In the not too distant past, you could park a car in the midst of the Mariposa Grove of Giant Sequoias (Sequoiadendron giganteum) at California’s Yosemite National Park. That is no longer possible thanks to a recently-completed $40 million restoration by the National Park Service (NPS) in partnership with the Yosemite Conservancy and Seattle-based multidisciplinary design firm Mithun.
Now, visitors park at a newly constructed, 300-vehicle-capacity terminal two miles away and take a shuttle bus to a main entry plaza at the lower grove.
“Before, it used to be a pass-through area. People didn’t even really notice it,” says Mithun senior associate Christian Runge, ASLA, about the restored lower grove. “They saw a couple of big trees, but it wasn’t a place. Now, it’s the centerpiece of the whole project.”
This transformation didn’t happen for its own sake. Years of heavy visitor traffic and poor planning took their toll on the storied trees, raising alarm about their future health.
The giant sequoia, which grows to approximately 300-feet high and can live for thousands of years, is an endangered species. This tree occupies a narrow ecological niche only 260-miles-wide on the western slopes of the Sierra Nevada mountains and requires specific environmental conditions to thrive. The Mariposa Grove is one of the few places on earth where the sequoia is able to reseed on its own.
“The Sequoias exist on the western slopes of the Sierras at a certain elevation, which is essentially at the rain-snow transitional zone,” says Runge. “If you go much lower, it’s all rain; if you go much higher, it’s all snow. That feeds the hydrology of these mountain wetland stream systems, which the sequoias tend to cluster closely around.”
“So, restoring hydrology and improving the natural hydrologic flow in the grove was really an important piece of the restoration puzzle.”
To achieve this, the design team removed the existing network of asphalt roads and paths, which were interfering with the grove’s natural drainage patterns.
One road that connected the lower and upper groves crossed streams and wetlands approximately 30 times, says Runge. “Those culverts were anywhere between 50-60 years old, and a lot of them weren’t even functioning anymore.”
In the place of asphalt and culverts, Mithun designed a series of elevated boardwalks and trails that allow for a variety of visitor experiences and do not interfere with the delicate hydrology needed to sustain the sequoias.
“If we keep those streams running and hope for the best with snowmelt, then we can imagine those populations will continue to be stable and hopefully grow into mature trees,” Runge says.
However, that outcome is not guaranteed. Giant sequoias are threatened by the effects of climate change, which could reduce the amount of groundwater available to the trees and make it more difficult for seedlings to survive.
Runge acknowledges that in the face of such forces, there is only so much that the project can accomplish.
“The best thing we can really do is improve and maintain the processes that keep the sequoias as healthy as possible in order to provide as much resilience as possible,” says Runge. “Improving those processes was really the focus of the restoration.”
Ensuring the survival of the Mariposa grove also required changes to the visitor experience. In addition to restoring groundwater hydrology, the elevated boardwalks also keep visitors at a distance from the trees in the grove’s most heavily trafficked areas.
“People want to get up close to them. It’s just a human, intuitive thing that you want to be able to do,” Runge says. But, “if everyone did that, there would be too much damage to the tree.”
Instead, Mithun created a series of loops that become progressively less contained as they lead further from the main entry plaza. “Each loop takes you further out and is closer to a wilderness experience. If you want to go up into the upper grove, that’s something that can only really be hiked into.”
In addition to the new trails, enhancements to the visitor experience include a new visitor center and comfort stations designed by Mithun architects Brendan Connolly and Susan Olmsted, ASLA.
While the design language and material choices were in some way constrained by the need to work within the rustic National Park aesthetic of stone and timber, Runge says the design team found room for creativity in the details.
“We didn’t argue about modern versus historic, but we did push for quality detailing and structural systems, thinking through stonework, and trying to understand what the Works Progress Administration (WPA)-era standards were in reality versus just giving the impression of something being historic. Making something that is durable, long-lasting, and in some sense beautiful was the key goal for us both in terms of the architectural elements and site elements, like the boardwalk.”
For Runge, striking this balance between ecology and the visitor experience defined Mithun’s approach to the project. “Ultimately, I feel like we got there,” he says. “It feels like a transformed place.”