Rites of Spring
Nature's patterns could help track a changing climate
By Sara Specht
Once there was a man who walked to work on the St. Paul campus each day for 50 years. And for each of those years, he watched the trees and plants on his route and took notes recording the events that signaled changes in the seasons—the first sprig of green, the early buds, the bursting flowers that signaled springtime.
It is something that many people do—remark upon the weather and the changes in the air—from avid gardeners to old friends over coffee. What makes this man unique is his individual record, consistently following the patterns of 14 different plant species from 1941 to 1991.
This man was entomologist Alexander Hodson, he of Hodson Hall on the CFANS campus, and his historical observations have become the foundation for new research into the effects of climate change on Minnesota's environment.
Armed with Hodson's record and a series of other diaries and notes from individuals and citizen scientists collected from around the state, forest ecologist Rebecca Montgomery is assembling a comprehensive historical record of seasonal plant events. She hopes to build a knowledge base that can be analyzed both to track changes in the environment and to predict and prepare for future consequences of climate change.
Spring's first blooming
It's called phenology—the observation and study of the seasonal activity of plants and animals each year. When birds migrate, when leaves appear and when plants flower are all signals of the biological rhythms of the environment, and they are closely related to climate and weather. In an era where the climate is changing, phenology can provide a way to measure how different plants and animals respond to the change and which species might be threatened by it.
"Phenology has emerged globally as one of the most coherent and widespread signals that plants and animals are sensing a difference in their environment, sensing climate change," says Montgomery, an associate professor in the Department of Forest Resources. "It made me realize we don't know that much about the phenology in our back yard. Then I found these amazing Minnesota phenologists who are passionate about tracking the changing of the seasons, and the data they had collected seemed like such a resource."
That finding and compiling of existing phenological records is just the beginning of Montgomery's project, funded by a three-year grant from the state's Environmental and Natural Resources Trust Fund. Her team is digitizing extensive collections like the Hodson record and the decades-worth of notes gathered by botanists at the Eloise Butler Wildflower Garden in Minneapolis. Montgomery also has discovered a community of northwoods naturalists and avid phenologists from around the state who have agreed to share their journals and data with her. Once the information is collated, Roger Moon, a professor in the Department of Entomology, will help analyze the patterns and compare phenological and historical temperature records.
"I'm starting with simple day-degree models to see if we can account for variation from year to year, with knowledge of what the weather was like," Moon says. "If it turns out we need to invoke other things, like day length or increasing fall chill levels, to better predict spring events, then we've already learned two things—what an individual plant needs to detect climate shifts and how to project timing of phenological events given any arbitrary weather scenario."
The temperature in Minnesota is, on average, two degrees warmer than it was in the 1940s, so how has that affected the state's environment? What if some species sense the change in seasons through day length and fall behind species that use temperature as a cue?
For instance, if one species changes the timing of its spring patterns in response to warmer temperatures—say, one tree-nesting bird nests earlier—and a second species doesn't adjust accordingly, all the nests sites may be occupied by the first, leaving the second without. This loss of nesting sites could cause the second species to decline. Highly managed urban systems also can be affected. For example, some trees might begin dropping leaves earlier than others in the fall, and corresponding changes in street sweeping schedules could improve efficiency.
"Everyone thinks, 'Oh, spring came earlier because it got warm faster,'" Montgomery says. "It's turning out that not all species have the same response to climate change—what does that mean for our ecological systems?"
The ability to predict changes in seasonal timing for individual species could identify vulnerable species, Montgomery says. Moon's data analysis will help Montgomery determine how individual species detect and react to environmental changes, and contribute to the knowledge base that informs management responses in a changing environment.
Assembling a comprehensive historical record of shifts in phenological timing is only Montgomery's first step in projecting the future of the state's environment. The next is to build an army of observers to extend the reach and consistency of phenology data into the future.
Researchers in her lab are following a broad set of plant species at the university field station at the Cedar Creek Ecosystem Science Reserve, coordinating with state and national phenology networks. Closer to home, Moon hopes to get the CFANS entomology club, Frenetae, to pick up Hodson's half-century record where he left off in 1991.
"Back in 2011, I was sitting in my house looking at my crabapple tree and was reminded of Hodson's spring events—one of them was the yearly apple bloom," Moon says. "Hodson is one of the intellectual fathers of our department. I thought it was a shame, so I'm trying to get the graduate students organized to carry on the record."
Montgomery also is beginning an outreach effort to recruit a network of citizen observers throughout the state to build a phenological record for a much larger area than her lab can cover. Beginning with training sessions about phenology practices and protocols, she and her colleagues will link the members of this Minnesota Phenology Network to a national database called Nature's Notebook that will make the information publicly available. She hopes this will give Minnesotans an opportunity to contribute real data to phenology research across the country.
"For me a part of Minnesota's natural heritage is that we have changing seasons—we're all excited when our daffodils come up or tell each other the lilacs are blooming earlier," Montgomery says. "Whether we're calling it phenology or writing it down in a notebook or entering it in a national database with an app on our phone, I feel like it can be a touchstone with the public. Teachers can use phenology as a way of educating about climate change in an era when people can get caught up in big global climate models that are hard to get a handle on. But we can say, 'Here is this aspen leafing record, and you too can go outside and look at your aspen and contribute to the research.' "