Credit: “Late Afternoon Sun over a Stream,” *Cooper Hewitt, Smithsonian Design Museum, public domain*

by Leah Palmer, TNC Writer/Editor

On June 21st, the Sun will swell to a dramatic crescendo on the longest day of the year in the Northern Hemisphere, Summer Solstice. Across history, cultures and geography, humans have paid special attention to this annual event, holding it as a day of ritual and reverence. The Summer Solstice stands as a threshold between Spring and Summer, marking a time to savor abundance and fresh starts.

It’s easy to see how people interact with Summer Solstice. But, are you aware of how nature experiences the Solstice? Alongside noisy human celebrations, quiet and subtle changes take place as flora and fauna respond to long summer days.

Ailene Ettinger, a Quantitative Ecologist at TNC Washington, says the summer solstice marks a transition in daylength patterns around the globe, which is an important cue that affects many organisms’ phenology, or the timing of recurring biological events. When plants experience lengthening daylight, for example, they may respond in a number of ways. Ettinger says the solstice, and daylength patterns across the growing season “help control how much carbon plants end up storing, or how much they grow in a season.”

Botanists used to think that length of daylight determined blooming, but studies have revealed it is actually the length of continuous darkness (night) that promotes blooming, a concept called photoperiodism.

Ettinger points out, “Some plants, such as California poppies, foxgloves, and many roses, and lilies,” require less than 12 hours of continuous darkness (night) in order to bloom. Botanists call these “long-day” plants. Their growth and blooming usually benefits around the Solstice. In short, you can thank lengthening daylight (and short nights) for the colorful backdrop for your rituals and celebrations.

But, Summer Solstice isn’t always a welcomed event, especially as Nature and people experience climate change—which is the result of mismanagement of our communities, relationships, and natural resources. This mismanagement means our communities can suffer during the Solstice, as we experience an increase of daylight in tandem with changing weather patterns. Ettinger says the heat wave that hit Washington State two summers ago is an example of this. As a Northern Latitude city, Seattle experiences more daylight during summer months, so add a heat dome and an extra-long day, and we’re in for hotter, more stressful conditions because there's more time when the sun is up causing pavement to heat up,” Ettinger says.

Credit: “Morning Landscape,” *Cooper Hewitt, Smithsonian Design Museum, public domain*

As we adjust to longer, hotter days, so do our plant relatives. “Species are responding to climate change by shifting their ranges—moving to higher latitudes or higher elevations.” Each latitude will experience the Solstice slightly differently, so plants that have relocated to adjust to climate change are undoubtedly “experiencing different patterns of daylight that they might not be adapted to.”

Adopting a scientific lens for the Solstice can enhance one’s experience of this day. “I really get joy out of some of the rituals that happen every year and look forward to those rituals. When I was doing research focused on phenology, one of my rituals became going out and observing tree buds or other phases of phenology at the same time every year. This was very grounding and connected me to ancestors of mine who probably harvested certain crops around the same time every year or paid attention to and aligned other activities closely with the seasons,” Ettinger says.

Thoughtful, fun and provocative resources for Summer Solstice:

For the homebody: