What can Henry David Thoreau Teach Us About Climate Change?

Researchers pull from Thoreau’s findings to investigate how climate change is affecting local environments.

By Katherine Gianni and Molly Gluck

As a leading naturalist, essayist, poet, and philosopher, Henry David Thoreau could teach courses across a variety of disciplines, but it’s his observations on fruiting that has guided Boston University Professor of Biology Richard Primack and his colleagues’ latest research. In a new article in Annals of Botany, the BU plant ecologists demonstrate that there is a strong sequence of fruiting in New England plants, with species such as blueberries fruiting in mid-summer and hollies fruiting much later in autumn. The findings help inform research on the biological effects of climate change across local environments. “Our lab group has been working with Thoreau’s observations for 19 years now, and Thoreau still has more to contribute to climate change research” says Primack, co-author of the study.

The researchers have combined Thoreau’s fruiting observations from the 1850s in Concord, Massachusetts with museum records from the past 150 years across New England. According to lead study author and BU Ph.D. candidate Tara Miller, this is the first time that Thoreau’s fruiting observations have been used in scientific research. The present study was possible because pressed plant specimens — also known as herbarium specimens — have only recently been digitized in large numbers and made available online. The study finds that both Thoreau’s observations and museum specimens detect similar patterns of plant fruiting times, confirming that historical observations and data from museum specimens can be combined to create larger and more powerful data sets for climate change and ecological research. We spoke with the researchers to learn more.

Photo by Eleanor Philips on Unspalsh.

Are there any takeaways from this study that people may find surprising?

Richard Primack: It is remarkable that Thoreau’s observations from 170 years ago still have so much to teach us about the natural world. For much of his life, Thoreau spent four hours a day or more walking around Concord, Massachusetts, and later writing down observations in his journal. By comparing these meticulous records with modern observations, we can detect the signature of climate change.

Tara Miller: People may find it surprising that the order of fruiting is very similar between two very different datasets — for example, the same species, like wild strawberries, fruit early in both datasets. Thoreau’s observations and the herbarium specimens span different time periods, different geographic areas, and use different methods to collect data (observations in the field vs. collecting and preserving plants), so it may be surprising that these datasets still capture similar biological trends.

What are the long-term effects of climate change on fruiting/flowering times? Why is this important for people to understand?

Primack: Thoreau’s spring observations clearly demonstrates that plants are now flowering much earlier and birds are migrating a little earlier than in the past. Fruiting times are not changing much, but migratory birds are departing later in the autumn. So this sets up a possible mismatch between fruiting plants and migrating birds, in which migrating birds have to find alternative food sources, which might be the fruits of non-native invasive plants.

Miller: The timing of fruiting is important because plants with fleshy fruits rely on animals to disperse their seeds to reproduce, and the animals rely on fruits for food. If the timing of fruiting changes, then peak fruit availability might not line up with when animals need the food (like when birds are migrating through, or when mammals are preparing for hibernation). Then plants may have fewer seeds dispersed and animals may have less food to eat.

Photo by Chandan Chaurasia on Unspalsh.

You note that your lab has been working with Thoreau’s observations for almost two decades and there is still more to learn from his findings as they relate to modern climate change research. From your perspective, what else could we continue to learn from Thoreau’s research and how does it impact how we think about climate change or other prominent environmental issues?

Primack: We continue to use Thoreau’s observations to gain new insights into the ecological effects of climate change. For example we now know, using Thoreau’s observations, that trees are more responsive to a warming spring than are wildflowers. This might cause trees to leaf out extra earlier and shade out wildflowers, causing their populations to decline. We are currently working with plant physiological ecologists to test these ideas experimentally.

Miller: We haven’t yet compared Thoreau’s fruiting observations to modern field observations of fruiting times. This is a new study that could be done to learn how fruiting times are changing with climate change in Massachusetts. Thoreau is well-known as an environmental thinker and philosopher, but his scientific work is less well known. By using his scientific observations in modern research, we’re able to connect to new audiences and communicate climate change research to people interested in history, philosophy, literature, and more.

Why is it important to digitize resources such as plant specimens when it comes to this type of research? What role do visual assets play when it comes to understanding/expanding your work?

Miller: Museum specimens are a rich source of information. I can sit at my desk and pull information on hundreds of plant species from across the United States. It really expands the scope of our research to be able to access specimens online rather than travel to every individual museum which holds specimens.

Primack: Digitized specimens also allow us to take a local fruiting study from Concord using the observations of Thoreau, and determine if the same pattern is happening across New England. With our study of trees and wildflowers, we are even using digitized specimens to expand our study area to include all of eastern North America.

Primack’s more recent research, published in Methods in Ecology and Evolution, reinforces the value of museum specimens. Along with an international team of researchers, Primack analyzed 1.4 million field observations and 73,000 museum records of over 22,000 species — and uncovered that museum collections of plants and animals provide a reliable reflection of most species’ abundance in the wild. This new approach of using museum records to study outdoor species will enable scientists to monitor species that are declining over time, and wildlife that needs extra protection in order to avoid extinction. It will also allow conservation biologists to study how the abundance of species changes over time due to disturbances including climate change and urban development. This approach will provide more insight into how ecosystems are responding to environmental changes as millions of museum specimens continue to become digitized and made accessible online.

In January, 2022, Primack’s team published a total of 13,441 phenological records in Ecology, spanning 118 years, with observations of many species including flowering plants, ferns, gymnosperms, and birds. Their latest research release also provides relative abundance data for an additional 200 plant species. The team hopes that scientists will use the dataset to better understand how plants and animals have altered their spring activity since the time of Thoreau.

Image credit: Richard Primack

Most recently, Primack and his team evaluated Thoreau’s observations using a three-step framework: assessing the rigor, accuracy, and utility of his data to investigate changes in plants and animals over time. Their research, publishing in BioScience, aims to provide both a better understanding of the quality of Thoreau’s work as a naturalist, and whether the historical data is appropriate to apply to answer current ecological questions. The research team concluded that Thoreau was in fact an accurate observer of nature and reliable scientist and describe how their approach can be used to evaluate other naturalists.

For additional commentary by Boston University experts, follow us on Twitter at @BUexperts. For research news and updates from the Primack Lab at Boston University, visit http://primacklab.blogspot.com/.



Cutting-edge research and commentary out of Boston University, home to Nobel laureates, Pulitzer winners and Guggenheim Scholars. Find an expert: bu.edu/experts

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BU Experts

Cutting-edge research and commentary out of Boston University, home to Nobel laureates, Pulitzer winners and Guggenheim Scholars. Find an expert: bu.edu/experts