As food production needs continue to increase, more land is converted to agriculture. This stresses ecosystems and limits land available for biodiversity preservation, so much so that land conversion to agriculture is thought to threaten wildlife and biodiversity to a degree that is on par with climate change. Two strategies to balance food production and biodiversity conservation have been debated over the past several decades. Land Sparing divides land into separate areas for high-yield farming and conservation, while Land Sharing farms a greater area of land with low intensity methods that are compatible with biodiversity conservation.
This article discusses some of the strengths and weaknesses of these strategies in regards to food production and biodiversity conservation. It is important to note that this does not consider social or economic aspects of the debate.
First, let’s take a look at some of the benefits of Land Sparing.
Land Sparing generally enables increased crop yield per area, which leaves more land available for biodiversity preservation. If this available land is used for conservation, it appears to be beneficial to biodiversity. Studies in Ghana and India found higher species density of birds and trees and greater avian functional group diversity in areas that implemented Land Sparing practices relative to areas using other land use strategies. Spared lands were found to be essential for the survival of species that do not tolerate any level of disturbance or those that require extensive natural areas.
Is Land Sparing as effective as it sounds? What are some benefits of the alternative, Land Sharing?
Although Land Sparing has many benefits, the intensive agricultural practices used to minimize land needed for crop production require high inputs of nutrients and pesticides. This has negative consequences for long-term food security and biodiversity.
Land Sparing practices may reduce the functional biodiversity in an area, including species that naturally control pests. This necessitates the use of pesticides, which can harm non-target species that provide essential ecosystem services, including pollinators and decomposers. Alternatively, the wildlife-friendly agricultural practices utilized in Land Sharing promote the maintenance of functional biodiversity, including natural predators that control pests without the use of pesticides, making the area more habitable to native species.
In addition to pesticides, high inputs of nutrients are required to sustain intensive agriculture. From the 1960’s to 1990’s, intensification of food production led to a substantial increase in the application of inorganic nitrogen fertilizers, in the United States and globally. While increased nitrogen produced greater crop yields, high input/output agriculture degraded the soil. As a result, even greater quantities of nitrogen were required to maintain the same level of crop production.
Inorganic nitrogen is typically used in high intensity agriculture because it is more readily available to plants than organic nitrogen. However, this also makes the nutrients more susceptible to leaching into ground water or volatizing into the atmosphere. Leaching and volatilization processes enable nitrogen applied on agricultural fields to spread to other areas, negatively affecting spared lands. In the United States, even areas designated as federal wilderness exhibit effects of increased nitrogen.
In aquatic ecosystems, excess nitrogen causes algal blooms and low oxygen levels, which degrade aquatic biodiversity and ecosystem processes. In terrestrial ecosystems, excess nitrogen positively affects plant growth. However, adding nitrogen to a system also changes which nutrients are limiting. This can change which plants have a competitive advantage. Suddenly, a species that adapted to low nitrogen is outcompeted by a species that requires more nutrients, which are now available because of nitrogen deposition. This can permanently alter the structure and composition of the biological community. In comparison, Land Sharing utilizes sustainable agricultural practices, such as crop diversification, crop rotation, and organic fertilizer, which reduce reliance on labile, inorganic fertilizer.
In addition to concerns of pesticide and fertilizer use, Land Sparing may not be as beneficial to biodiversity in spared areas as some comparative studies have suggested. These studies focused on species with small home ranges, which ignores species with large home ranges and species that disperse from their natal range. In particular, the small, isolated protected areas set aside in Land Sparing are often too small to support genetically viable carnivore populations. In addition to being well-known flagship species, large carnivores are important for maintaining ecosystem processes, including predation and scavenging. Healthy carnivore populations are thought to support biodiversity in other trophic levels, notably primary producers (plants). A study of snow leopards found that just 40% of protected areas in the species’ range were large enough for a single adult male and only 4-13% were large enough for 15 or more adult females. This illustrates the importance of farming methods compatible with animal movement and the maintenance of corridors to other protected areas to maintain genetic diversity, which are provided by Land Sharing.
Taking this into consideration, which strategy is more effective in meeting food production and biodiversity conservation goals?
Like most scientific debates, there doesn’t seem to be a clear answer. Both Land Sparing and Land Sharing have benefits and limitations, and using both strategies in tandem may be most effective. The strategy that benefits a particular species depends on its tolerance for disturbance, so the combination of both strategies may be most beneficial to overall biodiversity. The topography and productivity of a landscape also affect which strategy will be most effective. Areas with low productivity or heterogeneous topography are typically better suited to Land Sharing, while flat or high productivity areas lend themselves to Land Sparing. The area’s history and socioeconomics are also important to consider. However, care should be taken to consider the biophysical processes and animal movement that link areas around the globe. When various strategies along the gradient of Land Sparing to Land Sharing are applied to an appropriate context and used to complement each other, we can make progress towards a sustainable model for food production and biodiversity conservation.
Image courtesy of Flickr. Originally published by S&S on July 11, 2019.