The California sycamore ranges from Baja northwards to the Sacramento Valley and up into the Sierra Nevada foothills. It is absent from north coast ranges in what would seemingly be suitable habitat, but we'll get to that later. It is almost always associated with riparian woodland habitat and grows below 3,000 feet in elevation.
California sycamore is long-lived and grows up to 100 feet tall . The tree
usually has multiple trunks that can be up to five feet in diameter. These
trunks are usually reclining and resting along the ground. The sycamore
is an overstory/canopy species that is deciduous.
California sycamore's presence attests to the perennial abundance of near-surface water . It is an obligate phreatophyte, meaning the tree needs access to ground water within the root zone. Sycamore is usually in sites higher and drier than cottonwood and grows in coarse, porous sand and gravel. This suggests the need for adequate root aeration.
If traveling along the intermittent streams of the southern coast ranges and southern California, you would notice that California sycamore is a dominant tree of these areas. It forms open woodlands along the terraces. In the northern part of the tree's range however, it's dominance diminishes. Shanfield (1981) found that in this northern part of its range, P. racemosa had a cover value of 4.8% compared to cottonwood, elder, willow, oak, and walnut which ranged from 17% to 20%.
The fungus (Anthracnose) is a serious and prevalent disease of the California sycamore. It causes complete spring defoliation. This fungus is promoted by cool, wet springs and is currently stressing the sycamores in counties at the northern extent of the range.
California sycamore is not a pioneer species in the riparian habitat. This niche is occupied by the cottonwoods and the willows. Sycamore is considered a mid-successional species and forms older groves on the higher terraces. Land clearing of these upper terraces for buildings with a nice view has been the cause of a large reduction in the sycamore population of the Sacramento Valley.
Katibeh (1981) studied the riparian forests of California's central valley and found very few younger size classes of California sycamore. He noted that the central valley riparian wetlands once occupied 2 to 3 million acres, however they now have been reduced by 90%. The lack of continued recruitment into riparian vegetation communities indicates that over time, as existing adult trees age and die, systems are experiencing large structural and floristic shifts. This means that the ecological values (ability to support native riparian-dependent birds and other wildlife) of the vegetations are being progressively impaired.
Forty to ninety-seven percent of the vertebrate species
of the central valley use or depend upon the riparian system. Birds use
the canopy area of the riparian areas most heavily and therefore depend
upon species such as California sycamore. Birds such as red-tailed hawks,
red-shouldered hawks, Swainson's hawk, Downey and Nuttall woodpeckers and
various species of warblers would be largely eliminated by the absence
of the upper tree stratum.
Katibeh, Edwin F. 1981. A brief history of riparian forests in the central valley of California. In, California Riparian Ecosystems: Ecology, Productivity, and Productive Management. Warner, R.E. and K.M. Hendricks. University of California Press, Berkeley. 1981. This book is jam-packed full of information on riparian habitat systems. I found it to be extremely helpful in all aspects (productivity, diversity, disturbance, distribution, etc.). In terms of the individual article, it was useful in the sense of general information on riparian habitat.
Shanfield, Allan N. 1981. Alder, cottonwood, and sycamore distribution and regeneration along the Nacimiento River, California. In, California Riparian Ecosystems: Ecology, Productivity, and Productive Management. Warner, R.E. and K.M. Hendricks. University of California Press, Berkeley. 1981. As in the above reference, a great book. The paper by Shanfield was interesting in terms of how sycamores interact with the other species in the riparian ecosystem and the niche sycamore occupies.