Land for Food & Land for Nature?

Land for Food & Land for Nature? Andrew Balmford, Rhys Green & Ben Phalan Abstract: Opinions on how to limit the immense impact of agriculture on wild species are divided. Some think it best to retain as much wildlife as possible on farms, even at the cost of lowering yield (production per unit area). Others advocate the opposite: increasing yield so as to limit the area needed for farming, and then retaining larger areas under natural habitats. Still others support a mixture of the two extremes, or an intermediate approach. Here we summarize a model designed to resolve this disagreement, and review the Downloaded from http://direct.mit.edu/daed/article-pdf/144/4/57/1830685/daed_a_00354.pdf by guest on 01 October 2021 empirical evidence available to date. We conclude that this evidence largely supports the second, so-called land-sparing approach to reconciling agriculture and biodiversity conservation, but that important ques- tions remain over the generality of these ½ndings for different biota and for ecosystem services, how best to increase yields while limiting environmental externalities, and whether there are effective, socially just, and practical mechanisms for coupling yield growth to habitat retention and restoration. Cultivating crops and keeping livestock have radi- cally transformed the scale and complexity of human society, and have had greater impacts on the rest of the planet than any other human activity.1Crop production and permanent pasture now cover a combined 38 percent of Earth’s ice-free land surface, in- cluding around half of all former temperate decidu- ous forests and savannas, and almost three-quarters of the world’s grasslands. Continued conversion for ANDREWBALMFORDis Professor farming is the leading cause of tropical deforestation of Conservation Science in the De- by a considerable margin. Taken together, agricul- partment of Zoology at the Univer- ture and related land use are responsible for 17–31 sity of Cambridge. percent of all anthropogenic greenhouse gas emis- RHYS GREEN is Honorary Profes- sions. On top of this, farming accounts for around 70 sor of Conservation Science in the percent of human use of freshwater, and the manu- Department of Zoology at the Uni - facture of inorganic fertilizers is the main reason for versity of Cambridge and Principal the doubling in nitrogen ½xation and resulting rise Research Biologist at the Royal So- in eutrophication seen over the past century. Given ciety for the Protection of Birds. the magnitude of these environmental alterations it BEN PHALAN is the Zukerman Ju - is not surprising that agriculture threatens many nior Research Fellow at King’s Col - more species with extinction than any other sector.2 lege, Cambridge University. Serious as the situation already is, it seems in- (*See endnotes for complete contributor escapable that the footprint of farming will increase. biographies.) The expansion of the human population from about © 2015 by the American Academy of Arts & Sciences doi:10.1162/DAED_a_00354 57 Land for 7.4 billion today to between 9 and 10 bil- land sparing: increasing yields on farmed Food & lion, coupled with rapidly rising per capita land while at the same time sparing remain - Land for Nature? demand for noncrop products (such as ing habitat or freeing up land for habitat biofuels and rubber) and for animal pro- restoration elsewhere (right panels, Figure tein (especially in newly emerging econ - 1).8Thus, while land sharing focuses on en - omies) mean that total agricultural de- hancing biodiversity within farmland, land mand is likely to double between 2000 and sparing seeks to offset the impacts of high- 2050.3 Demand-side interventions could yield production by coupling it to conser- help curb this growth and, insofar as hun - vation in nonproductive parts of the land- ger and undernourishment are more about scape. Many other options between these food distribution and pricing than overall extremes are also possible (central panels, production, could do so without negatively Figure 1).9 impacting food security.4 Much could be In the following sections, we summarize Downloaded from http://direct.mit.edu/daed/article-pdf/144/4/57/1830685/daed_a_00354.pdf by guest on 01 October 2021 done to reduce the 30–40 percent post - a simple trade-off model10 we devised for harvest loss of potentially usable food in identifying which of these approaches will both developing and developed countries. maximize the persistence of the native Food consumption in general and that of wild species inhabiting a region; we also meat, dairy products, and eggs in particu- review the empirical evidence so far avail- lar could be reduced among well-off con- able for assessing their relative merits. We sumers.5We strongly support such efforts. then discuss a series of objections to our Nevertheless, given very limited