See one cherry tree’s rush to an early bloom, day by day

Two weeks ago, we started photographing the cherry trees whose spectacular white blooms mark the start of spring in the nation’s capital. We thought we had plenty of time to capture the buds gradually unfold. If history was any guide, the trees would reach peak bloom, when 70 percent of the Yoshino cherry blossoms are open, in late March.

History, it seems, provides less guidance than it used to. Day after day of unseasonable heat drove the cherry trees to reach peak bloom on March 17. Without planning to, we wound up capturing the second earliest peak bloom on record — a sign of how rising temperatures are shifting the cycles of the natural world.

9 days from peak bloom

10°F warmer than the 1951-1980 average

March 8

7 days from peak bloom

3°F warmer

March 10

6 days from peak bloom

1°F cooler

March 11

As temperatures rose early in the year, the cells in the bud became active and absorbed water from the branches of the tree.

5 days from peak bloom

10°F warmer

March 12

4 days from peak bloom

13°F warmer

March 13

After a few unusually warm days, the flower stalks lengthened, giving the flowers space to open.

3 days from peak bloom

15°F warmer

March 14

2 days from peak bloom

21°F warmer

March 15

Finally, the delicate petals emerged, unfurling as they ballooned with water.

1 day from peak bloom

13°F warmer

March 16

Peak bloom

14°F warmer

March 17

After peak bloom

10°F warmer

March 18

This year’s bloom came so fast that nearly all the experts were caught by surprise. “We seemed to go from 0 to 60 in about 3 seconds this year,” said Matthew Morrison, chief arborist for the National Mall and Memorial Parks, who is in charge of caring for the cherry trees.

It wasn’t just that March was hot. Since the start of the year, abnormal heat propelled the cherry trees to an early bloom. Jan. 26 clocked in as the hottest January day on record, and 65 of the 77 days leading up to peak bloom were hotter than average.

It is impossible to predict when the cherry trees will bloom next year or the year after that. But in 50 years, cherry trees will tend to bloom earlier than they do now.

That’s because plants respond to the steady accumulation of heat at the start of each year. Factors other than the temperature, such as precipitation, humidity and sunlight, have relatively little effect on the timing of spring, said Richard B. Primack, a biologist at Boston University.

Plants’ sensitivity to temperature explains why flowers in the countryside bloom later than in nearby cities, where concrete and asphalt trap more heat than natural landscapes. But even in rural areas, spring blooms are trending earlier, Primack said.

For D.C.’s cherry blossoms, the shift toward earlier peak blooms mirrors the steady rise in the city’s average daily temperature. Temperatures are projected to rise further as humans continue burning fuels that emit heat-trapping gases like carbon dioxide.

Hover on the chart to explore the data

Note: Trend lines created with LOESS smoothing.

The climate is always changing, but the current rate of global warming is fast — over the past century, the planet warmed about 10 times as fast as when it came out of historical ice ages. The pace of change can cause the seasonal cycles of plants and the creatures that depend on them, such as caterpillars and bees, to get out of sync.

“I’m seeing pollinators emerge when there’s no flowers. I’m seeing flowers when there’s no pollinators,” Morrison said. “It was never like it is now. And in my personal observations, it’s accelerating like a J-curve.”

The Tidal Basin’s cherry trees are bred to be sterile, so they don’t grow fruit. But seasonal mismatches between flowers and pollinators could pose problems for commercial fruit growers, particularly those that use native bees rather than bred honeybees to pollinate their crops.

Primack was less worried about the absence of spring bees than the presence of pest insects and fungal diseases, which become more common as temperatures rise. “If the temperatures get higher, it’s quite likely that in coming years we will see a diminished flower display,” Primack said.

Then there’s the flooding. The Tidal Basin, along which D.C.’s best-known cherry trees reside, has risen four feet over the past century — one foot because of sea-level rise and the rest because the land is sinking. Scientists project additional sea-level rise with future global warming.

In late May, work will begin on a $113 million rehabilitation project that will raise the Tidal Basin’s sea wall nearly five feet. Before construction can begin, workers will need to cut down 140 cherry trees, including the beloved Stumpy. The sea wall project is scheduled to be completed in 2027, after which 274 new cherry trees will be planted.

That’s good news, Morrison said, because the cherry trees at the Tidal Basin are in bad shape. Years of over-aggressive pruning and the accumulated bruises from lawn mowers and weed trimmers have caused damage that will in time doom all 3,700 of them.

Morrison has instituted healthier pruning practices and spread wood chips near the trees to protect them from wayward maintenance workers. That gives him high hopes for the new trees. “Your unborn grandchildren — when they inherit this park, they won’t have trees that are failing,” he said. “They’ll have trees that are growing as they would naturally in the real forest.”