Earth Out of Sync – Rising Temperatures Throwing off Seasonal Timing

A newly hatched chick waits with hungry mouth agape for a parent to deliver its first meal. A crocus peeks up through the snow. Rivers flow swiftly as ice breaks up and snows melt. Sleepy mammals emerge from hibernation, and early frog songs penetrate the night.

Spring awakening has long provided fodder for poets, artists, and almanac writers. Even for a notoriously fickle time of sunshine, rain, and temperature swings, some old-fashioned seasonal wisdom was consistent enough to be passed down through generations. The first blooming of a specific flower, for example, could traditionally signal when to find certain fish running the rivers, when to hunt for mushrooms, or when to plant crops. The timing of such seasonal events is coordinated in an intricate dance—a dance underappreciated, perhaps, until something jolts it out of step.

With global average temperatures up 0.5 degrees Celsius since the 1970s, springtime warming is coming earlier across the earth’s temperate regions.  A number of organisms have responded to the warming temperatures by altering the timing of key life-cycle events. The problem, however, is that not all species are adjusting at the same rate or in the same direction, thus disrupting the dance that connects predator and prey, butterfly and blossom, fish and phytoplankton, and the entire web of life.

The timing of seasonal biological events, otherwise known as phenology, has been tracked in some places for centuries. Japan’s much-feted cherry tree blossoming has been carefully recorded since before 1400. The trees showed no clear trend in timing until the early 20th century, when they began to bloom earlier, with a marked advancement since around 1950.

The meticulous records of Henry David Thoreau help us gauge how spring has changed in Concord, Massachusetts, since the mid-1800s. Comparing his notes on over 500 species and subspecies of plants with modern surveys and records in between, researchers found that springtime blooming advanced by an average of one week over the past 150 years as local springtime temperatures rose.

The plant varieties that advanced their timing appear to have thrived over the years, while others declined in numbers. The varieties left behind include asters, mints, orchids, lilies, and violets. Some native plants advanced their blossoming dramatically: the highbush blueberry by three weeks and the yellow wood sorrel herb by a month. Yet these native plants may be the exception rather than the rule; on average, non-native invasive plants advanced their bloom by 11 days more than natives. With exotic invasives appearing to adapt more quickly to warming temperatures, the concern is that they could outcompete some native plants, leading to their disappearance.

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