The site “Petrohan-Ponor” is a part of the territory of the Training and Experimental Forestry Enterprise (TEFE) “Petrohan” belongs to University of Forestry. It is situated on the northeast slopes of the West Balkan range (Berkovski Balkan) with a total area of 7192 ha. The relief of the region is typical mountain, steep, with deeply cut river valleys and secondary watersheds. The lowest point is an altitude 350 m, and highest – 1900 m a.s.l. The site has coordinates: 23°04′ N and 23°13′ E and altitude of 1470 m above sea level. The site “Petrohan-Ponor” is characterized with moderate continental climate. In the low mountain the vegetation period is about 5,5 months, mean annual temperature 8¬9° С and mean annual precipitation between 600-750 mm. In the middle mountain part the vegetation period is 4¬5 months, temperature is 5,5¬7° С, and precipitation 850 to 1000 mm. The hydrological network in the studied region is dense (rivers Burzia, Kadiiska, Gavaneshtiza etc.) with constant water flow during the whole year. The prevailing soil type in the region is brown forest soil (Distric-Eutric-Cambisols), on granite, with mean depth up to 80 cm, pH of the soil solution is 4.5 to 6.0 рН, C/N – 12-14 and the contents of nitrogen in the soil over 1%. The main tree species Fagus sylvatica L. cosists 81,7 % all area. The rest tree species are distributed as follows: Pinus sylvestris L. – 5,8 %, Picea abies (L.) Karst – 4,0 %, Carpinus betulus L.- 3,7 %, and other broadleaves – 2,0 %. The part of protective forest are high – 74,4 %, which is differentiated as area for water resources. The annual growth per ha – 5,8 m3 for beech stand 114 years old and 17,8 m3 for spruce stand 84 years old, respectively.


  • Available data

The main research topic of site is to study the reaction of trees to climate change and to make scientific forecasts for the effect of climate change to health, vitality, and adaptability of the forests. Ecosystem investigations, such as biodiversity, hydrochemical, physiological, soil, phytopathological, dendrochronological have been carried out for 30 years periodically. Photosynthesis, transpiration, primary bioproduction, structure, growth, increment, stands dynamic, precipitation chemistry, risk assessment of atmospheric pollutants are scientific topics. Hydrochemical investigations in this area include bulk and throughfall deposition of beech and spruce stands. The following parameters are observed: water quantity, рН, concentrations of NO3-, SO42-, Cl-, NH4+, K+, Na+, Ca2+, Mg2+, Pb2+, Cd2+ ions. Critical loads and their exedences for nitrogen, sulfur, acidity and heavy metals for forest soil and surface waters in the region have been determined and mapped, as a part of EMEP Bulgarian network according methodology of the International Co-operative Programme on Modelling ang Mapping of Critical Loads and Levels.

  • Facilities

The site does not have a field station, facilities, buildings. For the purposes of the studies, mobile devices for analysis, temporary deposition collectors and paid lab analyses are used.

  • Research projects
  1. Atmospheric Deposition Impact on Bioproductivity of Spruce Stands, University of Forestry, 2014-15.
  2. Stock and a role of dead biomass in beech ecosystems (Fagus sylvatica L.) in Western Balkan, University of Forestry, 2016-17.
  3. CO2 concentration impact on vitality and bioproductivity of beech (Fagus sylvatica L.) in the process of structural differentiation, 2012-14.
  4. Changes in the assimilation activity, the water regime and the state of the antioxidant protection system induced by the beech squirrel Orchestes fagi L. in the beech beet on the territory of the Petrohan, University of Forestry, 2015-16.
  5. Physiological aspects of natural regeneration in beech forests, University of Forestry, 2017-2018.
  6. Adaptation changes in common beech forests (Fagus sylvatica L.) after felling or natural disruption, University of Forestry, 2019-20.
  7. Database collection for calculation of critical loads for acidity, nitrogen, sulfur and heavy metals for Bulgaria, Executive Environmental Agency, 2016-18.
  8. Dendroarchaeology – Creating millennial rocks for dating material cultural heritage in the Balkans, National Science Fund of Bulgaria, 2017-2020.
  9. Dendrochronological analysis of the health status of off-shore oak forests, University of Forestry, 2019-2020.
  10. Environmental quality and pressures assessment across Europe: the LTER network as an integrated and shared system for ecosystem monitoring (EnvEurope), Life+Programme – LIFE08 ENV/IT 000399.
  11. eLTER (European Long-Term Ecosystem and socio-ecological Research Infrastructure), Horizont H2020, № 654359, funded by EC Horizon 2020.
  12. Subalpine forest development in Bulgaria under climate change; Funding from the Bulgarian-SWISS cooperation Programme funded by the Swiss national science foundation and the Bulgarian Ministry of Science and Education. 2013-2016; Project code: D02-16/18.01.2013 (IZEBZO143109).
  13. Natural disturbances and dynamics in pristine Norway spruce (Picea abies Karst) forests, National Science Fund of Bulgaria. Project code: DMU02/22/2009.
  14. Natural dynamics, structure and natural disturbances in Beech and mixed beech-conifer forests in Bulgaria. Project funded by the Science and Research Fund of the University of Forestry, 2018-2019.
  15. Natürliche Dynamik von Lawinenschutzwäldern, Project funded by the Velux Foundation, Switzerland; 2006-2011.


