A Harbor for Vernal Pools
At first no one knew what they were.
The lush pockets of green had sprung up along Interstate 80 between Sacramento and San Francisco and had perplexed travelers.
"This is a very visible project," said Kerry Dawson, a University of Georgia professor of landscape architecture and horticulture whose research is aimed at preserving fragile or endangered habitats from Georgia to California. "We had lots of calls from folks who thought we were building a golf course."
Instead of making putting greens, Dawson was helping the California Department of Transportation (CalTrans) build vernal pools - shallow depressions that hold water only during wet seasons and are defined by the types of plants and animals that inhabit them.
Many of California's vernal pools have been obliterated by agricultural, commercial and residential development. In complying with federal law - which requires states to budget 7 percent of their federal highway landscaping funds for wildflowers - CalTrans had already spent half a million dollars on unsuccessful efforts to establish vernal pool vegetation. That's when they sought Dawson's help.
"They wanted to determine the ecological conditions that would sustain vernal pools over the long haul and to see if the plants would respond," he said.
Respond, they did. But would the plants survive?
The real test for Dawson and CalTrans came last year, a decade after the project had begun. Dawson evaluated the pools in July to see whether they withstood the test of time.
The answer was yes.
He found that both the unseeded and the seeded pools contained a full spectrum of vernal pool species. Native plants like Downingia, acolorful sunflower cousin, were surviving,reproducing and holding their own against fierce competition.
"You just don't throw out some wildflower seeds," he said. "Past research on other methods of wildflower planting indicated that seeded populations along California highways always decrease over time. You have to create ecological conditions that will sustain them."
Unlike ponds, where water stands for long periods of time, vernal pools are ephemeral wetlands: Each year, they grow and flourish during a season or two and then dry up. In California, vernal pools mark the rainy season from December to June. Plants and animals that grow in these shallow depressions are adapted to a wet season-dry season life cycle. For example, when the pools dry up, fairy shrimp and other invertebrates burrow underground and wait for another rainy season.
"CalTrans wanted plants that would reproduce quickly on their own and would not require much management," he said. They could not argue with the benefits of successful vernal pools: reduced maintenance costs, aesthetically enhanced landscapes and environmental responsibility.
Dawson built 12 pools for $12,000 each: Six were built artificially with top soil from the site and six were made by relocating and reconstructing other vernal pools that were doomed by a warehouse construction project. He tried various seeding strategies, including leaving some pools unseeded to see if they would be colonized by seeds from nearby pools.
In addition to learning which vernal pool flowers will colonize unseeded pools, he also discovered that fully seeded pools behaved remarkably like natural ones, and that the more buoyant seeds migrated greater distances than less buoyant ones.
And the pools were low-maintenance. "You just mow them in the fall," he said.
Dawson's research has been good news for other vernal pools. For instance, in 1993, the widening of Highway 41 between Fresno and Sequoia National Park threatened to destroy several vernal pools, so CalTrans asked Dawson to aid in a mitigation plan rather than lose them to a bulldozer.
The wildflowers growing in the original dozen pools also have been good news for vernal pool bees and the researchers who study them.
"We don't know how the bees got there or where they came from, but we do know they spend their entire life cycle within 20 yards of the vernal pool," said Dawson, who has worked for two decades with agencies from coast to coast to restore, re-create and preserve native habitats and their flora and fauna.
For more information about UGA's School of Environmental Design, access http://www.sed.uga.edu/