O.K…. so we’re not Vermont. However we do have some pretty fall color displays. If you like the gold of aspen, you will see the same colors in our closely related cottonwood stands, both trees belonging to the genus Populus.
Cottonwoods are riparian trees, and the largest stands can be found along the Salinas River, particularly around Paso Robles and San Miguel. There are some lovely fall color trees along the banks of Shell Creek, Navajo Creek and the Estrella River. The gold color appears when the trees cannot replace the somewhat unstable chlorophyll compounds when water flow into the leaf becomes reduced. Chlorophyll is continually replaced during the ‘green’ months, the green being the wavelength of light that the leaf is not absorbed and converted to oxygen and carbohydrates. The yellow (or orange) comes from carotenoid compounds that break down blue and bluegreen wavelengths of light, but which are more stable than chlorophyll. The fact that the summer green of leaves varies between species is due to variance in the balance of the light absorbing compounds.
Willows also belong to the same family as the poplars, and can also show some pretty fall colors. Usually the willows hang on to their leaves into the winter months. Coon Creek in Montana de Oro State Park can have some pretty willow color. It also has lots of creek dogwood, which turns to a pretty but muted pink.
What Vermont has, and what we lack, are an abundance of trees like maple. Their leaves contain anthocyanin compounds that are bright red, and which are promoted by fall’s cooler temperatures. Fall is the time when we can really love poison oak, as it can turn the understory of places like the Los Osos Oaks Reserve into a little Vermont. However our intense drought has forced poison oak into early leaf drop, so that the
fall color can show up in mid-summer, and the plants are bare of leaves by the fall. Plants. like politicians, can turn red under stress.
– David Chipping