Anthropogenic biomes: A new framework for global ecology

Background/Question/Methods The global depiction of biological communities using traditional “Biome” classifications fails to recognize that human land use activities have substantially modified these biomes around the world. Recent efforts to address this issue have developed global maps of cropland, pasture, and urban areas. However, even these classifications are limited in their ability to fully address all the various ways in which humans interact with ecosystems. To address this challenge, we have developed a new map of “Anthropogenic Biomes” of the world by combining global data sets of human population density and land use practices. We further investigate whether anthropogenic biomes are a better predictor of ecosystem functioning compared to the traditional biomes. Results/Conclusions Our global map of anthropogenic biomes offers a new view of the world's landscapes as influenced by human activities. It reveals that nearly 80% of the world's ice-free land surface is under human influence. Furthermore anthropogenic biomes are inherently mosaics, composed of a mixture of forests, agricultural areas, settlements, etc. We also find that the concept of anthropogenic biomes can be a useful predictor of ecosystem functioning. Indeed, here we show that global patterns of net primary productivity (NPP) vary as a function of human population density. In highly productive biomes, NPP declines with both increased population density and cultivated land area, while in less productive biomes the opposite is observed. Thus, humans appear to exert a global leveling effect on terrestrial NPP. Although causality cannot be established by our empirical analysis alone, the population/NPP relationship merits greater study and inclusion in terrestrial ecosystem modeling.