The Science of Seasons on an Out-of-Sync Planet

On the fourth day of April, I shoveled snow off the sidewalk in front of my house in Madison, Wisconsin. As I dragged my snow boots out of the back of the closet where I thought they were safely packed away, I had to wonder, when will spring arrive? Before I woke up to several heavy inches of large white flakes, winter had seemed to be on its way out. While half of the country was bursting into bloom during an early spring, the rest of us were anxiously waiting for a day we didn’t need a heavy coat.

Although the sweltering temperatures today may make it difficult to remember, spring came late and wet to southeast Wisconsin this year. Many farmers across the state had to postpone planting in the soggy fields, which threatened both crops and profits. Then just a few weeks later in May, temperatures in Madison and Milwaukee soared to record-breaking 95 degrees. The unusual heat wave lasted for three days.

Weather isn’t the same as climate, of course, but patterns have been disrupted, and we humans aren’t the only ones affected. Many plant and animal species use temperatures to guide their life cycles, and anthropogenic climate change has altered the signs that tell them when to nest, migrate, breed, and bud. We know this because the USA National Phenology Network tracks phenological events of “nature’s calendar,” keeping a record of the “firsts” and “lasts” that occur throughout a year and allowing scientists to establish a sense of how species respond to natural cues such as temperature and day length. Both professional and citizen scientists participate in creating these data sets.

Do you notice the first time you hear a red-winged blackbird? For me, it is a welcome sign that spring is around the corner. Unfortunately, I can’t identify all the birds that start arriving in the tall dry grass along the lakes. Luckily, there are other people who stop in their tracks and take note as they hear the first bird song they recognize. When spring arrives, people all over the world take pictures to post to Instagram, Facebook and Twitter, as well as to online forums and websites such as the Phenology Network. Some document the first bird songs and sightings of the year. Others are drawn more towards the flora and notice the first crocuses and budding trees. There is a second bloom on the internet after the first bloom on the land. These actions are all part of phenological record-keeping.  Time lapse maps  telling us when spring has sprung, for example, are a direct result of citizen scientists reporting when the first leaf turns green or the first bloom blossomed.

Briefly noticing or snapping a picture of these first birds and buds of spring is one thing, but detailing the waves of new flora and fauna each season is an entirely different undertaking. One family made the systematic practice of phenology part of their daily routine. From their country home on the Wisconsin River, the Leopolds were prolific writers introducing generations to ecological thought and land stewardship. With their data, we can track not only how ecological communities existed in the past but also how they exist, now, in our changing present.

Aldo Leopold’s Phenology

Aldo Leopold was the first chair of the Department of Forest and Wildlife Ecology at the University of Wisconsin–Madison. His work and writings have inspired countless environmentalists, conservationists, and nature-goers. Leopold’s phenology is famous; he took extensive notes and kept meticulous records.

Leopold lived in Madison during the work week, but on the weekends he would go out to a shack on land that he and his family owned up in Baraboo on the Wisconsin River. There he would rise early in the morning and just observe and document the birds and plants that emerged that day. Almost 80 years later, ecologists recreated a soundscape of Leopold’s shack using the data that he took from this one particular spot.

The audio was created using the ecological and species identification expertise of Professor Stan Temple and the audio knowledge of Chrys Bocast, a graduate student and acoustic ecologist at the Nelson Institute for Environmental Studies at UW–Madison. The soundtrack transports the listener to a spring morning along the sandy shores of the Wisconsin River in the 1940s. This was the first time that today’s ecologists could experience what Leopold had decades earlier. It was also a way for the scientists to hear the differences in the acoustic landscape, not just see it on paper or graphs. Phenological records—records kept both then and now—allow scientists like Temple and Bocast to bridge the gaps between environmental past, present, and future.

Recreating a soundscape was not the only thing that came from Leopold’s phenology and his morning ritual of note-taking. In a serendipitous turn of events, one of Leopold’s daughters, Nina Leopold Bradley, returned to Madison in her later years and started spending time at the shack on the banks of the Wisconsin River. There she was able to continue her father’s legacy of stringent notetaking in observing the “firsts” of everything she saw out at the shack.

Their data were compiled in a study using both Leopold’s phenology and Henry David Thoreau’s observations of the species surrounding their respective homes. A paper by Elizabeth Elwood, Stan Temple, and others published in 2013  showed that—in Baraboo, Wisconsin and Concord, Massachusetts, at least—species were flowering earlier than in previously recorded history. This study showed that if species are flowering in relation to temperature, they are more sensitive to rising or erratic temperature, rather than other seasonal indicators such as sunlight. This finding by itself is important. Plants, however, also exist in a larger ecosystem. A change in plant phenology has the possibility to impact not just others in the plant community, but also the animals and people that exist within those ecosystems.

