Plant Communities of Mount Diablo State Park
Riparian woodland is found only along permanent streams and rivers, where the water table remains at or just below the surface all year. Our area has no true rivers, but there are several perennial streams -- some with fairly broad floodplains -- that support riparian woodland.
Because riparian woodlands have a guaranteed water supply, their component trees are very different from trees in most other environmental situations. These trees are not limited by the hot, dry days of summer; rather they can afford to grow fast and profligately right through the longest days of the year. Consequently, the derivation of riparian woodlands is entirely different from that of the rest of our flora. The closest relatives to riparian species come from summer-wet climates such as those across the Midwest and eastern parts of the United states. Wander in these forests if you are homesick for the look and feel of eastern hardwood forests.
Riparian trees -- because of their ancestry from eastern United States climates -- behave as though they still were adapted to cold winters. Nearly all are deciduous in winter, for they can afford to make whole new sets of leaves the following year, come what may. Leaves are also designed in ways that suggest water wastefulness: they're broad, thin, often lobed or compound, and held horizontally -- fully exposed to the summer sun. They are also borne in thick tiers from top to bottom. Riparian trees reach maturity quickly because they're able to grow over such long periods each year. Quick growth may cause weak wood, however, and many riparian trees are liabilities because of brittle limbs. They also have relatively short life spans.
Excerpted from MDIA's book Plants of the East Bay Parks, by Glenn Keator, Ph. D.
Madrone Canyon Mike Woodring