Applied Vegetation Science && (2017)
Revising Ellenberg’s indicator values for continentality based on global vascular plant species distribution Christian Berg
Keywords Bioindication; Ecogeographic gradients; Global distribution range; Indicator values; Oceanity; Range formulas Abbreviations alp = alpine belt; antarct = antarctic zone; arct = arctic zone; austr = austral zone; austrostrop = austrosubtropic zone; b = boreal zone; boreostrop = boreosubtropic zone; C-value = continentality value, the new indicator value for continentality; EIV-K = Ellenberg‘s indicator values for continentality; EIV-T = Ellenberg’s indicator values for temperature; euoz = euoceanic; k = continental; m = meridional zone; mo/demo = montane/demontane altitudinal belt; niv = nival belt; oz = oceanic; salp/dealp = sub-alpine/de-alpine belt; sm = submeridional zone; subk = subcontinental; suboz = suboceanic; temp = temperate zone, divided into south (s-temp) and north temperate (n-temp); trop = tropic zone. Nomenclature J€ ager (2011) Received 5 July 2016 Accepted 30 January 2017 Co-ordinating Editor: Angelika SchwabeKratochwil
, Erik Welk
€ger & Eckehart J. Ja
Abstract Questions: Misunderstandings and methodological inconsistencies have hampered the applicability of Ellenberg’s biogeographic indicator values for continentality. To redefine the indicator values we focused on the following questions: (1) what is meant by phytogeographic continentality as the basic principle behind Ellenberg’s indicator values for continentality; (2) can we redefine the continentality indicator values based on an assessment protocol rendering the values more reproducible; and (3) what are the differences between Ellenberg’s indicator values for continentality and the redefined ones as a statistical data set, and in application? Location: Northern Hemisphere, Central Europe. Methods: Biogeographic indicator values are based on global species distribution data. Species’ distribution information is converted to standardized range formulas that combine information on occurrence across floristic zones, altitudinal preferences and the distribution within the oceanity–continentality gradient. Improved and revised range formulas are converted to new indicator values for continentality (C-value) using simple algorithms. Results: New indicator values for continentality (C-values) and amplitudes for 2984 taxa of Central European vascular plants are presented. The main improvement is the application of a comprehensible assessment protocol. The new C-value gained a more balanced frequency distribution, rendering it more useful for broad-scale biogeographic analysis. Conclusions: For the first time, biogeographic indicator values derived with a consistent method that is based on distribution data are presented. Occurrence information and vegetation data are becoming increasingly available globally, while changing climatic conditions inevitably accelerate species range dynamics, and therefore the application of biogeographic indicator values will increase.
Berg, C. (corresponding author,
[email protected])1, Welk, E. (
[email protected])2,3, €ger, E.J. Ja (
[email protected])2 1 Institute of Plant Sciences, University of Graz, Holteigasse 6, 8010 Graz, Austria; 2 Department Geobotany and Botanical Garden, Martin-Luther-University Halle-Wittenberg, Am Kirchtor 1, 06108 Halle, Germany; 3 German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103 Leipzig, Germany
Applied Vegetation Science Doi: 10.1111/avsc.12306 © 2017 International Association for Vegetation Science
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Revising Ellenberg’s continentality values
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Introduction Ellenberg’s indicator values and species range formulas Ellenberg’s indicator values (EIV) are a widely used tool in vegetation science and ecology (Diekmann 2003; for history see B€ ocker et al. 1983). Ellenberg realised the potential benefits of transferring community composition data into numerical values, enabling researchers to compare plot lists of plant species or vegetation releves. Ellenberg0 s approach was to quantify the effects of species turnover in space and time for purposes of bioindication (Heink & Kowarik 2010). To that end the user is provided with empirical information about the relative position of a plant species within a multivariate space of different ecological gradients under the conditions of natural biotic interactions. EIV are therefore suitable for numeric analyses of communities and vegetation, yet not directly translatable into physical site conditions (Hawkes et al. 1997; Cornwell & Grubb 2003). Ellenberg’s indicator values for the vascular plant flora of Central Europe were published in a series of five issues (Ellenberg 1974, 1979; Ellenberg et al. 1991, 1992, 2001). For each issue the values were updated according to the current level of knowledge, and since 1991 bryophytes and lichens have been included. Ellenberg (1974) approached the development of his EIV in two ways: (1) he empirically deduced the values for soil moisture, reaction, nutrients and light, based mainly on ‘expert knowledge’ and only rarely on systematic measurements; (2) for the values for continentality (EIV-K) and temperature (EIV-T) he primarily used the condensed formalized descriptions of large-scale geographic and altitudinal species distribution (range formulas) developed by the Halle school of phytogeography (Meusel et al. 1965-1992; J€ ager 1968). Accordingly, these values do not rely on expert knowledge, as is frequently criticized (e.g. Wamelink et al. 2005), but rather on mapped distribution data. Concerning EIV-T, Ellenberg derived it later only partially from distribution range, and partially from local distribution and habitat heat load (Ellenberg et al. 2001). So the EIV-T became somehow a hybrid between an ecological site indicator and a biogeographic indicator value. The above-mentioned range formulas consider the zonal and altitudinal range and the distribution of species along the gradient of phytogeographic continentality mapped of J€ager (1968). Meusel et al. (1965-1992) divided the Earth into ten floristic zones: antarctic (antarct), austral (austr), austrosubtropic (austrostrop), tropic (trop), boreosubtropic (boreostrop), meridional (m), submeridional (sm), temperate (temp), later divided in two subzones: south temperate (stemp) and north temperate (ntemp), boreal (b) and arctic (arct; see Fig. 1). In the range
2
formulas, the respective species-specific zonal amplitudes are complemented by the distribution along the altitudinal belts: montane/demontane (mo/demo), sub-alpine/dealpine (salp/dealp) and alpine (alp). Based on the work of J€ ager (1968), ten classes of phytogeographic range continentality provide the third dimension of the range formulas (Fig. 1). However, Ellenberg (1974) used a simplified oceanity/ continentality classification for the EIV-K, presented in the range formulas in ‘Rothmaler - Exkursionsflora von Deutschland’ (Meusel & Schubert 1972). These formulas also contain ten, however somewhat fuzzily delimited continentality categories based on ill-defined amplitudes across four continentality classes spanning from coastal oceanic (oz) over suboceanic (suboz) and subcontinental (subk) to the innermost continental (k) regions. Ellenberg (1974, p.10) forced these ten continentality categories into his nine-step ordinal scale by arbitrarily merging the categories (suboz) and (subk) into one: euoz = EIV-K1, oz = EIV-K2, (oz) = EIV-K3, suboz = EIV-K4, (suboz) and (subk) = EIV-K5, subk = EIV-K6, (k) = EIV-K7, k = EIVK8, euk = EIV-K9 (the latter is not represented in the Central European flora). The above described simplifications resulted in considerable bias and lead to substantial deviation from the global plant geographic continentality pattern originally mapped by J€ ager (1968; see Table 1, Fig. S1-1 in Appendix S1). Since EIV-K1 is generally a subset of EIV-K2, and both are generally subsets of EIV-K3, it is critical to convert the classes into an ordinal scale. The class widths differ tremendously; they are larger in the central parts and become smaller towards the margins, especially in the western (oceanic) direction (Fig. S1-1 in Appendix S1; B€ ohling et al. 2002). According to J€ ager (1968), the bracketed classes (oz) and (k) indicate that these are widely distributed species, hardly bound to the continentality gradient, but were considered by Ellenberg (1974) as important indicator species: EIV-K3 for (oz) and EIV-K7 for (k). As an overall consequence, EIV-K applications rarely provide meaningful results either as mean values or as indicator value spectra. The concerning species, e.g. Alopecurus geniculatus, Carex echinata, Cladium mariscus, Persicaria maculosa or Veronica serpyllifolia (with EIV-K3), or for the opposite tendency Bromus inermis, Elymus repens, Equisetum pratense, Lactuca serriola, Pinus sylvestris or Tephroseris palustris (with EIV-K7) do not only inflate the frequency of indicator species – they bias any further numerical analysis. It is probably for such reasons that the EIV-K was used less frequently than any other EIV. Many studies using EIV, including studies carried out at larger scales, omit EIV-K, and sometimes EIV-T as well. In small-scale studies the inclusion of EIV-K analyses provided only barely interpretable results (e.g. Fischer et al. 2014; Koch & Jurasinski
Applied Vegetation Science Doi: 10.1111/avsc.12306 © 2017 International Association for Vegetation Science
Revising Ellenberg’s continentality values
C. Berg et al.
Fig. 1. Classification map of the phytogeographic continentality for the Holarctic based on J€ager (1968). The colours indicate the different continentality classes 1–10 (see Fig. 2). Black lines indicate the zonal borders, the dashed line divides the temperate zone into south (s-temp) and north (n-temp) temperate. bstrop = boreosubtropic, m = meridional, sm = submeridional, b = boreal, arct = arctic. The map is available as GeoTiff file in Appendix S4, described in Appendix S3.
