California poplar, better-known as black cottonwood (Populus balsamifera spp. trichocarpa), are often confused with Frémont cottonwood (Populus fremontii spp. fremontii).
It’s easy to mistake these siblings from a distance, as their size, bark, shape and colorations are similar, but look closely at their leaves and the difference is evident.
Black cottonwood have a darker, spear-pointed leaf, while Frémont cottonwood have a lighter-green, heart-shaped leaf, similar to aspen but with a toothy edge. Black cottonwood are the only poplar with willow-like leaves, though unlike willow, which are not aromatic, California poplar emit a strong odor from their buds in springtime.
The young specimen (pictured above) stands in a parking lot near Jenkinson Lake in Sly Park (Sierra Nevada, El Dorado County – US 50). It was planted there, though black cottonwood grow naturally near water. They thrive beside rushing streams “where water, rich in oxygen,” Jim Paruk writes in Sierra Nevada Tree Identifier, “speeds their growth.”
Native to both the east and west slope of the Sierra Nevada, black cottonwood are more often found on the west slope, growing up to 6,000 feet. However, the finest example of California poplar is found along Pine Creek, north of Bishop (Inyo County), where dense groves line the creek, as they have for millennia.
Cottonwood will peak after aspen do, because California poplar grow – on average – well below the 10,000′ upper limit for aspen. Cottonwood also lack the varied red, pink, orange, yellow and lime that appear in peaking aspen. They are uniformly gold at peak and thus aren’t photographed as often, though they have poignant sculptural beauty and are more widely dispersed.
Unlike aspen (which are limited to the Eastern Sierra, San Bernardino mountains and Cascades at elevations from 6,000′ to tree line), cottonwood are found throughout California, typically below 7,000′.
Within the two varieties, black cottonwood grow to the highest elevations (some as high as 9,000′), while Frémont cottonwood aren’t usually seen above 5,000′. Elevation is a good way to tell if the cottonwood is black or Frémont, at least until you can get close enough to see its leaf.
Presently, both California poplar and Frémont cottonwood are Just Starting (0-10%), but look for them to peak beginning in two weeks and continuing into December in Southern California drainages (i.e., Big Tujunga Canyon).