Distribution, Characteristics and Ecological Role of Protective Forest Belts in Silistra Municipality, Northeastern Bulgaria

Protective forest belts are developed as a defense against dry winds and soil moisture loss and considered as natural capital nowadays. Silistra municipality's protective forest belts were investigated about their distribution, floristic composition, vegetation structure and syntaxomony. During 2018 field season 32 relevés were collected following the Braun-Blanquet approach. Data about diversity of invasive and melliferous plants were collected also. Vegetation types were identified by numerical classification using hierarchical agglomerative clustering (PC-ORD). Descriptive statistics about the cover of tree, shrub and herb layers as well as cover of invasive and melliferous plants were graphically summarized in vertical box-and-whisker plots. The forest belts syntaxonomical diversity is represented by 2 associations (Cotino coggygriae-Quercetum cerris, Bromo sterilis-Robinietum) and Amorpha fruticosa-Morus alba plant community. Cotino coggygriae-Quercetum cerris has closed horizontal structure with dominants Quercus cerris and Cottinus coggygria in tree and shrub layers respectively. Bromo sterilis-Robinietum is characterized by poor species composition and vegetation dominated by Robinia pseudoacacia and Fraxinus americana, whereas Amorpha fruticosa-Morus alba community has local distribution and represents a final stage of vegetation degradation. Totally five alien species (Acer negundo, Amorpha fruticosa, Erigeron annuus, Fraxinus americana and Robinia pseudoacacia) and 26 melliferous plants were identified within the forest belts. The highest cover of invasive species and melliferous plants were found within Bromo sterilis-Robinietum and Amorpha fruticosa-Morus alba. The main melliferous plant species were Robinia pseudoacacia, Amorpha fruticosa, Morus alba and Prunus cerasifera. The investigated forest belt vegetation bears the characters of a long-standing anthropogenic impact. They have been subject to cutting, burning and pasturing during the last 50-60 years.