Diversity of ecological groups of species in cultural forests of South Bohemia

Karel Matějka

Published in Ekológia (Bratislava), Vol. 12 (1993), No. 3, 299-316.

Abstract

Species diversity is important, nevertheless not the sole diversity, which could be studied in ecosystems. Also the diversity of ecological groups of species (hereinafter called ecological diversity) is of importance. A functional relation between stability and ecological diversity is supposed.

To estimate the ecological diversity, a new bioindication method (IDGAI) has been used, based on the system of eco-indices (for used system see Ellenberg, 1974). The relation of species diversity, number of species, and indices of ecological diversity related to six environmental factors (light conditions, temperature, degree of oceanity/continentality, soil moisture, soil reaction, nitrogen activity) has been studied within the cultural forests of South Bohemia.

Introduction

The article attempts to answer following questions:

1. What is the structure of ecological groups of species in cultural and semi-cultural forests of South Bohemia.
2. Does a relation between diversity of the ecological groups of species and species diversity exist?
3. What is the relation between diversity and stability of phytocenoses from the viewpoint of the definition of diversity of ecological groups of species.
4. How does the stress intensity change depending on the level of ecological factor of phytocenoses of different stability.

Before the analysis of the problematics, some approaches and terms have to be explained:

Each species has an optimum and an amplitude of abundance at the gradient of each ecological factor. In this article we are speaking about the ecological optimum. The question of a normal-distribution-shape of the species response function is often discussed. In fact it is a pseudoproblem - the normality can be reached by an acceptable transformation of each variable describing the ecological factor level.

The definition of ecological groups of species is another problem. Having in account continuity of the species response on ecological factor level, it is obvious that strictly limited groups of species cannot exist. Similarly to the conception of the syntaxonomical unit as an arbitrary type, we can speak about certain types of behaviour of species, and those inclining in their real behaviour to one type can be included into one ecologic group.

The problem of representation of different ecological and plant coenological groups of species in different types of phytocoenose is mentioned in many papers. Nevertheless the results can be quantified with problems, due to a not very exact definition of groups of species, and different levels of definition of those groups along the gradient of environment.

Currently, the great amount of information of different plant species is available, nevertheless only few systems present complete knowledge of the behaviour of all (better to say of most) species in certain large region. The Ellenberg's system of eco-indices (Ellenberg, 1974, 1979) (although often critizied, the legitimacy left apart), is one of them.

The use of Ellenberg's eco-indices as well as other similar tables (Landolt, 1974; Zólyomi et al., 1967, etc.) was described in many papers (for instance Jurko, 1981, 1983a, b, 1984, 1985; Jurko, Kubíček, 1979; Jurko, Kubíček, Šomšák, 1981; Jurko, Kontriš, 1981, 1982; Rambousková, 1981, 1982, 1984 from Czechoslovakia; an interesting example was given by Reif, Teckelmann, Schulze, 1985). Different authors have a very distinct meaning, from an uncritical application of this method (several papers from Jurko above cited and others) to discounting for any using. Discussion to the problem linking with ecological indication has brought Mucina (1985) and Jurko (1986). There are two principles of a reasonable approach to this problematic:

1. The statistically oriented way based on comparing the species frequencies in the individual bioindication categories (as Klimeš, 1987).
2. Ordination of samples (plant cenological relevés) according to average values of eco-indices.

Hereinafter the second approach will be kept. It is based on a premise that ecological optima and value of eco-indices have equal or very similar trend (it means the arrangement of species according to eco-indices is little different from arrangement according to ecological optima). An often mentioned problem of a no-Gaussian response of some species along gradients (as bimodal distribution) is solved by not involving such species into group of indicators.

Assuming results of ordination modes using previously obtained (a priori) information about species' ecological characteristics, it would be better to compare them with the classical methods of indirect gradient analysis. After evaluating some uses of bioindication approaches (Clausman, 1980; Ter Braak, Gremmen, 1987), a new method, called In-Direct Gradient Analysis with apriori Information (IDGAI) was developed for this purpose. It was developed at the Institute of Soil Biology of the Czech Academy of Sciences in Ceské Budejovice by the author of this paper. An application of it for grass vegetation see in Matějka (1996), the method description is presented in the following text.

To specify the definition of species diversity is not necessary, but it is important to explain, what does the term "diversity of ecological groups of species" (i.e. ecological diversity) mean. In the context of ecological groups of species, the question is the diversity of the requirements of species on the level of environmental factor. A higher diversity consists in a more differentiated ecological optimum of certain species and their closer amplitudes (i.e. more specified demands).

Data collection and description of forest groups

The material from plant coenological study realized in 1982-1989 in the phytogeographic districts of 37h (Prachatické Předšumaví), 37i (Chvalšinské Předšumaví) and 38 (Českobudějovická pánev) with adjacent regions (37g, 37j, 37l; see Skalický in Hejný et Slavík, 1988) has been used. Studied forests grow at localities the altitudes of which are from 370 to 1100 m. Average year temperature varies from 4.5 to 8 °C and the year total of precipitations varies from 570 to 800 mm (Vesecký et al., 1958).

