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The study found that seed dispersal losses were particularly severe in the temperate regions of North America, Europe, South America, and Australia. On the basis of the international Red Lists, the experts calculated that in the event of the extinction of currently threatened species, nature’s ability to disperse seeds would decrease by a further 15 percent. “We have found regions where seed dispersal has already declined by 95 percent, even though they have only lost a few percent of their mammal and bird species,” says Fricke. Svenning believes that there is a realistic risk that tipping points will be reached in areas that are particularly hard hit, and that entire ecosystems will collapse if they are exceeded. “Climate change could definitely lead to a lack of forest regeneration, and the lack of animals could prevent colonization by newly introduced tree species that tolerate the new climate.”
Loss of birds, also in Europe, is already weakening ecosystems
In addition to the complete loss of entire species, the decline in many bird species is also weakening the resilience of forests and other ecosystems to climate change. Ornithologists recently determined that 600 million birds have been lost across Europe over the past four decades, mainly due to intensive agriculture. In Germany, experts from the umbrella organization of German avifaunists estimate that 16 million birds have disappeared in the same period – this corresponds to a loss of 40,000 birds per day. “Of course, the number of animals plays a major role in the performance of the entire system,” says Svenning. “Clearly, the massive decline in populations of many bird species has severely impacted their role as seed dispersers.”
It may come as a surprise that a songbird weighing just a few grams plays a similarly important role in seed distribution as a bison. But previous studies have shown just that: Blackcaps, robins and some thrush species such as the blackbird are particularly important, according to a study published in the journal »Nature«. These species overwinter in the Mediterranean and breed further north. By eating berries, they help many plant species from the Mediterranean region, which is particularly hard hit by climate change, to continue their journey north.
Svenning believes that the importance of animals in general for climate protection is still underestimated. Biodiversity researcher Josef Settele, co-author of the IPBES report mentioned at the beginning, takes a similar view. Only gradually is it recognized that biodiversity makes an ecosystem more resistant to external influences. “For example, species-rich forest is more resistant to pest infestation, which prevents entire forest stands from dying off and thus preserves the ability to store carbon.”
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