Why do leaves change color?

From the US Forest Service website:

How does autumn color happen?
For years, scientists have worked to understand the changes that happen to trees and shrubs in the autumn. Although we don't know all the details, we do know enough to explain the basics and help you to enjoy more fully Nature's multicolored autumn farewell. Three factors influence autumn leaf color-leaf pigments, length of night, and weather, but not quite in the way we think. The timing of color change and leaf fall are primarily regulated by the calendar, that is, the increasing length of night. None of the other environmental influences-temperature, rainfall, food supply, and so on-are as unvarying as the steadily increasing length of night during autumn. As days grow shorter, and nights grow longer and cooler, biochemical processes in the leaf begin to paint the landscape with Nature's autumn palette.

Where do autumn colors come from?
A color palette needs pigments, and there are three types that are involved in autumn color.

Chlorophyll, which gives leaves their basic green color. It is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to manufacture sugars for their food. Trees in the temperate zones store these sugars for their winter dormant period. Carotenoids, which produce yellow, orange, and brown colors in such things as corn, carrots, and daffodils, as well as rutabagas, buttercups, and bananas. Anthocyanins, which give color to such familiar things as cranberries, red apples, concord grapes, blueberries, cherries, strawberries, and plums. They are water soluble and appear in the watery liquid of leaf cells.

During the growing season, chlorophyll is continually being produced and broken down and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed. The carotenoids and anthocyanins that are present in the leaf are then unmasked and show their colors.

Certain colors are characteristic of particular species. Oaks turn red, brown, or russet; hickories, golden bronze; aspen and yellow-poplar, golden yellow; dogwood, purplish red; beech, light tan; and sourwood and black tupelo, crimson. Maples differ species by species-red maple turns brilliant scarlet; sugar maple, orange-red; and black maple, glowing yellow. Striped maple becomes almost colorless. Leaves of some species such as the elms simply shrivel up and fall, exhibiting little color other than drab brown.

The timing of the color change also varies by species. Sourwood in southern forests can become vividly colorful in late summer while all other species are still vigorously green. Oaks put on their colors long after other species have already shed their leaves. These differences in timing among species seem to be genetically inherited, for a particular species at the same latitude will show the same coloration in the cool temperatures of high mountain elevations at about the same time as it does in warmer lowlands.

How does weather affect autumn color?

The amount and brilliance of the colors that develop in any particular autumn season are related to weather conditions that occur before and during the time the chlorophyll in the leaves is dwindling. Temperature and moisture are the main influences.

A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions-lots of sugar and lots of light-spur production of the brilliant anthocyanin pigments, which tint reds, purples, and crimson. Because carotenoids are always present in leaves, the yellow and gold colors remain fairly constant from year to year.

What triggers leaf fall?

In early autumn, in response to the shortening days and declining intensity of sunlight, leaves begin the processes leading up to their fall. The veins that carry fluids into and out of the leaf gradually close off as a layer of cells forms at the base of each leaf. These clogged veins trap sugars in the leaf and promote production of anthocyanins. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.

What does all this do for the tree?

Winter is a certainty that all vegetation in the temperate zones must face each year. Perennial plants, including trees, must have some sort of protection to survive freezing temperatures and other harsh wintertime influences. Stems, twigs, and buds are equipped to survive extreme cold so that they can reawaken when spring heralds the start of another growing season. Tender leaf tissues, however, would freeze in winter, so plants must either toughen up and protect their leaves or dispose of them.

The evergreens-pines, spruces, cedars, firs, and so on-are able to survive winter because they have toughened up. Their needle-like or scale-like foliage is covered with a heavy wax coating and the fluid inside their cells contains substances that resist freezing. Thus the foliage of evergreens can safely withstand all but the severest winter conditions, such as those in the Arctic. Evergreen needles survive for some years but eventually fall because of old age.

The leaves of broadleaved plants, on the other hand, are tender and vulnerable to damage. These leaves are typically broad and thin and are not protected by any thick coverings. The fluid in cells of these leaves is usually a thin, watery sap that freezes readily. This means that the cells could not survive winter where temperatures fall below freezing. Tissues unable to overwinter must be sealed off and shed to ensure the plant's continued survival. Thus leaf fall precedes each winter in the temperate zones.



Our EarthRoamer traveling the back roads of Vermont



The view through our windshield in Vermont



Camping in the Green Mountain National Forest, Vermont



Shonah atop one of many waterfalls during our hike in the Green Mountain National Forest, Vermont

 

Shonah crossing the brook in Green Mountain National Forest, Vermont



Green Mountain National Forest, Vermont



Taftsville Covered Bridge in Woodstock, Vermont



Quechee, Vermont is known for their annual hot air balloon festival.  While we weren't there for the festival, locals still take to the skies most weekends in the Fall.



Of the 3 balloons launching on this day, this was our favorite



Now that's a big flame...



Ready for launch...



Of course they had to check out the EarthRoamer from above...



Can you imagine the views?



The Quechee Gorge in Quechee, Vermont is known as the "Grand Canyon of New England"



The view behind the Killington Grand Hotel in Killington, Vermont



The view from the top of the Killington Ski Resort



Todd getting in some mountain biking in Killington, Vermont

Fall in New England...

As the air has grown colder and the days shorter, we've been wandering our way through New England enjoying all that fall has to offer with scenic roads past covered bridges, coastal harbors, national parks, forests filled with changing colors and getting out when we can to hike, bike and paddle board.