Table 1. Selected examples for range formulas published by Meusel & Schubert (1972) vs Ja€ger (2011). Note especially the large deviations between the ten-class continentality amplitudes based on J€ager (1968) and single EIV-K (e.g. K5) of Ellenberg (1974) that were derived from the strongly simplified formulas given in the field flora of Meusel & Schubert (1972). Abbreviations are given at the beginning of the paper. TAXON
FORMULA 1972
EIV-K 1974
FORMULA 2011
Carum verticillatum Carex demissa Anthoxanthum aristatum Myosotis decumbens Bromus lepidus Consolida hispanica Galeopsis angustifolia Lysimachia punctata Silaum silaus Lycium barbarum Peucedanum officinale Lactuca quercina Viola collina Jurinea cyanoides Artemisia absinthium Festuca valesiaca Tanacetum parthenium Scorzonera parviflora Festuca nigrescens Potamogeton filiformis
m-temp.euozEUR sm-b.euozEUR-OAM m-temp.ozEUR m/mo-b/demo.ozEUR m-temp.(oz)EUR-WAS m-sm. (oz)EUR m-temp.subozEUR sm-temp.subozEUR sm-temp.(suboz)EUR m-stemp.(suboz)EUR-(WAS) m/mo-stemp.(subk)EUR sm-stemp.(subk)EUR m-temp.subkEURAS sm-stemp.subkEUR-WAS m/mo-b.(k)EUR-WAS m-temp.(k)EUR-WAS m/mo-sm/mo.kWAS m-stemp.kEUR-WAS sm/mo-tempEUR m/mo-arctCIRCPOL
K1 K1 K2 K2 K3 K3 K4 K4 K5 K5 K5 K5 K6 K6 K7 K7 K8 K8 Kx Kx
m-tempc1EUR sm-bc1-4EUR+(OAM) m-tempc1-2EUR m-stemp//mo+bc3-5EUR tempc1-3EUR m-smc4-7EUR-WAS sm-tempc1-3EUR sm-tempc3-6EUR sm-tempc1-3EUR m-stempc2-7EUR-WAS m/mo-stempc1-4EUR sm-stempc4-7EUR sm-tempc2-6EURAS sm-stempc4-9EUR-WAS m/mo-temp-(b)c1-8EUR-WAS m-tempc4-8EUR-WAS smc3-4VORDAS-KAUK m-stempc4-9EUR-WAS sm/mo-temp/democ2-3EUR m/mo-arct+litc2-9CIRCPOL
2014). Wehling & Diekmann (2010) tried to circumvent the described problem by including only EIV-K4 and EIVK6. The important review of Diekmann (2003), dealing
with EIV in general, excluded both bioclimatic values completely. Nevertheless, some successful applications do exist. Schwabe et al. (2007) found clear patterns and differences
Applied Vegetation Science Doi: 10.1111/avsc.12306 © 2017 International Association for Vegetation Science
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Revising Ellenberg’s continentality values
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at the landscape scale, and Franzaring et al. (2007) tested EIV-K against some functional traits and found that it correlated significantly with urbanophily values, the stressstrategy type of Grime’s C-S-R scheme (Grime 1979), and with the EIVs related to soil reaction and nutrient availability. Wehling & Diekmann (2010) found significant differences in wintergreen species when comparing EIV-K4 and EIV-K6 species, and Bartelheimer & Poschlod (2015) found a significant correspondence between EIV-K and timing of bud burst as well as frost resistance. In the field of plant geography, significant progress has led to an increase in the knowledge base of species distribution in the Northern Hemisphere. Welk (2002) provided reassessed range formulas for 1225 German species using the ten-step continentality classification of J€ager (1968). Further new range formulas were developed for the 19th issue of Rothmaler - Exkursionsflora von Deutschland (J€ ager & Werner 2005; see Table 1), based on improved floristic data and the on-going compilation of species range maps. With that edition, J€ager abandoned the inevitably subjective determination as to whether a plant distribution is basically oceanic or continental. The overly simplified four-step oceanity/continentality classification was changed to the original ten-step classification, showing the amplitude of a species distribution across ten global classes of phytogeographic continentality, as shown in Fig. 1. Additionally, the depiction of the zonal species distribution was reassessed; floristic zones only marginally occupied by a species are now included in parentheses in the range formulas (Table 1). The objective of this work is to present revisited indicator values for continentality using new insights into species distribution and phytogeographic continentality. For the first time ever, except for salinity values introduced by Ellenberg et al. (1991), the assessment approach for an indicator value is based on a consistent and comprehensible method that allows the user to adapt and apply the assessment method to other extratropical regions and to add further species, provided suitable distribution data are available. Phytogeographic continentality – scientific basis of the indicator values for continentality Climatic continentality is a complex phenomenon involving diurnal and seasonal temperature oscillations in relationship to the diurnal or seasonal aridity/humidity rhythm (Currey 1974). A general definition does not exist, and all existing maps of climatic oceanity or continentality (both have the same inverse relationship like heat and cold) differ. Climatic continentality has at least two main components: the thermic and the hygric gradient. As an environmental variable, the relative
4
ecological importance of temperature increases toward higher latitudes and altitudes, while the importance of humidity increases towards lower latitudes and altitudes. Continentality can thereby be defined as thermic continentality as it moves towards polar or alpine environments (Karlsen et al. 2005). In some regions continentality may be simply defined in terms of proximity to the ocean (Kleinebecker et al. 2007; Nishimura & Laroque 2011), however in subtropical areas with proximity to cold ocean currents (e.g. Morocco) this correlation does not hold. Many indices and equations for calculating climatic continentality have been developed. Some authors consider only the thermic component of continentality (Djamali et al. 2012; Lauva et al. 2012), while others use indices that include temperature and precipitation elements (Jensen et al. 2004; Botta-Duk at et al. 2005). For an overview of physical indices see Minetti (1989) and Gavil an (2005). All these abiotic, physical indices share a common feature in focusing on certain aspects of the complex ecoclimatic phenomenon of continentality. Their usage is therefore restricted to a limited context, e.g. regional comparisons. The relative impact of the thermic or the hygric component on an individual organism in a particular location depends on multiple further factors. The response of plants to physical climatic oceanity is not linear; it depends on the growth rhythm and the seasonal development of the species. Different factors may limit the performance and occurrence of a given species in different range parts. Consequently, maps of climatic continentality correspond to phytogeographic patterns only in small regions, and in some cases not at all, as in the case of comparison between the eastern and western sides of Eurasia and North America (see discussion in J€ ager 1968). For that reason J€ ager (1968) decided to synthesize the compound ecological effects of all components of continentality simultaneously as phytogeographic continentality. It describes the peripheral–central phytogeographic turnover in flora and vegetation. The accompanying map was drafted based on the comparison of hundreds of species distribution maps. Spatially clustered ‘bundles’ of longitudinal range limits of well-defined ‘floristic elements’ were used as guidelines to infer continentality classes. Globally, degrees of phytogeographic continentality have been determined based on the similarities in amplitude of the peripheral–central component of taxon distribution in different continents (niche conservatism). In a reciprocal feedback process, accumulation centres of relevant species indicate classes of a particular continentality, and isochors of higher species turnover indicate the borders of these classes. Figure 1 shows a map of phytogeographic continentality for the Holarctic floristic kingdom.
Applied Vegetation Science Doi: 10.1111/avsc.12306 © 2017 International Association for Vegetation Science
Revising Ellenberg’s continentality values
C. Berg et al.
Methods Species selection and nomenclature The study was begun with 2765 taxa listed in Ellenberg et al. (2001). We attached revised range formulas by incorporating a tabularized version of J€ager & Werner (2005; digitized and parsed by Welk et al. 2006). We added 280 taxa (species, subspecies) with sufficient global distribution range data. Where possible, we substituted taxa given as taxonomic aggregate by Ellenberg et al. (2001) with the constituting single taxa. Species were divided to subspecies level provided there was sufficient biogeographic information. Taxa with wider, well-documented distribution ranges were selected for the genera Alchemilla, Hieracium, Rubus and Sorbus. The genus Taraxacum and the Ranunculus auricomus aggregate were treated at the section or aggregate level, respectively. Thirty-seven taxa with uncertain taxonomy were omitted. J€ager (2011) and Fischer et al. (2008) provide the taxonomic and nomenclatural basis. All omissions are listed in Table S1-1 and all taxa added to the list in Table S1-2 (both in Appendix S1).
