Changing Leaves

Fall is in full swing. The sun keeps the air warm, but it's chilly in the shade. Honking geese fly overhead and crickets chirp throughout the lengthening nights. Dried leaves swirls about in the breeze, while those still in the trees for a riot of color. What is going on inside the tree that causes the color change?
Trees are getting ready for a long winter's nap. Like animals going into hibernation, everything is slowing down. Trees have been gorging themselves on sunlight all summer, and now their metabolism is slowing down. The chlorophyll is breaking down and water uptake is stopping. Chlorophyll absorbs all wavelengths of light except green, which is reflected back to us. Without chlorophyll, we see other chemicals in the leaf.

A yellow sugar maple catches the late morning sun

The yellow leaf of a sugar maple

Xanthophyll colors the leaves of aspens, birches, and beeches a bright yellow. It's also found in corn.  Red and purple in red maples and scarlet oaks comes from anthocyanin, which is produced when the chlorophyll stops and the leaf metabolizes extra sugars. Carotene, the same as what you find in a carrot, gives trees like sugar maple and sassafras their orange leaves. Orange can also come from a leaf that is showing both xanthophyll and anthocyanin. Brown, such as in oaks, comes from tannins. Carotene and Xanthophyll are present all year in the leaves, but are overshadowed by chlorophyll.

Another sugar maple, this one decked out in red

This red sugar maple leaf fell of a Canadian flag

The brilliance of each color, as well as the amount of colors relative to each other, are dependent on the weather. If fall is sunny and dry, trees will produce more anthocyanin. Trees will be a more brilliant red. Other years, trees won't produce as much or even none at all and nearly all leaves will change to yellow.
But of course, each tree is an individual so it may change well before its neighbor or have different or more vibrant colors, even among the same species. I've seen red maples that look like traffic lights with red, yellow, and green leaves on the same tree. I've even seen multi-colored leaves.

Brown oak leaf, rich in tannin

Yet another sugar maple, this time in orange

Get out there and enjoy some biochemistry in action before it's too late! The leaves have been great this year, peaking in my area this week and next. Up north you may be past peak, and down south it's on its way! This week's information comes from SUNY College of Environmental Science and Forestry and Montana Natural History Center.

Yellow and brown hickories and oaks basking in late
afternoon sunshine

Crickets

Fall has almost fallen. It's hard to believe summer was in full swing when you last read a fresh Nature Minute blog. Internet issues and life in general kept me from my regular schedule. Maybe where you are, the leaves are starting to turn, there's a bit of crispness in the air, mornings are full of fog, and nights are longer and full of chirping crickets.

Black field cricket Gryllus assimilis (Texas A&M) 

Here in Pennsylvania, crickets typically begin their nightly serenades in the late summer, continuing through the fall. Only the males chirp. They do so by rubbing their wings together, as a mating call for the females. They are most active at night, and even during daytime are hard to find. If they notice you getting close, they'll stop chirping so you really need to look hard if you want to find the source of the chirp. Warmer temperatures will produce more chirps, and the number of chirps drops with the temperature. I never counted chirps before, so I never noticed this.

Northern mole cricket Neocurtilla hexadactyla
(University of Florida)

Many people consider crickets to be a pest because the chirping gets annoying, but they are generally harmless. Since crickets favor loose soil, they are frequently found in flower beds, which are usually right under your bedroom window, giving you a front row seat. At the bottom of the food chain, in large numbers they have the potential to attract other unwanted guests to your home such as raccoons and spiders.

Carolina ground cricket Eunemobius carolinus
(Oklahoma Panhandle State University)

Nature Minute will return in October with more autumnal awesomeness. I'm taking a much-needed vacation. Until then, relax to the sound of the crickets. Don't let them drive you nuts. They'll only be around a few more weeks, and then it will be too cold to keep the windows open at night. This week's cricket facts come from Terro.