The differentiation of the habitats from Piatra Cetii and Cheile Tecsestilor Natural Reserves. The species that inhabit a certain region are not disposed randomly in space but according to the existing environmental gradients induced by the abiotic and biotic factors.
THE DIFFERENTIATION OF THE HABITATS FROM PIATRA CETII AND CHEILE TECSESTILOR NATURAL RESERVES
(TRASCAU MOUNTAINS, ROMANIA)
The differentiation of the species in space and time in a geographical area leads consequently to the differentiation of the biotic communities they assemble and then to the diversification of the biological component of the landscape. Usually the human activity is followed by the replacement of the local species and biotic communities that have specific ecological needs and are more or less the products of the local or regional evolutional processes with ruderal species and ruderal / ruderalized communities that have very large ranges (expanded by using the human infrastructure) and very broad ecological adaptations. This leads to the attenuation if not dissolution of the contrasts in concerning the species composition that exist between the different environmental “facets” of the various geographical areas. It can be said that the greater these contrasts are between the biocenotic types that can be found in an area the more various are the natural conditions encountered there but also the lesser is the intensity and variety of the human impact in the region (especially the human interferences of a “modern” not “traditional” kind).
Piatra Cetii and Cheile Tecsestilor areas, though prominent relief forms in the assemblage of the TrascauMountains are also difficult to be reached due to the poor quality of the road access. This induces a relative isolation of them from the main regional human “fluxes” around (especially the touristical ones) and consequently a better preservation of both the ecosystems and habitats and of the human traditional ways of life. In this study we wanted to show which the most commonly encountered species are in the two reservations, to statistically estimate also the real number of species that exists and which is the degree of differentiation between the habitats encountered. Nonetheless the nature of the habitats and of the differentiations between them was followed in this research.
The previous studies in Piatra Cetii massif were very scarce to the relatively hard access in the area. In fact there is only one done in the area, with a preliminary character which was done by Ghisa et al. (1965). However a rather great number of contribution were published in between the 60’s and the 90’s of the XXth century that largely outlined the typology and evolution of the vegetation in the calcareous massifs from the southern and eastern flanks of the ApuseniMountains.
The database that was used for statistical working was created by using the relevee technique as described in the phytotaxonomical methodology (see in ex. Cristea et al. 2004). We totally sampled 40 releves in 10 different habitats from the total of 12 identified in the field (Table 1) represented by 10 different types of vegetal associations that were identified according to Donita et al. (2005). In Table 2 the typology and national and international / European codes of these habitats are presented. The relevee database was then worked by using multivariate usual statistical techniques (UPGMA clustering, non-metric and principal component analysis ordinations) in order to see de differentiation between the habitats from the two natural reserves and also the nature of this differentiation. The statistical software package we made use of was the merituous freeware PAST 1.48. Also the total number of species from the two reserves was estimated by using a Jackknife estimator (Krebs 1999).
The total number of species encountered while sampling the releves is 272. From them 96 occur in only one sample / relevee. By using the formula of the Jackknife estimator a number of 365 species is appreciated to be really extant inside the reservation (with a minimum of and a maximum of at p<0.05). This means a quite high level of the parameter S (species richness) of inventory specific biodiversity (alpha diversity) on the relatively reduced area of the two natural reservations of approximately 1,12 sq kms. Most of the species are of a Dacian – west Balkan, Carpathian and Submediterranean origin due to the geographical position and the intrazonal (calciphile – saxicole) nature of most of the habitats. Many of these (7) are regional endemic habitats related strictly to low altitude calcareous rocky substrata.
The results of the multivariate analysis show a considerable differentiation between the cases when binary and quantitative data were used respectively. In the latter case not only the presence / absence of a species in one particular sample was taken into account but also the proportion (actually the coverage in percents at the ground level) of the individuals belonging to that species (fig. 1-9).
Both the cluster and the ordination techniques when binary data were used show that in fact we have two distinct sets of species and two main sets of habitats. These are the Beech forests (Festuco drymejae – Fagetum) noted as FAG. The samples taken from them every time distinctly stand apart from the other samples. By contrast the samples taken from the grassland and scrub habitats are more or less mixed up in various ways depending of the method used.