The protocol to derive indicator values for continentality – the C-value We used the same method as Ellenberg (1974) to calculate the C-value, while at the same time trying to avoid the downsides of his approach. Figure 1 shows the spatial distribution of the ten continentality classes from one to ten, which enables a more accurate assessment as opposed to Ellenberg0 s approach based on the simplified, four-class division. We used the published range formulas developed by J€ager and Welk (Welk 2002; J€ager & Werner 2005; J€ ager 2011), which describe the occurrence of every species along the gradient of continentality in addition to their zonal and altitudinal distribution. We derived the C-value from those distribution data by applying the following protocol: 1. The continentality class 3 represents the centre of the application area and therefore receives the central C-value 5. 2. Any higher continentality class increases the C-value by one step until 7 = C-value 9. The continentality classes 8–10 also receive a C-value 9. 3. Towards the lowest continentality classes (2 and 1) the C-value decreases by two steps. 4. The C-value is calculated from the mean of all the class values covered by the species, point 5 values are rounded to the next integer, values 5 to the next larger one. 5. Species that extend over more than four continentality classes are considered to be indifferent
(C-value x), unless their lower continentality border is located in class 2 or higher. The protocol must take into account the more oceanic situation in Central Europe within the Holarctic and the two-step rule (3) is necessary for that reason. The principal results of the C-value assessment are shown in Fig. 2. The list of taxa and the new values and amplitudes in comparison with the old one are given in Appendix S2. For users of the analysis program JUICE (Tich y 2002) we offer a compatible file on the programs homepage (www.sci.muni.cz/botany/juice/). Test data sets for numerical validation Two data sets with different gradients of continentality were used to test our new indicator values against the EIV. The first data set (Flor-D) contains floristic grid data from the German vascular plant mapping database (www.floraweb.de, accessed 26. Nov 2015) In a west–east transect of continuous grid cells throughout northern Germany. The grid cells with approximately 10 km 9 10 km resolution follow the map interface of the German topographic maps 1:25 000 from Emsland to the Odertal. Within the 43 grid cells a total of 1934 vascular plant taxa was recorded, with a mean number of 760 147 ((SD) per grid cell. The other data set (Veg-SAND) contains scattered vegetation plot data of Corynephorus canescens dominated dry grassland communities of MecklenburgVorpommern generated from the vegetation database of Mecklenburg-Vorpommern (Jansen et al. 2011). We selected all data belonging to the Corniculario aculeataeCorynephoretum canescentis, Helichryso arenarii-Jasionetum litoralis and Festucetum polesicae explained in detail in Dengler (2004). Relev es with less than four vascular plant species were omitted, leaving a total of 578 plots with a mean species number per relev e of 8.8 5.1).The plot size median is 16 m². Mean EIV can be used to compare two or more means within the same context (same vegetation type or species pool; Wamelink et al. 2005) of a spatial or temporal species turnover in the sense of environmental calibration. We calculated unweighted mean indicator values and medians for every plot, as well as indicator species spectra (percentages of indicator species per plot). Considering the properties of our data we used the Spearman rank correlation and the Mann-Whitney permutation test for significance of different medians. Trend lines were calculated by linear regression. We calculated indicator value histograms for all species. Means and medians sometimes hide the real changes in species composition. Analysing the whole frequency distribution of EIV-K provides biogeographic spectra without problems occurring with bimodal or skewed data
Applied Vegetation Science Doi: 10.1111/avsc.12306 © 2017 International Association for Vegetation Science
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Revising Ellenberg’s continentality values
Class 1 1-2 1-3
C1
1 1 1
