Leaving Summer Behind
The calendar says fall, but it feels like summer this week, with temperatures in the high 80’s and 90’s--between 10 and 20 degrees warmer than normal. But residents need only look up to see it’s autumn. The leaves are just starting to turn, bringing a touch of color to such far-flung places as a tree-lined street in Santa Ana and the country’s wild canyons. Orange County is no rival to New England, but the old myth that there are no seasons in Southern California isn’t quite true either. Forecasters predict cooler temperatures as early as Monday. And whatever the temperature, days will be growing shorter and fall’s colors will be emerging.
Cutting Off the Flow
Leaf Connection
Leaves receive water from the tree through a series of small tubes called transport vessels. These tubes pass through a special cells called the separation or abcession layer. Glucose, the “food” product of photosynthesis, flows back to the tree.
Coming to an End
In the fall, the cells of the separation layer begin to swell, forming a cork-like substance. This pinches the tubes and eventually cuts off the exchange of water-glucose. The cells disintegrate and a layer forms between the tree and leaf.
Colorful Fall
Without water, waste products and glucose remain trapped in the leaf. Chlorophyll, which requires water for renewal, begins to disappear and the leaves lose their green color, change hues and eventually drop.
A Chemical Change
The chemicals in leaves are responsible for the color changes in fall months. They are triggered by a drop in evening temperatures and fewer daylight hours.
Cholorphyll: A green pigment is a reflection of the red and blue light absorbed from sunlight. This pigment is essential in photosynthesis.
Carotenoid: Yellows pigment, begins to appear in leaves when the amounts of the dominant pigment, chlorophyll, is reduced. Both chlorophyll and carotenoid are always present in leaves.
Anthocyanin: Reds and purples are seen when the right combination of bright sunny days and cool nights are present. This produces large amounts of glucose in the leaves needed for red pigmentation.
Tannin: The brown color in leaves is formed by the breakdown of wast products.
Planting for Color
For a bit of fall color in your own yard, here is a list of trees known for producing a yellow only or a combination with red:
Betula pendula, silver birch
Ginko biloba, maidenhair tree
Lagerstroemia indica, crape myrtle
Liquidambar, sweet gum
Prunius
Pyrus, ornamental pear
Quercus palustris, pin oak
Quercus ruba, red oak
For Local Color
Popular areas for viewing local color
Silverado Canyon: All along Silverado Canyon Road, continues 3 miles or so.
Trabuco Canyon: On upaved Trabuco Creek Road, off Trabuco Canyhon Road. At road’s end is a 3.6 mile loop trail.
Bell Canyon: Within park a short distance from parking lot. An easy 2 1/2-mile stroll.
Researched by DORIS SHIELDS and JANICE JONES DODDS / Los Angeles Times
Sources: DK Nature Encyclopedia; Sunset Western Garden Book, Roger’s Gardens, Newport Beach arborist Michael Mahoney, various Web sites
Photosynthesis
Energy is absorbed from sunlight through the leaves’ green pigment, chlorophyll. Water from the roots and carbon dioxide from the air produce food for the tree, called glucose. Oxygen is a was the product from this process. It escapes into the air while the glucose travels back to the tree for energy and growth.
Leaf Structure
Epidermis: Flattened, transparent cells serve as a protective layer
Palisade Cells: Full of chloroplasts, essential in photosynthesis
Chlonoplast: Where photosynthesis takes place. Contain membranes that operate like solar panels, absorbing energy from the sun
Spongy Cells: Loosely arranged to allow diffusion of carbon dioxide.
Vein: Transports water into the leaves and carries back glucose
Stoma: Pore controlled by two guard cells. Opens in daylight to allow carbon dioxide in and closes at night to keep water out.
