19C3
Communities of quillwort (Isoetes lacustris)
Relationships with habitat classifications. EUNIS: C3.4113 Euro-Siberian quillwort swards; Pal. class.: 22.3113 Euro-Siberian quillwort swards; HD 92/43: 3130 Oligotrophic to mesotrophic standing waters with vegetation of Littorelletea uniflorae and/or of Isoeto-Nanojuncetea.
Conservation status. BDA, BC, HD.
Category. Endangered [EN – A1, 2 B1 C3 D3 E2 F1 G1 H2].
General characteristics. The habitat encompasses lake communities of quillwort (Isoetes lacustris). It is a small plant with corm-like stem and semi-cylindrical linear-awl shaped leaves that are completely submerged in oligotrophic or mesotrophic lakes. This Arctic-Boreal relic species is the only Bulgarian representative of family Isoetaceae and genus Isoetes from division Lycopodiophyta (club mosses). It occurs in the lakes above 1900 m alt. in Pirin Mts. The species prefers more shallow peripheral parts of the lakes, where the light is strong enough for intensive photosynthesis, there is much oxygen and the temperature in summers is relatively high. Almost always these localities are stony places with small to medium-size stones. A considerable part of the lake bottom is covered by the numerous and relatively long roots of the plant. It is much larger than the area covered by the above-ground parts of the plant. Thus, the occurance of other species is limited but not completely restricted, and in the same time favourable conditions for the development of the quillworts are provided since they are heliophytes and cannot survive in the shade. Therefore the monodominant coenoses are widely distributed and cover considerable areas in some lakes. The number of plants is high and the projective cover of the above-ground parts reaches 70–80% while underground parts cover much larger areas. Despite the mass development of the quillwort swards in some lakes, some other plants can also occur but mainly Sparganium angustifolium. The size of this species, up to 1 m in length and the numerous flat, linear leaves floating on the surface, cast shadow in the water and worsen the conditions for the quillwort. In the mixed coenoses the two species are present in a different ratio that illustrates the evolution of the vegetation in Pirin lakes. Sparganium angustifolium is also a rare species for the Bulgarian flora and for the Balkans. In Bulgaria it occurs in the lakes in Rila and Pirin Mts. above 1600 m alt. Outside Bulgaria the species occurs also in the lakes in R Macedonia. Sparganium angustifolium prefers the shallow parts of the lakes, while Isoetes lacustris profits by the extremely transparent water of the mountain lakes and can grow also in deeper places. Very rarely these two species are accompanied by Subularia aquatica. This is an annual to biennial plant that grows in some lakes in Rila and Pirin Mts. above 1800 m alt. It is also a rare species for the Bulgarian flora. Subularia aquatica is a small plant, up to 10 cm high, and is not a strong competitor of Isoetes lacustris in its coenoses and sometimes does not occur in them at all. The phytocoenoses of quillwort belong to the alliance Isoetion lacustris of the order Littorelletalia of class Isoeto-Littorelletea.
Characteristic taxa.
- Vascular plants: Isoetes lacustris, Ranunculus aquatilis, Sparganium angustifolium, Subularia aquatica.
Distribution in Bulgaria. Pirin Mts. – the lakes above 1900 m alt.
Conservation importance. Isoetes lacustris is an endangered species, a glacial relic that occurs only in Pirin Mts. In the composition of its coenoses can also participate some other rare and endangered plant species.
Threats. Change in the water regime of the lakes as a result of the accumulation of mud and other waste as well as the decrease of the water level; eutrophication and pollution of the lakes and the consequent turning into swamps and changing of the vegetation; climate aridisation.
Conservation measures taken. The habitat is in Annex № 1 of BDA. The localities of the habitat are within Pirin National Park and the relevant site of the European Ecological Network NATURA 2000. However, these protected areas are subjected to strong anthropogenic pressures caused by the development of tourism infrastructure.
Conservation measures needed. Preservation of the water quantity and its purity in the lakes; prohibition of swimming, boating, camping close to the lakes, construction of buildings and other facilities, water capturing, etc.; monitoring of the natural water regime of the lakes.
References. Tzonev 2005b.
Authors: Daniela Ivanova, Veska Roussakova