2 1-4
1
2-3 1-5
1
2-4
C. Berg et al.
C2
3 3 3 3 3 3 3
3 1-6
1
2-5
3 3
3-4 1-7
1
2-6
3 3
3-5
C3
1
2-7
3 3
3-6
5 5 5 5 5 5 5 5 5 5 5 5 5 5
4-5
1
2-8
3 3
3-7
5 5 5
4-6
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
5-7 1-10 2-9
1
3 3
C6
5 5 5
4-7
6 6 6 6
5-6 2-10 3-9
3
5 5
4-8
7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7
6 6 6
7 7 7 7 7 7
6 3-10 4-9
5
6 6
5-8
7 7 7
6-7
5-9 5-10 6-8 6-9 6-10 7-10 8 8-9
C9 C10
8
8 8
8 8 8
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
7 4-10
C8
7
7-9 3-8
C7
6
5 1-9
C5
5
4 1-8
C4
6
7 7 7
8 8 8 8 8 8
9
9 9
9 9 9
9
9 9
9 9 9 9 9 9
9 9 9 9
9 9 9
9 9 9
9 9 9 9 9 9 9 9 9 9 9 9
9 9 9
9 9 9 9 9 9 9 9 9
9
9 9 9
9 9
9 9
9 9 9 9 9 9 9
9
9
9
9 9
9 9
N Ampl Mean C-value 18
1
1.0
80
2
2.0
152
3
3.0
24
1
3.0
239
4
3.8
201
2
4.0
270
5
4.4
220
3
4.7
154
1
5.0
208
6
5.0
159
4
5.3
163
2
5.5
155
7
5.6
151
5
5.8
65
3
6.0
20
1
6.0
106
8
6.0
143
6
6.3
55
4
6.5
16
2
6.5
1
1
7.0
40
9
6.3
65
7
6.7
64
5
7.0
25
3
7.0
5
3
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7
10
6.6
21
8
7.0
0
3
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28
6
7.3
42
4
7.5
8
2
7.5
3
9
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9
7
7.6
26
5
7.8
0
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8
7.8
11
6
8.0
11
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8.3
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9.0
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9.0
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9.0
1 2 3 3 4 4 x 5 5 x 5 6 x 6 6 6 x 6 7 7 7 x 7 7 7 8 x 7 9 7 8 8 7 8 8 8 8 8 8 9 9 8 8 9 9 9 9 9 9 9
Diff 0.0 0.0 0.0 0.0 –0.3 0.0
–0.3 0.0
0.3 –0.5
–0.2 0.0 0.0
0.3 –0.5 –0.5 0.0
–0.3 0.0 0.0 0.0
0.0 0.0 0.3 –0.5 –0.5 0.2 –0.4 –0.2 0.0 –0.3 0.0 0.3 –0.5 0.0 0.1 0.4 –0.5 –0.3 –0.3 –0.2 0.0 0.0 0.0
Fig. 2. Amplitudes and occurrences of the Central European vascular plant flora in a continentality gradient from 1 to 10. Colours correspond to Fig. 1, numbers in the coloured fields are the allocated C-values for the particular continentality class. N = Number of species with that amplitude; Ampl = amplitude of continentality classes; Mean = mean of all coloured fields according to the protocol; C-value derived from the mean and additional rules of the protocol; Diff = difference between the mean and the C-value.
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Applied Vegetation Science Doi: 10.1111/avsc.12306 © 2017 International Association for Vegetation Science
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distributions (Kowarik & Seidling 1989; Ewald 2003). For correlation with climate data we used bioclimatic data in a 30-s grid resolution from the WorldClim data set (www.worldclim.org, accessed 30 Jul 2013).
Results Changes in indicator values for continentality The changes of the values in comparison to Ellenberg et al. (2001) are shown in Fig. 3. Following our approach 79.7% of the EIV-K rankings have changed. Histograms of the old and new values show the principal changes in the distribution of the biogeographic indicator values. The
(a) 1000 900 EIV-K
800
C-value
700 600 500 400 300 200 100 0
1
2
3
4
5
6
7
8
9
x
?
(b)
C1
C2
C3
C4
C5
C6
C7
C8
C9
Cx
omit
EIVK1
14
20
6
3
0
1
0
0
0
0
0
44
EIVK2
2
41
103
124
30
9
4
0
0
47
4
364
EIVK3
0
3
17
91
36
40
9
1
0
329
7
533
EIVK4
0
4
33
148
288
142
29
3
0
64
11
722
EIVK5
0
2
3
17
73
137
34
5
0
121
8
400
EIVK6
0
0
1
2
13
48
70
37
0
14
3
188
EIVK7
0
0
0
3
5
51
72
21
0
17
3
172
EIVK8
0
0
0
0
1
1
9
22
1
1
1
36
EIVK9
0
0
0
0
0
0
0
0
0
0
0
0
x
0
1
1
9
3
13
12
8
3
125
6
181
?
1
3
4
20
18
24
9
2
1
23
13
118
new
1
6
8
23
66
76
30
21
6
45
117
399
sum
18
80
176
440
533
542
278
120
11
786
56
2984
sum
Fig. 3. (a) Histogram of the Ellenberg’s indicator value for Continentality (EIV-K, n = 2765) and the new continentality indicator value (C-value, n = 2984). (b) Changes in the numbers of C-values in comparison to EIV-K. Marked fields indicate the highest numbers in the row/column, grey highlighted values are consistent with the original values; black box values are inconsistent with original values. x: indifferent; ?: taxa with uncertain judgement in Ellenberg et al. (2001); omit: taxa included in Ellenberg et al. (2001), but excluded for the new values; new: taxa not included in Ellenberg et al. (2001), but included in the new values.
