Comparison of indicator values of forest understory plant species in Western Carpathians (Slovakia) and Vosges Mountains (France)

Forest Ecology and Management 182 (2003) 1–11

Comparison of indicator values of forest understory plant species in Western Carpathians (Slovakia) and Vosges Mountains (France) Ge´gout Jean-Claudea,*, Krizova Evab a

Laboratoire d’Etude des Ressources Foreˆt-Bois, UMR INRA/ENGREF, Ecole Nationale du Ge´nie Rural, des Eaux et des Foreˆts, 14, rue Girardet-CS 4216, 54042 Nancy Cedex, France b Lesnicka Fakulta, Technicka Univerzita Zvolen, Masarykova 24, 96053 Zvolen, Slovak Republic Received 20 April 2000; received in revised form 11 September 2002; accepted 11 November 2002

Abstract The aim of this article is to make a comprehensive comparative study of plant species behaviour in the Vosges Mountains of Western Europe and the Western Carpathians of Central Europe. We will then look at the consequences of the differences observed on the calibration of environmental variables using the bioindicator values of the plant species. The variables altitude correlated to rainfall and temperature and pH of the A horizon of the soil are used to compare species behaviour. A response curve was established using a logistic model for each species according to these two variables. The response curve is used to determine the indicator values. Most of the species in the two regions react in a significant fashion to one or both of the variables. pH has a more marked effect than altitude in the Vosges Mountains (it affects 69% of species). The reverse is true in the Western Carpathians (pH affects only 28% of the species in this area). Species behaviour varies widely from one region to the other, both for pH and for altitude. The proportion of neutrophilous or subalpine species common to both areas is roughly twice as large in the Vosges Mountains as in the Western Carpathians. These differences in behaviour can be explained by the ecological contexts of each region. The high proportion of neutrophilous and subalpine species in Vosges Mountains is responsible for a shift of predictions of variables with vegetation towards large values of pH and altitude in this land. pH values are better predicted in the Vosges Mountains than in the Western Carpathians. Despite a smaller number of species sensitive to altitude in the Western Carpathians, this variable is better predicted in this land than in the Vosges Mountains. These results show that importance of a variable for vegetation has an influence on the quality of predictions. The wide difference in ecological behaviour of species from one region to the other and the very variable quality of predictions would suggest caution in the use of indicator values and their extrapolation to other regions. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Altitude; Calibration; Logistic regression; Soil pH; Response curves

1. Introduction *

Corresponding author. Tel.: þ33-3-83-39-6800; fax: þ33-3-83-30-2254. E-mail address: [email protected] (G. Jean-Claude).

The species indicator value method is the main approach used to predict an environmental variable

0378-1127/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-1127(03)00068-9

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by means of the flora. This approach can be used in a range of situations from the ecological characterisation of plant communities to the typology of forest sites (Tillesse and de Devillez, 1995; Nic, 1998; Lawesson, 2000; Wang, 2000; Wilson et al., 1998, 2001). It is also used to evaluate changes in plant cover linked to human activity (Thimonier et al., 1994; Diekmann and Dupre´ , 1997; Krizova, 1997). The indicator values determined by Ellenberg (Ellenberg et al., 1992) for Central Europe are the most frequently used (Persson, 1981; Melman et al., 1988; Hawkes et al., 1997; Ersten et al., 1998; Wamelink et al., 2002). They have recently been used in several Central European countries (Novakova, 1997; Roder et al., 1996) as well as in Western (Hill and Carey, 1997; Honnay et al., 1998; Preston and Hill, 1997; Schaffers and Sykora, 2000) and Northern Europe (Diekmann, 1996; Jonsson, 1998; Hannerz and Hanell, 1997). They employment in a variety of ecological contexts implies a homogeneity of ecological behaviour and therefore of indicator values over vast areas. Some studies, however, seem to show differences in ecological behaviour for certain species. Thus, Holub (1980) noted that the indicator value of a species varies from the centre to the edge of its habitat. Mucina (1985), Le Tacon and Timbal (1973), Diekmann and Lawesson (1999) and Hill et al. (2000) observed that certain species had different autecological and synecological behaviours in different areas. It is within this context that this article will attempt a detailed comparison of species behaviour and indicator values in the Vosges Mountains (north–east France) of Western Europe and the Western Carpathians (Slovakia) of Central Europe. For the purposes of this comparison, we chose to take two environmental factors into account, one climatic: altitude and the other edaphic: the pH of the A horizon of the soil. The acidity of the A horizon as measured by pH is representative of the soil nutrient availability, whose role is essential in respect of the mineral nutrition of plant species (Duchaufour, 1997; Baize and Jabiol, 1995; Moravec, 1994; Schoenholtz et al., 2000). Several climatic gradients are linked to variations in altitude: the average temperature of the air and the ground, and monthly and annual rainfall, which govern the intensity of hydric stress.

