Leaves turn green each spring as they use pigments (chlorophyll, xanthophyll, and carotenoids) to harness the sun’s energy. The chlorophyll absorbs red and blue wavelengths but not green ones that are reflected back to our eyes; hiding underneath the chlorophyll are the other compounds for photosynthesis. As temperatures cool and days get shorter, leaves on deciduous trees stop producing new chlorophyll, and the familiar green color breaks down to reveal the other pigments that have been masked all season. Chlorophyll is expensive to make (for the tree); so when there isn't enough light to make it worth expending energy on, the green fades and the colors beneath show. This is a photoperiod process, not a temperature-dependent process.
How is the Red Pigment Made? Continued sunny days and cool nights trap sugars in leaves, and some leaves will form the red pigment anthocyanin, which colors trees like dogwoods or the non-native sugar maple near the Yosemite Chapel in the Valley. Vines like the poison oak along the El Portal Road also turn a brilliant orange, pink, or even purple.
What Colors Do Leaves Change to in a Variety of Yosemite’s Tree Species?
Quaking aspen: Yellow Dogwood: Red Non-native sugar maple: Red Bigleaf maple: Bright Yellow Black oak: Orange/brown to golden yellow Ceanothus/Deer brush: Yellow White alder: Yellow Black cottonwood/Fremont cottonwood: Yellow Poison oak: Red to purple
What Weather is Needed
for Good Color?
The best autumn colors occur under clear, dry, and cool conditions but not freezing weather. The degree of color may vary from tree to tree and even leaf to leaf. Leaves directly exposed to the sun may turn red, while shaded leaves may be yellow. Leaves on marcescent trees, like some California black oaks, will wither but linger all winter and only fall next spring when new leaves emerge.
Do Some New Leaves Grow during Winter?
Live oaks, tanoaks, bay laurel, and the conifers keep their newest leaves throughout the winter to get a head start on food production next spring.
Where in Yosemite Promises Good Color?
A search for quaking aspen, for instance, can be found in some favorite glades within the park. Easy for leaf-peepers to drive by are roadside stands along the Tioga Road near the Tuolumne Grove trailhead and the Yosemite Creek picnic area, while more isloated aspens grow along the Glacier Point Road past Summit Meadow. Plus, consider a gentle walk along the old road from Badger Pass ski area to Bridalveil Creek Campground that leads to aspen groves. Read on for more suggestions on where to see fall color:
Valley: Bigleaf maple might blend in with the oak woodlands most of the summer, but during the fall, its splash of yellow outlines riparian areas along the southern wall of Yosemite Valley from below Bridalveil Creek past Sentinel Creek and beyond Happy Isles. In general, look for mostly golden yellows to dark orange/brown on the black oaks; reds, pinks and yellow on the dogwoods; brilliant yellow on the black cottonwood; and reds, oranges and yellows on shrubs and low-growing herbaceous plants. Also, view a favorite fall tree: the non-native sugar maple that turns a brilliant red near the Yosemite Chapel.
Glacier Point: Look for a lot of yellow, such as from deer brush yellows and low-growing shrubs and, in a few locations, the yellows and oranges from quaking aspen.
Wawona: Look for mostly yellows and dark orange/browns on the black oaks; reds, pinks and yellow on the dogwoods; brilliant yellow on the bigleaf maple and black cottonwood; and reds, oranges and yellows on shrubs and low-growing herbaceous plants.
Tuolumne: Look for oranges, yellows and reds from the low-growing vaccinium (grouseberry and whortleberry, for example) and other low-growing shrubs. A few small aspens, which would turn yellow, can be seen along the Highway 120 corridor.
Certain Meadows: Some meadows might have Indian hemp that turns a bright yellow; bracken ferns that can turn yellow (often is just brownish); and some sedges and grasses that look golden.
El Portal: Some willows along the riverbanks might turn yellow along with the Fremont and black cottonwoods. The oaks turn yellow to orange/brown, and the wild grape vines are yellow. Look for the beautiful reds of poison oak.
When Will Color Be at its Height in Yosemite This Year?
Hard to predict, depending on light and weather. Usually in late October and, generally, lingering until the first heavy winter storms or hard frosts often in early December.
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