new values emphasize more the middle, and the proportion of indifferent species strongly increased. The new values for continentality – application examples Within our two data sets the Spearman’s correlation coefficient (rho) between the EIV-K and C-value is 0.97, taking the continuous floristic grid mapping data, and 0.60 taking the scattered vegetation plot data. The span covered by mean indicator values increased from 0.62 (EIV-K) to 1.02 (C-value) in the floristic data set (N = 43) and from 3.00 (EIV-K) to 4.33 (C-value) in the vegetation data set (N = 559). Mean C-values generally increased so the general level of C-values clustered more towards the centre (value 5). Figure 4 illustrates this pattern for the Flor-D data set. Along the transect, the mean biogeographic values of continentality (both EIV-K and C-value) are increasing according to the geographic gradient from west to east (Fig. 4). Phytogeographic continentality is not easy to translate in simple climate data, especially concerning the hygric continentality. Using some temperature values to illustrate the thermic continentality, the rank correlation with indicator values of the Flor-D data set along this west–east transect, the Spearman rho for the difference between Jul and Jan temperature is 0.901 for EIV-K and 0.937 for the C-value, for the average winter (DJF) the temperature is 0.742 for EIV-K and 0.801 for the Cvalue, and for the minimum winter (DJF) the temperature is 0.726 for EIV-K and 0.790 for the C-value. According to the increasing number of indifferent species in the C-value, the percentage of indicator species per plot decreased from 77% to 40% in the Flor-D data set and from 85% to 61% in the Veg-SAND data set. With regard to the Veg-SAND data set, an increase of the proportion of continentally distributed species from west to east in Mecklenburg-Vorpommern can be expected (Dengler 2004). We tested the question whether this continentality gradient is detectable using mean indicator values. While the EIV-K shows no gradient, the C-values indicate a slight, yet significantly increasing slope (Fig. 5). The same result is obtained when using medians and the Mann-Whitney permutation test. The proportion of species with the respective indicator values for continentality was plotted for the transect data of the Flor-D data set (Fig. 6). Using EIV-K the value K3 is disproportionately frequent and covers around one-third of the result. The percentages of every single value in the C-value are more evenly distributed, and a slightly oceanic value (C4) dominates the western parts, a slightly continental value (C6) for the eastern parts. Displaying the whole histogram of the biogeographic spectra for three selected grid cells (west, central, east), the
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Mean indicator value
Oder Weser
5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0
Salzwedel
Elbe
Eberswalder Urstromtal
Lüneburger Heide Emsland
EIV-K 4
8
12
16
C-value 20
24
28
32
36
40
Mean value for continentality
Fig. 4. Mean EIV-K and C-values along a longitudinal transect with increasing continentality of the Flor-D data set from west to east in northern Germany. Some landscapes, cities and river valleys are indicated. N = 43.
7.5
r ² = 0.00, P = 0.125
7.0
r ² = 0.07, P = 0.001
6.5 6.0 5.5 5.0 4.5
C-value
4.0 3.5
EIV-K
3.0 2.5 2.0 11.5
12.0
12.5
13.0
13.5
14.0
Longitude Fig. 5. Linear regression lines of mean continentality indicator values per s of relev e with longitude as predictor variable. Data of 559 releve Corynephorus canescens-rich dry grassland along a west–east gradient through Mecklenburg-Vorpommern (NE Germany).
spectra of the C-values are more evenly distributed and indicate a continentality shift, while all EIV-K spectra are dominated by the value K3 (Fig. 7).
Discussion The indicator values presented here are doubtless a strong simplification of a highly complex phenomenon. We deliberately chose to follow in the footsteps of Ellenberg for two reasons: (1) in accordance with other authors (Ter Braak & Gremmen 1987; Schaffers & S ykora 2000) we are convinced that the high level of abstraction is one of the
8
advantages of the EIV; and (2) it would be impossible to present a species list of around 3000 Central European species with indicator values by calculating species distribution models and climatic niche characteristics for every species. Many authors, including Schaffers & S ykora (2000) and B€ ohling et al. (2002), have criticized the vague description of the EIV, and the absence of a distinction between indicator species with wide ecological amplitude and indifferent species. The data presented here give a definition matrix of indicator and indifferent species. In accordance with B€ ohling et al. (2002) we additionally provide the amplitude of continentality of the species as a proxy for the indicator quality (Appendix S2). Concerning the EIV-K vs C-value comparison, the proportion of indifferent species strongly increased. One could regret this as a loss of information; however, the high number of species with low indication power was one of the main issues in the application of the old EIV-K. Schaffers & S ykora (2000) emphasized that high proportions of indifferent indicator species do not necessarily characterize a poor quality indicator system, as long as this indifference corresponds to broad ecological amplitudes along a certain gradient. Ellenberg was fully aware that it is mathematically incorrect to calculate arithmetic means from values that are rather nominal than ordinal (Ter Braak & Gremmen 1987). Their successful application for describing and interpreting environmental conditions proves them right (T€ olgyesi et al. 2014; Wildi 2016). Their application may be legitimized if one regards the results with a healthy measure of mistrust (Kowarik & Seidling 1989). Mean indicator values can be compared within the same context, but the magnitude of the difference remains undefined. They are rather response than predictor variables (Wildi
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35
35
30
EIV-K3
Proportion of the new C-value
Proportion of EIV-K indicator species
30
25
20
EIV-K5 15
EIV-K4 10
25
20
15
C6 C4 C5
10
C7
5
EIV-K1+2 EIV-K7 EIV-K6
5
0
EIV-K8+9
0
C3 C8+9
10
20
30
40
10
20
30
40
C1+2
Fig. 6. Proportions (%) of indicator species groups for continentality along the longitudinal gradient of the Flor-D data set from west to east in northern Germany. EIV-K left, C-value right.