The total of 63 relevés has been classified. The sample area varied from 200 to 400 m². For the purpose of our work, data of herb layer of forests were analysed. Using the divisive classification procedure TWINSPAN (Hill, 1979), following four classification groups of phytocenoses have been stated:

• Stands of the alliance Dicrano-Pinion as secondary cultural stands of conifer species (Pinus sylvestris and Picea abies) in the 3rd or the 4th forest vegetation degree (Zlatník, 1976). Those stands are of relatively stabilized coenoses in acid soils (from high to moderate acidity). Mostly they are of the third generation of pinus or spruce cultures, influencing the soil degradation (change of accumulation and quality of organic matter, soil acidification, changes of nutrient dynamics, podzolization etc.). The group is represented by 22 relevés.
• Cultural forest stands of less changed species composition of trees in (mainly) the 3rd forest vegetation degree, where alliace Genisto germanicae-Quercion and suballiance Galio-Abietenion (assoc. Abieto-Quercetum) are prevailing. Stands of those two types can often be differentiated with problems (Neuhäusl, Neuhäuslová-Novotná, 1979). In the frame of the group, several subgroups according to dominants in herb layer (Calamagrostis arundinacea, Poa nemoralis) or without dominant species can be differentiated. The group is represented by 17 relevés.
• Forests of different degree of species composition change on rich soils. Sambucus racemosa or S. nigra in shrub layer prevail, species similar as Senecio fuchsii, Moehringia trinervia, Galium aparine and Urtica dioica grow in the herb layer. The forests with less changed tree species composition (of mostly 4th forest vegetation degree) represent a relatively independent subgroup. 18 relevés of this group have been studied.
• Forest stands in moist or wet soils (floodplain and spring areas) are represented by 6 stands in the material studied.

The IDGAI method description

The used designation: The primary data matrix X=[x_ij], 0<i<P and 0<j<N, where P is the total number of species in the data set, N is the total number of samples, x_ij

In the first time, the vector of primary ecological characteristics of samples is computed as the weighted arithmetical mean of the species eco-indices

In reality, this mean is given over p species with known eco-indices only (p≤P) [_kG_red or X_red(k) arise drom _kG or X by omitting all rows for which _kg_i is not known and we normalize X_red(k) to the sum equal to one for every column]

One can order of samples along the hypothetical gradient of ₀f_i. Let we assume the normal distribution of each species along such a gradient in the form

where

and

_kσ_ij = _(k-1)f_j-_kg_i

by

Under the condition that

acquire the least value, it is with satisfying the conditions

and

(we compute sums for n no-zero value of x_ij only, n ≤ N [We may fill a condition that the sum is calculated for x_ij > x^* only; x^* ≥ 0 is the earlier fixed real value]), one can estimate the parameters _kg_i, s_ik

Average of such k-th iteration of eco-indices of species is allowed to write as

The parameters sik and Ŕik are estimated by solving the two equations (4a) and (4b), that is by solving the matrix equation

The items of the matrix A (dimension 2*2) and the column vector B (dimension 2*1) are

(the condition for summing as in eq. (4a) and (4b)).

If the condition 4 (and eq. (6)) have not a solution (for s_ik is from R⁺) or s_ik > s_max (for fixed s_max>0) let us declare i-th species be indifferent (in k-th iteration) to the environmental factor studied, consequently kgi will not be defined (see eq. (5)).

Based on the computing the ₁G vector (in the first iteration or the _kG vector in the k-th iteration) or ₁G_red as a more real case may be, the computing of ₁F (or _kF) is possible similarly to the equation (2):

(this way is named 1st variant of IDGAI). The use of knowledge of the indication strength of species (eco-index weight coefficient P_ik) seems to be more suitable. For this case, we would use the equation

(summing for i in the case the _kg_i value is set up) (the 2^nd variant of IDGAI).

The possibility of iteration of this algorithm has been suggested earlier. It is carry out continuing by eq. (3) for k increased of one.

Concluding, the parameters differing several ways of IDGAI are as following:

1. The variant of IDGAI (selection between eq. (7) and (8));

2. The level of significant species representation x^*;

3. The upper limit of standard deviation, s_max (it is admissible s_max=+∞ by the 2nd variant).

Regarding to decrease of standard deviation of _kf_j (_kg_i) for increasing iteration degree k, the indices normalization is acceptable:

The last choice is

4. The normalization of the indices (eq. (9a) and (9b)).

Methods

The degree of combined scale for abundance and dominance of species of herb layer from the registrated relevés was transformed into the percentage of average covering. This was standardized to the sum of significance of all species equal to the total cover of herb layer. The known values of eco-indices for light conditions, temperature, level of oceanity/continentality, moisture, soil reaction and nitrogen activity were assigned to all species. Before next computation, values of the average eco-indices of the relevé were transformed into real scale using the function

where M is the maximum permissible value of respective eco-index (M = 9; M = 12 for soil moisture only). The data were processed by the method IDGAI. Similarly as the average eco-index of relevé computed using the weight (equal to the ratio of the real species cover and index P, see eq. (8)), also the standard deviation of average eco-index was computed. This value is considered to be the measure of ecological diversity.