St. Paul's Cathedral in Montreal, Canada



The altar in St. Paul's Cathedral in Montreal, Canada



St. Paul's Cathedral in Montreal, Canada

 


Shonah lighting a candle in memory of Grandma Garcia

 


Habitat 67, or simply Habitat, is a model community and housing complex in Montreal, Canada, designed by Israeli–Canadian architect Moshe Safdie. It was originally conceived as his master's thesis in architecture at McGill University and then built as a pavilion for Expo 67, the World's Fair held from April to October 1967.

 


Habitat 67 in Montreal, Canada

 

A Heron (we think?) in the park in Montreal, Canada



A Common Loon in Greenville, Maine



Lowe's Bridge in Guilford, Maine

 


Shonah hiking up Precipice Trail in Acadia National Park, Maine

 


View from Acadia National Park, Maine with the Queen Mary 2 docked in Bar Harbor, Maine



Todd hiking up Precipice Trail in Acadia National Park, Maine

A panorama view from Champlain Mountain Summit in Acadia National Park, Maine




Todd horsing around on an adult size rocking horse in Bar Harbor, Maine





The Penobscot Narrows Bridge is a 2,120 feet (646 m) long cable-stayed bridge that carries US 1/SR 3 over the Penobscot River. It connects Verona Island to Prospect, in the U.S. state of Maine.  A quick ride up provides panoramic views from the 3-level observation deck.

 


The scenic harbor in Camden, Maine



Shonah paddle boarding in Camden, Maine




Allan "Red" Gagnon has opened Red's Eats in 1938, originally in Boothbay, Maine. The shack was moved to its present location at the intersection of Water Street and Main Street in Wiscasset in 1954. It is known for some of the best lobster rolls in all of New England.

 


More than 1 entire lobster's meat goes into every lobster roll served - and boy was it delicious!  The melted butter and lemon was not necessary for this delicious treat.

 


A Heron (and it's reflection) in Boothbay Harbor, Maine

 


Boothbay Harbor, Maine at sunset


 


While near Portland Maine, we noticed that a crack in our windshield was getting bigger, so Todd supervised the windshield replacement in Portland, Maine.



Bug Light Lighthouse in Portland, Maine

 


Spring Point Lighthouse in South Portland, Maine

 


Portland Head Light Lighthouse in South Portland, Maine



A Monarch Butterfly in Portland, Maine





The start of Fall colors in Moultonborough, Maine

 


Castle in the Clouds (or Lucknow) is a 16-room mansion and 5,500-acre (2,200 ha) mountaintop estate in Moultonborough, New Hampshire.  The home was built in 1913-1914 in the Craftsman Style by millionaire shoe manufacturer Thomas Gustave Plant (1859-1941) for his second wife, Olive Cornelia Dewey.

 

This spectacular home included a few "modern" innovations such as a central vacuum system. (unfortunately the basement was closed at the time of our visit so we were unable to see the actual system)

A built in refrigerator with a central cooling system that also powered a walk-in refrigerator in the basement.

Each bathroom had a "needle" shower with body sprayers.  At the time the house was built, only a very small number of households had showers and it was even more rare for them to be in the lady of the house's bathroom.

A central intercom system that connected almost every room of the house and the stables down the hill.

There were a large number of built-in close organizers.  Each of these organizers looked as good as the modern day elfa or California Closet designs.



Views from Lucknow of Lake Winnipesaukee, New Hampshire

 


Fall foliage around one of our camping spots at Stinson Lake, New Hampshire

 


Enjoying some wine and reading on our beach camping spot at Stinson Lake, New Hampshire

 


Shonah with his morning coffee getting ready to paddle board on Stinson Lake, New Hampshire




Todd paddle boarding on Stinson Lake, New Hampshire

 


A Heron at Stinson Lake, New Hampshire



One of the residents taking his sea plane for a spin on Stinson Lake, New Hampshire





Todd on the Saco River Bridge in Conway, New Hampshire

 


Saco River Bridge in Conway, New Hampshire

 


Swift River Bridge in Conway, New Hampshire

 


Todd "golfing" in North Conway, New Hampshire

 


Shonah "golfing" in North Conway, New Hampshire

 


Despite being under par, Shonah still lost by one stroke




Echo Lake-Cathedral Ledge State Park, New Hampshire



Todd and Shonah atop Cathedral Ledge at Echo Lake-Cathedral Ledge State Park, New Hampshire

 


Todd and Shonah's homage to their friends Scott and Heather who like to take jumping pictures

 


A scenic viewpoint near Crawford Notch in the White Mountains of New Hampshire

 


The Mount Washington Hotel in Carroll, New Hampshire was the site of the Bretton Woods Monetary Conference convened by the Allies in 1944 and attended by 44 countries to establish regulations for an international monetary system that included the International Monetary Fund and the World Bank.





Shonah on the veranda of the Mount Washington Hotel in Bretton Woods, New Hampshire



Todd mountain biking in Bretton Woods, New Hampshire



Fall colors looking out on the Presidential Range of the White Mountains in New Hampshire
 

Todd and Shonah at "Santa's Village" in Jefferson, New Hampshire



Riverwalk Bridge and old Grist Mill in Littleton, New Hampshire

 


Miller's Run Bridge in Lyndon, Vermont

 


Schoolhouse Bridge in Lyndon, Vermont

 


Chamberlain Mill Bridge in Lyndon, Vermont

 


Some of the best cheddar cheese in the world is made at the Cabot Creamery in Cabot, Vermont.  Of course Shonah had to try it!

 


The State Capitol in Montpellier, Vermont

 


It just wouldn't be right to visit Vermont without stopping by the Ben and Jerry's factory in Waterbury for a tour and sample.