Implications of agricultural demand and development pathways for global biodiversity

Agriculture represents the single largest human use of global land area and one of humanity’s main sources of environmental impact. Past and present deforestation and land clearance for the establishment of crops and pasture contribute to a high rate of species extinction and loss of terrestrial biodiversity. Agricultural inputs, including fertilisers and pesticides, have led to dramatic changes in biogeochemical cycles at local to global scales, degradation of freshwater and marine ecosystems, and contribute substantially to human-induced global climate change. In this thesis, I characterise, quantify, and project changes in the global agricultural system, from demand through to production, and investigate and identify impacts, trade-offs, and opportunities therein.
I introduce the thesis by summarising and reviewing the relevant literature looking at global land use, food demand, and agricultural production strategies in a species-conservation context (Chapter 1). I find that projections of future land use and food demand vary widely across studies, mainly due to different assumptions and high uncertainty about future global development pathways. I systematically reviewed studies that have examined two key conservation strategies in an agricultural context; land sparing, where high-intensity production is combined with setting aside primary habitat for conservation (made possible by lowering the land required for production), and land sharing where the objectives of production and biodiversity conservation are integrated on the same land. I find that, while in most circumstances land sparing emerges as the more promising conservation strategy, only a limited amount of work has examined whether the two approaches are reconcilable (i.e., not competing) strategies; this is a gap in our understanding which may hinder the progress of conservation in agricultural landscapes.
The supply of food for direct human consumption is the largest and most important component of global agricultural demand. I developed a phenomenological-statistical modelling framework for characterising and quantifying human food demand, from national through to global scales, based on economic development (Chapter 2). This framework leverages empirical data and rigorous, state-of-the-art statistical inference. The primary aims of this approach are to avoid the highly-complex, often difficult-to-interpret (“black box”) models that are common in food-demand research, while simultaneously improving upon earlier work done using simpler statistical approaches. I found that this method produces similar future global-food-demand projections to those using more complex modelling frameworks, while being more readily interpretable, and more informative than earlier, simpler statistical models. Under a scenario where social, economic, and technological trends follow historical patterns, I estimate that total caloric food demand will increase by approximately 52% between 2013 and 2050. Using the same approach, I modelled the demand trends for important food groups while demonstrating the robustness of my aggregated caloric-demand estimates (Chapter 3). I found that per-capita demand for animal-derived food products has plateaued and is now stable in the most affluent regions, cereal demand is stable in all regions, while per-capita demand for vegetable oils and oil crops continues to increase in all regions. These findings have important implications for future global land use, with simulations of future demand for each of these groups showing strong dependence on assumptions about population growth and economic development.
Combined with demand, global crop yields are the primary determinant of global agricultural area. For a given crop, yields determine how much land area is required to produce the demanded quantity. I extend the approach used in Chapters 2 and 3 to model global crop-yield data. I find that closure of global crop yield gaps - the difference between observed and potential yields - for wheat, rice, maize, and barley are driven by per-capita GDP growth, which can be used as a semi-mechanistic basis for simulating plausible future global crop yields (Chapter 4). These simulations suggest that crop-yield growth will not keep pace with escalating crop demand for any future development scenario, if future relationships between development and production and demand remain similar to those exhibited in the past. A closer examination of the temporal rate of global crop-yield changes (Chapter 5), where I use a spatially explicit, global data set of wheat, rice, maize, and soybean crops, reveals where crop yields are and are not increasing at a sufficient rate. I pay particular attention to how these trends are changing in some of the world’s most ecologically important areas (e.g., biodiversity hotspots), and discuss potential implications for land use in these areas.
In Chapter 6, I explore the potential for reconciling land sparing and land sharing conservation strategies. Specifically, I consider the circumstances under which reducing pesticide use represents a viable wildlife-friendly farming strategy that is simultaneously compatible with high-yield farming. As a case study, I use a comprehensive, spatially explicit data set on bird population trends, use of pesticides, farm yields, and habitat availability in the contiguous United States. The results were ambiguous, likely being constrained by data limitations (e.g., missing or incomplete information) and the “noise” inherent in the underlying fine-scale observational data. I discuss why these specific data sets might not offer a useful path towards reconciling these conservation strategies. I make recommendations about how future data collection and study design could produce more illuminating results.
Finally, I conclude with a brief discussion of what these findings mean for future research, agriculture, conservation, and humanity. I caution that while many of the results appear to paint a bleak picture for the future of conservation in the face of ongoing population and demand growth, no pathway is set in stone, and there are many tools at our disposal for improving outcomes for agriculture, biodiversity and human development. While perfect solutions may be unrealistic or unobtainable, combinations of appropriate environmental and human-development policies, coupled with the conscious development and deployment of existing and emerging technologies and practices, offer substantial mitigation potential.