Biology Reference
In-Depth Information
In the last few decades, more than $100 million has been spent releasing
Central Valley rivers in the bay's watershed from their straightjackets.
Their channels and sandbars are being allowed to move and change, and
their banks to overtop, erode, and re-form. Still more effort has gone into
restoring the trees, brush, and plants associated with riparian habitats.
Along the 100 miles of the lower Sacramento River—between Red
Bluff and Colusa, where early settlers in centuries past fought so hard for
so long to control floods—public interests have secured more than 9,000
acres of “inner river zone” for an experiment in re-creating meander
function and regenerating forests. This was no easy task in a river reach
where more than half the cut banks—the clifflike outer bend of a mean-
der—are lined entirely with concrete. They have also been working to
revegetate the riverbanks and former floodplains, which once sustained
over 500,000 acres of riparian forest, but of which only 25,000 acres now
remain. As of 2009, they had cleared weeds, planted new trees, simulated
natural flooding conditions, and reintroduced riparian species to more
than 5,800 acres.
One species adapted to ever-changing river paths is the cottonwood
tree. Cottonwood evolved to take advantage of eroding banks and the
flash floods of natural flows in spring, which swept away old vegetation
and created fertile seedbeds. Generations of these trees once lined the
great waterways of the valley, ranging from silver-barked octogenarians
on the upper banks to middle-aged saplings and young seedlings closer to
the water. But on the Sacramento River in the 1990s, riparian ecologists
noted the seedlings weren't growing up. Modern dam operations and
shoreline riprap had changed river conditions until the light, hairy seeds
germinated too low on the riverbank and in places susceptible to winter
storms. In the last few decades, the Nature Conservancy has been working
NOT SO GOLDEN GRASS
California's summer hills were not always golden. Exotic, annual turf grasses
introduced by Spanish ranchers to benefit cattle are what dry up and turn yel-
low; the original native grasses stayed green all summer. The state has more
than 300 species of native grasses—most are perennial bunchgrasses that
leave space in the soil for other plants and wildlife. Conversion of native peren-
nial grassland to non-native turf has increased erosion, runoff, fire danger, and
weeds, and it has reduced water retention in the soil. Efforts to restore native
grasslands are now gaining ground with the help of fire and herbicides.
