Mural designed by Rafael de Cárdenas and Goldman Properties.

Driving north from downtown Miami, up NW Second Avenue, I spotted a nightmare tropical world thriving behind a chain-link fence. Mutant plants bloomed; shards of light fractured the sky; and a multi-eyed alligator emerged from a pile of mud. This lurid scene was a mural painted across a concrete wall by graffiti artist Brandon Opalka, and was also my introduction to Wynwood, a 100-block arts district hemmed in by highways and a freight-rail line, and seemingly glued together by spray-painted walls. Just north of Wynwood, more graffiti walls dot the 18 blocks of the Design District, a neighborhood in which dying wholesale furniture businesses are giving way to boutiques and restaurants.

Both neighborhoods pulse with creative energy. But they aren't particularly nice or safe. In Wynwood, the predominant buildings are painted-concrete warehouses, windowless and fortresslike; the Design District mixes such warehouses with empty storefronts and office buildings. Most of the streets are still desolate.

In the 1990s, the cheap rents and open, high-ceilinged buildings began quietly drawing artists and dealers along with collectors whose holdings had outgrown their homes. At that time there were only a few galleries in Miami, mainly in South Beach, and not many opportunities for local artists to get noticed. According to Terry Riley, director of the Miami Art Museum from 2006 to 2010, and partner in the local office of K/R Architects, the conditions fomented the artistic innovation that's increasingly difficult in expensive arts capitals like New York. "In Wynwood," he said, "anyone with a little money can open a store, a gallery. It's an important area for experimentation. That makes it a big asset for Miami."

In 2002, the inaugural Art Basel Miami Beach fair changed everything, putting the city's art world in the glare of the international spotlight. The museum-quality holdings of important Miami collectors received widespread attention. Dozens of galleries cropped up. Last year, Art Basel and some dozen satellite fairs brought more than 40,000 people to Miami.

Wynwood and the Design District, with their acres of spray-painted walls, have become a destination for viewers and artists alike. Primary Flight is an organization of street artists that began painting murals in the area in 2005. "We wanted to seize back the city by doing public art," says Books Bischof, a founder. "We wanted to develop Wynwood as an arts community and develop ourselves as artists. A lot of it was me riding around in my mom's van with paint spilling out, crammed with as many ladders as possible."

The group now manages many of the local painted-wall projects, playing matchmaker between artists and willing property owners in order to avoid neighborhood conflicts and criminal charges. They had to persuade Miami graffiti crews to host world-class street artists on their turf, and also had to befriend vagrants so they would accept out-of-towners and "watch their backs." That's how a brightly painted pregnant woman with a smoking gun can now appear beside the humble gray door of a sewing-machine wholesaler. To extend their influence beyond the few days of Art Basel, the collective recently opened its own exhibition space, Primary Projects, in the Design District.

Two decades ago, major private collectors started relocating their collections to these neighborhoods and opening them to the public. Their diverse approaches to collecting, displaying and supporting art have helped shape the area's eclectic nature.

Don and Mera Rubell were Wynwood pioneers. They moved their collection to a two-story, concrete warehouse, formerly used by the federal Drug Enforcement Agency, in 1993. They had begun collecting as a young couple in New York in 1964, setting aside $85 a week to acquire art. Now, they and their family add 200 to 300 works a year-many of them large-scale pieces with a pop flavor, like a neon-lit covered wagon by Matthew Day Jackson.

I asked Mera Rubell what drew them to Miami. "It's a great nexus of North and South America," she said. "Miami is too often dismissed as a party city, and that works against us. That's why we were instrumental in bringing Art Basel here."

Not far from the Rubell collection is a warehouse complex surrounded by chain-link fencing, crowned by razor wire and bearing no exterior signage. Inside, large installations and other works from Martin Z. Margulies's 4,000-piece collection sprawl throughout an untidy maze of rooms. He has especially deep holdings in photography, much of it focusing on themes of African or African-American identity.

He likes the sense of possibility that Wynwood allows and that can't be duplicated in pricier art districts. "Where else am I going to find 19-foot ceilings?" he asked me when I visited. "I've expanded this place three times by just busting through walls." The space, which opened in 1999, now totals 45,000 square feet. He says he hasn't done a refined overhaul of the buildings: "I don't pretend this is a museum." Nevertheless, Art Basel can bring the complex thousands of visitors in less than a week.

Farther north, in the Design District, is the collection Rosa and Carlos de la Cruz opened in 2009. The de la Cruzes grew up in Havana, moved to the United States during the Cuban revolution and married in 1962. He built a successful beverage business as she increasingly focused on their growing art collection. Paintings of fellow Cubans like Félix González-Torres anchor holdings that now include work by Guillermo Kuitca and Ugo Rondinone. Project spaces in the building highlight Miami artists.

Located downtown, but working closely with the artists and galleries in the budding arts neighborhoods just north of it, the Cisneros Fontanals Art Foundation (CIFO) serves as an oasis for abstract art. Ella Fontanals-Cisneros, the founder, wrote by e-mail that hers is "the only foundation in Florida completely dedicated to the support and promotion of emerging and midcareer artists from Latin America." CIFO features annual exhibitions selected from her collection by prominent outside curators-this year, Jesús Fuenmayor of Caracas, Venezuela, and Philippe Pirotte of Antwerp, Belgium-and commissions new work from emerging Latin American artists chosen by a jury.

Such collections, then, with their rotating exhibitions and commissioned projects, are in some respects functioning as museums in Miami. I wondered what effect they would have on their struggling public counterparts, and whether they have any plans to form the kind of alliances between collections and museums that have been forged elsewhere. Reflecting the sentiment I heard from other collectors, Mera Rubell said, "We're so hands-on, so engaged in what we're doing now, that we've not formally made any decision about the future."

