The answer is surprisingly clear and positive: trees grow back quickly on cleared areas as soon as land use ceases. Various animal groups also return. Overall biodiversity recovered to over 90% of its original level within approximately 30 years. Around three-quarters of the animal and plant species typical of the rainforest, which make up the characteristic species composition of the rainforest, re-established themselves within 30 years. This applies at least to the study area in Chocó, north-western Ecuador, a region where few patches of untouched rainforest and large areas of secondary forest – forests that regenerate naturally after destruction –remain. These patches form the reservoir for the many returning animal and plant species.
Researchers from over 30 universities and institutions have, for the first time, conducted a detailed study of the natural regeneration of animal, plant and bacterial species in a lowland tropical rainforest. Lead author Timo Metz carried out and summarized the extensive analyses as part of his PhD at Darmstadt Technical University. He emphasizes: “Rainforests, as complex ecosystems and species-rich communities, possess astonishing resilience and the ability to return to their original state. This stability has often been modelled theoretically, but until now it had not been demonstrated on the basis of such a comprehensive dataset.”
Senior author Nico Blüthgen is Professor of Ecology at TU Darmstadt and spokesperson for the Reassembly research group. He initiated the studies together with Dr. Martin Schaefer, who heads the Ecuadorian conservation organization “Jocotoco”. Nico Blüthgen emphasizes: “The many animal species that return quickly are not merely beneficiaries of forest regeneration, but are its key agents: bats, monkeys and other mammals, as well as birds, bring tree seeds back to the cleared areas; dung beetles bury the seeds in the soil; and hundreds of other animal species ensure pollination.”
Martin Schaefer adds: “Our findings that 75% of the species composition and 90% of the biodiversity of a rainforest returns within a human generation without human intervention show just how effectively we can protect nature. By buying and protecting land, we can preserve the diversity of life and the foundations of our societies – soil, water, and the pollination of the plants that form the basis of our food supply.”
Forty-one colleagues, primarily from Germany and Ecuador, were closely involved in the study and were able to contribute their expertise to a hitherto unique investigation of over 8,500 species from 17 different organism groups. Together with their Ecuadorian counterpart Prof. David Donoso (Polytechnic University Quito), Prof. Heike Feldhaar and the PhD student Nina Grella of the University of Bayreuth contributed their results on the diversity and resilience of ants to the study – a group comprising 300 species that are important predators of herbivores and that contribute to the dispersal of small seeds. A total of 62 sites were compared, which have been protected for several decades by the conservation organization Jocotoco and integrated into a large nature reserve: actively used pastures and cacao plantations, secondary forests of varying ages that were formerly used as pastures and plantations, and untouched primary forests.
Tropical rainforests are currently being lost at a rapid pace, and as a result, many animal and plant species in the affected regions are disappearing, or are even becoming irretrievably extinct globally. Furthermore, with the rainforests, valuable ecosystems are being lost that regulate the climate and water balance, act as sinks for greenhouse gases and thus slow down climate change. Most rainforests are cleared for agriculture. It was therefore particularly important to determine whether this loss can be reversed. For trees, this has been well documented to date: it takes around 100 years to restore the original diversity and large mass of tree trunks. For most animal species, however, whose habitats are disappearing, little was previously known about whether and how quickly they return. The results show that regeneration often occurs more quickly for cacao plantations than for cattle pastures. Because the plantation trees are left in place, shade-providing trees and foliage are already present in the early stages, rather than the highly competitive pasture grasses.
