Less than a decade ago, the largest mid-elevation meadow at Yosemite National Park, nestled in foothills near Hetch Hetchy Reservoir, was privately owned rangeland. It was widely trampled on by cattle, dried up and of little or no interest to visitors. Today, the area is a whole different place. An $18 million makeover of what’s known as Ackerson Meadow, which was recently acquired by the National Park Service, is transforming this dusty tract on the park’s western edge into a vibrant hub of wildflowers, songbirds and water-loving grasses — an effort billed as the biggest restoration project in Yosemite history. …  The hope is that the revived meadow, like a sponge, will hold more water for native plants, wildlife and downstream communities that depend on the region for water supplies.