, using inductively coupled plasma analysis (ICP-AES, Varian Liberty 200, Palo Alto, CA) thereafter. Laboratory methods are described in Blum et al. (1996).

Site Coulissenhieb/Bavaria
The site is part of the Lehstenbach catchment in the Fichtelgebirge in Northern Bavaria/Germany (50°09' N, 11°52' E). It represents a 2.5-ha large, 150-yr-old Norway spruce stand. The granite bedrock was weathered deeply during the Tertiary. The average precipitation in the area is 1000 mm and the annual average temperature is 6°C. The acidic soils are classified as dystric Cambisols and Podzols according to FAO-classification (FAO, 1998). Soil chemical parameters (Table 1) indicated a high degree of soil acidification, documented by low pools of exchangeable Ca and Mg, and by low pH values.

Since 1992 precipitation was sampled with 20 open throughfall collectors with a cross-section area of 326 cm2, arranged along a transect at the 2-m interval. Starting in July 1992, soil solution samples at the site were collected biweekly, and monthly starting in 1997 at sampling depths of 20 and 90 cm using ceramic suction lysimeters at a tension of 40 kPa (P-80, Berliner Porzellanmanufaktur, Germany). In total, 20 replicate lysimeters per depth were installed, each located adjacent to a throughfall sampler.

Water samples were filtered (0.45 µm) and stored at 2°C before analysis. After filtration Ca and Al were measured ICP-AES (Integra XMP, GBC, Arlington Heights, IL). Nitrate and sulfate concentrations were determined by ion chromatography (Dionex IC 2100i, Sunnyvale, CA). The pH value was measured with a glass electrode.

Thirty-eight soil profiles were sampled along a regular grid of 300 by 300 m. Samples were taken from soil pits according to pedogenetic horizons and were analyzed individually. The CEC was determined by percolating 2.5 g of soil with 100 mL of 1 M NH4Cl during approximately 4 h. Samples were soaked with a few milliliters of the extraction solution overnight before the percolation. Cations (Na, K, Ca, Mg, Mn, Al, and Fe) were measured by ICP-AES. The CEC was calculated by summation of the extracted cations. Base saturation (BS) was calculated as (Na+K + Ca + Mg)/CEC. The pH was measured by a glass electrode in distilled water (pHH2O) at a soil/solution ratio of 1:2.5. Water extractable SO2–4 was determined by five sequential batch extractions of field moist soil with distilled water using a soil/solution ratio of 1:5. Sulfate in the extracts was determined by ion chromatography.

Needles were sampled from the upper canopy in autumn (October, November) 1992 (26 trees), 1994, 1995, 1996, and in April 1999 (five trees each year), separated according to needle age, and analyzed as composite mixed samples per needle age and tree. After drying at 60°C the samples were milled and 100 mg was digested in 1 mL of 1M HNO3 at 170°C for cation analysis by ICP-AES. Nutrient concentrations in needles from 1992 to 1999 were published by Alsheimer et al. (1998) and Alewell et al. (2000b).

