Will protecting half the Earth save biodiversity? Depends which half

How much of the Earth should we protect to save species from going extinct?

Article by Shreya Dasgupta.

How much of the Earth should we protect to save species from going extinct? Some conservationists have suggested an ambitious number: half of the planet.

Prominent biologist Edward O. Wilson, for instance, proposes in his book, Half-Earth: Our Planets Fight for Life, that devoting half the world to nature would help save the majority of species. Other researchers have backed the Nature Needs Half theme in policy and advocacy papers: protecting 50 percent of Earths land by 2050 would help make the planet more livable for humanity.

But what half do we protect? Achieving this figure simply by creating large protected areas isnt going to save much biodiversity, says a new study published in Science Advances.

Theres an increasing call for a Half-Earth, lead author Stuart Pimm, Doris Duke professor of conservation ecology at Duke University in the U.S., told Mongabay. But theres a danger I think in asking for large areas to be protected when in fact we need to protect the right areas, we need to protect the places that really have species in them rather than drawing huge swathes on the map.

Pimm, along with colleagues Binbin Li, an assistant professor at Duke Kunshan University in China, and Clinton Jenkins, a researcher with Brazils Institute for Ecological Research (Instituto de Pesquisas Ecológicas, or IPÊ), set out to explore how well current protected areas protect some 20,000 species of birds, mammals and amphibians.

They also analyzed how many more species would be covered if currently unprotected wild areas were combined with protected areas to get to the 50 percent Half-Earth mark, not including Antarctica. The team defined wild areas as places with small human populations and impacts areas we tend to call wilderness.

The political low hanging fruit is going to be to protect the areas that we call wild typically areas that are remote, cold and arid; areas that have very, very few people in them, Pimm said. So the team included areas that had a Global Human Footprint Index of less than 3.3 (the index is a measure of relative human influence, and runs on a scale of 0 to 50.)

The researchers found that adding large swaths of wild areas to the protected area network does not mean that more species get protected or that a more significant portion of a species range gets covered. Overall, wild areas performed less than expected by chance at protecting species.

As we point out very carefully, there are important reasons to protect remote places, and large places and we dont argue against that, Pimm said. But if we just do that and dont also focus on the small, special places then we are not going to save biodiversity.

In the context of India, for example, emphasizing protection of areas in the Western Ghats, the eastern Himalayas and Indias grasslands could cover more species than protecting large areas in the higher-elevation areas of the Himalayas above the tree line, Pimm said.

There are really good reasons to protect these areas too [higher elevation areas of the Himalayas] because they are important for water, he said. But its a matter of not being seduced by areas because they are big but to prioritize areas because they are special and/or have key species in them.

William Laurance, a tropical ecologist at Australias James Cook University, who was not involved in the study, said the size of a protected area also needs to be an important consideration. Other factors being equal, larger reserves are always desirable because they are more robust to external disturbances, conserve larger and less extinction-prone populations, and can better withstand environmental vicissitudes such as climate change, he told Mongabay.

Of course, other factors are almost never equal, he added. What the authors correctly argue is that if you focus only on establishing big reserves in an effort to save half the Earth youll be forced to establish new reserves in areas that have low biodiversity notably places that are cold or arid. This is a critical point.

When looking at how well protected areas protect wildlife on a species-by-species basis, though something which took a colossal amount of computation Pimm and his colleagues found a surprising trend: the worlds parks already cover at least some of the range of most bird species, and somewhat fewer mammals and amphibians.

What is surprising is how well existing protected areas cover many of these species, Jenkins of IPÊ said. For birds, for example, about half the species with the smallest geographical ranges have some of their range protected to a degree.

Noëlle Kümpel, head of policy at BirdLife International, who was not part of the study, said it was reassuring to see that their efforts are paying off. The study reports that a higher percentage of birds are found in protected areas, likely due to a focus on protecting International Bird and Biodiversity Areas for small-ranged, threatened bird species, facilitated by the data and advocacy provided by BirdLife and its Partners, Kümpel said in an email.

However, all species are counted equally in the study and so wide-ranging species dont do so well with the fraction of their ranges protected close to random, she added. Given it is not likely to be feasible to secure their entire ranges inside new protected areas, conservation efforts are needed outside protected areas too.

Kümpel agreed that the idea of Half-Earth should not just be about hitting a percentage target, but must shift towards a quality over quantity approach, as Pimmet al make clear.

In the United States, for instance, most of the big national parks are in the remote and arid parts of the western U.S., Pimm said. But theres a huge amount of biodiversity in the southeast that is not being adequately protected.

This is mainly because creating protected areas in areas with more people and development potential is harder to do.

It requires political will, Pimm said. Politicians generally want an easy victory. You might creep up from protecting 13% of your country to 13.2% of your country and protect a lot more species than going from 13% to 15% if you just protect remote areas.

The study only looked at birds, mammals and amphibians because these groups have relatively well-estimated distributions compared to others, the researchers say. Its unclear whether including data on groups like insects and plants would change the studys findings.

Protecting areas can also serve other purposes than just protecting biodiversity. It can be about protecting and conserving both biodiversity and ecosystem services, Kümpel said, which are not necessarily in the same place as Pimm et al note.

Once weve adequately covered important areas for biodiversity, factoring in areas of importance for ecosystem services is likely to mean we actually need substantially more than half the earth conserved in some way, through a variety of mechanisms in addition to formal protection, she said.

Banner image: A golden snub-nosed monkey. The species has a range of about 300,000 square kilometers (116,000 square miles) in southwest China, of which about 7 percent lies within national nature reserves, another 7 percent in provincial reserves, and a further 7 percent in sparsely populated places. Image by Binbin Li.

Editors note: William Laurance is a member of Mongabays advisory board.


Stuart L. Pimm, Clinton N. Jenkins, Binbin V. Li. How to protect half of Earth to ensure it protects sufficient biodiversity. Science Advances, 2018; 4 (8): eaat2616 DOI: 10.1126/sciadv.aat2616

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