Phenology and the arrival of spring

I haven’t written anything on this blog for awhile. I got busy with work. I had bronchitis. I was also playing music and enjoying some downtime. My priority was completing (and even enjoying?) the many end-of-the-year academic tasks and celebrations that are part of my job and the rhythms of family life. And in the meantime, I persistently monitored the arrival of spring.

Spring is my favorite season. After a gray, cold, and damp winter, I always relish the arrival of milder temperatures, colorful plant growth, and the soundtrack of birds. Starting in March, I keep a nearly daily watch for any new signs of spring: a little green sprout here, a flower there, the shift toward consistently longer daylight hours and weather forecasts that breed optimism rather than gloom. And spring always arrives! Not always when I feel I most need it, and not with daily consistency, but gradually the season shifts and another winter comes to a close.

Daffodils (Narcissus) are an early bloomer in spring in North America. Own photo (© Erin Gerecke).

Some years ago, I learned the word phenology. It’s a lovely word, I think—it rolls off the tongue and has that official “-ology” at the end. Phenology is the study of the timing of aspects of living things relative to climate and other environmental factors. Phenology can also refer to the organismal activities and responses themselves. Scientists who study phenology look at flowering, mating, hibernation, migration, and other seasonal or annual features of plants, animals, and other types of living things. It’s an area of scientific inquiry deeply rooted in some of the most fundamental questions of survival on a planet that rotates on a tilted axis relative to the sun. How do daily light and temperature patterns shift with the seasons in different habitats around the world and impact living things? Phenology also covers the curious questions of a child—or of a scientist in her own backyard: How do the daffodils know it’s time to emerge from the soil, and then bloom? Why do the tulips lag a few weeks behind? How do robins know to return and claim their iconic role as “the harbinger of spring,” and then find a mate and make a nest later in the spring? Why do my twin buckeye trees leaf out before all the other species in my yard, bloom, create their iconic nuts…and then drop their leaves in July or August, rather than October or November? How do some plants “know” to drop their leaves at all? The answers vary—or may be poorly understood in some cases—but they tend to center around how organisms monitor daylight hours and/or temperature changes that accompany the seasonal transitions.

Leaves beginning to open on a buckeye tree (Aesculus glabra). Own photo (© Erin Gerecke).

The general reliability of phenology in our daily lives provides the backdrop for our own experiences with seasonal change. From winter to spring, spring to summer, and then the slow retreat of autumn to another winter—or sometimes abrupt changes that leave us startled: these patterns of seasonal change and the corresponding responses of living things are part of our own environment. They’re also part of our agricultural seasons: understanding the timing of plant growth, pollination, and maturation are critical to maintaining a garden or a large-scale food supply. We learn to understand the phenological responses of the organisms with which we share our habitat and rely on their behaviors to mark the inevitable passage of time.

Phenology focuses on two major categories of environmental factors: light and temperature. Together, these parameters create the climate features of a particular geographic area over the short and long term, and thus the responses of living things to that climate. The Earth’s climate is changing, though, due to increased levels of CO2 and other greenhouse gases that are thickening our atmosphere and warming the surface of the planet. (For more on my thoughts on climate change, see this blog post from 2018.) Just this past week, we recorded the highest concentration of atmospheric CO2 in the experience of humans on the planet: 415 ppm. Scientists have been busy trying to figure out what a change in temperature means for overall climate features in different parts of the planet, and how organisms will respond in turn. We know organisms can adapt to changing environments through natural selection and other forces. But we also know that adaptations and interactions in natural ecosystems honed over very long periods of time are in careful balance, and the likelihood of negative impacts from an abrupt change in the environment is high. And so, much new scientific research is focused on phenology and climate change: a quick Google Scholar search turned up thousands of research articles in 2019 alone. Here’s a brief list of interesting topics: grapevine plants (wine, anyone?), African bird migration, agricultural pest management, forest fires, butterflies, leaf growth in European trees, fish spawning, phytoplankton, invasive species…even pollen and seasonal allergies. The list goes on and on. While we don’t have definitive answers about the resiliency or risk for most species to the effects of climate change on phenological adaptations, it’s clear that scientists are making this area of research a priority.

Living in balance and harmony with our ecological neighbors has become a regional and global challenge for a growing and expanding human population. And yet, we rely on our incomplete understanding of plants, animals, fungi, bacteria, and protists to feed us, house us, prevent and treat illness, and so much more. So the curiosity and wonder that accompany spring have become the base of a vigorous line of formal scientific inquiry in the face of climate change. As we learn more about the intricacies of the world around us, we understand more about the special planet we call home, and what we need to do to live sustainably and prosperously upon its surface alongside other species. So I don’t feel too silly when I stop and smell the flowers, marvel at the green things, welcome the spring—and then remember to consider the work going on behind the scenes to fill in our understanding with new connections and ideas for the future. Many aspects of our changing world may depend on the answers.

Lilac (Syringa vulgaris) flowers smell amazing in mid-spring. Own photo (© Erin Gerecke).

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