Statistical Analysis
Soil data from the intensive monitoring plot at Weilhartsforst were analyzed by analysis of variance (ANOVA) and a subsequent multiple comparison of means for the Years 1990, 1995, and 2000 (procedure GLM, Duncan test). The different soil layers were analyzed separately. Differences were considered significant at p < 0.05 and marginally significant at p < 0.1. The 1985 data were not included in the analysis because only pooled samples but no measure for the variation was available. From the data of the Austrian Forest Monitoring Program the correlation between the log-transformed soil exchangeable Ca concentration in the upper 10 cm versus Ca concentration in needles and yield class, respectively, was calculated with procedure CORR. For the Coulissenhieb site, the temporal trend of the Ca concentration in needles was calculated as linear regression (procedure REG). Differences between years were tested with a repeated measures analysis of variance (procedure GLM, SAS Institute, 1989). A linear regression was used to test the relation between soil solution and needle data. The significance of the derived equations was tested by ANOVA with the statistics module of SigmaPlot for Windows 2001 (SPSS Science, Chicago, IL).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Weilhartsforst/Upper Austria
The change in the concentration of exchangeable Ca and the decline in BS at Weilhartsforst in Upper Austria between 1985 and 2000 is shown in Fig. 1 . A typical depth gradient of exchangeable Ca in decalcified soils shows high concentrations in the upper mineral soil horizon, a decline with depth and an increase in the deeper soil horizons, if undissolved carbonates are present (Ulrich and Malessa, 1989). At the first sampling date in 1985 the concentration of exchangeable Ca in the upper mineral soil was highest, and declined strongly until 1995. In 2000, values were only slightly lower than in 1990, but much higher than in 1995. The changes in Ca concentrations were largest in the upper mineral soil, and declined with depth. The concentrations for the time span 1990 to 2000 were significantly different in the 0- to 5-cm layer (1995 < 2000 < 1990). At the 5- to 10-cm depth, exchangeable Ca in 1995 was marginally lower than in 1990 and 2000 (1995 < 1990 = 2000). Below the 10-cm depth the differences were not significant.



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  		Fig. 1. Temporal variability of chemical soil properties at the Weilhartsforst plot in Upper Austria over 15 yr, (a) exchangeable Ca and (b) base saturation. Symbols are mean values, the error bar indicates the average standard deviation of the means.

 
A similar trend was found for the BS, which declined from between 30 to 40% in 1985 to values below 5% in 1995 and increased to 8 to 10% in 2000. The BS in 1990 was significantly higher than in 1995 and 2000 throughout the entire soil profile (1990 > 1995 = 2000). Other differences were not statistically significant. A low BS is typical in the entire region. Changes in the concentration of soil organic matter cannot account for the decline in BS, because CEC remained constant over the entire period. The uptake of Ca in the growing biomass was calculated as 3 to 4 mmol Ca m–2 per year and could not account for the Ca loss from the mineral soil, because the mature stand annually returns a large part to the soil as litterfall. The average pH in the upper mineral soil was 3.2 and increased to 3.8 in the 30- to 50-cm depth and changed only marginally during the investigation.

The Ca concentration of needles both in the Weilhartsforst and in the growth region remained relatively stable over time and did not reflect the decline in exchangeable Ca from the forest soils (Fig. 2) . Fluctuations between years may be driven by meteorological factors, but indicated neither a decline nor a recovery of forests. The needle Ca concentration at Weilhartsforst was always in the range of medium to low supply and only intermittently in the range of deficiency.



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  		Fig. 2. Temporal trend of the Ca concentration in needles over time at the Weilhartsforst plot (n = 5) and in the growth region (n = 59; mean, minima, maxima). The horizontal line represents the Ca sufficiency threshold value according to Bergmann (1992).

 
Figure 3 shows that in the data set of the Austrian Forest Monitoring Program the yield class, an indicator of the growth rate, and exchangeable soil Ca were not correlated at all. Obviously, other factors such as climate, soil water regime, and N supply exerted a strong influence on stand growth and overrode the effect of the Ca supply. The correlation between Ca concentrations in soils (0–10 cm) and needles was loose, yet significant (r = 0.43, p < 0.0001; n = 330). Needle Ca concentrations ranging from deficiency (approximately 1.5 mg g–1) to good supply (>3.5 mg g–1) were found at low soil Ca.



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  		Fig. 3. Concentration of exchangeable Ca in the soil (0–10 cm) versus (a) Ca concentration of needles and (b) yield class. Data include 330 sampling sites on non-calcareous bedrock from the regular grid of the Austrian Forest Monitoring Program.

 
The relation between Ca in soils and needles might be better reflected if pools instead of concentrations in the respective compartments had been compared. No such data were available for our experimental sites, but data from other studies have shown weak if any correlations (Johnson and Lindberg, 1992; Schulze, 2000).

