Riparian woodlands occur in ribbon-like bands along stream beds where rich soils and high humidity produce a natural greenhouse effect. Although this unique community accounts for less than one per cent of California's total forest acreage, it supports one of the most diverse ecological communities of plants and animals. Tall deciduous trees such as big-leaf maple, Acer macrophyllum, and the evergreen California bay laurel tower above a lush understory of ferns and delicate wildflowers. Unfortunately, many riparian woodlands have been destroyed over the last century because the fertile soils along rivers are among the most sought after for agricultural lands, and because numerous rivers have been channelized for flood control projects.
Where rainfall is heavy, as along the north coast, riparian woodlands mingle with adjacent forests. The predominantly deciduous trees, with their bright green leaves, contrast sharply with their dark green coniferous neighbors. Along the south coast, where drier conditions prevail, the contrast between the lush, green riparian community and the drier, brown surroundings may be even more striking.
Common to practically all riparian communities are big-leaf maple and California bay laurel. Red alder, Alnus oregona, and black cottonwood, Populus trichocarpa, are typical of northern and central coast regions, whereas Fremont cottonwood, Populus fremontii, and western sycamore, Platanus racemosa, are common riparian trees in central and southern coastal regions.
Below the canopy of trees, rich riparian soils support many species of ferns and willows such as the coarse and wiry bracken fern, Pteridium aquilinum; tall, graceful lady fern, Athyrium filix-femina; and sandbar willow, Salix hindsiana. Velvety-leaved canyon gooseberry, Ribes menziesii; California blackberry, Rubus vitifolius; and twinberry, Lonicera involucrata, are frequently encountered shrubs in riparian communities.
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