Large herbivores can bend the curve of biodiversity loss in tropical forests

Morro do Diabo
© Wikimedia Commons

Large herbivores can bend the curve of biodiversity loss in tropical forests

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A 10-year experiment in Brazil’s endangered Atlantic Forest, led by NIOO-researcher Nacho Villar, has found that there's less biodiversity loss in areas where large herbivores can roam free. The results have been published in the Journal of Applied Ecology, in a special issue on "nature-based solutions for a changing world".

Many forests around the world are suffering substantial losses in biodiversity due to fragmentation and deforestation, climate change and the removal of key species from the ecosystem. Nacho Villar and his co-author, Patricia Medici from Brazil's Lowland Tapir Conservation Initiative (LTCI), now provide the first experimental evidence that large herbivores can bend the curve of biodiversity loss in these ecosystems.

They conducted their experiment in the Morro do Diabo nature reserve in São Paulo state: an area covered by Brazil's Atlantic Forest, which is known as a global biodiversity hotspot, but which - paradoxically - is also one of the most endangered biomes on the planet.

In the past decade, says Villar, some areas of the Atlantic Forest have suffered a dramatic 20% decline in the abundance and diversity of regenerating plant communities. "Morro do Diabo is a catalogue of the pervasive impact of the Anthropocene on ecosystems, including deforestation and fragmentation, illegal hunting, land-clearing and fires, construction of major infrastructure, and shifts in seasonal rainfall and temperature patterns due to climate change."

Endangered forest, endangered species

This natural “diversity apocalypse” scenario made Morro do Diabo the ideal set-up for testing the effects of large herbivores on diversity decline, argue the researchers. Especially as similar declines in diversity and compositional changes in plant communities are likely to be widespread across the Atlantic Forest and in other forest ecosystems. 

For their experiment, they compared areas used by herbivorous mammals - including the lowland tapir (Tapirus terrestris) and the white-lipped peccary (Tayassu pecari) - and areas from which these animals were barred through fenced exclosures over a 10-year period from 2004-2014. The lowland tapir is classified as 'vulnerable' in the International Union for Conservation of Nature (IUCN) Red List throughout its distribution range. The white-lipped peccary is listed as 'critically endangered' in the Atlantic Forest. Both species are hunted illegally across South & Central America.

The team established 100 fenced plots that barred access to large herbivores, and 100 control plots where the animals could roam free. “We studied the role of large herbivores against the decline of plant diversity over time", explains Villar. "We examined their effect on the abundance of plants in the sapling stage, as well as species richness and diversity, and the temporal diversity and the rate of change of forest composition."

Images
  • Photo: Bernard Dupont (https://www.flickr.com/photos/berniedup/)
    Lowland tapir
  • Photo: Bernard Dupont (https://www.flickr.com/photos/berniedup/)
    White-lipped peccary

Old-growth vs secondary forest

The researchers also studied if large herbivores have a different effect on mature 'old-growth' forests than on secondary forests (i.e. forests regrown after a timber harvest). "This is an important question, especially relevant as the United Nations are endorsing the need for effective nature-based solutions for ecosystem restoration, and simultaneously, forest restoration is gaining momentum as a major carbon sink solution” says Villar.

“Surprisingly though, until now this question had not yet been explored in trophic rewilding (i.e. the introduction of species to restore top-down trophic interactions and promote self-regulating biodiverse ecosystems) and forest restoration studies. In fact, the massive potential engineering role of large herbivore rewilding is being blatantly ignored in practically all forest conservation and restoration initiatives in tropical forests".

As highlighted by the cover of the special issue, the study has demonstrated that it's mature forests which benefit the most from the presence of large herbivores. The results suggest that this is because large herbivores' 'buffering' effect on diversity loss is larger in areas where diversity is much higher. "In secondary forests, we identified ca. half the number of species when compared with mature forests. Our results clearly show that large herbivores are most effective in protecting 'diversity hotspots' within the forest. Such hotspots are more abundant in mature forests".

Rewilding and restoration

The results of the study are especially timely in a year when the United Nations has launched its Decade on Ecosystem Restoration (2021-2030), as they may serve as guidance for future forest conservation initiatives. The active restoration of neotropical forests with large herbivores may, in fact, be the most efficient way to improve the state of conservation of many species, and contribute significantly to the diversity of tropical forests in the long run.

"Protection of these animals and trophic rewilding are gaining momentum as important tools to restore forest ecosystems and avoid the acute effects of global changes on biodiversity", say Villar and Medici. But such nature-based solutions have not yet been explored as a conservation option.

"We believe our study highlights a strategic win-win nature-based solution - simultaneously beneficial for both large herbivores and forest conservation - and hopefully paves the way for many other similar studies elsewhere."

Photo: Nacho Villar / Journal of Applied Ecology
Nacho Villar's experiment on the cover of the Journal of Applied Ecology