Elm forests in North Bulgaria and conservation strategies.
From the genus Ulmus, the naturally spread species in Bulgaria are Ulmus minor, U. laevis, and U. glabra. The main reason for the decreasing of the number and density of the elm populations in Bulgaria are the epyphytonic expressions of the Dutch elm disease (DED) (caused by Ophiostoma ulmi) in the 1920s and 1970s, after which the representatives of genus Ulmus today occur predominantly as solitaire trees, biogroups and rarely form stands. In connection with the preservation of the genepool of the elms after the in situ method, an inventory of their genetic resources in North Bulgaria has started in 2002. To study the variability according to morphological signs and health status 17 permanent sample plots have been established and 60 plus trees have been determined. For the needs of the afforestation six seed stands were established. The ex situ conservation method was carried out through clone collections, progeny trials and experimental plantations.