2. Material and methods 2.1. Data The data consist of 765 and 165 releve´ s from hardwood forest taken in the Vosges Mountains and the Western Carpathians, respectively. The plots are distributed over a large range of altitude and soil nutrient status in a well-drained environment and without calcareous substratum (forests over scree were also excluded). In both regions, all the releve´ s were chosen in naturally established, without damage and mature stands mainly of Fagus sylvatica, Abies alba and Quercus petraea. The releve´ s were made on a floristically homogeneous surface area of about 400 m2. At each site, the abundance-dominance of all vascular plant species was recorded with a scale of 7 levels (Braun-Blanquet, 1932): absence, rare and cover <5%, abundant and cover <5%, >5 cover <25%, >25 cover <50%, >50 cover <75%, >75 cover <100%. A sample of the A horizon of the soil was taken at the same time as the floristic sample to allow the water pH to be measured in the laboratory. For a sub-set of 306 releve´ s carried out in the Vosges Mountains, soils samples were air-dried, sieved at 2 mm and exchangeable Ca, K, Mg, Al were measured by spectrometry after an extraction at soil pH with NH4Cl 0.5 M. The mean and standard deviation of the samples’ pH are, respectively, 5:5  1:1 in the Western Carpathians and 4:3  0:7 in the Vosges Mountains. These values correspond to the siliceous character of the two mountain ranges being studied. They allow us to study the species ecology over a common pH interval from 3.5 to 6.5. The mean and standard deviation of the altitude are 732  241 m in the Western Carpathians and 602  202 m in the Vosges Mountains. Most of the sample sites are therefore situated in a mountainous context and allow study of species behaviour over a common altitude range from 300 to 1300 m. Temperature and rainfall data as a function of altitude were calculated for each region. For the Vosges Mountains, they were taken from the work of Cachan (1974) and from the AURHELY model, which allows climatic data for the whole of the region to be spatialised (Benichou and Le Breton, 1987). For the Western Carpathians, the data came from 25 weather stations spread over an altitude range from 300 to 2000 m.

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For data analyses, the data sets of the two regions were randomly divided into two subsets: a training subset with the 2/3 of the releve´ s and a test subset with 1/3 of the releve´ s. The training subsets were used to fit models of species behaviour in relation to ecological variables in each region. Using these models, variables were predicted and compared to the measured values with the test subsets.

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Vosges Mountains and for the Western Carpathians and two others were calculated for the altitude. For species present in only one region, two indicator values were calculated. The species were then grouped according to their indicator values. The limits chosen for each class were the same for the both regions. For pH, they correspond to the limits used by the ‘‘Re´ fe´ rentiel Pe´ dologique’’ to classify soils according to their acidity (Baize, 1998).

2.2. Determination of species ecology 155 and 108 species, of which 57 were common to both regions, were studied, respectively, in 510 releve´ s of the Vosges Mountains and 110 of the Western Carpathians. The tree species, whose presence partly depends on forestry workings, and the species present in <5 sample sites in training set in each region were eliminated. The species response curves were modeled using logistic regression (Ter Braak and Looman, 1986; Huisman et al., 1993) separately for the two regions. An unimodal model was first tested for each variable for each species. When the relationship between the variable and the species was not significant, we tested a strictly increasing or decreasing sigmoid response curve (Fig. 1) (Odland et al., 1995). The species which presented a non-significant link with the variable for this second model were considered indifferent or of wide amplitude for the factor. The species indicator values were obtained from the response curves. The indicator value of a species for a variable is the value that corresponds to the mode of it’s response curve (Fig. 1) (Ter Braak and Looman, 1986; Ter Braak and Gremmen, 1987). For each of the 57 species common to both regions, two indicator values were calculated for pH, respectively, for the

Indicator value for pH

Species

<4.2 4.2 pH <5 5 pH <6 6 No indicator value

Hyperacidophilous Acidophilous Acid-tolerant Neutrophilous Indifferent

For altitude, the limits used for each class are those chosen for establishing bioclimatic stages as defined by Rameau et al. (1993) for the Vosges Mountains and Zlatnik (1976) or Moravec (1994) for the Western Carpathians. Indicator value for altitude (m)

Species

<500 500 altitude <1100 1100 No indicator value

Colline Montane Subalpine Indifferent

A contingency table was made to show the behaviour of plant species in each region according to the altitude and to pH. For each variable, the number of species in each class respectively in the Vosges Mountains and in the Western Carpathians was observed.

