Forests with a quiet past without fires, glaciers or tropical storms lose a particularly large number of species when parts of them are cleared. This is the conclusion reached by Matthew Betts from Oregon State University in Corvallis (Oregon, USA) and his colleagues in a study recently published in the journal Science. They analyzed the results of 73 studies in which 4489 animal species were examined worldwide.
Especially in lowland regions such as the Amazon, in Central Africa and on the island of Borneo in Southeast Asia, natural disasters that do not destroy the entire forest, but only individual areas in it, have often failed to materialize in the past ten thousand years , Especially in these previously non-fragmented forests, large contiguous areas should be protected from axes, saws and slash-and-burn, the researchers demand.
For many species, clearings are not a ray of hope
“Even if many scientists expected such a result, this work is very important,” explains Tobias Kümmerle, who does research on nature conservation at the Humboldt University in Berlin. Scientists and conservationists have long suspected that many species of animals already get into difficulties if only individual areas are cleared in forests, but nature is also supposed to remain untouched. Clearances and aisles created in this way often pose problems for forest specialists. But also the surrounding nature, in which no trees fell, feels the effects: “Species like the black stork in Central Europe live in seclusion and in the interior of near-natural forests. If new clearings arise there and human influence increases, these species often do not cope well with them, ”says Kümmerle.
So far, a solid scientific basis has been lacking. Because although the disappearance of species from cleared areas in nature can be observed, it is considerably more difficult to prove the consequences for the areas not directly affected by such fragmentation. For decades, many researchers have therefore been discussing the impact that habitat fragmentation actually has on the decimation of biodiversity. To this end, Betts and his colleagues provide an important clue to the past: the researchers searched a large data set about clearing for connections with previous disturbances that had fragmented a forest area in the past ten thousand years. These include forest fires and tropical storms, which can wreak havoc in forests while the nature next to it remains intact. The glaciers of the ice age also crushed forests in many places, but often left the trees on ridges right next to the ice. If species in these remaining forest fragments could not cope with the new conditions, they died out there. Other species, however, adapted to the new environment and survived.
Certain groups of animals are particularly susceptible
“Extinction filters” are what evolutionary biologists call this process, in which only those species that can adapt well to the new conditions survive. After such an endurance test, these species could also react more robustly to new faults and, for example, survive clearing better. And that's exactly what Matthew Betts and his colleagues find in their analysis of previous studies: In the areas where in the past neither large fires nor tropical storms or glaciers dismembered the forests, the number of species living with one was among the animals living there Now fragmentation, which was occurring, had great difficulties, almost three times higher. This effect was particularly strong in birds and certain groups of invertebrates such as insects and spiders.
The situation is different for forests that have been cleared by humans in the past centuries or a few millennia ago to create fields there or to graze cattle. There, the ability to adapt to new clearing was significantly less than in areas that had been hit by fires and storms for thousands of years. Perhaps the extinction filter had simply not had enough time for its full effect there, the researchers think.
Protection of large, undisturbed areas important
In the rainforests in the tropical lowlands of the Amazon, Central Africa and Borneo, which have apparently been spared from such natural disasters and human hands until recently, the species, however, have so far rarely been faced with disturbances. They are therefore particularly sensitive to the fragmentation of the forests. “Large areas that have not yet been dismembered should therefore be protected there,” says Kümmerle. In doing so, he says exactly what ecology researchers from Oregon also conclude from their study.
In Europe, on the other hand, almost all primeval forests have long been cleared and turned into fields, pastures, cultivated forests and settlements including roads and paths , “With us,” says Kümmerle, “small remnants of primeval forest and near-natural forest fragments therefore play an important role and should definitely be protected.”