  • Main references
  1. Anev S, 2016. Comparative study on physiological potential of Pinus sylvestris L. and Pinus bungeana Zucc. ex Endl. to grow in Bulgarian urban parks. Foresry Ideas, 22(2): 188-197, ISSN:1314-3905.
  2. Anev S, 2016. Gas-exchange dynamics within the crown of Norway spruce. Forestry Ideas, 22(1): 43-48, ISSN:1314-3905.
  3. Anev S, Georgieva S, Dimitrova-Mateva P, Chaneva G, 2015. Effect of beech weevil (Orchestes fagi L.) infestation on photosynthesis and water regime of common beech (Fagus sylvatica L.) leaves. Journal of Bioscience and Biotechnology, special edition: 235-238, ISSN:1314-6246.
  4. Anev S, Ivanova A, Tzvetkova N, Panayotov M, Yurukov S, 2016. Stomatal control on photosynthesis in drought-treated subalpine pine saplings. Genetics and Plant Physiology, 6(1-2): 43-53, ISSN:1314-6394.
  5. Anev S, Tzvetkova N, 2018. Gas-exchange response of Norway maple (Acer platanoides L.) and Silver lime (Tilia tomentosa Moench) saplings to forest thinning. Foresry Ideas, 24(2): 201-207, ISSN:2603-2996.
  6. Anev S., Damyanova S., Tonchev T. , Tzvetkova N. Transmittance coefficient of leaves from different crown parts of young beech (Fagus sylvatica L.) trees. Silva Balkanica, 2015, 16(2), 53-59.
  7. Tzvetkova N, Anev S, 2012. Chapter 5. Physiological activity and net primary productivity of young beech forests In: Mirchev S (Ed.), Bioproductivity of beech forests. University of Forestry, Sofia, pp. 60-91. ISBN:978-954-332-099-8 (In Bulgarian).
  8. Tonchev, T., Dimitrova, V., Dimitrov, M., Mihov, I. 2012. Investigation of the aboveground phytomass and annual growth of the beech forests. Forestry Ideas, vol. 18, No. 2.
  9. Damyanova S., Fikova R. An assessment of heavy metal impact on aquatic ecosystems using a critical loads approach. Comptes rendus de l’Acad´emie bulgare des Sciences, 2017, 70(1), 81-90.
  10. Damyanova S. Chemical composition of a dead wood biomass in beech communities. Journal of BioScience and Biotechnology, 2017, 85-88.
  11. Damyanova S. Evaluation of atmospheric deposition at spruce stands in Bulgaria. Procedings of the International Conference on Application ofInformation and Communoication Technilogy and Statistics in Economy and Education (ICAICTSEE – 2015), 2016, 710-713.
  12. Damyanova S. Precipitation Element Fluxes at Mountain Beech Stands. Comptes rendus de l’Acad´emie bulgare des Sciences, 2015, 68(11), pp. 1393-1400.
  13. 2015. Floristic investigations of spruce (Picea abies (L.) Karst.) stands in West Balkan Mountain, Bulgaria, Journal Sustainable Development, vol. 4 (25), pp.108-112.
  14. Biomass in the herbaceous layer of spruce (Pinaceae) forest stands in Bulgaria Phytologia Balkanica, 22 (2): 155 – 160.
  15. Tonchev, Yavor Poryazov, V. Dimitrova. 2015. Aboveground biomass for norway spruce stands in western Balkan Range. International scientific confеrence “Forestry: Bridge to the Future”, 6-9.05. 2015, Book of Abstracts.
  16. Dimitrova V., Tashev A., 2019. Medical plants on the territory of Petrohan Training and Experimental Forest Range, Bulgaria. conspec. sci., vol. 84, No. 1 (37-46).
  17. Zafirov, N., G. Kostov, 2019. Main stress factors in coppice oak forests in Western Bulgaria. Silva Balcanica, vol. 20 (1), pp. 37–52.
  18. Zafirov, N., K. Banev, 2018. Dynamics of the health status of coppice oak forests in Southwestern Bulgaria. Seminar of Ecology 2018 with International Participation, April 26–27, 2018, Sofia, Bulgaria.
  19. Bräuning A., M. De Ridder, N. Zafirov, I. García-González, D. P. Dimitrov, H. Gärtner. 2016. Tree-ring features: Indicators of extreme event impacts. IAWA Journal, 37 (2), pp. 206–231.
  20. Cailleret, M., S. Jansen, E.M.R. Robert, L. Desoto, T. Aakala, J.A. Antos, B. Beikircher, C. Bigler, H. Bugmann, M. Caccianiga, V. Čada, J.J. Camarero, P. Cherubini, H. Cochard, M.R. Coyea, K. Čufar, A.J. Das, H. Davi, S. Delzon, M. Dorman, G. Gea-Izquierdo, S. Gillner, L.J. Haavik, H. Hartmann, A.-M. Hereş, K.R. Hultine, P. Janda, J.M. Kane, V.I. Kharuk, T. Kitzberger, T. Klein, K. Kramer, F. Lens, T. Levanic, J.C. Linares Calderon, F. Lloret, R. Lobo-Do-Vale, F. Lombardi, R. López Rodríguez, H. Mäkinen, S. Mayr, I. Mészáros, J.M. Metsaranta, F. Minunno, W. Oberhuber, A. Papadopoulos, M. Peltoniemi, A.M. Petritan, B. Rohner, G. Sangüesa-Barreda, D. Sarris, J.M. Smith, A.B. Stan, F. Sterck, D.B. Stojanović, M.L. Suarez, M. Svoboda, R. Tognetti, J.M. Torres-Ruiz, V. Trotsiuk, R. Villalba, F. Vodde, A.R. Westwood, P.H. Wyckoff, N. Zafirov, J. Martínez-Vilalta, 2017. A synthesis of radial growth patterns preceding tree mortality. Global Change Biology, vol. 23 (4), pp. 1675–1690.
  21. Panayotov, M., Gogushev, G., Tsavkov, E., Vasileva, P., Tsvetanov, N., Kulakowski, D., Bebi, P. (2017). Abiotic disturbances in Bulgarian mountain coniferous forests – an overview. Forest Ecology and Management 388: 13-28; doi:
  22. Kulakowski, D., Seidl R., Holeksa J., Kuuluvainen T., Nagel T., Panayotov M., Svoboda M., Thorn S., Vacchiano G., Whitlock K.,Wohlgemuth T, Bebi P. (2017) A walk on the wild side: Disturbance dynamics and the conservation and management of European mountain forest ecosystems. Forest Ecology and Management 388: 120-130; doi:
  23. Panayotov, M., N. Tsvetanov, G. Gogushev, E. Tsavkov, T. Zlatanov, S. Anev, A. Ivanova, T. Nedelin, N. Zafirov, N. Aleksandrov, A. Dountchev, P. Vasileva, V. Shishkova, B. Stoyanov, N. Sotirova, A. Vatov, P. Bebi and S. Yurukov. (2016). Mountain coniferous forests in Bulgaria – structure and natural dynamics. University of Forestry and Geosoft, Sofia, 332 pp, ISBN: 978-954-332-146-9
  24. Panayotov, M., Kulakowski, D., Tsvetanov, N., Krumm, F., Berbeito, I., Bebi, P. (2016). Climate extremes during high competition contribute to mortality in unmanaged self-thinning Norway spruce stands in Bulgaria. Forest Ecology and Management 369: 74-88.
  25. Panayotov, M., Bebi, P., Tsvetanov, N., Alexandrov, N., Laranjeiro, L. and Kulakowski, D. (2015). The disturbance regime of Norway spruce forests in Bulgaria. Canadian Journal of Forest Research, Vol. 45(9): 1143-1153, doi: 1143-1153, 10.1139/cjfr-2014-0505.


Responsible Institution:

University of Forestry

Address: 10 Kl. Ohridsky Blv., 1797 Sofia, BULGARIA

Phone: +359 2 91907/ 350

Fax: +359 2 8622830



Site coordinator:

Aassoc. prof. Sonya Dmyanova, PhD

Phone: 0886 839 493