SAN FRANCISCO (KGO) -- Stroll along the dense wooded tails in the Presidio and you'll journey through a hidden patch of San Francisco history -- and Presidio Trust Forester Steven Duffy says hidden is just the way the army wanted it.
"So originally, this was chaparral. This was dune scrub. This was anything but forest. And the army had one thing in mind, and that was protection or camouflage for their base," Duffy said.
Easy to understand when you roll back the clock and gaze at the Presidio of the 1800s. A wide open, windswept plane, where cows could graze on the grass and anyone passing by could survey the scene. But all that changed when the army began planting what you might call the great camouflage forest: groves of Monterey pine, cypress and blue gum Eucalyptus. With many of the tallest trees perched closely together on the highest ridges, giving the illusion that the Presidio is much bigger than it really is and shading the valleys from prying eyes.
"They were not concerned with forest health. They were concerned with making this place look larger and imposing and a better hiding place for their goings about," Duffy said.
So flash forward a century or so, and many of those original trees are now dying off or toppling in storms, creating a problem and an historic opportunity.
"This is coyote bush right here. It's a common native plant throughout California," said Presidio Associate Director of Natural Resources Lou Stringer, pointing to a lush bush.
Stringer and Duffy are part of a team that's busy restoring the Presidio's historic forests, with an eye to making them healthier at the same time. Those plans include, not just on trees, but native plants.
"These are plants that were indigenous to the Presidio, prior to the army planting the forest here. And we were figuring out ways so that they can coexist," Stringer said.
And he says the key is diversity. Keep an eye out and you'll spot a variety of new groves. Some on their way to becoming mature trees, others just planted from seedlings.
"Yeah, so here we have a bunch of little pine trees. And these were grown from seed in the Presidio," says Nursery Manager Annette Russell, showing off rows of miniature trees.
She said the trees and many native plants are also being raised from samples collected in the Presidio. Providing a natural habitat for local pollinators, like the Variable Checkerspot Butterfly recently reintroduced to the Presidio, and native Quail are also being considered for reintroduction -- and all coexisting with the rejuvenated forest.
"So when the trees get tall, they have the stature that looks like the historic forest. But underneath them will have all of these different flowering plants that will make it possible for more insects to thrive, and then birds to nest," Stringer said.
And with the broad biodiversity, comes perhaps the long-term benefit, making the Presidio's ecosystem more resilient to climate change. It is a new 21st century battle the Presidio's early military planners could never have envisioned when they transformed a sprawling plane into the forested paradise we enjoy today.
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