Regional and global shifts in crop diversity through the Anthropocene

The Anthropocene epoch is partly defined by anthropogenic spread of crops beyond their centres of origin. At global scales, evidence indicates that species-level taxonomic diversity of crops being cultivated on large-scale agricultural lands has increased linearly over the past 50 years. Yet environmental and socio-economic differences support expectations that temporal changes in crop diversity vary across regions. Ecological theory also suggests that changes in crop taxonomic diversity may not necessarily reflect changes in the evolutionary diversity of crops. We used data from the Food and Agricultural Organization (FAO) of the United Nations to assess changes in crop taxonomic- and phylogenetic diversity across 22 subcontinental-scale regions from 1961–2014. We document certain broad consistencies across nearly all regions: i) little change in crop diversity from 1961 through to the late 1970s; followed by ii) a 10-year period of sharp diversification through the early 1980s; followed by iii) a “levelling-off” of crop diversification beginning in the early 1990s. However, the specific onset and duration of these distinct periods differs significantly across regions and are unrelated to agricultural expansion, indicating that unique policy or environmental conditions influence the crops being grown within a given region. Additionally, while the 1970s and 1980s are defined by region-scale increases in crop diversity this period marks the increasing dominance of a small number of crop species and lineages; a trend resulting in detectable increases in the similarity of crops being grown across regions. Broad similarities in the species-level taxonomic and phylogenetic diversity of crops being grown across regions, primarily at large industrial scales captured by FAO data, represent a unique feature of the Anthropocene epoch. Yet nuanced asymmetries in regional-scale trends suggest that environmental and socio-economic factors play a key role in shaping observed macro-ecological changes in the plant diversity on agricultural lands.

人类世（Anthropocene）的部分定义，是作物突破起源中心向外人为扩散的现象。在全球尺度上，现有证据表明，大型农田中种植的作物物种分类多样性在过去50年间呈线性增长趋势。然而，环境与社会经济层面的差异表明，作物多样性的时间变化存在显著的区域异质性。生态学理论亦指出，作物分类多样性的变化未必能反映其进化多样性的变动。本研究借助联合国粮食及农业组织（Food and Agricultural Organization, FAO）的数据，评估了1961年至2014年间22个次大陆尺度区域内作物分类多样性与系统发育多样性的变化情况。研究发现几乎所有区域均呈现以下共性趋势：其一，1961年至20世纪70年代末，作物多样性几乎无明显变化；其二，20世纪80年代初的十年间，作物多样性快速提升；其三，20世纪90年代初起，作物多样性增长趋于平缓。但上述三个阶段的具体起始时间与持续时长存在显著区域差异，且与农业扩张并无关联，这表明特定区域的独特政策或环境条件会影响当地种植的作物种类。此外，尽管20世纪70至80年代各区域的作物多样性均有所提升，但这一时期内少数作物物种与演化支的优势地位不断强化；该趋势使得不同区域种植的作物相似性出现可观测的提升。在FAO数据覆盖的大型工业化农田尺度下，不同区域作物的物种分类多样性与系统发育多样性呈现广泛的相似性，这是人类世的一个独特特征。但区域尺度趋势中存在的细微不对称性表明，环境与社会经济因素在塑造农田植物多样性的宏观生态变化中发挥着关键作用。