Earlier this month I went to the 2012 European Congress of Conservation Biology where the best session by far was one on land sharing vs land sparing (see a summary of the session by Joern Fischer here). This session was inspired by the Science paper by Ben Phalan and resulting back-and-forth.
The main idea behind the paper was that with increasing global population we need to increase food production. We can either do this by increasing the area of agriculture or intensifying production in the agricultural land we currently use. To limit the impact of both these options on biodiversity we could use wildlife friendly farming, termed land sharing. Another option is to spare natural ecosystems from conversion in the case of intensification, termed land sparing.
Thus land sharing aims to integrate goals for food production and biodiversity protection on the same land, while land sparing aims to separate intensive farming from protected ecosystems at the larger scale (A caricature of this continuum is provided below) .
Phalan et al took these options and tested their potential effects on bird and tree populations in Ghana and Northern India by looking at landscapes which represented these differing strategies. Using this data they plotted yield against species density to define how populations may change with increased yield. These changes allowed them to classify species as ‘losers’ or ‘winners’ following agricultural conversion as well as defining the land use options most likely to be beneficial for maintenance of their populations.
On the whole they found that land sparing was the best option for most species, particularly for those species with small global ranges.This is important since it is largely these species that are considered to be conservation priorities.
However, some people have interpreted this as meaning that the authors advocate land sparing in all situations. Even if they do, it is obvious that land sparing might not be the best strategy in all situations. Different landscapes have different histories of land use, which will have inevitably had an effect on biodiversity and consequently what we see as priorities for protection.
For example, much of Western Europe has been cultivated for centuries if not millennia and has little forest cover. As a result the biodiversity we value here consists largely of generalist species which thrive in low intensity farmland and require some form of agricultural practice for persistence. Meadows are a great example of a cultural landscape that is highly valued in Europe but requires disturbance, such as grazing, to exist. In situations like these it is entirely possible that land sharing may help to boost the populations of priority species.
In addition the taxonomic group which you aim to protect will determine the scale at which management should be undertaken. What constitutes land sparing for an invertebrate will not be the same as that for a bird. Phalan et al’s paper arguably chose taxonomic groups which would be likely to benefit from large scale land sparing, it will be interesting to see how research into other taxa differs in their findings.
Ecosystem services will also be affected by these different land use strategies. Land sharing may favour services which rely on fragments of semi-natural habitat in order to be distributed throughout the landscape, such as pollination. Meanwhile services which are supplied far away from ecosystems which generate them, such as carbon storage and water purification, will be favoured by land sparing.
Though food production is an obvious priority, lots of conservation essentially adds up to how best to use particular parcels of land to meet multiple goals. Land sparing vs land sharing could be applied to urban planning and energy production to name just two. Hopefully, if my PhD doesn’t get in the way, I will explore this issues further in the coming weeks.
The land sparing vs land sharing debate is obviously set to run and run. However, it seems likely that with more research we may be able to form some generalisations. In areas where there are many species which depend on forests, or any other ecosystem incompatible with agriculture, land sparing may be best while land sharing may work best in areas with a long history of extensive farming and little forest cover.
Much work is needed to determine the consequences of these options for ecosystem services and also the social implications. For example, could promoting land sparing further add to our lack of connection with nature? What exactly is the relationship between provision of particular ecosystem services and these different options? I don’t have the answer to these questions. However, given that agriculture is the biggest single threat to biodiversity, but is something none of us can live without, I hope we will at least have a few more answers in the near future.