Tzonev, Rossen, Marius Dimitrov, Chavdar Gussev, Vladimir Vulchev, and Ivailo Nikolov. 2018. “Classificaton of the Relict Forest Communites of Palla’s Black Pine (Pinus Nigra Subsp. Pallasiana) in Bulgaria”. Hacquetia 17 (2). https://doi.org/10.1515/hacq-2017-0011 .