How long will it take for new forests to grow back?

The environmental group the WWF says it will take at least two decades for new forests in areas of Greece destroyed by recent fires to grow back. The fires which killed 65 people raged across much of southern Greece in August. The WWF director in Greece Dimitris Karavellas told BBC that they would establish a group of lawyers to intervene if lands developers try to take advantage of the disaster.
Question: How long will it take for new forests to grow back?