The instinctive response of many environmentalists  is to to fence off protected areas as rapidly and extensively as possible. That thought certainly dominates discussions of the Convention on Biological Diversity, the main relevant international treaty. An eight-year-old addendum to the pact calls for 17% of the world’s land surface and 10% of the ocean’s water column (that is, the water under 10% of the ocean’s surface) to be protected by 2020. Currently, those figures are 15% and 6%. Campaigners want the next set of targets, now under discussion, to aim for 30% by 2030—and even 50% by 2050. This last goal, biogeographers estimate, would preserve 85% of life’s richness in the long run.  As rallying cries go, “Nature needs half” has a ring to it, but not one that sounds so tuneful in the poor countries where much of the rhetorically required half will have to be found. Many people in such places already feel “Cornered by Protected Areas.” (See also Biodiversity and Human Rights)

James Watson, chief scientist at the Wildlife Conservation Society (wcs), another American charity, has an additional worry about focusing on the fence-it-off approach. If you care about the presence of species rather than the absence of humans, he warns, “‘nature needs half’ could be a catastrophe—if you get the wrong half.” Many terrestrial protected areas are places that are mountainous or desert or both. Expanding them may not translate into saving more species. Moreover, in 2009 Lucas Joppa and Alexander Pfaff, both then at Duke University in North Carolina, showed that protected areas disproportionately occupy land that could well be fine even had it been left unprotected: agriculture-unfriendly slopes, areas remote from transport links or human settlements, and so on. Cordoning off more such places may have little practical effect.

 In the United States it is the underprotected southern Appalachians, in the south-east of the country, that harbour the main biodiversity hotspots. The largest patches of ring-fenced wilderness, however, sit in the spectacular but barren mountain ranges of the west and north-west. In Brazil, the world’s most speciose country, the principal hotspots are not, as might naively be assumed, in the vast expanse of the Amazon basin, but rather in the few remaining patches of Atlantic rainforest that hug the south-eastern coast.

Nor is speciosity the only consideration. So is risk-spreading. A team from the University of Queensland, in Australia, led by Ove Hoegh-Guldberg, has used a piece of financial mathematics called modern portfolio theory to select 50 coral reefs around the world as suitable, collectively, for preservation. Just as asset managers pick uncorrelated stocks and bonds in order to spread risk, Dr Hoegh-Guldberg and his colleagues picked reefs that have different exposures to rising water temperatures, wave damage from cyclones and so on. The resulting portfolio includes reefs in northern Sumatra and the southern Red Sea that have not previously registered on conservationists’ radar screens…

Another common finding—counterintuitive to those who take the “fence-it-all-off” approach—is that a mixed economy of conservation and exploitation can work. For example, rates of deforestation in a partly protected region of Peru, the Alto Mayo, declined by 78% between 2011 and 2017, even as coffee production increased from 20 tonnes a year to 500 tonnes.

Environmental groups can also draw on a growing body of academic research into the effective stewardship of particular species. For too long, says William Sutherland, of Cambridge University, conservationists have relied on gut feelings. Fed up with his fellow practitioners’ confident but unsubstantiated claims about their methods, and inspired by the idea of “evidence-based medicine”, he launched, in 2004, an online repository of relevant peer-reviewed literature called Conservation Evidence.  Today this repository contains more than 5,400 summaries of documented interventions. These are rated for effectiveness, certainty and harms. Want to conserve bird life threatened by farming, for example? The repository lists 27 interventions, ranging from leaving a mixture of seed for wild birds to peck (highly beneficial, based on 41 studies of various species in different countries) to marking bird nests during harvest (likely to be harmful or ineffective, based on a single study of lapwing in the Netherlands). The book version of their compendium, “What Works in Conservation”, runs to 662 pages. It has been downloaded 35,000 times.

Excerpts from How to preserve nature on a tight budget, Economist, Feb. 9, 2919