Using Ellenberg-Pignatti values to estimate habitat preferences of wild food and medicinal plants: an example from northeastern Istria (Croatia)

Ellenberg values are indices given to each species in a flora to express the species’ environmental preferences [1, 2]. The system was first introduced by the prominent German phytosociologist Heinz Ellenberg (1913–1997), and applied to the vegetation of central Europe. It consists of the following indices: Light, Temperature, Continentality, Soil Moisture, Reaction, Nitrogen and Salinity. Later it was modified to incorporate local differences in species’ environmental preferences, e.g. in Switzerland, Poland, British Isles and Italy [3‐6]. Ellenberg-Pignatti values from Italy are used in the Mediterranean part of Croatia, as the climate and vegetation zones of Croatia bear many similarities to those of the adjacent Italy.

The values are usually given on a ten grade scale (0–9), apart from Light, Temperature and Soil Moisture, expressed on a 0–12 scale and salinity on a 0–3 scale. They are based on the field experiences of ecologists. Although looking at single species values does not have much practical use, comparison of average values for different sites and habitats can be used for phytoindication and characterizing environmental conditions at a given site [7, 8]. Some reductionist-oriented ecologists criticise the values for being based on biased choices and impressions and for mixing the absolute requirements of species with their ecological niches, which are the results of competition [9, 10]. Being aware of the constraints in using these values in our article, we aimed at applying them to ethnobotanical data.

The data matrix in an ethnobotanical study has many similarities with a phytosociological study. In the latter we obtain a data sheet composed of a species x releve matrix, whereas in the former we usually have a similar species x informant matrix which is later analysed. In both cases the same indices and tools may be used to describe the data: species frequency, diversity indices, ordination methods etc. Increasing quantification of ethnobotanical studies has been continuously advocated by some ethnobotanists, particularly by Ulysses de Albuquerque and his colleagues [11, 12]. This would strengthen the discipline and provide rigorous testing methods. Species frequency and diversity indices are probably used in at least half of ethnobotanical papers. However, other numerical methods and tools used in ecology, such as ordination techniques (see e.g. [13] from the similar study area), are used less frequently.

Traditional knowledge usually extends to different habitats surrounding human settlements. However, it has been noticed that it is not evenly distributed. For example ruderal “weedy” species tend to be over-utilized compared to the species of primary forest habitats [14, 15], although the opposite can be true in some cultures as well [16]. Writing this paper we wanted to explore the use of Ellenberg values to establish whether there are differences between the environmental preferences of wild medicinal and food plants. We assumed that some Ellenberg values would be different for food and medicinal plants, as medicinal plants are often rich in essential oils and alkaloids, so they would tend to grow in dry pastures and grasslands, while food plants should be gathered from more nutrient-rich and mesic habitats. An additional aim was to document the use of plants from the whole food-medicine spectrum in the area.

For our case study we used the area of Ćićarija in the north-eastern part of the Istria peninsula. Only two ethnobotanical studies dealing with plant remedies had previously been carried out there, covering several villages in the core part of Ćićarija [13, 17]. One of these studies concerned Croatians [13], another – Istro-Romanians [17]. In this paper we extended the research topic to food plants and included more villages from the area at the base of Ćićarija. The study was made easier by the fact that the first authors had carried out long term phytosociological research in the same area between 2003 and 2015 [18‐21] and acquired a good level of knowledge about the local community and available key informants over the years. Our study was restricted to inhabitants of Croatian nationality.

The research was carried out following the Principles of Professional Responsibility of the American Anthropological Association and the International Society of Ethnobiology Code of Ethics (2006) [31, 32]. Data were collected using semi-structured interviews, mainly applying the free listing method, accompanied by informal walks (and talks) with selected key informants, from May to September 2015. To help elicit answers, separate questions were asked about the food use of green parts and fruits as well as medicinal plants that had been personally used by the informants. Additional notes were taken, and audio recordings were made during the interviews when possible. Participants were approached outside, during their farm work, or selected based on recommendation as the most knowledgeable people in the village.

