05H2

H. Inland rock habitats

Mountain siliceous screes

Relationships with habitat classifications. EUNIS: H2.31 Alpine siliceous screes; PAL. CLASS.: 61.11 Alpine siliceous screes; HD 92/43: 8110 Siliceous screes of montane to snow level (Androsacetalia alpinae and Galeopsetalia ladani).

Conservation status. BDA, HD.

Category. Vulnerable [VU – A1, 2 B2 C1 D1 E1 F1 G1 H2 I J L1].

General characteristics. The screes in the mountains occur mainly in the upper sub-alpine and lower alpine belts, mainly below the vertical rocks and rock walls. Therefore the scree areas are most frequent in Rila Mts., relatively frequent in Pirin Mts. and less frequent in the remaining Bulgarian mountains. The typical screes are mobile or slightly fixed rock pieces of different size, from very small-sized gravel to large rock pieces; the combination of these can vary considerably. The composition and structure of the vegetation depend to a great extent on the size of the rock pieces. The exposure is another important factor since it determines the sun radiation that reaches the plants and also impacts the quantity and dynamics of soil humidity throughout the season. The screes vegetation is most typical for northern and northeastern steep slopes. In many places snow is accumulated, hence the vegetation period is delayed but the soil humidity is enough. In this unstable and diverse environment the plants react to all changes in the local environment and the phytocoenoses in the different parts of this habitat type are very diverse. Class Thlaspietea rotundifolii and order Androsacetalia alpinae encompass this diversity of screes vegetation that occurs in the Bulgarian mountains with two alliances, Androsacion alpinae and Festucion pictae. The first of them include the mezophilic hasmophytic phytocoenoses in which Androsace alpina, Geum reptans, Oxyria digyna, Poa laxa, Saxifraga bryoides, S. pedemontana subsp. cymosa, and Solorina crocea are characteristic species for the alliance. Two associations from this alliance have been described so far: 1. Oxyrio-Poetum contractae, in the coenoses of which participate the following species: Acinos alpinus, Arenaria biflora, Armeria alpina, Dianthus microlepis, Dicranoweisia crispula, Geum reptans, Oxyria digyna, Pedicularis verticillata, Poa cenisia subsp. contracta, Polytrichum piliferum, Primula minima, Ranunculus crenatus, Saxifraga bryoides, S. pedemontana subsp. cymosa, Soldanella pusilla, etc. This syntaxon is related with wet, steep screes of small-sized gravel below rocks with northern or eastern exposure and are at high altitude or in the glacial cirques. 2. Association Senecioni-Juncetum trifidi includes the phytocoenoses on screes with large stones of different size. The exposure is mainly northern or with northern component, the slope is steep (very often the altitude is also high) or the area is flat. Among the large stones fine soil accumulates and remains almost permanently humid. Characteristic species are Festuca picta, Juncus trifidus, Saxifraga pedemontana subsp. cymosa, Senecio glaberrimus with the participation of Achillea clusiana, Alopecurus gerardii, A. riloensis, Anthoxanthum odoratum, Bartsia alpina, Gentiana punctata, Geum bulgaricum, G. montanum, Hypericum richeri subsp. grisebachii, Leontodon rilaensis, Ligusticum mutellina, Luzula alpinopilosa, Poa alpina, P. media, Sesleria comosa, Vaccinium uliginosum,etc. The succession is towards subalpine herbaceous coenoses. In the alpine belt of Rila and Pirin Mts. there are large areas of stone screes where the vegetation develops very slowly. They are poor in species and the species abundance is low. Apart from the two dominating species Carex curvula, Festuca riloensis, Saxifraga pedemontana subsp. cymosa, and Sesleria comosa also occur. The floristic diversity of the above-mentioned association is very rich since it includes almost all the flora of the alpine belt and the upper sub-alpine belt. However, the number of species in the phytocoenoses is low and their abundance is negligible. The projective cover of the vegetation is always very low, the underground parts of the plants covering larger areas than the aboveground parts. In screes with small to medium-sized stones with fine soil among them that retains the water from the melting snow, the coenoses are dominated by Luzula alpinopilosa develop. In some classification schemes they are included in the pre-steppic vegetation Salicetea herbaceae. The alliance Festucion pictae is represented by one association and one subassociation – Festucetum pictae achilleetosum clusianae, but its role in the subalpine vegetation is very important. Achillea clusiana, Alopecurus gerardii, A. riloensis, Anthoxanthum odoratum, Bartsia alpina, Festuca picta, Gentiana punctata, Geum bulgaricum, G. montanum, Hypericum richeri subsp. grisebachii, Juncus trifidus, Leontodon rilaensis, Ligusticum mutellina, Luzula alpinopilosa, Poa alpina, P. media, Ranunculus montanus, Sesleria comosa, Vaccinium uliginosum, etc. are among the characteristic species for the association. Southern exposure of the slopes is rare. On the northern slopes the soil humidity is high and the projective cover often varies between 40 and 70%; hence the development of the vegetation is more advanced. The screes, mainly with medium- to small-sized stones, are almost fixed and in some places there is a soil cover. The species diversity of the association is high, but in the separate phytocoenoses it is low. The scree vegetation carries the features of a transitional stage between the hasmophytic and meadow vegetation, which develops after a possible stabilization of the screes.

Characteristic taxa.

Distribution in Bulgaria. All mountains in Bulgaria but more frequently in the high ones.

Conservation importance. Very rare phytocoenoses and vascular plants of conservation value, including some protected plants: Alyssum pulvinare, A. stribrnyi, Anemone narcissiflora, Aquilegia aurea, Brassica jordanoffii, Gentiana lutea, G, punctata, Luzula glabrata subsp. deflexa, Minuartia bulgarica, M. rhodopaea, Rhodiola rosea, Sibbaldia procumbens.

Threats. Grazing, accumulation of new stones and rocks, denudation and erosion processes, etc. In some places the mobility of the substrate destroys the vegetation or the whole vegetation cover, avalanches. Tourism activities in the protected areas that cause direct destruction of the screes in the high mountain parts.

Conservation measures taken. The habitat is in Annex №1 of BDA. Part of the mountain siliceous screes are within sites from the European Ecological Network NATURA 2000 and in other protected areas: Central Balkan, Rila and Pirin National Parks, Vitosha Nature Park, etc.

Conservation measures needed. Prohibition of grazing, complete floristic and phytcoenological study; identification of priority localities and monitoring.

References. Horvat et al. 1937; Roussakova 2000; Simon 1958.

Author: Veska Roussakova


Mountain siliceous screes (distribution map)