Rising rents may soon write the final chapter in the story of two vintage bookstores after more than 20 years of book sales on 16th Street.

By year’s end the landmark shops, Adobe Books and Forest Books, which jointly house more than 45,000 used volumes, could vanish from the Mission’s literary scene as pressures from gentrification and e-book sales squeeze out independent booksellers.

“The book business is not as healthy as it once was,” said Adobe’s owner, Andrew McKinley. “People don’t accumulate libraries like they used to.” Without commercial rent control, San Francisco landlords can raise rents at will if a shop isn’t under lease.

“We’ve paid a low rent,” McKinley said, but now he faces a 50 percent increase. “A new landlord and the hotness of the Mission have combined to push us out.” The property management firm for McKinley’s landlord did not return calls seeking comment.

“Bookstores dignify a neighborhood,” said Jakushū Gregory Wood, the 63-year-old Soto Zen monk who opened Forest Books in 1989. The shop may close at year’s end rather than pay triple its current rent.

“The whole point of the store is to create a space for peace and a contemplative atmosphere,” said Wood, who wears small spectacles and keeps his gray hair close-cropped.

Walking into Forest Books, customers are greeted by the smell of incense. A fountain bubbles near the register and chimes ring when a customer comes or goes. Prayer flags hang near the entrance. Custom-built shelves line the walls and create wide aisles where readers browse books with subjects ranging from Taoism to contemporary literature.

Despite his peacable monk’s demeanor, Wood is waging a fierce fight to save Forest Books. A red-lettered petition reads: “Forest Books is being forced to close its doors! After 23 years in this location our greedy landlord, Mission Housing Development Corporation, has raised our rent 300 percent!” He’s gathered more than 100 signatures so far.

An 80-year-old Forest Books customer who gave his name as Edward was browsing the translations section for works from Scandinavia. “They have a very interesting collection of books, and a good selection of translations from different countries,” he said.

He is sad that Adobe is closing. “That seems to happen,” he said. “They’re chasing all the good things away.”

Forest Books’ landlord, Mission Housing Development Corporation (MHDC), is a nonprofit organization that owns about 30 buildings in the Mission and also provides low-income housing and services to more than 1,000 families, according to its president and CEO Larry Del Carlo.

“We don’t want Forest Books to leave,” Del Carlo said. But in order to continue to provide its services, MHDC must raise below-market rents on its commercial properties to market level, he said. Grant money that MHDC formerly received has dried up, forcing a shift as the Mission becomes more popular.

MHDC offered Wood a gradual increase, Del Carlo said, beginning with a 50 percent hike this year and more than tripling to a market rate of $3.38 per square foot in 2016.

“I might be able to handle a 10 to 15 percent increase over that period, but 300 percent is just inconceivable,” Wood said.

Wood rejected the gradual plan and received a letter from MHDC in July saying that his rent would be $3 per square foot effective September 2012, he said.

Del Carlo asserts that the conversation is still open.

“We’re trying to do the right thing with Forest Books, but we also have a fiduciary responsibility as a nonprofit that’s providing not only housing to our low-income families, but also providing services.”

Originally, Wood said, his lease was for 40 years, with five-year options to renew. Currently Forest Books is on a month-to-month basis, something Wood said he wasn’t told about until it was too late.

Even the shop’s size is in dispute: Wood said that MHDC is trying to charge him for 1,876 square feet when his original lease said 1,792 square feet.

“There’s been some misunderstanding about the term gentrification,” said Wood. “It’s often used to describe anything that’s new and nice. The problem is that when you have businesses move in that are corporately based, that don’t have an interaction with the community, that don’t give back to the community, that take money out of the community, or that just think a standard formula for business will just fit in anywhere they put it — that kind of gentrification destroys communities.”

McKinley of Adobe Books agreed that gentrification is driving his rent hike.

“When we moved in, the neighborhood was a bad place. Now it’s a desirable place. Back then the Mission was shabbier but in some ways more human.”

Adobe has its own distinct vibe. Narrow aisles are cluttered with novels, art books, chairs and couches. In the back is a small gallery. It’s not uncommon to find regular visitors sleeping in the afternoons. Up front, Willie Nelson’s voice resonates softly over the speakers. The owner has to squeeze through tight spaces and step over boxes to answer the phone.

Clad in green corduroy pants and maroon sweatshirt, the 55-year-old McKinley recalled the old Mission. “It was affordable, it was human and it had some foot traffic. There was a real bohemian element,” he said.

That sense of community fostered by the bookstores also helped make the Mission a magnet for the commercial forces now driving them out.

The shop’s regulars are bracing for the loss.

“It’s a people place for me,” said Adobe customer J. Lee, 42. “It’s really too bad about the closing.” Lee said he’s been stopping into Adobe about twice a week for the last 12 years to hang out, socialize or write poetry.

“It’s the remnants of the bohemian Mission,” Lee said. “This is an institution. A mental institution, sometimes,” he joked.

“Maybe small businesses are doomed. The old way of doing business here is getting kicked out,” said McKinley, who is reassessing his business model.

Among the possible rescue strategies for Adobe is a plan to turn the store into a cooperative, with customers paying to be members. McKinley envisions crowd-funding providing enough to keep the store afloat while changes are implemented.

“Adobe has until the end of the year to get its act together,” he said.

Barring a reprieve, both shop owners say they may have to put their stock in storage and start selling books online, or even move. That’s a step neither relishes; both would prefer to stay put.

“This is where we’re gonna make our stand,” McKinley said.