Focus on Phenology: Spring Unsprung

by Danny Schissler, Project Coordinator

March 7, 2017

Honey bee visiting Ozark Witch-hazel (Hamamelis vernalis)

Focus on Phenology: Spring Unsprung

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Can you remember February 24, a balmy 73 degree day that brought flocks of visitors to the Arboretum? In the ample sunshine and unseasonably warm temperatures, it felt as though spring had suddenly arrived on the grounds. And indeed, with a week-long spate of warm weather came swelling buds, early-blooming perennials, and honey bees buzzing among flowering witch-hazels. By the following weekend, only seven days later, the temperature had plunged to a frigid 9 degrees (a drop of 64 degrees!), bringing the second coldest night of the winter and grumbles from those of us ready for an early spring.

Here in New England, we’re feeling the effects of yet another untimely transition into spring. As pleasant we might find these warm days, unseasonably high temperatures early in the year can confuse plants and humans alike. Normally, gradually warming air and soil temperatures, along with extended day length, trigger a cascade of molecular signals that initiate leaf-out and flowering, the beloved signs of spring. A quick response to changing environmental conditions can provide benefits to a plant, such as extended growing periods and access to pollinators—but these potential advantages come at a cost.

Warm weather can quickly coax plants out of winter dormancy, with some species lowering their guard and losing frost-protection mechanisms in only a few days. Extreme temperature fluctuations in rapid succession can spell doom for vulnerable exposed tissues. Food crops in particular can suffer enormous losses when an early spring is interrupted by frost. Luckily, it appears that most of the Arboretum’s early blooming accessions, including many of the beloved magnolias, escaped damage from last weekend’s cold spell.

The onset of an early spring is not unique to the Northeast. According to the Spring Indices of the National Phenology Network, an organization that monitors the influence of climate on plant and animal species across the US, spring is arriving up to 20 days earlier than a long-term average throughout much of the South and mid-Atlantic—a staggering statistic! With our changing climate, we can expect these erratic temperatures and early springs to occur frequently, along with the economic and health challenges that follow. Fortunately, a growing number of researchers—many of them working here at the Arboretum—are studying the impacts of climate on plant phenology to help us better shape a vision for the future of our planet.

NPN Leaf Index Anomaly Map

National Phenology Network Spring Leaf Index Anomaly heat map, showing the early onset of spring through the South and mid-Atlantic as of March 5, 2017.

If you are interested in learning more about phenology, botany, or ecology, join the Arnold Aboretum Tree Spotters, a group of citizen scientists who collect data from 11 species throughout the Arboretum to assist studies focused on plant responses to climate change. Read more about Tree Spotters in Silva [pdf].

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