Notre-Dame burned so quickly because of the massive amounts of wood in the structure - but people are already offering up more trees for its reconstruction

• Notre-Dame Cathedral burned for hours on Monday before some 500 French firefighters managed to extinguish the flames.
• The fire burned so quickly, in part, because the medieval gothic cathedral is supported by a massive "forest" of ancient oak trees from the 1200s.
• French timber producers are already offering up new trees for the church's reconstruction.

The flames are out at Notre-Dame Cathedral, where a raging fire carved huge holes in the roof on Monday. The cathedral has stood in the center of Paris since medieval times.

Many of the church's most priceless artifacts, which include a crown of thorns that legend has it Jesus wore, have been saved. The famous bell towers out front and inventive flying buttresses that support the back of the church - the very first of their kind in the world - have also been saved.

But underneath new gaping holes in the ceiling of Notre-Dame, huge pieces of timber now litter the floor of the ancient gothic church. These beams are the trees of the so-called "forest" of Notre-Dame Cathedral, the church's frame, which was a network of some 1,300 oak trees that was put in during the 13th century. They caught fire in a hurry on Monday evening, after flames broke out while a planned $6.8 million renovation was underway at the church.

"That the fire blew up like this is an indication that it probably started with a small fire, which went on for quite a long time, and then it blew up," Mechtild Rössler, Director of the UNESCO World Heritage Centre, told Business Insider on Tuesday.

She says fires are common occurrences at these kinds of renovation sites: "It happens quite often because there's a lot of chemicals and other materials involved."

As of Tuesday afternoon in Paris, less than 24 hours after the Notre-Dame fire first broke out, more than $780 million in donation pledges had poured in for the church's repairs, according to Le Monde newspaper.

Rössler says it's important, not just for French people, but for the whole world, that the inevitable re-construction of Notre-Dame be done so that it looks as similar to the old church as possible. This could involve a new "forest" of oak trees supporting the church's weight.

Read More: Why Notre-Dame Cathedral, a medieval stone church, has burned so quickly

"We'll use modern methods, but it should be done by the books," Rössler said. "Which includes a lot of craftsmanship."

Already, the timber industry is offering to lend a hand with that.

The Fondation Fransylva, which is a French federation representing private timber growers in France, has already asked all its members to offer up an oak tree for Notre-Dame.

"Loggers want Notre-Dame's 'forêt-charpente' re-constructed with French oak trees, in keeping with the same traditions and good quality of the first builders," Fransylva's press release reads in French.

Groupama insurance company is also offering to pay for 1,300 oak trees to re-build the church frame, which the company says would come from the forests of Normandy, in keeping with the original construction.

Others aren't so sure that's a good idea, given how quickly the structure burned on Monday evening.

"I doubt they'll use wood," Carolyn Malone, a professor of art history and gothic architecture at the University of Southern California told Business Insider in an email.

No matter how the church roof comes into place, no one's ready to give guesses yet on how long the eventual reconstruction may take.

"We have seen long-term work that includes, for example, our work we have been doing in Angkor since 1992," Rössler said, referring to the rebuilding of Angkor Wat temples in Cambodia, which some consider the eighth wonder of the world.

"We still have restoration workers there so it can go either way, but I hope it [Notre-Dame] is done more quickly."