- Land sharing vs. land sparing: scientists have been debating for decades whether it’s better to set aside huge blocks of wilderness and intensively farm the rest or create a more mosaic ecosystem where farms and forest coexist.
- This new study found forested land housed far more distinct bird families than those in small-scale farming communities, which may still contain a lot of species but not a lot of different groups.
- But critics say the study does not take into consideration future scenarios or migrations.
What’s the best way to save life on Earth? Should we set aside huge blocks of wilderness and intensively farm the rest or should we create a mosaic ecosystem – i.e., a quilt-like mix of farms, forests and everything in-between?
Conservationists, ecologists and farmers have been passionately debating this dichotomy – what they call either “land sparing” or “land sharing” – for decades. It’s not an ivory tower argument: with seven billion human mouths to feed (and rising daily) and a global extinction crisis on our hands, the answer has massive real-world applications. Last month, a new study in Current Biology took a novel view of the debate by asking not what was best for birds in general, but what was best for preserving the full-breadth and depth of bird evolution, something scientists call “phylogenetic diversity.”
Land Sparing for Phylogenetic Diversity
The study, headed by David Edwards with the University of Sheffield and James Gilroy with the Norwegian University of Life Sciences, found that land sparing (i.e., big parks coupled with intensive agriculture) was the best way forward for preserving birds’ great evolutionary heritage – at least in Colombia’s avian-rich Chocó-Andes ecosystem.
“The Chocó-Andes are a hotspot of endemism and have been widely impacted by low-intensity farming, making this one of the most threatened faunas on Earth,” Edwards said in a press release. “It is vital to consider how best to farm here, but also to use this region as a model for how best to farm in other locations.”
Comparing 318 bird species found in three sites across the region (including both forest and cattle land) the researchers write that they “found a severe depletion of phylogenetic diversity in low-intensity farmland communities [examples of land sharing] relative to forest.”
In other words, forested land housed far more distinct bird families than those in small-scale farming communities, which may still contain a lot of species but not a lot of different groups.
“This is because species that do well in farmland have tended to come from a few families: things like seedeaters and finches, and orioles and blackbirds. Forest communities are made up by birds from lots of different families, from tinamous to antbirds to trogons,” Edwards explained to Mongabay.
In all, the researchers write that the jump from pristine forest to low-intensity agriculture represented a loss of “650 million years of evolutionary history.” But how did the scientists come to such an impressively large number?
“For each species we can estimate the number of years since it split from its most closely related sister species–these represent years of unique evolutionary history,” Edwards said. “We add up all of these years of unique history for the entire community in a landscape, and when we do this we find that the sum of history is lower under sharing than sparing.”
Edwards also said although this particularly study only focused on birds it likely implies to other types of life as well.
“Birds tend to be good indicators of patterns in other taxa, so it is likely that these patterns are more generally applicable to other groups. For instance, we have found similar patterns of species richness for dung beetles but we have not looked at evolutionary history of dung beetles yet.”
Other research has come to similar results. A study in Science in 2011 found that land sparing was better both for bird and tree species than land sharing in both Ghana and India. Moreover, they found that agriculture that was also “biodiversity friendly” produced less food (in terms of energy) and made less profit.
“In an era of continued farmland expansion into natural habitat, we need to seek mechanisms for allowing us to produce more food on land that is already farmed,” Edwards said. “While there is lots of evidence that low-intensity farming retains more wildlife than intensive farming, the challenge is to produce enough food to meet societies growing needs…Our fear is that the land sharing approach ultimately won’t be able to produce enough food for society without having to encroach on these remaining natural habitats. In an ideal world, we would do both, but unfortunately hard decisions must be made about the future of agricultural expansion.”
But those against agriculture intensification argue that global hunger isn’t caused by not producing enough food, but getting the food to the people that need it.
Indeed, Edwards and Gilroy’s research is not without its detractors.
Debating the Findings
John Vandermeer, an ecologist with the University of Michigan who has studied biodiversity in land sharing mosaics in Central America, told Mongabay that he appreciated the fact that the new study ” goes further than most overly simplistic biodiversity assessments by examining [phylogenetic diversity].”