Altogether we obtained data from 50 interviews involving 76 local informants (33 single informant interviews and 17 interviews involving two or three people). There were 37 female and 39 male informants, with a mean age of 67 (age range: 33–101, median: 67).

The interviews were carried out on the territory of three municipalities: Buzet (7 settlements: Buzet, Gornja Nugla, Hum, Kompanj, Počekaji, Roč, Sveti Martin), Lanišće (11 settlements: Brest, Brgudac, Dane, Jelovice, Klenovšćak, Lanišće, Podgaće, Prapoće, Račja Vas, Slum, Vodice) and Lupoglav (1 settlement: Lupoglav).

Plant names used follow the Plant List [33].

The division between wild and domesticated species is often blurred. Several taxa (mainly fruits and aromatic herbs) listed by the informants occur both in wild and domesticated states. We included them in the species list if we observed significant wild or feral populations of these species in the study area, as in other studies on wild foods in Croatia [34‐36].

Altogether 121 species were recorded as food or medicine, used or previously used in the study area (Table 1). Thirty-one species are used exclusively as food or everyday drink, 50 species are used exclusively as medicine and the use of 40 species overlaps. The mean frequency of species mentioned per questionnaire was 30 (mean no. of exclusively medicinal species 5, exclusively food species 8, and 17 from the food-medicine spectrum).

The most commonly used exclusively food species are: Cornus mas L., Cichorium intybus L., Chenopodium album L., Prunus domestica L., Pyrus amygdaliformis Vill., Rubus idaeus L., Clematis vitalba L., Diplotaxis tenuifolia (L.) DC., Fragaria vesca L. and Allium ampeloprasum L. The commonest species used exclusively as medicine are: Achillea millefolium L., Tilia platyphyllos Scop., Hypericum perforatum L., Sempervivum tectorum L., Artemisia absinthium L., Plantago lanceolata L., Gentiana lutea L. ssp. symphyandra (Murb.) Hayek, Althaea officinalis L., Matricaria chamomilla L., and Pinus nigra J.F.Arnold. The most commonly used food-medicine spectrum species are: Rubus caesius L., Sambucus nigra L., Urtica dioica L., Dioscoraea communis L., Taraxacum spp., Asparagus acutifolius L., Rosa canina L., Foeniculum vulgare Mill., Prunus spinosa L. and Sorbus domestica L.

Wild plants are used for food mainly in the form of preserves (jams, juice), wild vegetables served as salad, manestra soup (served with beans or dried meat) or with omelettes (fritaja), herbal teas or as aromatic additives to alcohol. The mixture of wild vegetables used for the soup is called zelenjava. Its commonest components are Chenopodium, Cichorium, Diplotaxis, Foeniculum and sometimes Humulus or Urtica. Medicinal plants are usually used in the form of infusions and decoctions (“herbal teas”). Such ways of administration were recorded for 52% of medicinal plant taxa.

Among the most commonly used food and food-medicinal plants woody species, particularly those of woodland edges are dominant, whereas among medicinal plants it is herbaceous plants from grassland that dominate (Table 2). However, the differences between Ellenberg-Pignatti values (Figs. 3 and 4; Table 3) in the three categories of useful plants were small and statistically insignificant (Mann-Whitney U test; P > 0.05) apart from the difference between Nitrogen indicator value between the Exclusively Medicinal and the Exclusively Food category (P = 0.02). For Light and Continentality the highest indicator values were observed for medicinal plants and the lowest for food plants (Fig. 6). However median values for these two variables were identified in all three categories (Fig. 7). For Nitrogen the opposite trend was observed – the highest value (and the highest median) was observed for food plants (Figs. 6 and 7). For Temperature and Reaction (pH) the highest indicator values were observed for plants used both for food and medicine (Fig. 6).

