USE OF HIMALAYAN BIRCH (BETULA UTILIS) IN LANDSCAPING IN BULGARIA - BENEFITS AND RISKS

The Himalayan birch (Betula utilis) is a valuable exotic species for landscaping, possessing a number of medicinal properties. Unfortunately, this is one of the host plants of the highly aggressive pest Japanese beetle (Popillia japonica), which has not yet been registered on the territory of the Balkan Peninsula. The aim of the present study which is held in September, 2024 is to present current data on the import of Himalayan birch in Bulgaria, the possibilities for its use in landscaping and the risk associated with the spread of the invasive Japanese beetle on the territory of the country.

To achieve the aim of the study, the following tasks are set: 1. Study of the import and distribution of the species for the needs of landscaping on the territory of Bulgaria; 2. A case study of an artificial plant community in the region of Lomazzo (North Italy) where the species Betula utilis var. jacquemontii (Spach) Winckler dominated the tree layer and is in poor health status. 3. Assessment of the defoliation of B. utilis individuals (in %) 4. Identification of the potential benefits and risks of using B. utilis in Bulgarian horticultural practice.

The survey shows that some garden centers and horticulture stores in Bulgaria (mainly in the cities of Sofia, Varna and Plovdiv) offer B. utilis and its subtaxa such as B. utilis 'Doorenbos' (form of Betula utilis var. jacquemontii), B. utilis 'Long Trunk' (weeping form). Both- whole individuals and graft plants are imported from Romania, Italy and the Netherlands. At the current stage, the species is distributed on the territory of the country in small quantities - single units intended for private home gardens.

The studied artificial plant community on the territory of Italian town Lomazzo has a clear three-layer structure and a mosaic distribution of the dominant heliophyte species. The total coverage of the tree floor is about 55%, and it is dominated by B. utilis var. jacquemontii (35% projected coverage), Over 80% defoliation of the crowns is recorded in all individuals as a result of an attack by Popillia japonica. For the rest of the plant species in the community, a large part of which are also found in Bulgaria at that stage, no damages caused by this pest were detected.

The conditions in Bulgaria at the moment (and given the climatic prospects) are far from the ecological requirements of the Himalayan birch, but nevertheless it is clear that its subtaxa are already being imported and planted in our country. This makes the species a potential vector for the expansion of Japanese beetle range. Therefore, along with the valuable decorative qualities and medicinal properties, the use of the Himalayan birch in landscaping carries some serious risks, the most significant of which is its vulnerability to Popillia japonica, and for this reason its import to our country as a decorative species must be strictly controlled.