However, he said the study had a fatal flaw.
“It retains the error of other studies by presuming the current state of biodiversity, whether in farms or preserves, will somehow represent the biodiversity in the future,” noted Vandermeer. “Their simulations thus reflect this error, effectively predicting the future by presuming a static pattern in different habitat types.”
For many proponents of land sharing, mosaic and biodiversity-friendly agriculture represents a space for wildlife to move or migrate through as needed, as opposed to the desert-like conditions of intensive monocultures.
“The fact is that biodiversity is determined over the long term by a balance between local extinction and regional migration, a profoundly dynamic process and one that cannot be understood from the static framework [Edwards and Gilroy] use,” Vandermeer said.
Luke Frishkoff, a recent graduate of Yale University who has also compared biodiversity in forests, farms and plantations – including research cited in the Edwards and Gilroy’s study – agreed that the current study may take its claims too far. He noted that he also wasn’t “convinced” of the new study’s finding that “land-sparing is definitively better for phylogenetic diversity.”
For one thing, Frishkoff said the study ignored questions of yield. In other words, it simply assumed that agricultural yields would be higher in land sparing landscapes in the long-term.
“How yield responds to land-sharing is largely unknown, and likely incredibly dependent on local context and type of agriculture. Within cattle pastures (the form of agriculture investigated in the study), farmers often choose to include wildlife habitat in the form of trees because these trees provide shade and wind breaks for the cattle. In this case yield and wildlife are both maximized by some degree of land-sharing. An overzealous proclamation that land sparing is best without quantifying yield runs the risk of encouraging agricultural approaches that harm wildlife, and even harm yield.”
Frishkoff also pointed to the fact that the researchers made their evaluations based on a study area that included a large area of unbroken forest.
“The simulations used here all require the pre-existence of a large contiguous forest preserve in the landscape, because land-sparing gains presuppose that spared land is being added directly onto this large preserve. It’s unclear to me whether these results would hold if there wasn’t already assumed to be a large contiguous forest.”
Frishkoff adds that so-called spared forest may just as easily be turned into “low-density housing” or “luxury agricultural products.” In other words, in the real world, land spared from intensive agriculture may just become something else – and not a biodiversity preserve.
“The land sparing/land sharing debate hinges on the assumption that this is a zero sum game—i.e. that increases in yield [via land sparing] will necessarily mean a decrease in land area used for [agriculture], and a commensurate increase in land set aside for wildlife,” Frishkoff told Mongabay. “This may or may not be the case. Increasing yields may just decrease the price of a given commodity while maintaining the same amount of area under agricultural production.”
Edwards called this the “nightmare scenario.” To counter just this happening, Edwards suggests that governments should consider moving funds that are now supporting land sharing initiatives toward setting aside still-pristine forests.
“My feeling is that land-sparing-type approaches – such as biodiversity offsets, which can protect larger tracts of natural habitat – are gaining traction, but there is a long way to go for expansion of such policies writ large,” Edwards said, telling Mongabay that “capacity building with tropical governments” could go a long way in helping put such policies in place.
But Frishkoff argued that the answer is not a carte blanche for land sparing, but a mix of both methods.
“The question needs to be not land-sharing: yes or no, but land-sharing: when and how much?”
It’s unlikely that Edwards and Gilroy’s new study will quell the debate over land sparing and land sharing anytime soon, but it certainly adds more data to the discussion.
“This is a single study in a single region on a single group of organisms with in a single type of agriculture,” Frishkoff said. ” This study highlights a small piece of the total puzzle, and uses interesting modeling approaches to do so. But ultimately the best way to preserve the evolutionary history of life on Earth remains to be seen.”
- Phalan, Ben, Malvika Onial, Andrew Balmford, and Rhys E. Green. “Reconciling food production and biodiversity conservation: land sharing and land sparing compared.” Science 333, no. 6047 (2011): 1289-1291.
- Edwards, David P., James J. Gilroy, Gavin H. Thomas, Claudia A. Medina Uribe, and Torbjørn Haugaasen. “Land-Sparing Agriculture Best Protects Avian Phylogenetic Diversity.” Current Biology 25, no. 18 (2015): 2384-2391.