Fritz H. Schweingruber was born on 29 February 1936 in Krauchthal (Canton Bern, Switzerland). From 1956 to 1965 he was a primary school teacher and an organist in Rüderswil (Emmental). He liked teaching, but he felt a pressing curiosity for scientific knowledge, most likely initiated with his first (handmade) microscope provided by his father. During his long lasting scientific career, he opened new lines of research, explored new topics and published numerous scientific papers and books. With this obituary we do not intend to write about or cite his enormous list of scientific publications, we rather intend to present Fritz as the gifted teacher and inspiring scientist he was.
In the early 1960s Fritz read a National Geographic paper by A.E. Douglass titled ‘The Secret of the Southwest Solved by Talkative Tree Rings’ and from then on, he got more and more interested in plants, plant anatomy, and dendrochronology. At that time, he also guided botanical excursions in the Swiss Alps. Motivated by his strong interest in plant science, in 1963 Fritz started attending lectures by Hans H. Bosshard at the ETH in Zürich, although as a schoolteacher he was not allowed to enrol at a university. Fritz expressed his interest in dendrochronology to Bosshard, who then invited the tree physiologist and dendrochronologist Bruno Huber for a seminar. When Fritz told about his meeting with Huber, he always remembered that the prominent professor was very pessimistic about the future of dendrochronology as a science. Fritz took this as a good reason to get more and more involved in it. Those years were very intense and costly both for Fritz, his wife and the three children. Due to financial constraints in the summer of 1964 he decided to go back to teaching at the primary school. Suddenly Fritz got the chance of his life in 1965: the canton of Bern trained too many teachers in the years before, so they were now allowed to enrol at university. After nine years of teaching at elementary school, he was allowed to follow his urge to study the secrets of plants and the natural environment. Fritz was now officially a student at the University of Bern where he attended his first lectures at the age of 29. He studied Botany, Zoology, Geology as well as Pre- and Early History. His PhD-thesis was supervised by Max Welten at the University of Bern, where he graduated in 1972 in systematic plant sociology.
In 1971 he started working at the Federal Institute for Forest Research (EAFV), nowadays named the Swiss Federal Research Institute for Forest, Snow and Landscape (WSL) in Birmensdorf. As he often remembered, he was told to ‘do something with wood’, so he got the chance to decide his own field of research. He soon got involved in both dendrochronology and wood anatomy. Fritz decided to sample trees and visit established dendrochronologists abroad, which was exceptional for the Institute at that time. His networking idea resulted in tensions with the former WSL director Oscar Lenz, who said anyway: ‘Dä macht ja sowieso was er wott!’ [He will anyway do what he wants].
Fritz’s first scientific journey led him to Banks Island in the arctic, a five-week trip financed by the German Research Foundation. In 1976 he became associate professor at the University of Basel. This professorship was based on his habilitation titled “Prähistorisches Holz” [prehistoric wood]. Meanwhile at WSL he established an active research group on Dendrochronology. In cooperation with colleagues from the UK (Keith Briffa), and Russia (Eugene Vaganov and Stepan Shijatov) he created the northern hemispheric network for dendroclimatology. In 1986 he started teaching the meanwhile famous “Dendroecological Fieldweek” where, over the years, he trained hundreds of dedroclimatologists and dendroecologists from European countries and (quite exceptional at that time) Russia.
After his retirement from WSL in 2001, he started focusing full time on wood anatomy and teaching new generations. One result of this new focus was the international course on “Wood Anatomy & Tree-Ring Ecology”. In 2001 this first course was “
Fritz taught generations of students from many disciplines, from dendrochronology to wood anatomy, through archeobotany, anthracology and plant ecology. Hundreds of students from each discipline interacted while attending one of the dendroecological field weeks or wood anatomy courses. All students who attended Fritz’s classes have memories related to Fritz, a frequent one being “Now look through the microscope, polarizing the light, and enjoy the beauty of this section!”. Many of such memories are related to the beauty in plant anatomy, love for connecting the environment to the cellular microstructure and for understanding of physiological processes supported by those structures. However, some may also remember Fritz for his firm criticism of research methods and interpretations he disagreed with—never aimed at persons but always based on his scientific convictions.
During the 2019 edition of the “Wood Anatomy & Tree-Ring Ecology” course held in Klosters (CH), where he delivered his iconic and applauded lecture on plant evolution, he had a chat with each participant asking “What are you doing? What is your topic?” and always providing encouraging comments and advice, often followed by “Greetings to your supervisor, she/he was here many years ago!” Countless research projects started by taking the car (often full of students) off the road and looking at the vegetation nearby. There, just nearby an anonymous road he would list several possible research questions to be answer by anatomical investigation of herbs, shrubs and trees. Alan remembers the trip he had with Fritz, Jiri Dolezal and others in Ladakh in September 2015. Fritz was walking around at 5800 m asl busy identifying the plant species growing there and feeling confused because he was not able to guess their age. During the trip, he was looking forward to getting back home to cut thin sections of the specimens and count the number of growth rings. But he was also eager to stay there longer to be able to understand more about the local growing conditions of plants on the roof of the world. Having ‘muddy shoes’ was for him an approach to be proud of, as opposed to textbook-based learning. He was a fine observer of nature at different scales, from the landscape, to the anatomical details of small herbs. After describing the vegetation belts visible on a mountain slope, he often said ‘Now go on your knees, and look at this little herb, it has growth rings, therefore you can age it!’.
Over the last 20 years he focused on sampling plant material for anatomical investigations along two main transects in the northern hemisphere: from the polar regions to the Sahel, and from western Europe to the Himalayas, collecting at high elevation lands. The result is an impressive collection of double stained permanent slides that he pictured to illustrate his numerous books. It was about 20 years ago when by chance he discovered the possibility to double-stain thin sections in one step. He was then angry with some in the wood science community who he felt were responsible for hindering progress in wood anatomy by suggesting staining only with safranin. Safranin-stained sections show the anatomical details by just increasing contrast, as opposed to safranin and astrablue staining which also shows lignified and unlignified cell walls, an important piece of information. Fritz’s slide collection consisting of about 40 000 slides representing about 12 000 species will soon be available to be studied on request at WSL.
IAWA recognized Fritz’s great contributions with a belated but much deserved honorary membership in 2017. We owe him very much.
Alan Crivellaro, Department of Geography, University of Cambridge, Cambridge, United Kingdom
Holger Gärtner, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland