London, June 12 : A new study has suggested that for a rainforest to regenerate completely, it might take up to 4000 years.
According to a report in New Scientist, the study, which focused on the Brazilian Atlantic forest, determined that though certain aspects of a rainforest may return in just 65 years, for the landscape to truly regain its native identity takes a lot longer - up to 4000 years.
The Atlantic forest originally stretched along the southern half of Brazil's Atlantic coast, covering some 1.2 million square kilometers. Once lush, the forest has been continually exploited for food, wood and space.
Today, land it used to occupy is home to most of the country's population, including Brazil's two largest cities, Sao Paulo and Rio de Janeiro, and only 100,000 square kilometers of forest remain.
To determine how long it would take for the forest to regenerate, Marcia Marques and colleagues at the Federal University of Parana collected data on different parcels of forest that had been virtually cleared and left to recover for varying amounts of time.
They then plugged the data into a computer model to calculate how long it would take for the forest to recover entirely.
The researchers looked at four different measures of forest regrowth: the proportion of tree species whose seeds are dispersed by animals, the proportion of species that can grow in shade, tree height, and the number of native species.
Animals are key to the successful regeneration of cleared areas and, typically, 80% of the tree species in a mature tropical rainforest are animal-dispersed. The researchers found that it took just 65 years for a forest to recover to this level.
Another indication of forest regeneration is the existence of a high proportion of shade-loving trees.
This is because immediately after trees are felled, the land tends to be repopulated by opportunistic species that thrive in the Sun. Shade-lovers take considerably longer to find their way back into the forest - about 160 years, according to Marques.
But it's recovering the proportion of native species that are unique to the original forest which takes the longest time - the model predicts this will take up to 4000 years.
Native species that are unique to the Atlantic forest have been isolated over the years into separate plots of forest. As a result, their seeds take a long time to disperse to protected areas.
"If endemic species do not germinate and grow, the forest cannot recover fully," said Marques.