35
18
30
16
25
14 12
20
10
15
8 6
10
4 2
5
0
0 EIV-K1
EIV-K2
EIV-K3
EIV-K4
3110
EIV-K5
3121
EIV-K6
EIV-K7
EIV-K8
EIV-T9
C value C value C value C value C value C value C value C value C value 1 2 3 4 5 6 7 8 9
3110
3150
3121
3150
Fig. 7. Histogram of continentality indicator proportions (%) for three selected grid cells of the Flor-D data set: 3110 Wahn/Han. (Emsland, west); 3121 €rverden (Weser-Aller-valley, centre) and 3151 Oderberg (Oder-valley, east) regarding EIV-K and C-values. Do
2016; e.g. for thermal climate models, Reger et al. 2011) and include species composition information that is not entirely shaped by abiotic habitat conditions (Zelen y & Schaffers 2012). Therefore, mean indicator values should never be mistaken for measured variables when attempting to explain species composition, because they inherit species composition information (Exner et al. 2002; Smart & Scott 2004; Wildi 2016). Mean indicator values should never be mixed up with measured variables, and provide no significance in constrained ordinations, predictive models, ANOVA or other methods with high requirements on the data quality and independence (Smart & Scott 2004; Zelen y & Schaffers 2012; Szymura et al. 2014; Wildi 2016). As for statistical testing, see Wildi (2016).
One important difference between ecological and biogeographic indicator values is that the mean of ecological indicator values are referred to as habitat responses and can be carefully (see Godefroid & Dana 2007) interpolated and recalculated according to the co-occurrence of species in the sense of Hill et al. (2000), e.g. Ertsen et al. (1998), Lawesson (2003) or Fanelli et al. (2007). It is impossible to recalculate geographic indicator values in the same manner, because global distribution properties are basically a fixed species-specific characteristic and do not differ between regions, rendering the attempt to do so by Hill et al. (2000) unsuccessful. But it is not necessary to recalculate them. Our approach can easily be transferred to other regions of the Holarctic, providing sufficient species
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distribution data are available. The values simply have to be re-centred, as Pignatti (2005) and Guarino et al. (2012) did for Italy. It has to be noted that the distances between the single continentality values cannot be even. Especially towards the European Atlantic coast, a highly structured rapid species turnover leads to repeated bundles of range limits, rendering the lower continentality classes quite narrow. However an e.g. very narrow, regionally derived hyperoceanic class might not be feasible at the Holarctic scale. It seems to be more easy to re-centre the C-values for larger areas like Eastern Europe, and much more difficult to do so for smaller areas like the British Isles (see Preston & Hill 1997; Hill et al. 2000). The future approach for a European indicator value system (Dengler et al. 2016) might abandon the centring entirely and use ordinal-scaled continentality and zonality classes instead.
Main conclusions The redefined C-values represent completely renewed indicator values for continentality. The essential step forward in comparison to Ellenberg is that we present continentality indicator values derived from a consistent and comprehensible method. To retain comparability, we preserve many basic principles of Ellenberg, like the nine-step scale, and centring at the value 5. Since globally distributed floristic and vegetation data are rapidly becoming more readily available, and changing climatic conditions are increasingly accelerating the range dynamics of species, the importance of biogeographic indicator values as a response proxy for global change studies will increase.
Acknowledgements We are grateful for the services of volunteer botanists and vegetation scientists whose work enabled the databases of biogeographic, floristic and vegetation data. Timothy Mark was a great help in improving the English. C.B. and E.J.J. conceived the ideas; C.B., E.W. and E.J.J. collected the data; C.B. and E.W. analysed the data and led the writing.
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Supporting Information Additional Supporting Information may be found in the online version of this article: Appendix S1. Changes and assignment of the new values. Appendix S2. List of 2984 taxa of the Central European vascular plant flora with C-indicator values, amplitudes and comparison with Ellenbergs IV for continentality (EIV-K). Appendix S3. Explanation to GIS-compatible data sets given in Appendix S4 for a classification map of the phytogeographic continentality for the Holarctic. Appendix S4. GIS-compatible data sets of the classification map of the phytogeographic continentality for the Holarctic (Fig. 1).
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