The small differences between Ellenberg values for medicinal and food plants can probably be explained by the fact that both these groups incorporate species with very diverse organs used and very diverse phytochemical composition. When designing this study we did however expect that the Light indicator values for medicinal plants would be higher than those of food plants, as many of the medicinal plants grow on dry pastures and roadsides and contain aromatic essential oils. Such a difference actually does occur in our data, but it is not significant. Dry-habitat plants from the Lamiaceae family (13 taxa in our study), rich in essential oils, are some of the basic elements of both local traditional pharmacopeias in the Mediterranean and in Central Europe, and the medicinal plants recommended by written official pharmacopeias. They are particularly useful in healing digestive problems and fighting microbial infection. However, these are usually a few species in a given set of locally used species, and their effect was not significant in a larger matrix of data with species containing different kinds of medicinally active substances. The significant difference in Nitrogen value probably arose due to the fact that several edible plants are nitrophilous weeds, whereas among medicinal plants, as previously mentioned, there are many dry grassland species growing on skeletal soils.

In the use of food the total caloric value is very important and it can be better achieved with higher biomass yields, which are obviously more likely in nitrogen-rich habitats. Most edible green vegetables are plants growing in cultivated crops, on field edges, road margins and other locations in the home yards which have been either intentionally manured, often for centuries, or unintentionally fertilized with human and animal excrements and urine. As a larger biomass of is needed, for food plants compared to medicinal plants, they are more likely to be gathered in a closer vicinity to the house than in these fertilized agro-ecosystems.

The species used in the area are a mix of species typically used in the Mediterranean and in Central Europe, which reflects the character of the vegetation in the study area, intermediate between the two zones. All the species used were reported in other ethnobotanical works from Croatia or neighbouring countries, e.g. [34‐44]. A particular feature of the local cuisine is scrambled eggs (fritaja) prepared with young shoots of Ruscus aculeatus and Cannabis sativa seeds and oil, used against diabetes and high pressure, and to boost immunity. It is interesting that Humulus lupulus is still used as a vegetable, unlike on the north Adriatic island of Krk, where people used to use it, but it is now completely forgotten [36]. Previous studies also paid attention to a relatively “unoriginal” list of plant remedies used in Ćićarija [13, 17]. However, this may be explained by the fact that phytotherapy was quite developed in this part of Europe, hence most medicinal plants in the area had already been described in detail in Renaissance herbals. A similar high correspondence between the written pharmacopeias and the present choice of plants used can be found in other European countries as well [45‐47]. Compared to the previous study of Croatian plant folk remedies in Ćićarija [13] we found more plant remedies used (even when the list was restricted to the same villages studied by Pieroni & Giusti). Pieroni and Giusti mentioned 25 plants. We confirmed the use of all the wild and semi-wild species mentioned by them (19 taxa), except for two taxa where we found the use of a different species but within the genus mentioned in their work (Malva and Mentha). In our study we found 54 species of plants mentioned by our respondents in the villages studied by those authors (Jelovice, Dane, Vodice, Trstenik, Račja Vas, Lanišće, Prapoće, Brgudac). It is difficult to compare these studies as in this previous work the number of respondents and frequency of citation was not mentioned. We can however hypothesize that the larger number of species recorded in our study stems mainly from two factors. First of all the previous researchers were outsiders speaking Italian to local residents, who may not have been able to express everything in Italian. The first author of our study has spent twelve years researching Ćićarija and thus knows many people well, which may have given respondents more confidence. Secondly, in recent years more and more literature on herbal remedies has become available to the general public, which may result in some new uses, the re-invention of old uses or help in the remembrance of old uses [45, 46]. This may have happened even in spite of our intention not to record “literature” uses little ingrained in the habits of local people, or very recently acquired.

The differences between Ellenberg values of medicinal and food plants collected in the study area are negligible. The only significant differences were detected for the Nitrogen value. This is probably caused by the fact that edible green vegetables are mainly species of nitrogen-rich agro-ecosystems. It could be interesting to carry out a similar study in some other regions of Europe where Ellenberg values are accessible in order to see if the results we achieved show a typical pattern in the relation between food and medicinal plants.