Fig. 1. Probability of presence and indicator values (*) of Polygonatum multiflorum (a), Polygonatum verticillatum (b) and Cicerbita alpina (c) for altitude in the Western Carpathians. Polygonatum verticillatum presents a unimodal curve, Polygonatum multiflorum and Cicerbita alpina have a monotone response.

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2.3. Prediction of environmental variables using the plant species The prediction of variable values using plant species was based on the very often used weighted averaging method (Ellenberg et al., 1992; Ter Braak and Looman, 1986). An estimation of the value of the variable is simply derived from the mean of the indicator values of the species present on the site being studied. The predictions were made on the test sets of 255 releve´ s in Vosges Mountains and 55 releve´ s in Western Carpathians. For purposes of comparison, three predictions were made for each sample site and each variable:  the first was made using the indicator values established in the region where the study site is situated (e.g.: predictions in Western Carpathians with indicator values established in Western Carpathians). The indicator values of all of the species present were used;  the second was also made using indicator values established in the region where the study site is situated, but only species common to both regions were included;  the third was made using the indicator values established in the other region being studied (e.g.: predictions in Western Carpathians with indicator values established in Vosges Mountains). In this case, the indicator values used are necessarily those of the species common to the two regions. Approaches using species common to both regions under study allow us to compare the two sets of predictions. The predictions made using all of the species allow the validity of the predictions made with the sub-set of common species to be checked. Two measures were used to evaluate the quality of the predictions. The first, which gives the difference between measured and predicted values, is the root mean square error (RMSE) of prediction: ffi sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Z 1 n 2 RMSE ¼ ðxi  ^xi Þ ; n i¼1 where n is the number of plots in the data set, xi and ^xi are the measured and predicted values of the variable in the site i. The second measure of quality is the square of the linear correlation coefficient between the measured

and estimated values (R2). On the contrary to the RMSE measure, the R2 is independent of any possible bias in the predictions that could be corrected by a linear calibration. It also allows comparisons of prediction efficiency between both variables.

3. Results 3.1. Effect of the variables on the plant species The pH and altitude have very important effects on the species of the two regions, as 6/10 of the species in the Western Carpathians and 8/10 in the Vosges Mountains show a significant response to one or other of these factors (Table 1). The relative importance of the two factors is, however, different: pH affects more species in the Vosges Mountains than altitude (affecting 69% of species) whereas the opposite is true in the Western Carpathians. In this region pH only affects 28% of species. Beyond the simple effect of the variables, we should note the distribution of the optima of species sensitive to pH and to altitude in the two regions, where many species show an optimum at one or other of the extreme values for the variables (Fig. 2). There are marked differences in behaviour between the plant species of the two regions: the majority of the pH sensitive species (57 species or 53%) show an optimum for high pH levels in the Vosges Mountains, whereas, the proportion is relatively small in the Western Carpathians (8 species or 27%). Moreover, the majority of altitude sensitive species show an optimum in the colline zone in the Western Carpathians: 22 species or 47% as against 12 subalpine

Table 1 Proportion of species sensitive to pH and/or altitude in the Vosges Mountains and in the Western Carpathians Variable

pH only pH and altitude Altitude only None variable Total

Vosges Mountains

Western Carpathians

Number

Number

Percentage

Percentage

58 49 18 30

37 32 12 19

16 14 33 45

15 13 30 42

155

100

135

100

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Fig. 2. Distribution of species indicator values for pH and altitude in the Vosges Mountains and the Western Carpathians.