Using Phenology to Identify Ecological Mismatch

The Leopolds recorded data with a pen and field notebook and then went back to that data to look for patterns. This created not just a resource for their own observational work but also a great resource for the public. There are few scientists and writers that documented their daily observations so thoroughly. The Aldo Leopold foundation and University of Wisconsin received a grant in 2007 to take on the task of digitizing his records. This includes journals, letters, and drawings from his earliest years. Anyone can search through the entirely digitized records in the University of Wisconsin Archives.

Currently, scientists are following in the Leopold model of observation to find many examples of phenologically-based disruption within ecosystems. While some flowering plants respond to changes in temperature to direct them in their yearly cycle, other species such as birds use clues from the sun. This is an example of a phenological mismatch. Mismatch in timing may not matter much for a few species, but it could have potentially devastating impacts for others and change the demographics of ecological landscapes. Alterations in the composition of plants, animals and insects in an environment could produce wide-ranging—and perhaps unwelcome—effects. For example, rising temperatures are changing when insects emerge and interact with flowering plants. Because humans rely on pollinators for a functioning food system, this phenological mismatch could have significant consequences. Other insects that humans are not as fond of, such as crop pests, are also reacting to higher nighttime temperatures and milder winters, so pest pressure ends up being higher in the growing season.

Both Nina Leopold Bradley and A. Carl Leopold, one of Aldo Leopold’s sons, noticed potential phenological mismatches. They used their father’s phenological records as well as their own from Wisconsin to highlight spring events happening earlier every year. They also made clear in their study that rising temperatures only impacted some species. Other species used other yearly events, such as photoperiod, or day length, to time their life cycle events. This meant that species such as birds were not fitting in seamlessly with the plants they use to make nests or eat.

One of the most striking impacts of a phenological mismatch occurs in agriculture. In Finland, tractors and birds are now in the fields at the same time for the first time, causing harm to the bird populations. The warmer temperatures have caused farmers to get out into the fields earlier in the season, while the ground nesting farmland birds are still nesting during the same time of the year. In the past, the ground nesting birds would have already had their fledglings hatched and mobile. However, with tractors in the fields earlier, the eggs in the nests are completely defenseless against the formidable farm equipment.

Another example of phenological mismatch involves not just two species, but three. Kodiak brown bears now have two of their favorite foods coming into season simultaneously. Red elderberries are reacting to the warmer temperatures in Alaska and ripening earlier in the season, while salmon are still spawning in streams. Berries and salmon are available at the same time, for the first time, and the bears are choosing the fruit over the fish. This impacts both the stream ecosystem and the entire forest. The nutrients bears once gained from the salmon are no longer brought onto the land and instead remain in the water.

Phenological mismatch affects human behaviors within the ecological community as well. This winter, with an early cold snap and a mild winter a year before, residents in Vermont did not stock as much wood as they had in previous years. This led to wood shortages and residents having to turn to more expensive alternative fuels to heat their homes for the remainder of the winter.

Using Phenology as a Tool in a Changing Environment

In recent decades our climate has been changing at a much quicker rate, and in a more tumultuous way, due to human influence—mostly from actions in developed countries. With the advent of the internet we can bring the dynamic climate close to home. At the touch of a button, we can see how hot the average daily temperature was last summer compared to the one before that. Phenological data, which can now be shared over the internet with citizens as well as scientists, can help societies chart these changes and take preemptive action.

Phenology is one science that everyone can take part in, making it part of a diverse array of citizen scientist initiatives. Urban and rural, young and old are participating. It does not take thousands of dollars of equipment or complex laboratories and protocols. All it needs is for someone to take note of the first time they see a bird in the spring or a muskrat silently paddling through a recently de-iced lake. Such observations are more important than they might seem. We are better able to understand the impacts climate change is having on specific communities if we pay attention to the small details that make up a larger whole.

It is alluring to think that Aldo Leopold—knowingly or unknowingly—in his phenological work saw how the first bud was an indicator of a whole community. In “The Ecological Conscience,” Leopold writes, “The practice of conservation must spring from a conviction of what is ethically right, as well as what is economically expedient. A thing is right only when it tends to preserve the integrity, stability, and beauty of the community, and the community includes the soil, waters, fauna, and flora, as well as people.”

When a group of ecologists hears what the sandy shores of the Wisconsin River sounded like 80 years ago from Leopold’s phenological notes, it alerts them to what has changed as humans have altered the landscape. Such replications inform people to what has changed and they can be useful tools in creating more sustainable societies. The climate is constantly changing and phenology is one of the links that shows us how the climate instigates change. It is not only the temperature that is fluctuating but also the relationships between the flora and fauna that create the ecological community.

Featured image: Shortly after the ice has melted, a red-winged blackbird comes to rest on the edge of Lake Monona. Photo by Jamie Bugel, 2018.

Jamie Bugel is a master’s student in the Agroecology Program at UW–Madison. She has worked in agriculture in Pennsylvania, Kansas, and now Wisconsin for the past five years. She researches plant breeding for flavor in sweet corn and plans to work in sustainable approaches to land practices after graduating. Wisconsin winters have made her even more interested in phenology and seasonal changes, especially those that mark spring. Instagram. Contact.