At some point, the National Mall is going to run out of room. It’s an inescapable fact.

Already, workers have broken ground in the Tidal Basin near the Lincoln Memorial and Franklin Delano Roosevelt Memorial for the new Martin Luther King Jr. National Memorial. And construction of the National Museum of African American History and Culture, which will be located close to the Washington Monument, is scheduled to begin in 2012.

According to professor Kirk Savage, chairman of the history of art and architecture department at the University of Pittsburgh, the Mall’s finite space raises important questions about the process of choosing and designing new memorials, monuments and museums, and what the memorial landscape will ultimately look like in the future — questions that have gone unanswered but are beginning to loom large.

To avoid what could eventually become an overly cluttered Mall, Savage has proposed erecting temporary monuments instead of permanent structures.

While lasting monuments are often sponsored by narrow interest groups and must pass through a gauntlet of planning committees, temporary monuments and memorials can be much bolder in their appearance, generate more discussion about the themes present on the National Mall and might even give the public a better sense of “agency,” or autonomy, throughout the planning process, Savage said in an interview.

Savage told an audience at a recent lecture at the Smithsonian’s National Portrait Gallery that he first broached this idea in his book “Monument Wars: Washington, D.C., the National Mall and the Transformation of the Memorial Landscape.”

He actually began with the mindset that temporary monuments weren’t realistic, but “the more I talk with people the more convinced I become that it’s a good idea,” he said.

Temporary or ephemeral monuments can range from something as simple as a single photograph to full-blown art installations.

One of the main drawbacks with permanent monuments and memorials, Savage said, is that they often exist in relative isolation from one another; connections between and among them are rarely made, which Savage finds unfortunate because many monuments inside the Beltway are related. In addition, they often attempt to bring closure to events whose fallout is still being felt in the United States and around the world.

Another problem is that getting Congressional approval to build new monuments has become such a “one-by-one, piecemeal” process, bigger questions such as “Why are we erecting some monuments and not others?” and “What are the overall themes of the memorial landscape?” tend not to get asked, Savage said.

“There’s not really a place in the process for those bigger questions,” he said. This often results in public apathy toward new monuments.

“It’s not that the public’s not interested” in the process of selecting various monuments and memorials, he said. “It’s just that erecting a monument is a mysterious process orchestrated by mysterious people unknown to them.”

On the other hand, an ephemeral structure could spark a broader public discussion about who and what should be commemorated, he said.

As an example, Savage points to what is known as the “Fourth Plinth” in London’s Trafalgar Square. The plinth — or platform upon which a column, pedestal, monument or other statuary structure typically stands — lay empty from 1841 until 1999; it was sometimes referred to as the “empty plinth,” according to its Web site. But now the plinth is home to a rotation of various works of art commissioned by national and international artists.

“It’s essentially a rotating monument,” Savage said.

One of the worries District of Columbia planners have raised to Savage about erecting such monuments is that some people may get so attached to an ephemeral project, they could demand that it become permanent.

Savage said he thinks the planners share a valid concern, which is that temporary projects must be planned carefully so that everybody understands the concept of the structures.

The upshot of all of this would be to start a conversation about what the “sum total” of all the monuments on the National Mall stand for while also creating a commemorative place for various interest groups to express themselves without encroaching upon long-standing structures, he said.

Looking forward, Savage sees technology playing a prominent role in making connections throughout the memorial landscape, too. Tools such as iPhone applications could easily teach viewers unknown facts and messages about monuments and ultimately help convey the overarching themes present on the National Mall in a way that has never been done before, he said.

Although the future of the National Mall remains uncertain, it will soon become clearer as decisions are made about its remaining space — what goes where, and for whom? Savage’s idea to embrace an impermanent mode of commemoration could be one way to deal with those challenges.