Species diversity and their components were described by three basic indices (Shannon-Wiener's index of species diversity H', total number of species S and equitability e=H'/log₂S). The relation among all the values described has been studied using current statistical methods.

Results

Indices of the first iteration of the procedure IDGAI (the second variant using eq. (8)), with following parameters, were used:

• minimum considerable cover of single (different) species 0.5 %,
• maximum share of indifferent species 60 % (by all environmental factors),
• minimum number of samples for average computation 5.

The minimum, maximum and average of eco-indices of relevés for different environmental factors (the number of relevés with assignated eco-indices is presented in brackets):

The fact, that the first three indices describing global characteristics of the environment are of very limited descriptive capacity and utility, and that the last three describing soil characteristics are much more suitable, is evident. Therefore in the following text an attention will be paid to those three later ones. The survay of the computed eco-indices and of the indices of diversity is presented in Table 1. Some species - indicators are listed in Table 2.

The correlation between the index of species diversity (Shannon-Wiener index H'), their compounds (number of species S and equitability e) and

The distribution of relevés in the space of three axis of ecological diversity in relation to soil reaction, to nitrogen activity and to moisture (Fig. 1) shows the existence of three groups of plant coenoses. The group of low (same as the group of high) levels of these ecological diversity indices are not constituated any specific types of plant communities. The low ecological diversity is connected mainly with plant coenoses with a low number of species, the high diversity can be observed in coenoses with medial or higher number of species. The fact, that the relation between ecological diversity related to soil reaction and the one related to nitrogen activity is not significant, is also of interest (Fig.2). Next two relations are presented at the Fig. 3.

The correlation between indices of species diversity and indices of ecological diversity is not significant, nevertheless in data obtained had been observed some symptoms of the positive correlation (with the exclusion of the ecological diversity related to oceanity/continentality, where negative values of coefficients of correlation to indices H', e, S were measured; all values were statistically nonsignificant). It is not possible to say, which of three indices of species diversity (H', e, S) is more affecting the value of the indices of ecological diversity (there is a different index for each factor studied).

Following characteristics are typical for ecological diversity of groups of forest phytocenoses:

1. In the group of acidophil conifer forests, the diversity is more or less irregularly divided in subgroups. This fact is supported also by high homogeneity of sampled material of the group.
2. In the group of (semi-)natural oak stands, the differences can be observed between assoc. Abieto-Quercetum (higher ecological diversity in relation to moisture) and Luzulo-Quercetum (the same characteristic of lower value).
3. The group of beech forest vegetation degree shows a higher diversity (mainly in relation to soil moisture and soil reaction, partially also to the nitrogen activity) in forests which have the tree composition similar to natural ones.
4. Hygrophile forest cannot be evaluated due to the low number of relevés.

Attention is to be paid also to phytocenoses of high values of ecological diversity indices (see Fig. 4), where higher stability in conditions of changes of environmental factor is supposed. In the history of those phytocenoses, a higher fluctuation of the level of this environmental factor can be supposed. Whether it is really a higher ecological diversity must be considered always in relation to the indicated level of the factor: in a limit level of environmental factor, also a relatively lower value of the index of ecological diversity in comparison with phytocenoses of non-limit level of this environmental factor can be considered to increas (see Fig. 4A). In phytocenoses of a limit level of environmental factor more frequent occurrence of increased ecological diversity can be expected (see Figs. 4C and 4D).

Discussion and conclusion

Attention is to be paid to the relation of diversity and stability of phytocenoses. Species diversity was mistaking for ecological diversity which resulted in many errors. Similar approach could be useful also for the solution of the relation between diversity and productivity - in this case the study of the niche diversity would be more pertinent. Nevertheless, it is supposed that there can be a certain relation between diversity of niche and diversity of ecological groups of species.

It is probable that the lower diversity of ecological groups of species causes the lower stability of coenose (without consideration of species diversity).

In that sense also the effect of liming of acid forest soil with purpouse of compensation of the influence of acid rains can be contemplated. In naturally acid soil of mountain spruce forests different edafon species are prevailing, adapted to low values of soil reaction. Many of them are intolerant to lime added and thus eliminated by liming. Only species of wide amplitude of the response on changes of the factor "soil reaction" are surviving. Thus not only species diversity, but also diversity of ecological groups of species is decreased. It is a reason for the decrease of stability of the community.

In such a way, relations among different terms used in current ecology of phytocenoses can be mentioned: definition of coenose, continuum, coenological units, ecotones, spatial organization of sub-coenological level, species diversity, diversity of ecological groups of species, niche diversity, diversity of units of sub-coenological level, stability (resistance, resilience, persistence), stress (acute, chronic), environmental factors (continuity in space, discrete or continuous levels) and others.

Other terms related could be:

• significance of year dynamics of coenoses and populations (well known factor by study of invertebrata);
• significance of the character (changeability) of the medium where cenose develop (soil, hydrosphere, open air, phylosphere, parasitic cenoses etc.) and possibilities of the movement of organisms creating certain coenose (active and passive movement).

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See also

Table 1

Table 2

Figures

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