Humans Are Altering Fall Foliage, Studies Find

by Cole Mellino

Fall foliage may be changing later due to climate change. As certain regions experience warmer average temperatures, the growth season has been extended, causing leaves to change colors and drop later than in the past. Studies from Europe and Japan show that trees are starting to change colors and drop later, so researchers are looking at whether the phenomenon is happening in the U.S. too.

There have been no comprehensive studies performed in the U.S. yet. But a recent AP story on various pieces of research shows that the trend may be taking place:

Researchers at the NASA Goddard Space Flight Center and at Seoul National University in South Korea used satellites to show the end of the growing season was delayed by 6 1/2 days from 1982 to 2008 in the Northern Hemisphere.

In Massachusetts, the 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 who’s continuing to collect data.

In New Hampshire, data collected at the federal Hubbard Brook Experimental Forest in Woodstock suggests sugar maples are going dormant two to five days later than they were two decades ago.

In Vermont, state foresters studying sugar maples at the Proctor Maple Research Center in Underhill found that the growing season ended later than the statistical average in seven out of the last 10 years.

Researchers at the National Phenology Network have spent the last four years coming up with standards to be used by observers in reporting foliage color changes. These standards are due out in the next couple weeks. The U.S. Geological Survey is using satellites from NASA and the National Oceanic and Atmospheric Administration to look at fall foliage from space.

— Cole Mellino is an intern with the energy team at the Center for American Progress

9 Responses to Humans Are Altering Fall Foliage, Studies Find

  1. Joan Savage says:

    Fall foliage viewing is big business in the Northeast, and the AP story wrapped with a comment alluding to the state of the economy affecting the tourist industry.
    One of obvious features of climate change in the Northeast is that weather conditions become less predictable, so it is not going to get any easier for B&Bs to know when to post their “season” rates.
    Another phenologic change for trees is leaf drop, which seems to be more consistently later in the year. A public works supervisor in a nearby town has been quoted as providing the following observation.
    Twenty years ago he had to be sure the edges of the streets were cleared of the piles of fallen leaves before Halloween, to avoid the tragedies that befell when children played in the leaves and were run over by cars.
    Nowadays, leaves are commonly still on the trees at Halloween.

  2. Mossy says:

    Having just returned on a trip from the Boston area to Burlinton, VT, I can attest to the fact that the hills do not exhibit the spectacular foliage of the past. Columbus Day weekend was a little early this year, and, as the leaves are turning later, this could be explained simply.

    However, as everything in the climate, there is no simple explanation. What we observed in reality were more brown and green, than brilliant color. Had I just looked at the trees, I would have assumed that we were experiencing an extra-dry fall. Many leaves are simply turning brown and falling off.

    I propose that we think outside the box. Tropospheric ozone is more toxic to plants than even people. Could ozone be burning the leaves? Could pollutants, especially reactive nitrogen, be damaging them?

    Furthermore, many trees are in a state of demise, dropping leaves earlier than normal. This include all types of birch, ash, and sugar maples. Their leaves are remarkably smaller than normal, despite the wet season. Extra CO2 has been found to cause leaves to close their stoma to prevent too much excess; could this be a factor that actually limits their size?

    There is a lengthened period of foliage, as different types of trees respond differently to the stress, some dropping leaves earlier, and some later. This obviously results in less color on any given day.

    A huge disappointment was the sumac plant, which normally turns bright red along the roadways, but was instead going directly from green to brown, dropping leaves prematurely, and exhibiting excessive brown seed pods that remained.

    Thanks to the blog curator at for tree research! She’s “on” to something, but is anyone listening?

  3. Daniel J. Andrews says:

    Also anecdotal, but 20 to 30 years ago, by our Thanksgiving (around the 10th of October in Canada), the tree colours were about 10 days or so past their peak…or gone altogether. Now for the past few years colours are either at their peak or only slightly past their peak on the same long weekend.

    Our colours this year though are spectacular. We’ve had two weeks of sunny warm weather with little wind so the leaves aren’t being blown off the trees. We did have some high winds before then which denuded some trees, but there were still enough ‘clothed’ trees left that when their foliage turned during the calm period, the leaves stayed around.

    Over the past two weekends we traveled to Algonquin Park, and this weekend to Killarney, and the reds and oranges are simply gorgeous–one of the falls you remember for a long time.

  4. Hank says:

    FWIW, I live in Massachusetts and regularly visit the White Mountains of New Hampshire for hiking trips. The simple truth is that it’s been business as usual for foliage around here. If anything, September and the first part of October have been cooler than normal.

  5. Shouldn’t this be discernible as a shift in the “phase” of the annual CO2 cycle in the Mauna Loa data?

  6. Andy G says:

    My own experience is that the 6 1/2 day is right on. I lived in Western Mass from 1974-1978 and the peak of fall foliage was always the first week of October.

    Now I go to visit my son just north of Albany, and the peak of fall foliage is mid-October.

  7. catman306 says:

    Gail’s explanation is quite compelling. Ozone, VOCs, ethanol motor fuel, problems with the nitrogen cycle.
    No other explanation considers the damage to photosynthetic life is basically everywhere, not dependent upon local pollution or drought situations.

  8. catman306 says:

    Mossy, didn’t see your comment. But, of course, Witsend is on to something.

  9. Nick Schordje says:

    Interesting article. It seems to be the other bookend to Project Bud Burst.