Why do leaves change color in the fall?

Fall colors • It's the time of year when nature begins winterizing. For trees, the process brings autumn splendor.

This is an archived article that was published on sltrib.com in 2010, and information in the article may be outdated. It is provided only for personal research purposes and may not be reprinted.

Many people think the first frost of the season causes autumn leaves to begin to change colors. But the process is far more complex than that.

Rita Dodge, a conservation botanist at Red Butte Garden, said a combination of the length of days shortening and temperatures dropping causes leaves to begin changing colors.

"When leaves are photosynthesizing," she said, "they are green and contain energy, water and nutrients. The tree begins to pull nutrients into its roots for storage in the winter. Fall and winter months are when shrubs and trees do more root growth. When spring comes, the process reverses and begins going into the leaves."

Leaves begin to fall off trees because the tree cuts off the leaf from getting any water or nutrients and eventually closes off the stem where the leaf is attached.

According to the U.S. Forest Service, certain colors are associated with particular species. For example, oaks turn red or brown and aspen yellow. Maples differ in color by species, ranging from glowing yellow to brilliant scarlet.

As chlorophyll — which gives leaves their green color in spring and summer — production slows down in the fall and eventually stops, the carotenoids in the leaves that produce the color are unmasked.

Weather also plays a factor as to the brilliance and amount of colors that develop in any autumn season, according to a Forest Service report that can be viewed in detail at www.na.fs.fed.us/spfo/pubs/leaves/leaves.htm. That report said temperature and moisture are the main influences in how intense the leaf displays are in a given year.

"A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays," the report said.

According to National Forest spokeswoman Kathy Jo Pollock, the agency has a national autumn leaf hot line — 1-800-354-4595 — which usually begins operation the first full week of September.

But the forest service website said actually predicting when the colors reach their height is difficult. And it varies throughout the country.

That's why travelers going to places such as New England or the Great Smoky Mountains to enjoy fall colors need to do some advance research by talking to area travel councils or looking up travel agents who specialize in such tours before taking a trip to see the leaves in other parts of the country.

Fall travel is great close to home as well.

"Fall is a great time to come up," said Craig McCarthy of the Park City Chamber of Commerce. "After Labor Day, lodging deals get even better than during the summer. All the major properties are eager to get people in."

Special events in Park City include the Tour des Suds Mountain Bike Climb from Main Street to Guardsmen's Pass Sept. 19, when bikers and bikes are decorated; the Park Silly Sunday Market on Sundays through Sept. 26, which features vendors, live music, gourmet food and street performers; the Egyptian Theater production of "The Great American Trailer Park" Sept. 17 through Oct. 3, Thursdays through Sundays; the Park City Film Series Friday, Saturday and Sunday at the City Library; and the exhibit "Living in Harmony: Music Makes Community" at the Park City Historical Museum.

Snowbird's Oktoberfest runs Saturdays and Sundays through Oct. 10 and features music, a vendors market, beer and German food as well as a number of outdoor activities and tram rides.

Monta Giles of the Heber Valley Chamber of Commerce said fall is one of the nicest times to be in the Heber Valley with temperatures near perfect in the 60s and 70s. In addition to scenic drives and golf, visitors can ride the Heber Valley Railroad to see the sights. Heber City will also hosts its 16th annual Cowboy Poetry Gathering Nov. 1-7.

wharton@sltrib.com —

Ten great Utah autumn drives

1. Big Cottonwood Canyon/Guardsman Pass/Park City/Midway • This complex of roads – some paved, some gravel — offers many beautiful options for a close-to-Salt Lake fall experience. Access Guardsman Pass by driving up Big Cottonwood Canyon, from near the top of Park City's Main Street or past the Wasatch Mountain State Park campground on State Road 224.

2. Alpine Loop • This narrow 24-mile long road, State Road 92, connects American Fork and Provo Canyons and provides great views of Mt. Timpanogos. Consider a short side trip to Cascade Springs, a nice place for an easy stroll on the boardwalks.

3. Nebo Loop • This 32-mile road follows the east side of the Mt. Nebo Wilderness Area including side trips to Payson Lakes, several interpretive sites, six overlooks, some picnic areas and campgrounds, and the Devil's Kitchen geologic site. The road can be accessed just east of Nephi or from Payson.

4. Logan Canyon • This 41-mile road follows U.S. 89 from Logan to the Utah-Idaho border. The canyon itself offers excellent fly fishing, great leaf displays, Tony Grove Lake, hiking into the Mt. Naomi Wilderness Area, campgrounds and picnic areas. Add to that the reward of great views of Bear Lake at the top.

5. Bountiful-Farmington Loop • This 24-mile mostly gravel road connects the towns of Farmington and Bountiful and partially runs across the top of Davis County providing great views of not only autumn leaves but of the Great Salt Lake. There are U.S. Forest Service campgrounds on both ends of the road.

6. Ogden River/Monte Cristo • Some locals call upper part of this the 44-mile State Road 39 that begins in Ogden, runs up Ogden Canyon and past Pineview Reservoir to the Wasatch-Cache-Uinta National Forest Boundary near Woodruff the Monte Cristo Highway because a peak by the same name guards it. Whatever you call it, it's beautiful in the fall. Add campgrounds and some nice dining spots as well as good fishing and it's a great place in the autumn.

7. Skyline Drive • This is a classic fall four-wheel drive adventure. The 86-mile mostly dirt road runs from U.S. 6 18 miles east of Thistle across the top of the Wasatch Plateau to I-70 18 miles east of Salina. Shorter routes are available by going up canyons from Fairview, Huntington, Ferron, Ephraim, Manti and Mayfield.

8. Red Cloud-Dry Fork Loop • Travelers looking for an eastern Utah adventure might try this 45-mile loop road that begins off U.S. 191 14 miles north of Vernal and runs west and south to Dry Fork. Much of the road is dirt and it can be rough in spots but there are some pretty streams and a few reservoirs for anglers.

9. Brian Head-Panguitch Lake • This pretty road runs 55 miles on State Road 143 and connects Parowan with Panguitch. Aspens and maples make this a particularly pretty drive. Stops at Panguitch Lake or the town of Brian Head provide places to enjoy a meal. It's also possible to take a side trip to Cedar Breaks National Monument on State Road 148.

10. Abajo Loop • This is a 35-mile single lane dirt road that travels west from Monticello and utilizes Forest Roads 105 to its junction with 079. This is a high elevation road that reaches heights of 10,300 feet, ends in Blanding and offers not only fall leaves but some great views of Canyonlands National Park and the Four Corners Region.

Source: Utah Office of Tourism