Autumn's glow put at risk by climate change
Climatologists and phenologists — those who study the effects of seasonal changes on plants and animals — are increasingly concerned about the effects of rising temperatures and erratic weather patterns on fall foliage.
While most average leaf peepers aren't noticing any dramatic changes, consider what's happened in the Northeast since August 2011:
- Tourism literally came to a halt in New England when Hurricane Irene wiped out bridges and roads on some scenic leaf-peeping routes.
- The freak October snowstorm damaged or destroyed thousands of trees.
- At the 64th annual foliage festival in Warner, N.H., it was 80 degrees on Oct. 8 and the leaves were still green.
Scotty Johnston, who led foliage tours for Tauck Tours for half a century and was the company's official foliologist, notices the nuances.
"I don't want to give the impression it's a radical change," Johnston said of the march of foliage time. "I think Mother Nature has been very, very predictable. But there has been a slight delay in the turning, which has come from a warming trend."
Two factors influence when the leaves turn, according to Johnston. The first — the seasonal decrease in daylight — is constant. The second is the drop in temperature: "That's where the variable has come in. With more prolonged warm, and a later cold snap, your foliage is going to turn later." In eastern Connecticut, where Johnston lives, that's translating to a four- or five-day delay, with foliage season lasting into November.
Tourism officials in New England have noted a change in foliage season bookings — people are waiting longer before committing, hoping to get a more accurate read on how the colors are progressing, as well as, just maybe, a last-minute deal.
Studies in Europe and Japan have found that leaves are changing color later that usual, and new research by U.S. scientists is coming up with similar results:
- In New Hampshire, data collected at the federal Hubbard Brook Experimental Forest in Woodstock suggest that sugar maples are going dormant two to five days later than they were two decades ago.
- In Massachusetts, leaves are changing about three days later than they were two decades ago at the Harvard Forest 65 miles west of Boston, according to data collected by John O'Keefe, a retired Harvard professor and museum coordinator.
The New England Climate Coalition predicted a few years ago that if temperatures continue to climb unabated, "the fall foliage for which the region is famous will disappear as birch, maple and spruce species migrate north or die out altogether." New Hampshire's Department of Environmental Services has been predicting that the state's hardwood trees could move north by up to 300 miles.
Johnston notes that when he drives around his town these days, he sees tree species that could never have survived here in the past. "We used to be a 6 Hardiness Zone," he said, referring to the U.S. Department of Agriculture's system of geographically defined areas in which a specific category of plant life can grow, particularly based on its ability to withstand the minimum temperatures of the zone. "Now we're a 6A or a 7" — zones with a higher minimum temperature. That's good for those wimpy trees that never could hack a Zone 6, and bad for the original trees that have dug into the zone for the long haul and may not be able to withstand the new lay of the land.
Finally, some researchers fear the reason we love foliage is in danger: The colors themselves could fade.
The golds, yellows and oranges that rely on the physical breakdown of chlorophyll to come out and shine won't be affected. But anthocyanin, the chemical that produces red leaves, relies on a chemical process that requires a precise, yet not fully understood, combination of sugar, temperature and light. That bright red color is a particular signature of maple trees, which make up an unusually large percentage of New England forests. Scientists have found that those are particularly endangered by irregular weather, and a professor at the University of New Hampshire has already found that sugar levels are dropping in maples trees.
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