As the world's population grows, so will the need for more agricultural land to feed this population. It is not easy to choose which areas to convert. This depends on the agricultural and environmental priorities. These priorities can vary greatly.Princeton University's study illustrates the difficulty of this puzzle by using multiple approaches to solve it. Given a set amount of food, where should we plant new crops to minimize biodiversity or environmental impacts?Researchers used Zambia as a case study because it has a lot of biodiversity, but is likely to see an increase in agricultural growth. The researchers looked at the most common methods of measuring biodiversity. This included counting the species that are present in the area and calculating the relative rarity of the species within the geographic region.Different areas were recommended for agricultural development depending on the factor that they used to optimize land use. The overlap between the recommended areas was actually less than 4%.These findings were published in Ecological Applications. They indicate a need for consensus. When small differences can lead to almost entirely different results, inconsistent models could become a roadblock rather than a guideline for policymakers.Researchers suggested that conservation biologists need to use more consistent methods for prioritizing biodiversity conservation and be more transparent about how they justify their decisions.Christopher Crawford, Ph.D. candidate at Princeton's School of Public and International Affairs, said that "the sheer size of agriculture today means we need to think strategically about where we produce food in the future." "Our paper places the stakes in the natural world into greater context. It shows that how you measure and prioritize it can have major consequences for biodiversity.David Wilcove (co-author of Crawford's book, and professor of ecology, evolutionary biology, and the High Meadows Environmental Institute), explains these effects in greater detail.Let's suppose you decide on which areas to preserve for nature and which ones to convert to cropland. This might produce a different answer from if you were to focus on mammals. Wilcove stated that if your decision is based on the protection of the most species, it might yield a different result than if your decision was based on the most endangered species.Crawford and Wilcove collaborated with Lyndon Estes, Clark University, and Tim Searchinger (also of SPIA), whose 2016 paper was the inspiration for this study. The team examined the factors that influenced four different methods of measuring biodiversity.An analysis of four widely used methods for measuring biodiversity was done. The results were first published in academic journals. The four main methodological decisions underpinning the differences among the four published methods were identified and a new set was created to measure the impact of each decision on land prioritization.The first considers the number of vertebrates, such as birds, mammals, and reptiles, in a given region. Expert advice is also provided on conservation priorities. The second considers the number of vertebrate species in a region, calculating their importance according to their extinction risk and their rarity within that ecosystem. The third method focuses on the types of vegetation in different regions. It weighs them in terms how intact they are, their rarity, and whether they are endangered. The fourth method calculates the number of species found in each region, weighted according to their geographic ranges.The researchers ran each approach through their model and found that very different areas of Zambia were recommended to be developed for agriculture. Sometimes, there was as little as 0.3% overlap. It is clear that there is no one-size-fits all solution for prioritizing land use. While some decisions such as changing the species groups or the way they are counted had a greater impact on final land-use recommendations than others, even minor and often overlooked methodological changes can lead to wildly divergent recommendations.These findings show the complexity of land conversions for policymakers. These decisions can have enormous consequences for biodiversity depending on the method used. Although the focus of the research was on biodiversity, this is only one part of the puzzle. The land-use priority must consider the suitability of each region for agriculture, the amount and cost of transporting the crops from the intended agricultural area to the markets. Because of the inevitable tradeoffs, even just two of these factors can make it difficult to make a decision.Wilcove stated that focusing on specific species, how they are compared and the spatial scale of the analysis can produce strikingly different results when it comes to the question of where to save and develop. Scientists can create complex algorithms to balance conservation and development. But if they don't think carefully about how they compared and counted the animals and plants they want to save, their results could be meaningless."###The paper "Consequences under-explored variation biodiversity indices used to land-use prioritization" was published online in Ecological Applications, June 27. The High Meadows Foundation supported this work.