Old-growth forests in Bulgaria: distribution, characteristics and conservation issues

Natural diversity of relief, climate variability, geographical as well as historical reasons contribute to the presence of old-growth forest patches in various forest types in Bulgaria. For reasons of biodiversity protection, scientific studies and forest certification several projects aimed at locating and collecting data for old-growth forests in Bulgaria. Our aim is to summarize the available findings and contribute for a general map of these forests. The sources of data combine inventory data, including fieldwork collection of forest structure data by members of our team, and verification of satellite and aerial images. Most widely distributed old-growth forests in the country are Fagus sylvatica in the Balkan Range Mountains. Isolated patches of old oak forests were preserved in the lower mountains and lowlands. Coniferous forests were preserved on hardly accessible steep slopes or deep valleys in the high mountains in southern Bulgaria. Of them most impressive are Pinus peuce and Pinus heldreichii forests in the Pirin Mountains, Picea abies forests in Rila and Rhodopes Mts., Pinus nigra in the Rhodopes and beech-fir-spruce forests in isolated locations. There is also one Juniperus excelsa forest, which although affected in the past by selective logging and pasturing, still preserves the largest species locality on the Balkan Peninsula with trees often exceeding 150-200 years. Old-growth beech forests are characterized by numerous small-sized gaps. Dead wood amount largely varies depending of site condition and past disturbances but rarely exceeds 100 m3/ha. DBH distributions resemble a rotated sigmoidal curve (Zlatanov et al. 2013). Old-growth Picea-dominated forests are characterized by younger and older patches resulting from windthrows and rarely fires of various sizes. Dead wood often exceeds 70-100 m3/ha. DBH distribution is resembles J-reversed. Typical for old-growth pine forests in the Pirin Mts. is high number of live old and dead trees with DBH often exceeding 100 cm and age > 500. Most important disturbances were fires, avalanches and rarely windthrows (Panayotov et al. 2017). Numerous fire traces in old Pinus nigra forests show that they were shaped by periodic fires. However, present day fire exclusion and past management guide dynamics towards increase of deciduous species in the understory. The total amount of deadwood rarely exceeds 30-40 m3/ha. The biggest threat to old-growth forests in Bulgaria is logging, including the potentially desired sanitary fellings in National Parks. In few locations conflicts arise also from desires to expand tourist infrastructure in old-growth forests. References: 1. Panayotov et al., 2017. Abiotic disturbances in Bulgarian mountain coniferous forests - an overview. Forest Ecology and Management, 388:13-28 2. Zlatanov et al., 2013. Index for identification and evaluation of old-growth forests in Bulgaria. Forest science, 17-28peerReviewe