Remembering ecologist Margaret Bryan Davis (1931–2024)

Abstract

Margaret Bryan Davis, a prominent ecologist, died on May 22, 2024. She was a Regents Professor at the University of Minnesota and a member of the National Academy of Sciences. Her students remember her as a creative and clear-thinking scientist who combined the tools and perspectives of paleoecology with ideas and problems of ecology in order to understand long-term forest dynamics. She was a champion of diversity and equity in science.

Margaret Bryan Davis (October 23, 1931—May 22, 2024) will be remembered as a scientist who contributed greatly to expanding paleoecology from a subdiscipline of Quaternary science into the realm of community ecology. She is also recognized as a champion of diversity and equity in science and for excellence in mentoring students, postdocs, and junior scientists. Margaret’s work at the intersection of Quaternary paleoecology and ecology strengthened both disciplines. To ecologists, she demonstrated the importance of thinking on long time scales, and to paleoecologists, she introduced the subtle complexities of ecology. Margaret’s writing was clear and free of jargon, resulting in many of her papers becoming classics in long-term studies of community stability and species invasions and building a foundation for many of today’s questions about ecological responses to a changing climate.

Margaret Bryan Davis, happily working with rope during a winter coring trip in Sylvania Wilderness. Image Credit: Randy Calcote (photographer).

This retrospective is written by four of Margaret’s former graduate students whose careers at the University of Minnesota overlapped in the 1980s and 1990s. We remember Margaret as an excellent and sometimes difficult advisor who had a major role in shaping who we are now. She was an independent thinker and expected the same of her students, believing that students should design their own research projects and secure funding for their work. The Davis lab was a cheerful, supportive place: students, postdocs, and Margaret regularly gathered at the corner table by the window for lunch and a weekly journal club. Margaret set an example by approaching research with curiosity, humility, rigor, and pleasure, emphasizing the importance of questioning and testing assumptions.

Margaret was born in Cambridge, Massachusetts, in 1931, the youngest of four children. Her father, Kirk Bryan, was a geologist and geographer at Harvard University. Margaret saw that her dad was having fun being a scientist, and she preferred that lifestyle to the options most women had at the time. Her father told her that women should not become scientists, but Margaret clearly disagreed. With a B.S. from Radcliffe (1953) and a Fulbright fellowship to study palynology at the Danish Geological Survey at the University of Copenhagen (1953–1954), Margaret completed her Ph.D. at Harvard (1957) under the mentorship of Hugh Raup, ecologist and director of Harvard Forest.

Before joining the faculty of the University of Minnesota in 1976, Margaret was on the faculties at Yale and the University of Michigan. Her accomplishments led to many leadership roles and academic honors, including being elected President of the Ecological Society of America (1987–1988) and the American Quaternary Association (1978–1980) and named Regents’ Professor at the University of Minnesota (1983), fellow of the American Academy of Arts and Sciences (1991), and member of the National Academy of Sciences (1982).

Scientific Accomplishments

Margaret was a leader in shaping Quaternary paleoecology into a field that demands rigorous calibration and experimental design. Her first major achievement was to develop correction factors to transform pollen percentage data into quantitative estimates of tree abundance. Her analyses of R-values, the ratio of the percentage of a taxon in a pollen sample to the percentage of that taxon in the surrounding vegetation, influenced pollen-based vegetation reconstructions for decades (1–3). Her quest to improve the interpretation of pollen data also led her to pioneer the calculation of pollen accumulation rates (4, 5) and consider the effects of sediment focusing in lakes (6).

One of Margaret’s earliest and most important contributions to ecology was to demonstrate that forest communities did not function as units, marching northward as the climate warmed after the last glaciation. Rather, the sensitivity of individual tree species to climate changes, local soils, and ecological interactions shaped the reorganization of forest communities over time. The question of whether ecological communities are tightly coevolved units or shifting assemblages of individual taxa was not new. Margaret settled the issue by mapping the dates of increase in pollen of different tree taxa across the eastern United States over the time since glaciation. These maps convincingly demonstrated that tree species shifted their ranges northward at different rates and by different pathways. She also established that the forest communities we see today formed relatively recently and are still changing (7).

