Status and dispersal map of orchid populations of Chréa National Park (southwest of Algiers, Algeria)

Study area

The national park of Chréa was created in September 1925, on the initiative of the Natural History Society of North Africa. Originally, it covered only 1351 ha including the dense cedar forests of Djebel Gureouane, Djebel Ferroukha and the forest of Beni Salah (DGF, 2000). In 1983, the surface of the park was extended to 26587 ha with forest formations occupying 20.3% of the total surface and scrubland which accounts for more than 63% of the surface of the park (Halimi, 1980; Marre, 1992).

Located 50 km southwest of Algiers, the park which is within the Tell Atlas, extends along the central heights of the Blidean Atlas. It dominates about the north of Metidja plains, towards the south Medea plateau, towards the west the massif of Dahra and surroundings in the east the massif of Djurdjura. It includes from east to west the mountains of Hammam Melouane, the ridges of Chréa and Djebel Temesguida (Halimi, 1980). This park is confined to the department of Blida and Medea and overlaps the limits of Ain Defla province. The Blidean Atlas is a mountainous region of the alpine fold with the highest point reaching 1629 m (Koudiat Abdel Kader). It is divided into compartments and well-limited siltation basins (Marre, 1992).

According to Halimi (1980), the park is a rocky barrier with a very rough topography and a dense hydrographic network including a series of wadis oriented south-north. The geology of the Blidean Atlas is very homogeneous, composed only of deposits of schist that are more or less clay-like and rarely fossiliferous (Halimi, 1980; Marre, 1992).

The climate is of Mediterranean type, characterized in this region by a long period of dryness and by relatively warm and rainy winters with determined by frost (Halimi, 1980). The Blidean Atlas suffers from both the severe winter and the dryness of summer, which occurs just when vegetation most needs water (Emberger, 1930; Seltzer, 1946; Daget, 1977; Pons & Quézel, 1998; Le Houerou, 2007; Colmet-Daâge et al., 2018). The intermediate seasons (spring and autumn) are the most favorable for the plant structuring of natural habitats in the Mediterranean region (Daget, 1977; Pons & Quézel, 1998). The intermediate seasons (spring and autumn) are the most favorable to vegetation.

Our surveys focused on three sectors according to the recommendations of the national park of Chréa’s forestry engineers who assert that “these are the sectors that constitute the largest areas of ecological interest and natural diversity”. In each sector, study sites were selected according to their accessibility; a total of 10 sites were the subject of floristic survey (Figure 1, Table 1).

Figure 1:

El Hamdania sector: Located in the west of Medea province, it is characterized by important natural resources (gorges of the Chiffa, waterfalls, the high-altitude lake of Tamesguida). Two localities in this sector were surveyed (Sidi Rabeh and Zeta), characterized by the presence of arborescent maquis dominated by Quercus ilex L.

Chréa sector: This sector is located in the center of the park area and includes a centenary cedar grove, a rich and varied arboretum, places for summer and winter sports activities. Four localities were selected here (pure cedar forest, Beni Ali ropeway, Beni Ali and Oued Aberer), where a very important tree flora has been recorded, in particular Cedrus atlantica (Endl.) Manetti ex-Carrière, Cupressus sempervirens L., Pinus halepensis Mill., Prunus avium (L.) L., Quercus ilex L. and Q. suber L.

Hammam Melouane sector: It is a mountainous area, located in the east of the region of Chréa. It is characterized by its thermal resources, an important rural vocation, and relaxation places in nature. Four localities were prospected here (Sidi Aissa, Douar Bou Hmar, Tabainet and Sidi Serhane). The vegetation in these localities is diverse and includes forests of Quercus ilex and Pinus halepensis, as well as low maquis shrublands, grasslands, and horticultural crops.