Coulissenhieb/Bavaria
The results of Coulissenhieb demonstrated a much closer relation between soil solution chemistry and forest nutrition. Needle analyses revealed a decrease of the Ca concentration in all needle age classes with time (Fig. 4) . The highest concentrations were consistently observed in 1992 and the lowest in 1999. The Ca concentration decreased in all age classes by about 2 mg g–1, from 4.3 to 1.9 mg g–1 in the youngest needles and from 5.2 to 2.6 mg g–1 in the 4-yr-old needles. A linear regression and repeated measures of ANOVA confirmed a statistically significant effect of the year on the Ca concentration in needles. A significant interaction between years showed that the decline of Ca concentrations varied over time.



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  		Fig. 4. Calcium concentration of spruce needles at Coulissenhieb, data from Alewell et al. (2000b). The horizontal line represents the Ca sufficiency threshold value according to Bergmann (1992).

 
Between 1988 and 1999 the mean annual Ca concentration in throughfall decreased by about 70% (Alewell et al., 2000b). The Ca concentration in the soil solution at the 20-cm depth partly reflected the change in throughfall chemistry (Fig. 5) . A statistically significant decrease by almost 80% was observed during the period from 1992 to 1999. At the 90-cm depth, the Ca concentrations in the soil solution decreased significantly by about 77%. The molar Ca/Al ratios of the soil solution decreased significantly with time, both at the 20- and the 90-cm depth. At the 20-cm depth, the Ca/Al ratios were around 0.9 in 1992 and decreased to 0.3 in 1999 ({Delta} = –65%). The ratios were generally lower at the 90-cm depth and showed a statistically significant decrease from 0.41 to 0.17 during the 8 yr of observation. Although a linear regression between Ca concentrations in the needles and the soil solution was not statistically significant, both parameters showed a declining trend with time.



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  		Fig. 5. Temporal trend of the (a) Ca concentration and (b) molar Ca/Al ratios in the soil solution in the 20-cm depth at the Coulissenhieb site.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
Our study of the plot in the Weilhartsforst represents one of very few studies where chemical soil analysis has been performed repeatedly during the last 20 yr. The trend toward low soil Ca levels (Fig. 1) is consistent with the deposition history. Sulfate is now released from previously accumulated soil sulfate pools and nitrate comes from recent atmospheric N deposition (Kölling and Prietzel, 1996; Rennenberg et al., 1998; Prietzel and Kölling, 1999; Alewell et al., 2000a). The pace of Ca loss at this particular plot between 1985 and 1995 was quick and would theoretically have depleted the pool of exchangeable Ca within a few decades. The temporal trend was not linear, however, as Ca levels increased in 2000 compared with 1995. Cation leaching driven by mobile anions would have led to a consistent trend toward low Ca levels. The apparent fluctuation could be caused by the small-scale variability of soil properties, or by a recovery of soils due to the recent reduction of the input of acidity from deposition. Nevertheless, the soils at Weilhartsforst have suffered a net loss of exchangeable Ca in the last 15 yr. A clear temporal trend in the base cation pools is often difficult to detect due to small-scale spatial heterogeneity of chemical soil properties, slight differences in soil sampling techniques between individuals, and slow development of trends over time (Yanai et al., 1999). Remarkably, the change in soil pH over time was small, although the BS and the concentration of exchangeable Ca changed considerably over time. We believe that soils had entered the Al-buffer range before our study was initiated. Since then, the pH remained at a low level and acidity entering the soil was buffered by the destruction of silicates and by the desorption of base cations (Schwertmann et al., 1987).

The study at Coulissenhieb showed a decrease in the Ca concentration in the soil solution (Fig. 5). Despite emission reductions, the SO2–4 concentration in the soil solution remained high (Alewell et al., 2000b). For this site, throughfall was an important Ca source, and reduced Ca deposition became quickly apparent (Alewell et al., 2000b). The exchangeable soil Ca pool down to the 90-cm depth was extremely low, representing only about 10 times the deposition of 1993 (Table 1). Due to the Ca loss, the Ca/Al ratio of the soil solution continued to decrease (Fig. 5).

