The evolution in time of the concept of fast growing tree species: is it possible to use a definition applicable to all environmental conditions?

Although the expression “fast-growing species” (FGS) referred to tree species has been since long time used, a clear definition has not been adopted for decades. Starting from the Italian historical background, we searched for the definitions of FGS formulated over time at a national and international level. The mean annual increment (MAI) of 10 m 3 ha -1 , identified by the FAO, has been the most commonly considered threshold until recently. Subsequently, experimental activities and research efforts have consistently enhanced the productivity of FGS, and other definitions have been proposed accordingly. Hence, FGS should provide annual wood yields of 15-25 m 3 ha -1 with rotations of less than 25-30 years. In Europe, the maximum MAI can reach about 20-25 m 3 ha -1 , while in fast-growing tropical plantations the MAI frequently exceeds 30-35 m 3 ha -1 . However, we deem that the threshold of 10 m 3 ha -1 year -1 is still reliable for Mediterranean conditions. Since the fast-growing is a relative concept, strongly affected by species’ traits, environmental conditions and cultural practices, a future increase in the productivity levels of wood plantations can be expected.