progress approach–some of which we consider to on these fronts to date, we consider it like- be misconceptions about the model’s scope, ly that demand for crops and livestock will as well as some important challenges. We rise dramatically over the next half century. end with a brief exploration of other con- The question that therefore arises for texts besides food production in which the conservationists, and that occupies us for land-sharing/sparing framework might the rest of this essay, is how the demand for usefully be applied. agricultural products can be met by the planet’s limited supply of land at the least Our trade-off model evaluates plausible cost to other species. One option, widely alternative farming systems–all of which advocated by conservationists and reflected meet a region’s production targets–ac- in the European Union’s €5 billion per year cording to their consequences for the long- program of agri-environment payments to term persistence of its species.11 We infer farmers, is land sharing: producing both the probability of long-term persistence of food and wildlife in the same parts of the each species from its expected total popu- landscape by maintaining or restoring the lation size in all of the region’s farmed and conservation value of the farmed land it- unfarmed land combined, relative to what self, through providing nonfarmed habitat its population would be in the absence of elements (such as shade trees and ponds), farming. To make options comparable, we limiting the use of harmful chemicals, and only consider scenarios that meet the same other interventions (see the left panels of production target for the region (solutions Figure 1).6 A very different approach, put occupying the same row of Figure 1). This forward by agricultural scientists in re- could be achieved by farming the entire response to the observation that land-shar- gion at the lowest yield suf½cient to meet ing interventions typically lower yields and the target (extreme land sharing), farming therefore require a larger area to be farmed some of it at the highest achievable yield to achieve a given production target,7 is and maintaining (or restoring) the rest as 58 Dædalus, the Journal ofthe American Academy of Arts & Sciences Figure 1 Andrew Schematic Illustration of Land Sharing, Land Sparing, and Mixed-Yield Landscapes Balmford, Rhys Green & Ben Phalan 40 Land use Relative yield Natural habitat 0 30 Low-yield farm 0.5 Medium-yield farm 0.75 HOW MUCH 1 20 High-yield farm Production target Downloaded from http://direct.mit.edu/daed/article-pdf/144/4/57/1830685/daed_a_00354.pdf by guest on 01 October 2021 land sharing land sparing with low-yield farming HOW with high-yield farming Each of the nine panels is a schematic map of a region with natural habitat (black: agricultural yield = 0 units), low- yield farmland (dark grey: yield = 0.5 units), medium-yield (mid-grey: yield = 0.75 units), and high-yield farmland (light grey: yield = 1.0 units). Region maps in the same row all produce the same quantity of agricultural products, but with different amounts of high-, medium-, and low-yield farming and with natural habitat on all land not needed to provide the production target. The three rows show results (from bottom to top) for low (120 units), medium (180), and high (240) production targets. Source: Figure prepared by authors. intact habitat (extreme land sparing), or er under some or all farming regimes than by some intermediate solution. in the absence of farming. These loser spe - The key to quantifying how the total cies are the primary focus of our concern. population size of a species (and hence its For both winners and losers, the ap- likelihood of persistence) varies across proach to farming that maximizes their re- these options is how its mean population gional population size depends on the density is related to the agricultural yield shape of their density-yield curves. Math- of a piece of land: a response we term its ematical modeling shows that for those density-yield curve. Some species can be with simple concave curves (panels A and considered bene½ciaries of agriculture D) their total population size is greatest (“winners”) because they live at consis- when the entire region is farmed at the tently higher densities in farmed land than lowest yield capable of meeting the pro- in their natural, zero-yielding habitat (pan - duction target (extreme land sharing). This els A, B, and Cin Figure 2). Given that these is easiest to see for loser species (panel D), are likely to have larger regional popula- because their densities decline only slight- tions under any form of farming than they ly under low-yield farming but fall steeply had before the arrival of agriculture, such under the high-yields associated with land species are of limited conservation con- sparing. The situation is very different for cern.

Load more