The reasons for continued net losses of Ca from forest soils were manifold. Continued leaching of sulfate and nitrate from the soils, and a decrease in Ca deposition were major factors (Alewell et al., 2000a; Likens et al., 1996). The shallow rooting Norway spruce can accentuate the acidification of the upper mineral soil, because the entire base cation uptake of the forest is obtained from a small part of the mineral soil. Calcium is temporarily removed from the soil, but not lost from the ecosystem, because it is retained in the tree biomass.

The Ca concentration in Norway spruce needles generally increases with needle age. According to Bergmann (1992), sufficient supply of Ca in 1- or 2-yr old Norway spruce needles ranges from 3.5 to 8.0 mg g–1. The Ca concentration of the needles, both at the plot in the Weilhartsforst and the surrounding growth region varied between years, but did not show a correlation with soil Ca (Fig. 2). Even at a broad regional scale (Fig. 3a), the soil Ca concentration varied over two orders of magnitude, but the Ca concentration in the needles varied considerably less and showed a large scatter within the range of low soil Ca concentrations. The yield class, which integrates several site factors, was totally unrelated to soil Ca (Fig. 3b). Concentrations of foliar Ca at the Coulissenhieb site decreased over time to levels below 2 mg g–1 in 1999 in current needles (Fig. 4). A decline of the Ca concentration in solution occurred simultaneously (Fig. 5). Comparison of Fig. 4 and 5 suggests that the decline in Ca availability is responsible for the observed change in tree nutrition.

Plant available Ca sources are not necessarily reflected by exchangeable soil Ca, and the ratio of Ca/Al in solution may be a better indicator of the Ca nutrition. The standard soil analysis overestimates the pool of plant available Ca, because the surfaces of aggregates in the range of middle and wide pores, where most roots are growing, is considerably more acidic than the analysis of a soil bulk sample would suggest (Hildebrand, 1994). On the other hand, Ca can be made available directly from rocks. Mycorrhizal fungi are able to dissolve Ca from Ca-feldspars and apatite (Blum et al., 2002; van Breemen et al., 2000). Also the soil skeleton that is routinely removed from the soil sample, contains Ca (Kohler et al., 2000). Rock-derived Ca can be a significant Ca source in base-poor forest ecosystems. At both sites, the rock content of the soil is large and these processes may be an important source of Ca.

Although the pool of exchangeable soil Ca declines at many sites in Central Europe, no consistent decline in foliar Ca is observed. The need for liming to improve the Ca nutrition of forests cannot be substantiated with our data. There are, however, factors besides forest nutrition and wood production that are increasingly important. Soil acidification leads to a decline in the microbial activity and can cause a change in biogeochemical nutrient cycles (Anderson and Domsch, 1993). Blagodatskaya and Anderson (1999) have demonstrated that the bacterial biomass suffers from soil acidification and that its activity can be restored with liming. Moreover, forest soils fulfill an important role in landscape ecology due to their role on water quality and quantity (USDA-Forest Service, 2000). Liming adds alkalinity to the soil. The maintenance of a moderate Ca saturation of the exchange complex ensures the high chemical quality of the ground water.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
Forest soils in Central Europe lose Ca due to human induced processes. Driving forces are the deposition of S in the past and the conversion of mixed-species stands into pure Norway spruce forests. Despite the reduction of S emissions 20 yr ago, the Ca loss from the soil and the narrowing of the Ca/Al ratio in the soil solution is an on-going process. A decline in soil Ca concentrations was most obvious in the upper part of the soil profile, where Ca was both lost by leaching and absorbed by the abundant roots of Norway spruce. Our data demonstrate that the concentration of exchangeable Ca did not reflect the Ca nutrition. Instead, the Ca concentration in the soil solution was a better indicator for the Ca concentration in needles. We found no evidence that forest growth is affected the Ca loss from the soil, suggesting that trees may access Ca from sources that are not reflected by the concentration of exchangeable Ca. Our data showed that the Ca level in needles can be quite high, even when the Ca concentrations in the soil were low. High concentrations of soil Ca were therefore more important for the ground water quality than for trees nutrition.

Received for publication February 15, 2002.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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