Study method and sampling

Our work aims to compile a systematic inventory of orchids present in Chréa National Park. As part of this study, several surveys were conducted between April 2022 and June 2023. We placed particular emphasis on random sampling based on the presence/absence of the different taxa studied in the Orchidaceae family. As part of each survey (25m²), we compiled a systematic inventory of all the flora associated with orchids (Frontier & Pichod-Viale, 1998), assigning each species a Braun-Blanquet abundance-dominance value (Braun-Blanquet, 1932). We thus established a matrix of 27 floristic surveys covering all species co-occurring with the identified orchid. The identification of orchids and main co-occurring species was based on the Algerian flora of Quézel & Santa (1962–1963) and the North African flora of Maire (1959), but also, especially for orchids, based on Martin et al. (2020), Kreutz et al. (2013, 2015), Rebbas & Véla (2013), and Rebbas et al. (2023). The nomenclature was updated according to Euro+Med PlantBase (2024), International Plant Name Index (IPNI, 2024), and African Plant Database (APD, 2025). The Plants of the World Online (POWO, 2024) and Euro+Med PlantBase (2024) indicate the general distribution of the taxa, allowing the determination of the categories of endemism, which was also checked in Le Floc’h et al. (2010) and Dobignard & Chatelain (2010). Taxa were classified in alphabetical order and their synonyms in the Algerian or North African flora were indicated.

The size (height) of individuals of orchids observed was measured in situ. The mapping of the sites and study localities, as well as the dispersal maps of the orchid species studied, were established by the ARC-GIS 10.8 software.

Statistical analysis

One of the methods applied to the processing of ecological plant data is certainly correspondence analysis (CA), which is indeed the most appropriate method for discriminating between plant groups (Legendre & Legendre, 1984; Dervin, 1988). This method is the most suitable for our fieldwork, given that Braun Blanquet’s abundance-dominance cover estimates are semi-quantitative.

In a first step, a CFA was used to highlight the significant interactions between the main factors. This includes finding the best simultaneous representation of two clusters comprising the “plant species” rows and the “survey” columns of a data table and testing the link between these two clusters (Legendre & Legendre, 1984). In our case, this involves a census of matrix species, where we note a Braun-Blanquet abundance-dominance coefficient for each plant species. The term ‘matching’ in CFA comes from the fact that we are trying to match characteristics. Correspondence factor analysis describes the dependence or correspondence between sets of character data. Thus, CFA is mainly descriptive (Dervin, 1988), allowing us to describe the floristic environment that accompanies each orchid species in a multidimensional analysis and to establish the reason for the grouping of these species or their isolated occurrence.

Inventory

In the ten localities distributed across the three sectors of the Chréa national park (the Sector of Chréa, the sector of El Hamadania and the sector of Hammam Melouane), 19 species of orchids were identified (Figure 2A–J), including 2 subendemics (Orchis laeta, an Algerian-Tunisian endemic, and Ophrys atlantica Munby, a taxon with distribution area limited to Spain, Morocco, Algeria, and Tunisia, Table 2), and 131 co-occurring species. The most represented genus of orchids in the study area is Ophrys (7 species), followed by Orchis (3 species), then Anacamptis, Himantoglossum and Neotinea (2 species each). In the field, 378 individuals of orchids were recorded.

Figure 2:

Ophrys lutea Cav. is the most abundant in the study area (113 individuals), followed by Anacamptis coriophora (L.) R.M.Bateman, Pridgeon & M.W.Chase and Ophrys bombyliflora Link (71 and 50 individuals respectively). On the other hand, Himantoglossum hircinum (L.) Spreng. and H. robertianum (Loisel.) P.Delforge are the least abundant with only 3 individuals for each of them (Figure 3). The study area offers suitable conditions for orchids to thrive and is also an ecological optimum for some of these species, with their populations reaching fairly high densities compared with others orchids (Figure 4).

Figure 3:

Figure 4:

Floristic composition of co-occurring species

The factorial analysis highlights a clear distribution of orchids according to the companion species in each study site. Graph with second and third axis gives ecologcally most sound result, therefore we decided to present this graph.

The analysis divides the orchids in 2 groups which are distributed on the factorial axis 2 from right to left according to a gradient of plant density and the third settles at the limit of the factorial axis 3 (Figure 5). This distribution follows the plant physiognomic formation of each locality studied. Figure 6 supports the distribution of localities according to the plant density of the survey itself where the orchid species is reported; this one divides the localities into 3 sectors according to the altitude and the exposition of the survey. The analysis of the plant procession of each orchid locality highlights the floristic niche of these species and their sociability with each other.

