Parallel Productivity
Commercial Plant Production and Natural Vegetation Patterns Align
Written by: Isabella Armour
Edited by: Grace Owens-Kurtz, Katie Hill, Katie Kelly, Madeline Nicol
The latitudinal gradient of biodiversity is one of the most striking biological patterns found in the natural world. Moving from the poles to the equator, the number of plant and animal species increases dramatically. Until only recently, the natural resources available for human use were dictated entirely by this gradient, meaning the plants at our disposal were limited to those in our immediate surroundings. There were no potatoes growing in Ireland and no pineapples being consumed in Europe. It was not until the mid-1600s that ships began transporting plants, seeds, and botanical knowledge around the world. International trade freed nations from their close ties to native flora and allowed them to expand their diets to foreign plant products.
Economists have long studied the effects of international trade on patterns of consumption and production of commodities. Comparative advantage theory states that nations can increase their wealth by focusing on producing goods that are most cost-effective for them and then import the rest. This usually means that they focus on cultivating native plants that are already adapted to their country’s environmental conditions. The most profit is had by those who play to their own agricultural strengths.
This is relatively straight forward, but trade policies, subsidies, and other governmental regulations on agriculture can limit access to foreign markets and thus disrupt the elegant simplicity of comparative advantage theory. It is difficult for a country to specialize in producing a small subset of agricultural goods for a number of reasons. Trade sanctions may inhibit access to certain goods, meaning domestic farmers must produce a wider variety of products to replace them. In developing countries, focusing on growing cash crops and importing all other necessities may be financially infeasible, so subsistence farmers persist. Specialization may also be impeded by growing incomes since higher per-capita GDP leads to a demand for a greater diversity of foodstuffs that is most often meet by imports. [1] It is also possible that farmers around the world are resistant to narrowing their production diversity because of culture or tradition.
A diverse team of professionals, ranging from economists to ecologists, published a paper in October of 2016 that sought to investigate how globalization has changed the ways society, economy, and biodiversity are intertwined. The first goal of Nelson et al. 2016’s research was to test the effects of trade openness, government policy, and per capita income on the phylogenetic diversity of plant production and consumption. They wanted to know from which and from how many different branches of the tree of life nations were picking their produce. Past statistical analyses have shown that most countries cultivate crops that are already adapted to their local environmental conditions. The researchers predicted that this strategy of cost-cutting via crop specialization would be exaggerated over time as countries traded with each other more and more. Biodiversity of production in individual countries was projected to continually narrow while consumption would diversify.
The second goal of their research was to explore how latitude affects the species diversity and richness of agricultural production and consumption, focusing on tropical versus temperate regions. Species richness is the number of species present, while species diversity accounts for both the number of species and the abundance of each species. Latitude functions as a proxy for climate and biogeographical patterns.
To address these two goals, Nelson et al. performed a meta-analysis of commercial plant production, export, and import data gathered between 1992 and 2010 from 142 different countries. Three metrics of biodiversity were used to process the data for each country: species richness (SR), phylogenetic species variability (PSV), and Simpson’s evenness (E). PSV is based on plant trait diversity. Understanding specific physical attributes of different plant species allows us to estimate the average evolutionary relatedness of those species. Both SR and E are species diversity metrics.
Three predictions were made pertaining to these three metrics. The first was that PSV and E would decrease as trade openness increased (Figure 1).
The second was that a country’s consumption PSV, SR, and E would increase with increases in per capita GDP and trade openness (Figure 2).
The third was that gaps between produced and consumed PSV, SR, and E within a country would increase with higher incomes and greater trade openness (Figure 3).
Analytical modeling revealed some interesting differences in plant production and consumption by latitudinal zone. More tropical nations were found to produce and consume a greater phylogenetic diversity of foods than temperate ones. At the same time, temperate countries generally have more complex, wealthier economies, which translates into the ability to demand and produce a greater species diversity of plant products. In the temperate zone, people demand a greater number of species, but those species are usually closely related and thus functionally similar. A smaller number of plant species are consumed in the tropics, but the species that are consumed come from more distantly related branches of the tree of life.
When it comes to the effects of trade openness, it seems that the data followed comparative advantage theory only when confounding variables like lagged economic response to market changes were omitted from the model. The correlation between plant production specialization and trade openness was positive but tenuous. Phylogenetic diversity of consumed plants stayed the same regardless of international market pressures, meaning the latitudinal gradient of cultivated plants paralleled that of natural vegetation. This pattern may be conserved as a result of cultural tradition guiding food demand within countries, rather than external market forces. Small farmers in developing countries may also be resistant to switching over to cash crops because they would rather grow their own food than deal with volatile food markets within their own country. Even in wealthier countries there is an emerging demand for locally grown food that is so strong it has divided the agricultural sector in two. There is now one section that services the subsistence demands of locals and another that specializes in exports. The combination of these factors do not affect PSV, but they do result in a decline in E production over time in regions dominated by export agriculture.
As per capita GDP increases, so does the diversity of plants consumed, as expected. Unexpectedly, consumers in higher latitudes use more of their income to purchase a greater number of closely related plant species, reducing their consumption PSV while increasing SR. Unlike trends in production, consumed species richness increased with trade openness at almost all latitudes.
Overall, low latitude countries consistently consume a more evolutionarily diverse set of plants than temperate countries, and there is no evidence that market pressure, trade sanctions, or economic theories have any affect on this. Globalization and increasing wealth seemingly have had no bearing on the latitudinal gradient of agricultural biodiversity. The maintenance of this pattern may make global agriculture more resilient in the face of global climate change. Crop redundancy around the world can protect against societal and climatic catastrophe. That said, agricultural redundancy is not the most efficient way to utilize the Earth’s limited stores of arable land. With a projected human population of nine billion by the year 2050, we must take into account both climate change resilience and efficiently feeding the growing human population when analyzing the costs and benefits of cultivating plants in accordance with the latitudinal gradient of biodiversity.
Works Cited
1. Nelson, E. et al. Commercial Plant Production and Consumption Still Follow the Latitudinal Gradient in Species Diversity despite Economic Globalization. PLOS ONE 11, e0163002 (2016).
2. Godfray, H. et al. Food Security: The Challenge of Feeding 9 Billion People. Science 327, 812–818 (2010).
