How long does it take for a forest to recover from deforestation and other human interference? Scientists have investigated this on rainforest areas in the Ivory Coast where trees were felled up to 45 years ago. They found: Even after such a long time, the forest ecosystem has not yet fully regenerated. The forest structure is still changing and some frog species have not returned to this day.
Taï National Park in western Ivory Coast is the largest remaining rainforest in West Africa. Like many other tropical forests around the world, the area is under great pressure: road construction, agriculture and forestry have severely restricted the habitat for numerous species, and there are increasingly unpredictable rains. For decades, deforestation in this area was hardly restricted.
How long does a forest need to regenerate?
A research team led by Tokouaho Flora Kpan from the Museum für Naturkunde in Berlin took the opportunity to investigate in the Taï National Park how long it takes for a forest to recover from human interference. To do this, they examined several forest areas every 15 years in which trees had been felled 30 or 45 years earlier. “In 1970 wood was cut here,” explains co-author Raffael Ernst from the Senckenberg Natural History Collections in Dresden. “Since then, the forest has been able to regenerate naturally. We wanted to know whether the biodiversity and composition have been restored. “
To this end, the scientists analyzed the structure, species composition and age of the trees in the regrown forest in order to record the changes in the habitat. On the other hand, they determined how the amphibian fauna has changed and developed in these forest areas compared to untouched rainforest areas. “Amphibians are particularly suitable as indicators of environmental changes,” explains Kpan’s colleague Mark-Oliver Rödel. “They have complex life-cycle strategies and rapid reproduction cycles and therefore often have specialized requirements for their habitat.” The researchers examined the populations of a total of 33 frog species in a previously managed area, compared them with data from 2000 and with the surrounding, untouched forest .
Even after 45 years, it’s not the same again
The comparative studies showed that although the forest had recovered overall, the composition of the species still deviated significantly from its original state more than forty years after the deforestation. In the regrown, “secondary” forest, there is a lack of large trees that give structure. “Until now, it was assumed in forestry that it takes about thirty years for a forest to be renewed and that you can only think about using it economically again,” says Ernst. “Now we see that it will probably take 40 to 60 years until the original ecosystem is restored in its depth and breadth.”
This was also evident from the amphibians in the regrown forest areas: some frog species have not returned to the renatured forests even after 45 years. As a result, the diversity of amphibians in these areas still lags behind the untouched forest – despite the long regeneration time. An example is Phrynobatrachus guineensis, a tiny but well-climbing species of leaf litter frog with orange toes. The tadpoles take 21 days to fully develop, but only thrive in small water-filled tree holes or snail shells. “The frogs follow the growth of the trees. The slowest organisms set the pace for the fast-moving ones, ”explain the researchers.
The complex interplay of different living beings in an ecosystem must always be taken into account.
Source: Senckenberg Society for Nature Research; Technical article: Forest Ecology and Management, doi: 10.1016 / j.foreco.2021.119489