One of the things we admire most about Margaret’s work is her career-long persistence in designing research that tested the influence of ecological interactions on species ranges and community dynamics under a changing climate. In a classic paper from 1981, Margaret proposed an ecological, rather than climatic, explanation for the abrupt decline of hemlock pollen percentages at sites throughout eastern North America about 5,000 years ago (8). She hypothesized that a hemlock-specific pathogen or insect outbreak was the cause of the decline, and in a follow-up study, her research group documented the similarity of the hemlock pollen decline to the rapid decline in elm pollen due to Dutch elm disease in the early 20th century (9). As was often the case, Margaret’s insights dominated the conversation about the hemlock decline for decades. More recent studies have demonstrated that there were also climate changes at the time and that Margaret’s hypothesis and its logic remain relevant (10).

A major ecological issue in the 1980s concerned the degree to which species’ ranges were out of equilibrium with climate (11–16). Margaret designed a set of observations to determine how closely hemlock and beech, two tree species with very different dispersal characteristics, tracked climate change as they migrated into the midwestern United States over the past 8,000 years. Using this natural experiment to test an ecological hypothesis required concurrent studies of the spatial resolution of pollen data in order to design and test methods of tracking changes in species range limits over time (17, 18). By developing a network of sites across Michigan and Wisconsin, Margaret and her students demonstrated that hemlock, with its wind-dispersed seeds, established populations west of Lake Michigan earlier than beech did, with its relatively large, animal-dispersed seeds (19, 20).

Margaret continued to challenge the spatial resolution of pollen data in a study of the long-term dynamics of a remnant old-growth forest in the Sylvania Wilderness of upper Michigan. The forest is heterogeneous, with some patches dominated by hemlock and yellow birch, while others are primarily sugar maple and basswood. Using pollen collected from small basins under the forest canopy, Margaret’s lab demonstrated that the modern mosaic formed on a preexisting template: hemlock established in white pine stands, which then remained hemlock-dominated for 3,000 years. Preexisting stands with more oak trees developed into modern maple-basswood stands (21). Although observations of modern feedbacks are sufficient to explain the maintenance of the forest mosaic today (22–24), understanding long-term stability and change in these forest communities could only be achieved using paleoecological tools, which in turn required both theoretical and empirical studies to develop and test the reliability of pollen interpretations at the spatial scale of individual forest stands.

When the first general circulation models were used to predict the global climate impacts of doubling atmospheric CO₂, Margaret applied the logic of species’ responses to previous climate changes to make predictions about how forests will respond to future climate change (25, 26). Underscoring the importance of a paleoecological approach to ecological thinking, she argued near the end of her career that the rate at which a species adapts to environmental change will affect its population growth and dispersal—and hence migration rate, probability of extinction, and productivity of local vegetation (27, 28). Margaret foresaw that combining an understanding of community dynamics from the past with studies of modern populations using molecular tools would contribute to more effective assessments of the ecological effects of future global change.

Equity and Diversity

Margaret was a tireless champion for gender equity. At the University of Michigan, she fought for pay comparable to her male colleagues, a request that was addressed only after the threat of a lawsuit. She continued to advocate for gender equity in pay at the University of Minnesota, and there she was asked to chair a committee to investigate salary discrepancies based on gender. The report of the committee to the Board of Regents concluded that “Unredressed grievances have wasted the talents of highly valuable faculty and staff, and the resulting adversarial processes have created an atmosphere of antagonism and mistrust…. Equity and diversity are among the keys to excellence, and proactive leadership on these issues will strengthen the University as a whole” (29).

A Full Life

Although Margaret occasionally appeared at Halloween events in costume and hosted parties for which she wrote songs and made food-based sculptures of imaginary creatures, she was generally quite reserved. She seemed to be most at ease while walking through the forest on field trips to Sylvania. On these occasions, she could be mirthful, singing, and telling stories. She particularly enjoyed pecan sandies and her thermos of coffee while out in the woods.

At home, Margaret enjoyed classical music concerts, gardening, and canoeing or skating on Minneapolis lakes. Her creativity was not limited to science. She enjoyed woodworking and once built a harpsichord. She also built a greenhouse on the side of her Minneapolis house and a round dining room table for her cabin near Sylvania. In her retirement, she moved to Arizona, where she rekindled her interest in landscape painting, and then to Colorado.

Margaret’s creativity, persistence, and rigor shaped the trajectories of modern ecology and global change research. With these qualities, her drive to work toward justice, and her wry sense of humor, Margaret continues to inspire us.