Such Seasonal Splendor -- The Foliage Of The Fall Is A Sight For The Eyes

It smells like vanilla or sweet oranges, depending on your nose, at the Washington Park Arboretum this week.

It's not the first sign of fall in the lush park, but when the round-leafed katsura trees behind the Visitors Center turn golden yellow and fragrant, the splendor of the season has truly arrived.

In the park, in the cities and beyond, fall's golds, crimsons and purple-reds are quickly overtaking the leafy greens.

Which prompts the annual question: Why do leaves change colors?

Credit the cooler, shorter days of fall, which means less time for leaves to photosynthesis energy from the sun. That's the process that produces, among other things, chlorophyll to keep leaves green.

As the greens fade, underlying orange and yellow pigments show through the leaves, explains Arthur Lee Jacobson, author of "Trees of Seattle" (Sasquatch Books). Leaves with more sugar, like those of many maples and sourwoods, turn red.

Weather is a big factor in how good a fall display we get, notes Paul West, Seattle's urban forester. "Sunny days and cold nights give us the best color, which is why this may be a real good year for foliage."

Summer weather also counts toward fall colors, West says. "The amount of heat, drought and stress on the trees makes a big difference. And location. You can have two vine maples nearby. One is glorious and the other so-so, because of the varying sun and rain each gets."

On the East Coast, seasonal color changes, like the weather, are intense and fast. Puget Sound weather is more subtle, and so are the shifts in color, which some years extend from September into November.

Here are some places to see the fall displays:

The arboretum, tucked at the edge of Lake Washington about a mile south of the University of Washington, is a delightful place to stroll or drive. You'll see many kinds of maples, mountain ash laden with bright clusters of red berries, oaks, chestnuts, hickories, the tall red-leafed sourwoods, the golden katsuras and much more. Visit the Japanese Garden, where trees have been carefully planted to show their seasonal colors.

In the arboretum and elsewhere, the most colorful trees are often imports, says arboretum gardener John Candy. "Our native trees don't color as much, and our big leaf maples turn brown. But kids like them, the leaves are fun to play in."

Many arboretum plants have name plates so you can tell what you're seeing. Free guided walks on Saturdays and Sundays leave the Graham Visitor Center at 1 p.m.

The sprawling UW campus and surrounding neighborhoods are a good place to see fall foliage. On campus Jacobson has counted at least 475 different kinds of trees.

Many city streets are lined with big maple, oak, cherry, ash, elm, hickory or gingko trees turning color. Older neighborhoods like Capitol Hill and Magnolia are good places to look, as are parks such as Volunteer, Discovery and Woodland.

In South Seattle, many leaf-seekers like the Japanese-inspired foliage of Kubota Garden. The park has maples, bamboo and other more exotic plants changing colors. Climb to the lookout above the waterfall, to see fall tapestries set against evergreens, streams, ponds and a bright red foot bridge.

On the Eastside, Lake Sammamish State Park near Issaquah has trees in shades of fall. Bellevue's Lake Hills Greenbelt leads to shimmering red blueberry fields near Larsen and Phantom lakes. St. Edwards State Park in Kirkland and roads near Fall City and Carnation are good.

Marymoor Park in Redmond has many unusual older trees turning colors. South, Maple Valley is true to its name.

Once you've seen leaves up close, consider places to view them afar. West, the urban forester, likes east Alki. High above the beach are big-leaf maples; across the water are the tree-covered hillsides of Beacon and Queen Anne hills.

Lake Washington Boulevard, from all sides of the lake, offers tree views. If you're heading east on the I-90 bridge, watch for a vivid splash of reds and purples along the stairclimb, just before you enter the tunnel.

Jacobson's "Trees of Seattle," "Northwest Trees" by Stephen Amo and Ramona Hammerly (The Mountaineers) and "The Garden in Autumn" by Allen Lacy (Henry Holt and Company) may help you identify what you see. ----------------------------------------------------------------- MOUNTAINS ABLAZE WITH COLOR, TOO

Fall foliage in the lowlands is more colorful by the day. But this weekend - and, depending on the weather, for at least the next week or so - the foothills and passes of the state's mountains are lovely.

Highway 2 across Stevens Pass is a popular route, particularly this weekend when the Leavenworth Autumn Leaf Festival runs through tomorrow. The festival features art and oompah music, and other activities.

But foliage is the focus. Just outside the Bavarian-themed village, Tumwater Canyon and Icicle Valley are vivid forests of vine maple, cottonwood and aspen. Scarlet swaths of blueberry and huckleberry bushes add to the color. Soon the larch tree needles will turn vivid gold.

Leavenworth is about 120 miles east of Seattle. Many people like to go via Stevens Pass, then loop home across Blewett and Snoqualmie (I-90) passes.

You can do it in a day, or make it a weekend. But rooms are scarce tonight in Leavenworth and nearby towns such as Wenatchee due to the festival. Information: (509) 548-5807.

Another leaf route with a festival is the scenic Mountain Loop Highway out of Granite Falls. This weekend Granite Falls Railroad Days has a carnival both days, a logging and railroad display today. Information: (360) 691-6441) Other mountain routes, including the North Cascades Highway 20, offer great vistas.

If you'd rather ride than drive, the Metro Employees Historic Vehicle Association takes a restored motor bus on a four-hour foliage trip through the Cascade foothills tomorrow. You don't need reservations, though seating is limited. The bus leaves at 11 a.m. tomorrow from Second Avenue South and South Main Street in Seattle. ($4 adults, $3 seniors and kids 2-11.) Information: 633-4590.