Some collectors are, however, at odds with the Miami Art Museum's quest to move out of its small, isolated downtown pomposity by Philip Johnson and into a new, vine-draped pavilion, likewise downtown, by Swiss architects Herzog & de Meuron. The new building, scheduled to open in fall 2013, is mostly publicly funded. Margulies doesn't believe that local officials can get the project done efficiently. "The government here is corrupt," he said, mentioning the mismanaged Adrienne Arsht Center for the Performing Arts, completed in 2006 after years of delays and cost overruns. Fontanals-Cisneros doesn't find the collection strong enough. "The museum needs to consider its constituency, which is made up of a largely Latin American community in South Florida," she wrote by e-mail. "They need to focus their energies on an exhibition program that their public would want to see."

Riley, who got the museum project off the ground during his directorship, thinks resistance will fade with the successful completion of the building. And Thom Collins, the museum's current director, said, "I have personally felt very embraced by the local collectors," citing substantial donations and board participation. He sees the museum becoming a hub for the collectors, the gallery scene, other local museums and the art fairs. "Our building is at the physical center of all these activities."

He draws a distinction between what private collectors do and the obligations of a public museum. "We are a public trust, a repository for public materials. We have an obligation to make them available and conserve them. There's no onus on private collectors to collect with any critical frame or to be encyclopedic. They can buy and sell at will and are under no obligation to make their collections public."

The scene in the Design District and Wynwood can look organic and freewheeling, but it is increasingly shaped-even curated-by two key real-estate figures: Craig Robins and Tony Goldman.

Robins began developing the Design District in 1994. His Dacra Development breathed new life into the neighborhood by bringing in high-end furniture retailers. In 2005, he founded Design Miami as an architecture and design complement to Art Basel Miami Beach. At his office, which resembles an art gallery and features works from his personal collection, I asked him how seeding growth in peripheral neighborhoods like the Design District and Wynwood made sense. "Miami is a city of the future," he said. "It's an urban, tropical paradise and the meeting point of Afro-Cuban, Latin American, American and European cultures." He sees that mixing as the reason Art Basel has flourished here.

Lately Robins has attracted well-regarded restaurants and fashion designers including Tomas Maier and Christian Louboutin to the Design District. He expects many of the brands in the Louis Vuitton Moët Hennessy empire to open stores in the neighborhood. Though he sees the Design District and Wynwood as a singular evolving phenomenon, he says the former "has an important cultural community emerging at a more sophisticated level and at a different cost structure. Fashion brands are willing to put resources into art and design. A lot of what they do is similar to our own agenda to merge commerce and culture in wonderful ways."

Goldman, a Manhattan developer who pioneered arts-driven commercial development in SoHo and also recognized early the potential of South Beach, has done much to focus Wynwood's identity. He has created a destination amid the uniform blocks of warehouses with "Wynwood Walls," a growing public exhibition of spectacular murals that L.A. MOCA director Jeffrey Deitch helped curate. So far, Goldman's buildings have been spray-painted with 25 murals, including those by Shepard Fairey, Aiko, and Ron English. Some of them surround diners in the garden of his Wynwood Kitchen and Bar.

"My focus is to make this the central art community of Miami," Goldman said by telephone. "We use what's already there, adapting existing buildings and reprogramming them for new uses at inexpensive rents. Then we let the world know about it." Except during Art Basel and the Wynwood Art Walk, which happens the second Saturday of every month, the streets are generally empty. But Goldman expects that to change. "I see streets filled with people, an active restaurant and art zone, cutting-edge boutique fashion and furnishings." That sounds like the Design District, but it looks like a bigger challenge in Wynwood, given the area's forbidding industrial character.

Goldman views the street art as a draw for the neighborhood. He hopes to get murals lit at night and to create mobile-phone apps that map their locations and connect visitors to artists. "The street art needs to be directed, not controlled. It can't lose its free-form, instinctual, of-the-moment quality."

Local economic development officials have long sought to emulate the "Bilbao effect" of Frank Gehry's Guggenheim branch in Spain. And indeed, the success of these arts districts may soon have people headed to Miami to check out the Art Basel effect. The rise in the neighborhoods' fortunes, however, could threaten their distinctive ethos. Robins's mingling of art and high-end commerce in the Design District could put an end to the artistic experimentation that's currently still engaged in there. Goldman's vision might lead to the kind of gentrification that drove artists and the most innovative exhibition venues out of places like SoHo. "That will happen over 20 or 30 years," Goldman said. "But as long as it stays creative and artistic, I'm happy. When it becomes a mall, I'm unhappy."

"It's interesting that developers want to use work for real estate purposes that was created by artists working illegally," observed Primary Flight's Bischof. "You have people coming through now in Benzes and BMWs, but it is us, the ones who know the locals, who have beautified the neighborhood." He applauds Art Basel for the visibility it brought street artists. Miami-based crews now travel to other cities to work. Still, he says, studio space "is absolutely getting too expensive. The neighborhood is becoming about clubs, food trucks, hemp jewelry and T-shirts sold on the streets. It's not the art district we hoped it would be."

But he finds more and more artists are inspired by the street art in Miami. This year alone, Primary Flight has received 300 submissions for mural projects. "There are not enough walls in the district for that," Bischof says. "People find us. They want to come here and paint. That's what's amazing about street-art culture."

James S. Russell is the architecture critic at Bloomberg News in New York. He writes frequently about trends in urban growth and is the author of The Agile City: Building Well-Being and Wealth in an Era of Climate Change, just published by Island Press.

Antonia Wright is a  Miami-based artist and was a curator of the Wynwood Art Fair this year.