On the contrary, when quantitative database was worked it can clarly be seen with rare exceptions that the differentiation between the various grassland and scrub habitats becomes obvious.
The main conclusion that can be drawn here is that there exists a deep contrast between the Beech forests on one side and the rock scrub and grasslands in concerning the species composition. The origin and especially the ecology of these species that can be distinctively grouped in two sets is so different that the ecotone borders between the forests and grasslands / scrub communities respectively is very thin and contain a very reduced number of species. Also the number of species that can be involved on both sides is reduced (15 from a total of 272 in the samples). The forests cover mainly the northern, north-eastern and north-western clines in the two reservations (that are also not so steep) while the rest ones are dominated by grasslands, scrubs and rock crude primitive communities.
As a second conclusion we can say that while the species group that makes the Beech forests do not differentiate in various types of habitats (only the mentioned type is found in the whole area regardless of the local variations) the group that is involved in the calciphile grasslands, scrubs and certainly in the crude primitive communities from the rocky walls and scree evolves in a quite large mosaic of habitats depending on the local minute variations (slope and exposition especially). They are differentiated strictly by the dominant species. In fact, here we face with a single set of species adapted to open and semi-open rocky calcareous habitats within which, depending on the local peculiar conditions, one species or another assumes the dominance (Helictotrichon decorum on sunny and half-sunny expositions, Sesleria rigida and Sesleria heuffleriana on shaded and half-shaded abrupt ones while the calciphile shrubs Spiraea ulmifolia and Rosa spinosissima tend to invade the plateaus and the less inclined sunny or half-sunny clines. That means that the “characteristic species” mentioned by phytotaxonomists which dealt with these communities, and that make the differences between the vegetal associations and alliances that correspond to the types of calciphile grasslands and scrubs mentioned here should be reconsidered further, in our opinion.
A third important conclusion that can be drawn from these analyses is that the gradient that is assumed empirically by most ecologists for the structure and the transformation of the vegetation in the calcareous massifs (crude limestone outcrops – calciphile grasslands – calciphile scrub – Beech forests) is questionable. In fact as can be seen especially from the ordinograms (fig. 6-9) the communities that stand closest to the Beech forest habitats are the ones with Sesleria rigida. These are installed especially the shaded and half-shaded steep calcareous cline. The scrub calciphile habitat which is expected to bridge the gap between the grasslands and the forests in fact does not assume this role. Seemingly more or less the Rosa spinosissima – Spiraea ulmifolia scrub is the product of direct local invasions of these shrubs over the calciphile grasslands while the local species composition remains largely unaltered and does not gradually get enriched in forest species – such a phenomenon was never evidentiated. The calciphile scrubs are not therefore the precursors of the beech forests. On the other hand seemingly when the Beech forest has the possibility to expand on the shaded and half-shaded clines it does this by directly transgressing over and replacing the Sesleria rigida or even other grassland communities and not through the intermediation of calciphile scrubs.
Fig. 1 – Cluster binary analysis based on Jaccard index of similarity. Refer to Table 1 and Table 2 or to the text for the annotations (samples’ labels).
Fig. 2 – Cluster binary analysis based on Simpson index of similarity
Fig. 3 – Cluster quantitative analysis based on Chord distance
Fig. 4 – Cluster quantitative analysis based on Manhattan distance
Fig. 5 – Cluster quantitative analysis based on Euclidean distance
Fig. 6 – Non-metric binary ordination based on Simpson index of similarity
Fig. 7 – Non-metric quantitative ordination based on Manhattan distance
Fig. 8 – Principal Component Analysis based on binary data
Fig. 9 – Principal Component Analysis based on quantitative data
Cristea, V., Pedrotti, N., Gafta, V. (2004) – Fitocenologie, Ed. Presa Universitara Clujeana.
Donita, N., Popescu, A., Pauca-Comanescu, M. (2005) – The Habitats from Romania, Editura Tehnica Silvica Bucuresti.
Ghisa, E., Kovacs, A., Silaghi, Gh. (1965) – Floristical and Phytocenological researches in the ApuseniMountains at Piatra Cetii (in Romanian). Contributii Botanice, 23.
Krebs, J (1999) – Ecological Methodology. John Wiley and sons, New York, London, Singapore.