in the Vosges Mountains, whereas, the opposite is true in the Western Carpathians (Tables 2 and 3). Overall, the comparison of species ecology between the two regions shows the same characteristics that are observed when studying all of the species. A shift of the species’ optima towards high pH levels is observed in the Vosges Mountains: 7% of species are neutrophilous in the Western Carpathians, whereas, 56% have the same behaviour in the Vosges Mountains (Table 2, Fig. 3). Six hyperacidophilous or acid-tolerant species in the Western Carpathians are thus neutrophilous in the Vosges Mountains (Geranium robertianum, Impatiens noli-tangere, Mycelis muralis, Stachys sylvatica, Stellaria nemorum, Urtica dioica). Moreover, the majority of species indifferent for pH in the Western

species or 26% (Fig. 2). Conversely, in the Vosges Mountains, a slight majority of the altitude sensitives species shows an optimum in the subalpine zone. The ecological behaviour of the plant species of the Western Carpathians is therefore very different to that of the Vosges Mountains both for altitude and for pH. In order to find out whether these differences were attributable to different species or to changes in behaviour of individual species, an analysis of the 57 species present in both the Vosges Mountains and the Western Carpathians was carried out. 3.2. Behaviour of species common to both regions As for all species studied, the species common to both regions are more sensitive to pH than to altitude

Table 2 Species behaviour in relation to pH in Vosges Mountains and Western Carpathians Western Carpathians, Vosges Mountains

Hyperacid

Acidophilous

Acid-tolerant

Neutrophilous

Indifferent

Total Vosges Mountains

Hyperacidophilous Acidophilous Acid-tolerant Neutrophilous Indifferent Total Western Carpathians

3 0 2 2 5 12

0 0 0 0 0 0

0 0 0 4 1 5

0 0 2 2 0 4

1 1 3 23 8 36

4 1 7 31 14 57

Rows shows species’ indicator characteristics in the Western Carpathians and columns indicator characteristics in the Vosges Mountains.

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Table 3 Species behaviour in relation to altitude in the Vosges Mountains and the Western Carpathians Western Carpathians, Vosges Mountains Colline Montane Subalpine Indifferent Total Western Carpathians

Colline

Montane

Subalpine

Indifferent

Total Vosges Mountains

3 0 2 7

0 4 5 1

0 1 6 0

4 2 6 16

7 7 19 24

12

10

7

28

57

Carpathians have their optima for high pH levels in the Vosges Mountains. For altitude, the results observed for species common to both regions were also similar at those found for all the species (Table 3). The majority (58%) of the sensitive species to altitude has a subalpine optimum in the Vosges Mountains, whereas, the proportion of subalpine species is weak in the Western Carpathians (24% of subalpine species). Several species have therefore an optimum in the subalpine zone in the Vosges Mountains, but in the colline (Luzula luzuloides, Viola reichenbachiana) or montane zone (Impatiens noli-tangere, Lunaria rediviva, Polygonatum verticillatum, Prenanthes purpurea, Urtica dioica) in the Western Carpathians. 3.3. Prediction Only those values found within the ranges studied, 3.5–6.5 for pH and 300–1300 m for altitude, were predicted for each region. The graphs of measured versus predicted values are shown for both variables in

Fig. 4. The average of predicted values, the RMSE and the R2 are also shown in this figure. The comparison of predicted and measured values gives rise to several points:  In all cases, use of all the species at a site gives a better estimation of the variable than use of the subset of species common to the two regions. However, predictions derived from the sub-set of common species, although less accurate, have a similar bias to those derived from all the species.  In a given region, the variable, which affects the larger number of species is more accurately predicted than the variable influencing fewer species.  Finally, predicted pH and altitude values in the Vosges Mountains are much larger than the measured values. The comparison of predictions between the two regions gives surprising results:  The smaller number of species in the Western Carpathians sensitive to altitude (48) as against

Fig. 3. Response curves for some neutrophilous species in the Vosges Mountains that demonstrate a more or less acidophilous behaviour in the Western Carpathians: (a) Alliaria petiolata; (b) Stachys sylvatica; (c) Impatiens noli-tangere.

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Fig. 4. Relationships for pH and altitude between measured and predicted values with indicator values of plant species in the Vosges Mountains and the Western Carpathians. The prediction mean (m), the RMSE and the R2 are added to each graph. The line y ¼ x and the regression line are also shown. The mean measured values are as follows: 5.5 (pH, Western Carpathians), 4.2 (pH, Vosges Mountains), 732 m (altitude, Western Carpathians), 615 m (altitude, Vosges Mountains).

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in the Vosges Mountains (67) does not lead to a reduction in prediction quality: the variable is more accurately predicted in the Western Carpathians than in the Vosges Mountains (Fig. 4g–j).  With the same set of species (both land species), the predictions realised with indicator values from the other land have a quality comparable with those carried out with indicator values from the studied land. Indicator values from the other land are less efficient only for prediction of altitude in Western Carpathians (Fig. 4h–i). For the pH in the Vosges Mountains, the RMSE is the weakest with the indicator values established in the Western Carpathians (Fig. 4f).  The same indicator values can be more effective to predict a variable in another region than in the region where there were established. Indicator values from Western Carpathians are more efficient to predict pH values in the Vosges Mountains than in Western Carpathians (Fig. 4f–b). Altitude indicator values from Vosges Mountains are more efficient in the Western Carpathians than in the Vosges Mountains. (Fig. 4i–k).

4. Discussion 4.1. Species behaviour A study of the role of both ecological variables in species behaviour in the Vosges Mountains and the Western Carpathians brings to light some important differences that require further examination. The small number of samples taken from the Western Carpathians can explain a low level of differences in behaviour. This small number can lead to non-significant effects in the Western Carpathians, whereas, they are significant in the Vosges Mountains. The choice of logistic model to characterise species’ behaviour probably leads to response curves which do not correspond exactly to the real species behaviour (Austin, 1987; Austin and Gaywood, 1994; Epstein et al., 1996). However, neither the difference in sample numbers nor the choice of model can explain the different effects of the variables in the regions or the marked differences in behaviour observed. The different behaviour of species in the two regions is made apparent essentially by two phenomena: from a

nutritional point of view, neutrophilous species in the Vosges Mountains are often indifferent, acid-tolerant or hyperacidophilous in the Western Carpathians and from the climatic point of view, subalpine species in the Vosges Mountains prefer lower altitudes in the Western Carpathians. In comparison with Ellenberg indicator values from central Europe, the pH shift of some species optima was shown for other areas in Europe. Some forest species prefer more acid soils in north of Europe (Diekmann, 1995), more basic soils in The Netherlands (Schaffers and Sykora, 2000) or for more basic or more acid soils in Britain (Hill et al., 2000). In the Vosges Mountains, the neutrophilous character of many species could be explained by the large amounts of available aluminium present in the brown and podzolic soils most often found in this region. This cation was detected in the A horizon of more than 300 soils used in our study. They contained on average 3:9  2:8 cmol/kg of available aluminium. In 46% of the soils, aluminium represents more than 50% of the cation exchange capacity. As pH has a very significant negative correlation with the logarithm of the amount of aluminium in the soil (r ¼ 0:56), it seems natural that species sensitive to aluminium toxicity are only found in sites with a large pH. In the Western Carpathians, on the other hand, the most common soils are andosols. Aluminium is often present in these types of soil in an amorphous and nontoxic form (Moravec, 1994; Baize, 1998). Although no analyses for exchangeable aluminium is available and it is possible that this element is present in small quantities in this region. This hypothesis would explain the presence of aluminium sensitive species on most of the sites. Thus, root development of Brachypodium sylvaticum, Carex sylvatica or Galium odoratum measured under laboratory conditions is severely affected by a high level of available aluminium (Sverdrup and Warfvinge, 1993). These species are found only on neutral soils in the Vosges Mountains, whereas, they occur across the whole range of pH values in the Western Carpathians. The subalpine character of many species in the Vosges Mountains needs to be looked at in terms of those factors (temperature and rainfall) that are strongly correlated to altitude and which influence species directly. In both regions, an increase in altitude engenders a very significant increase in rainfall and a fall in

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temperature. When moving from 300 to 1300 m, annual rainfall increases from 1020 to 1950 mm in Vosges Mountains and from 720 to 1040 mm in Western Carpathians. For the same altitudinal range, the annual mean temperature decreases from 9.0 to 6.0 8C, in the Vosges Moutains and from 7.9 to 2.9 8C, in the Western Carpathians. Mean annual temperature of 6 8C is found at 1300 m in the Vosges Mountains and at 700 m in the Western Carpathians and this difference explains the shift in species preference from the subalpine to the montane zone as we move from the west to the centre of Europe. These observations on the variations of the plant species behaviour across Europe complement the sudies of Ozenda (1985) or Ellenberg (1987) on forest tree species. When moving from 300 to 1300 m, the increase in rainfall is three times greater and the decrease in temperature is weaker in the Vosges Mountains than in the Western Carpathians. High altitude zones in the Vosges Mountains are therefore relatively wetter and warmer compared to those in the Western Carpathians. Higher temperature as well as higher rainfall (which limits hydric stress) encourage species development. The more favourable climate conditions of the high altitudes in the Vosges Mountains explain the high proportion of species with an optimum at the subalpine zone in this region. 4.2. Prediction The considerable differences between predicted and measured variables realised with indicator values from Vosges Mountains can be ascribed in large part to an important shift towards large predicted pH or altitude. This discrepancy implies that most species present on the sample sites have optima for very different (much larger) values than those of the sites. The different bias of predictions between Vosges Mountains and Western Carpathians are consistent with results of Elgersma and Dhillion (2002) who found in Norway a variation of soil pH values with the area for a same vegetal community. The high proportion (more than 58% of sensitive species) of neutrophilous species is also the cause of the weak correlation (as measured by the R2) between pH measured in the Vosges Mountains and pH predicted using indicator values from this region. All of these species have indicator values ranging between 6