Figure 5:

Figure 6:

In the mountainous localities we observe a specific installation for some populations of orchids such as: Ophrys atlantica Munby and Neotinea maculata (Desf.) Stearn where the orchid is surrounded by a companion flora. on the other hand, in open localities with low plant density, such as: rocky lawns and clearings of cork oaks, we see a clustering of different species of orchids associated with a specific flora constituting a population of orchids very characteristic of the nature of the habitat where they are found. Giving example to the population of: Anacamptis papilionacea (L.) R.M.Bateman, Pridgeon & M.W. Chase, Ophrys bombyliflora Link, Orchis anthropophora (L.) All., and O. mascula (L.) L.

Figure 7 illustrates the floristic niche of the orchids recorded during our field survey. The factor analysis thus identifies five distinct groups of orchids (G1, G2, G3, G4 and G5). Each group is characterised by a set of orchid species accompanied by a floristic composition characteristic of the biotic environment. However, the factorial plot of the analysis brings together all the companion species common to all the habitats studied during our work.

• Flora Group number. 1: Himantoglossum robertianum, Cephalanthera longifolia, Ophrys tenthredinifera, Ophrys lutea, Ophrys speculum, Malope malacoides, Asplenium obovatum, Pallenis maritima, Chamaerops humilis, Nigella damascena, Squilla maritima and Anagallis arvensis.

• Flora Group number. 2: Neotinea maculata, Myosotis discolor, Crataegus azarolus, Ranunculus spicatus, Hyacinthoides hispanica, Smyrnium perfoliatum and Leucanthemum glabrum.

• Flora Group number. 3: Orchis anthropophora, Anacamptis papilionacea, Ophrys bombyliflora, Orchis mascula, Orchis laeta, Ophrys fusca, Anacamptis coriophora, Serapias parviflora, Himantoglossum hircinum, Neotinea tridentata, Asplenium trichomanes, Asphodelus ramosus, Bromus scoparius, Allium triquetrum, Orobanche purpurea, Stachys marrubiifolia, Dactylis glomerata, Bellis annua, Pinus halepensis, Valeriana tuberosa, Papaver rhoeas and Gladiolus byzantinus.

• Flora Group number. 4: Ophrys apifera, Orchis laeta, Limodorum abortivum, Plantago major, Geranium molle, Quercus suber, Erica arborea and Genista tricuspidata.

• Flora Group number. 5: Ophrys atlantica, Hypochoeris radicata, Eryngium tricuspidatum, Astragalus armatus, Polygala nicaeensis, Hypericum perfoliatum, Cedrus atlantica, Ranunculus macrophyllus, Sedum caeruleum, Funaria hygrometrica, Paronychia argentea and Viola munbyana.

Figure 7:

Orchid dispersal in the study area

The distribution maps, combined with graphs showing the diversity of orchids at each study site and the abundance of each species (Figure 8A, B, C, D, E, F), highlight the genera with a wide distribution and those with a limited distribution within the study area. Thus, the genus Ophrys exhibits a fairly broad ecological profile, occupying all the habitat types studied during our fieldwork. The genus Orchis exhibits habitat specificity, being restricted to cedar forests at an altitude ranging from 550 to 815 metres across just two sites. The genus Himantoglossum is present at only four sites, and the two species characteristic of this genus do not overlap in their distribution, as is the case for the genera Neotinea and Anacamptis. These maps and graphs enable a clearer distinction to be made between orchids with a broad ecological profile, i.e. those that colonise various habitats studied (mixed forest of Quercus ilex and Pinus halepensis, Quercus suber scrub, cedar forest), such as Ophrys, Serapias, Himantoglossum and Neotinea, and orchids with a specialised ecological profile, such as the Orchis species that grow only in mixed forests, or Limodorum and Cephalanthera.

Figure 8A:

Figure 8B:

Figure 8C:

Figure 8D:

Figure 8E:

Figure 8F: