Our Window on Nature

. . . exploring the world around us

Searching for Spring

Filed under: Plants — Lowell Christie -- March 24, 2016 @ 7:59 pm

Columbine-LTwo thirds of the way through March is the beginning of the season we call spring. Often those in the colder parts of the country celebrate with snow shovels, digging out from a late winter storm.

[Originally written in 2009] Headlines such as last year’s are not unusual: March 21, 2008 – EARLY SPRING SNOWSTORM SOCKS MIDWEST; March 21, 2008 – NASTY SPRING SNOWSTORM AFFECTING FLIGHTS IN AND OUT OF CHICAGO; March 22, 2008 – SNOW SUSPENDS SPRING.

What is this thing called spring? Can we really pin its beginning to a particular date? Or does the date depend on specific plants – when they bloom, or when your particular locality turns green instead of white? Like many things in nature, spring seems to be a process, a gradual transition that doesn’t really have a beginning or an end.

Let’s start by examining why, on this year’s calendar, March 20th is marked as the beginning of spring. Then we’ll show how you can take part in a project to help define the other spring – the one that doesn’t have a date.

As the earth makes its annual journey around the sun, the slight tilt of the planet’s axis causes different areas to receive varying amounts of sunlight and makes the days and nights of unequal length. But twice each year the sun is lined up precisely above the equator, and on these two days the periods of sunlight and darkness are almost equal. That’s why they are called the equinoxes (equal nights in Latin), one around the 20th of March and the other six months later in September.

The dates and times of these crossings will vary slightly because our calendars don’t quite match the natural year. That’s why we have leap years, adding February 29th every four years in our attempt to get back in synchronization with nature. Collectively we have chosen to call this astronomical event the beginning of spring.

But there’s a lot more to spring than just crossing off a date on the calendar, and by some definitions the start of spring is getting a little earlier each year.

In Washington D.C. the annual National Cherry Blossom Festival is a popular attraction. Over three thousand cherry trees burst into bloom, turning the tidal basin into a sea of pink and white. The blossoms are considered at their peak when 70 percent of the flowers are open, and the blooming period lasts about two weeks.

Using a specific percentage of flowers opening allows a precise definition of the time of peak bloom, and this peak is coming earlier by an average of eight hours each season. Thirty years ago the peak occurred on April 5th. Now you have to visit in late March to catch the height of the color.

It’s not just in Washington that you see an advance in the timing of spring. Another example occurs in Arizona. For over 25 years Dave Bertelsen, a self-trained biologist, has hiked the same trail up Finger Rock Canyon near Tucson, cataloging all the plants that line the path. The trail climbs over 4,000 feet in elevation, and Bertelsen has made the trip over a thousand times, tracking the blooming dates of almost 600 species of plants.

A close study of Bertelsen’s records reveals that many of the plants along the trail are, over the years, gradually moving as much as 1,000 feet higher than in the past. The most likely explanation is a gradual increase in temperatures making the higher elevations more hospitable to the plants. This would be the elevation equivalent of earlier springs in Washington – temperatures at the same elevation increasing slightly for any particular date.

These two examples deal with changes in the blooming dates of plants, but there are many direct links between the life cycle of plants and those of animals. An example can be found in the tulip poplar tree in the Northeast. The tulip poplar produces nectar important to honeybees in the area, and the honeybees in turn provide pollination services to the trees. But gradually the tulip poplar has been blooming earlier each year, perhaps as much as twenty-five days earlier according to some records.

Bees evidently weren’t able to make that rapid a change in their feeding habits and instead changed their preferred nectar source to the black locust tree. With fewer bees visiting the tulip poplar for pollination, the numbers of that tree species rapidly declined. Perhaps it’s a warning of the types of changes that can occur with an earlier spring.

Too little is known about the long-term changes that occur in plant communities, because there have been too few long-term studies. Typically, research is done by students in doctoral programs, and the length of the study is determined, not by importance, but by how long it takes to earn a degree. A case like that of Dave Bertelsen and the Finger Rock Canyon trail is truly the exception.

But there is a new program that may eventually help solve the lack of long-term studies. Like Finger Rock Canyon this one will depend upon private individuals. It’s called Project BudBurst, and if you have an interest in plants, you can participate.

Started in 2007 as a collaborative partnership that includes federal agencies, the academic community, and the general public, Project BudBurst is tracking information about when plants begin flowering, leafing, or reproducing. Much of the data collected comes from private individuals willing to watch one or more species of plants growing in easily accessible areas. Over the Internet, participants can download or print out identification guides and information about how to observe many common plants, perhaps even some growing in their own back yard.

By tracking specific species throughout the United States over a number of years, Project BudBurst can discover changes in the timing of plant growth cycles like that seen in the cherry trees of Washington, D.C.
The project has selected a large list of plants that are widely distributed and easily identifiable. It includes 30 native trees/shrubs, 24 native wildflowers, 3 common exotic weeds, and 2 common exotic ornamentals. In addition, they will accept observations and store data on other plants you find of particular interest. You can sign up or get more information about Project BudBurst at www.budburst.org.

Whether you participate or not, tracking when plants have their first buds, leaves, and seeds will help you form a closer relationship with nature. And you just might discover when spring really starts in your part of the world.


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