Hans Trass is a distinguished lichenologist, botanist and ecologist. He was born on 02 May 1928, and studied at Tartu University. His Candidate’s thesis, which in the Soviet system actually corresponded to a PhD thesis in most countries, was completed in 1955, and dealt with vegetation structure and dynamics in eutrophic fen ecosystems of western Estonia. He had already been the head of the Department of Plant Systematics and Geobotany of Tartu University for more than ten years when, in 1969, he finished his Doctor’s thesis, entitled “The analysis of the Estonian lichen flora”. In 1971 he became a Professor and continued his work as head of the department up to 1991. From 1991 to 1993 he was an extraordinary professor; presently he has retired from the position of professor, but continues his work both as a teacher and researcher, being a professor emeritus of the same department.

Hans Trass has published numerous papers on lichenology, vegetation ecology, plant geography, and the history of science. The list of earlier papers has been published in 1988 (Bibliography of the published papers of professor Hans Trass, 1988, Tartu University Press, 82 pp.); the last ten years have added almost fifty papers more. He has been engaged in many studies of vegetation ecology. Among the most cited papers, one has to mention, for example, a major article on vegetation classification in the ‘Handbook of Vegetation Science’, edited by R.H. Whittaker, published in 1973. In 1976 Hans Trass published a book: ‘Vegetation Science: History and Contemporary Trends of Development’, which has been a guide to vegetation ecology for a whole generation of plant ecologists. Very unfortunately, the English translation of this book, which was prepared by Academic Press, was never published due to the resistance of Soviet bureaucracy.  He has studied the lichen flora of Estonia, and as a result of the long term work of the whole research team, a book ‘Estonian Macrolichens’, edited by H. Trass and T. Randlane, was published in 1994. In addition to lichenological research in Estonia, Hans Trass has led expeditions to remote areas of Russia, such as the Murmansk Region, Kamchatka, the Sikhote-Alin Range and other areas in the Far East, Lake Baikal and the Taymir Peninsula in Siberia, Kazakhstan and the Caucasus Mts, arctic zones of Finland and Canada, etc. He especially promoted the study of lichens as pollution monitors, e.g. in 1968 with a paper entitled “An index for the utilization of lichen groups to determine air pollution”. He developed his own Index of Poleotolerance (IP) based on lichens, and several of his students are continuing the work. Hans Trass also contributed to the Handbook of the Lichens of the USSR by publishing the accounts of three families in it.

Hans Trass has kept numerous direct contacts with ecologists and botanists all over the world. During the soviet years, the establishment of international contacts and the exchange of scientific information were rather complicated and, in many cases, science in Estonia developed in isolation. Hans Trass is someone who always tried to work within the framework of  ‘world science’. His creativeness and activity on an international level resulted in a good standard of botanical and ecological science in Estonia. Presently there is a whole group of active young and middle-aged scientists in the field of plant science in Estonia, many of them students of Hans Trass. In particular, Hans Trass maintained good relations with both Russian and western lichenologists, often acting as a bridge of knowledge between them, to the benefit of ecology and botany. In the east he was known for his excellent lichen library and by Russian students was regarded as a “western professor”.

Last but not least, Hans Trass has not been just a "dull scientist", regarding nature only as an object of research. For him, nature has always been a source of inspiration. In this connection, nature protection has always been one of Hans Trass's main interests, beginning his contribution to the establishment of the nature conservation movement in Soviet Estonia in the fifties, up to his recent activities in the protection of virgin forest ecosystems in Estonia in conditions of rapidly developing forestry. 

Hans Trass has been PhD thesis supervisor for the following persons:
S.Liiv, currrently a researcher in the Botanical Garden of Tallinn
J.Martin, currently a vice rector of the European University
T.Randlane, currently an associated professor in lichenology, Institute of botany and ecology, Tartu University
A.-L.Sõmermaa, currently an associated professor, Institute of Plant protection, Estonian Agricultural University
M.Zobel, currently a professor of plant ecology, head of the Institute of Botany and Ecology, Tartu University
K.Zobel, currently an associated professor in plant ecology, Institute of Botany and Ecology, Tartu University
H.Tamm, currently a director of the Botanical Garden of Tartu University

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