Climate-change deal unlikely by year's end

NF Reporter · 11-15-2009, 08:35 AM

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Climate-change deal unlikely by year's end

waltky · 10-08-2011, 07:35 PM

I've noticed that grass cutting season is longer and leaves turning seems to be later than I remember as a kid...

Is Climate Change Affecting Fall Foliage?
6 Oct.`11 – Clocks may not be the only thing falling back: That signature autumn change in leaf colors may be drifting further down the calendar.

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Scientists don't quite know if global warming is changing the signs of fall like it already has with an earlier-arriving spring. They're turning their attention to fall foliage in hopes of determining whether climate change is leading to a later arrival of autumn's golden, orange and red hues. Studies in Europe and in Japan already indicate leaves are changing color and dropping later, so it stands to reason that it's happening here as well, said Richard Primack, professor of biology at Boston University. "The fall foliage is going to get pushed back," Primack warned.

Down the road, scientists say there could be implications not just for ecology but for the economy if duller or delayed colors discourage leaf-peeping tourists. Phenology is the study of timing in nature, whether it's crocuses emerging in the spring, leaves falling from trees, or Canada geese heading south for the winter. And it's tricky business for fall foliage. The budding of plants each spring is tied almost exclusively to warming temperatures, while fall's changing colors are linked to cooling temperatures, decreasing sunlight and soil moisture.

The brilliant colors associated with fall happen when production of chlorophyll, the green pigment in plants that's crucial to photosynthesis, slows down as the days get shorter and the nights grow longer. That exposes leaves' yellow, red and orange pigments that are normally hidden from view. How and when that happens depends on temperatures and moisture levels. In some years, the colors are more vibrant than others. Further complicating matters: A tree that's stressed may simply drop its leaves, with no color change, or brown leaves. "Fall is still an enigma," said Jake Weltzin, executive director of the National Phenology Network in Arizona and an ecologist with the U.S. Geological Survey.

Scientists caution that heavy rain, drought-like conditions or temperature extremes can cause dramatic year-to-year fluctuations that don't establish a long-term trend. For example, heavy rainfall in New England this spring, followed by a deluge caused by Irene, is causing fungal growth that's causing some trees' leaves to turn brown and drop earlier than normal. William Ostrofsky, forest pathologist with the Maine Forest Service, is skeptical about whether there's a proven link between fall foliage and climate change. "I just don't know that there's any evidence to indicate there's a trend one way or the other," said Ostrofsky, who points out that year-to-year fluctuations make it difficult to discern long-term trends. "I really don't think we've seen any long-term trend, as far as I can tell."

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Fall colors depend on weather changes
10/15/2010 4:42 PM | So, why do the leaves change color each fall?

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"Every autumn across the Northern Hemisphere, diminishing daylight hours and falling temperatures induce trees to prepare for winter," says Bassam Shakhashiri, chemistry professor at the University of Wisconsin-Madison. Broadleaf, green trees turn to brilliant shades of yellow, orange, and red. Their color changes because the tree's growth factory shuts down for the winter. Winter is a bad time for growing: too little water, too little sun, and too much cold. So the tree stops producing chlorophyll, stores sugars for antifreeze protection, and sheds tender leaves.

"During summer, the leaves of trees are factories producing sugar from carbon dioxide and water by the action of light on chlorophyll [photosynthesis]," says Shakhashiri. To get energy, the large chlorophyll molecules absorb red and blue light from sunlight and reflect green light. That's why trees look green during summer. Chlorophyll molecules use the light energy to change carbon dioxide and water into oxygen, sugars, and starches. The leaves exhale the waste oxygen and keep the food. Water and nutrients flow up from roots through branches and into the leaves. Sugars manufactured during photosynthesis flow out from the leaves to the rest of the tree and the chemical energy of the sugar fuels tree growth. The tree stores any excess energy.

Chlorophyll, however, breaks down easily in bright sunlight. So leaves constantly churn out chlorophyll all summer long and the leaves stay green. The leaves of many trees (for example, birches) also contain the yellow pigment, carotene, which traps blue-green and blue light. As the nights get shorter and cooler, the tree must protect itself for winter. Its stems, twigs, and buds are tough enough to withstand winter, but not so its fragile broad, thin leaves. The watery sap in leaf cells freezes easily. So the tree seals off its leaves and sheds them.

To begin the sealing-off process, the tree grows a corky membrane between each branch and leaf stem. The membrane hinders the flow of nutrients into the leaf which stops the leaf from making new chlorophyll. The old chlorophyll quickly decomposes and the leaf's green color fades. If the leaf contains carotene, birch trees for example, the fading leaf changes from green to yellow. Carotene, a more stable compound than chlorophyll, persists in leaves even after all the chlorophyll is gone. The leaves of those trees now look yellow. The birches, aspens, and cottonwoods in the forest shimmer gold.

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