Skip to contents

Spring, Interrupted

Millenia-old evolutionary relationships are out of sync

Apple blossoms in springtime.
Image source: Pixabay.
  • Credibility:

With the planetary climate steadily warming because of carbon emissions, it’s no surprise that spring is coming earlier to the Northeast. For decades, the timing of the early signs of spring has been shifting ever so slightly earlier: the first migrating birds, the first blooms on apple trees. Spring now regularly arrives a week or two earlier than it did a few decades ago.

If all climate change did was move the spring back, most living creatures could probably adjust to the shift. But there’s a deeper problem: The signs of spring are slowly drifting out of phase with one another, disrupting evolutionary relationships that have taken millennia to develop.

The study of the timing of biological phenomena as the seasons unfold is called “phenology”—literally, from the Greek, phaino, “to show,” and –logia, “study.” Phenologists track how different signs of the seasons are changing, and look for evidence to explain which cues in the environment are triggering them. For instance, some plants rely on lengthening days to tell them when leaves and buds should emerge. Others are coaxed into bloom by warmer weather.

As anyone with apple trees knows, blooming at the wrong time can be a danger to plants. Here in upstate New York, where fluctuating spring temperatures are becoming more and more common, an early warm spell can wreak havoc on the year’s apple crop by coaxing trees into early bloom.

The shifting climate is also disrupting the delicate early spring dance between plants, pollinators and predators. Sara Peach, a climate advice columnist at Yale Climate Connectionsdescribes in a recent column how species responding to different climate cues are beginning to drift apart from one another: 

For many creatures, adjusting to an earlier spring isn’t as simple as changing the date of an appointment. That’s because organisms use a few different methods to calibrate their internal calendars. Some species know that it’s spring when air temperatures grow warm, for example. But others rely on day length, which expands as winter ends, to determine when spring has sprung. So when air temperatures warm up early—but day length is unchanged from years past—species start to disagree about spring’s start date.

Those sorts of disputes can lead to mismatches. In the Netherlands, for example, scientists have found that the period of time when caterpillars are most abundant has fallen out of sync with the breeding dates of birds known as great tits. Meanwhile, Arctic plants are greening up earlier in the year, but Greenland caribou haven’t adjusted the timing of their migration, so they’re missing out on a tender, nutritious food source. If such species are unable to evolve quickly enough to keep up with ever-earlier springs, their populations may decrease over the long term. We’ll have more caterpillars and Arctic plants but fewer great tits and caribou.

In a clever demonstration of how species falling out of sync affects the delicate vernal dance, Peach takes a classical ode to the season—Vivaldi’s “Spring,” from The Four Seasons—and rearranges it, so that the various musical parts enter at slightly different times. Listening to the out-of-sync version, you can still hear Vivaldi’s original melody, but there’s a cacophony to the music as the lines collide and drift apart.

Backyard Science

Here in the Hudson Valley, small changes in the timing of spring phenomena are helping to shed light on climate change. At the Cary Institute for Ecological Studies in Millbrook, phenologists and volunteer scientists are part of the ongoing effort to document the unfolding of natural events in the spring and fall. Cary scientist William Schlesinger writes:

The relationships that characterize spring phenology are the products of long-term coevolution. Birds arrive when there are insects to eat, and plants flower when there are bees to pollinate them. Leaf emergence in the temperate forests of North America has advanced about seven days over the past 30 years, whereas bird arrival has advanced only about half that amount. Unless the timing of various species is precisely coordinated in response to changing climate, the historical relationships between species will be disrupted, to the detriment of their reproductive success and persistence. 

The toll climate change is taking on local ecological communities is alarming, but it’s also a fantastic opportunity for people to get involved in citizen science. The USA National Phenology Network is always looking for volunteers across the country to observe the signs of spring unfolding in their own backyards, and help build a valuable database for ecologists. Citizen scientists can sign up at their website to track forest pests, the timing of spring leaves and flowers, mayfly hatches, flowering of important food sources for butterflies and bats, and more.

Locally, the state Department of Conservation hosts a citizen science project every spring in the Hudson Valley: The Amphibian Migration and Road Crossings Project. On warm spring nights in March and April, when the conditions are right to trigger mass movements of frogs and salamanders, DEC volunteers observe the migrations, documenting which species are on the move and when, and helping rare and fragile amphibians get safely across roadways. For more information, visit the DEC’s webpage about the project, or download the agency’s volunteer handbook.

No place on the globe is unaffected by climate change, but every place will face its own set of challenges. The impact of climate change on the ecosystems of the Hudson Valley is a deep topic that deserves careful and thorough reporting. We’re building a newsroom to explore local issues with national (and international) resonance, and we need your help.