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and 6.5. They have, however, different behaviours: some have a wide range and can be found on acid soils and others have a narrow range and are restricted to neutral soils (Fig. 3). As a result, even though their indicator values are the same, they do not share the same indicator characteristics: species with a wide range generally indicate more acid soils than species with a narrow range. The pH range of neutrophilous species in the Vosges Mountains is correlated to their indicator value in the Carpathians: the wider the range, the more acidophilous they are in the Western Carpathians (Fig. 3). This relation can explain the weak shift and the good RMSE of pH predictions realised in Vosges Mountains with Carpathians indicator values. The difference of predictions efficiency depends on the quality of indicator values and on the number of indicator values used to realise predictions (e.g. predictions realised with whole species are best than those realised with both land species). The effectiveness of the indicator values for predicting an environmental variable also depends on the importance of variable for the vegetation in the studied area. The same indicator values could be effective in an area where the studied variable is significant and ineffective in an area where the importance of the studied variable is weak. This phenomenon explains the effectiveness of pH indicator values from Western Carpathians to predict pH in Vosges Mountains and their inefficiency in Western Carpathians. It also could explain the differences of predictions quality observed in different areas for the prediction of pH with Ellenberg indicator values (Hill and Carey, 1997; Ersten et al., 1998; Schaffers and Sykora, 2000).

5. Conclusion The wide discrepancy in the Vosges Mountains between the optimum of species present on a site and the measured values of environmental variables on this same site increases our understanding of mechanisms that determine the species occurrence in unfavourable or toxic environments. It is possible that such studies call into question the uniform or independent distribution of optima along the gradients proposed by some theories (Gauch and Whittaker, 1972; Gleason, 1926 in Austin and Smith, 1989). In Vosges Mountains, there is thus a large part of species

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that have their optima closed to values of environmental variables favourable to species’ development. The differences in species’ behaviour between the oceanic Vosges Mountains and the continental Western Carpathians are more pronounced than expected as they involve 50% of species for altitude and more than 75% for pH. These differences in behaviour can be explained at least in part by the different distribution in the two regions of underlying factors (aluminium, temperature, rainfall) that are correlated to the variables being studied and are important for plants. In order to limit the effect of particular ecological contexts in the study of species’ behaviour, it would be useful to carry out studies, as Ersten et al. (1998) have done and as Hawkes et al. (1997) suggest, using a large number of sample sites over large regions. From the point of view of application, the change in species’ behaviour from one region to another and the variable quality of predictions would indicate the need for caution in use of indicator values and in their extrapolation to other areas. Acknowledgements Research results from Western Carpathians presented in this paper were supported by finance of Grant VEGA No. 1/7057/20. References Austin, M.P., 1987. Models for the analysis of species’ response to environmental gradients. Vegetation 69, 35–45. Austin, M.P., Gaywood, M.J., 1994. Current problems of environmental gradients and species response curves in relation to continuum theory. J. Veg. Sci. 5, 473–482. Austin, M.P., Smith, T.M., 1989. A new model for the continuum concept. Vegetation 83, 35–47. Baize, D., 1998. A sound reference base for soils. The ‘‘Re´ fe´ rentiel pe´ dologique’’. AFES, INRA, Paris. Baize, D., Jabiol, B., 1995. Guide pour la description des sols. Collection Techniques et Pratiques. INRA, Paris. Benichou, P., Le Breton, O., 1987. Prise en compte de la topographie pour la cartographie des champs pluviome´ triques statistiques. La Me´ te´ orologie 7, 1–19. Braun-Blanquet J., 1932. Plant Sociology. McGraw-Hill, New-York. Cachan, P., 1974. Etude bioclimatique du massif Vosgien. Bull. E.N.S.A.I.A. Nancy XVI (1/2), 1–45. Diekmann, M., 1995. Use and improvement of Ellenberg’s Indicator values in deciduous forests of the Borea-nemoral zone in Sweden. Ecography 18, 178–189.

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