Carbon Storage in Tropical Forests Recovers Faster Than Biodiversity: Conservation Implications

Carbon storage is a huge part of reducing emissions in our atmosphere as our climate changes. Now, scientists have discovered that when tropical forests regrow, plant biodiversity takes longer to recover than carbon storage. The findings could have important implications for conservation in the future.

Over half of all tropical forests have already been converted for agriculture, logged or burnt in the recent past. Re-growing these forests could potentially help soak up carbon emissions while at the same time reducing species' extinction. Yet how fast these forests recover has long remained a source of speculation. That's why researchers decided to investigate a bit further.

The scientists conducted a synthesis of data collected from more than 600 secondary forest sites from 74 previous studies, describing carbon pools and plant biodiversity. Each site had comparable data for a nearby site that was relatively free of human disturbance.

It turns out that although carbon recovered most quickly, even after 80 years of re-growing forests tended to have less carbon than old-growth forests. This is probably because these forests are often dominated by small, fast growing trees. In fact, it may take centuries for larger trees, which hold more carbon, to become established. The number of tree species, in contrast, recovered relatively rapidly. However, many species characteristic of old-growth forests were rare--a worrying sign since these species are the most vulnerable to extinction.

"We think plant species normally found in old-growth forests are failing to colonize re-growing forests because their seeds never get there," said Phil Martin, the lead author of the new study, in a news release. "These recovering forests are often far from old-growth forests and surrounded by farmland. This means forest animals cannot move seeds between the two forests. We suggest that when conservationists aim to restore tropical forests they should help dispersal of seeds from undisturbed to re-growing areas by planting trees throughout the wider landscape."

The findings reveal that forests that are re-growing following agricultural use may be more valuable for the carbon that they store than for their biodiversity for the first 100 years. While policies often assume that carbon and biodiversity are interchangeable, this study reveals that this is clearly not the case.

"Our results clearly indicate that preservation of old-growth forests is vital for the conservation of specialist species," said James Bullock, one of the researchers, in a news release. "While the re-growth of forests following clearance is valuable in soaking up carbon, the biodiversity benefits will take a very long time to emerge."

The findings are published in the journal Proceedings of the Royal Society B.