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2. Apostolova, I., & Meshinev, T. (2000). Biodiversity of plant communities in Central Balkan National Park. In: Sakalian, M. (Ed.), Biological diversity of the Central Balkan National Park. USAID, Sofia, Pensoft: 169–267. [in Bulgarian]
3. Bern Convention (https://eur-lex.europa.eu/BG/legal-content/summary/bern-convention.html).
4. Bern Convention On The Conservation Of European Wildlife And Natural Habitats 1979. Resolution No. 4 (1996) listing endangered natural habitats requiring specific conservation measures. https://www.coe.int/en/web/bern-convention, https://www.coe.int/en/web/bern-convention/resolutions.
5. Biserkov, V., Gussev, Ch., Popov, V., Hibaum, G., Roussakova, V., Pandurski, I,. Uzunov, Y., Dimitrov, M., Tzonev, R., & Tsoneva, S. (Eds.) (2015). Red Data Book of the Republic of Bulgaria. Volume 3, Natural habitats, 422 pp.