Fall Colors

Why are these leaves changing color, and what is the "right" color? The answer lies in the process of leaf color change. Leaves are green most of the year because the chlorophyll the tree puts into them masks their true color. As fall approaches, the tree starts to kill the cells at the base of the leaf, so the supply of chlorophyll is cut off. With less green to mask true color, the apparent color changes. As this process goes on, the leaf essentially dies of thirst and shrivels. The leaf falls when the connection to the branch is so weak that the branch no longer has enough strength to hold onto the leaf. (That is why a lot of leaves fall when the wind blows: the extra force exerted is enough to break the fragile connection.

Okay, so that explains the yellows and browns. Why do some trees have beautiful oranges and reds? Remember that trees, using the energy from sunlight, convert carbon dioxide and water from the air into sugars; these are used by the tree for energy and growth. The more sunlight, the more sugar produced. Certain chemicals in the leaf, in the presence of sugar, may turn the leaf red or orange. As the connection between the leaf and the rest of the tree is being shut down, the sugar stays in the leaf and so does the color.

In northwestern Nevada, color change starts around the beginning of September (although some Cottonwood trees (Populus spp.) get a few yellow leaves starting in midsummer). Each tree species has its own "biological clock" of color turning. Some of the trees which start changing early are Honeylocust (Gleditsia tricanthos) and Green Ash (Fraxinus pennsylvanica).

There is not really much change in leaf color before mid-September, but by that time you can notice that normally dark green leaves look a little yellow. The number of tree species turning color and the intensity of color both increase until about mid-October, when fall colors are at their height. After a particular tree reaches its most intense color, the leaves commonly start to fall off. So, starting around mid-October, some trees are bare of leaves, some are very colorful, and still others are still green.

This process continues until early November, by which time all the leaves which are going to fall before spring have fallen. Some oaks, for example Pin Oak (Quercus palustris) and English Oak (Quercus rubra) keep brown leaves on until the next year's leaves appear. Other woody plant species, for example Oregon Grape (Mahonia spp.) keep their fall color until spring. Some trees, for example, White Mulberry (Morus alba), lose all their leaves at almost one instant (making raking of leaves a one-time affair), but others lose a few at a time.

This is the best of possible situations: you can see the change over a period of time. There is a photo page in this website celebrating the changing colors, Fall Color Watch 2007.

You can also check out our archive of 2005 Fall Colors and 2006 Fall Colors.

Although there are trees which exhibit fall colors all over northwestern Nevada, cities may be the best places because there is a wide variety of tree species and thus a wide variety of color change scenarios. Older neighborhoods are a wise choice because the trees are bigger and thus more spectacular.

Parks and arboretums are good places too, because trees of different fall color scenarios are juxtaposed. Reno's Idlewild Park is an excellent place, because there are about 100 species of deciduous trees (those which lose leaves in fall) with all kinds of colors and timing. There is a page on this website celebrating Idlewild Park's fall colors.

In the Sierra Nevada, there are stands of Aspen (Populus tremuloides) in canyons and moist hillsides. A spectacular area is on Mount Rose Highway (Nevada 431) at the turnoff to the East Bowl of Mount Rose Ski Area.

Rules of thumb for Fall colors:

 1.  Different plant species have different Fall colors.
 2.  Conifers may have Fall colors.
 3.  Different individual plants of a species don't all turn color at the same time.
 4.  Variations in color make a more interesting Fall scene.
 5.  Plants turn color at different times in different situations.
 6.  Some plants turn color before Fall under stress.
 7.  Most trees don't turn at the same time all over the tree.
 8.  Rain, snow, wind and cold snaps can cause leaf drop and shriveling.
 9.  Color intensity varies with different species.
10. The same tree may turn color at a different time or with a different color in different years.