# Human Appropriation of Net Primary Production: From a Planet to a Pixel
## 5 Discussion: HANPP Tells Different Stories at Different Scales  
One of the strengths of HANPP as a sustainability indicator and ecological footprint measure is that it is applicable across scales--both temporal and spatial, though here we focus on the latter. At the different scales explored above, HANPP illuminates different narratives about human-ecological relationships and their sustainability. At a planetary scale, HANPP is at the center of the debate about planetary limits. It is itself an improvement on the \"changes in land use\" limit of 15% cropland proposed by [PERSON] et al. (2009) [9]. As argued by [PERSON] (2012) [29], NPP, the photosynthetic capacity of Earth, is the appropriate measuring stick against which to apply a planetary limit because it is this ecological space, rather than the cruder land areal measuring stick, that represents the fundamental biological resource that humans share with other species. Moreover, the agricultural and forestry processes humans use to harvest NPP also bear directly and dominantly upon other planetary limits--freshwater use, nitrogen cycle, phosphorus cycle--directly and importantly upon others--biodiversity, climate change, chemical pollution--and indirectly upon ocean acidification. It is thus critical to monitor the percentage of global NPP that humans appropriate. We do not propose here a precise planetary HANPP limit; however, this illustrates the conceptual flaws in setting global  
Figure 5: HANPP (harvest) density (gCm\({}^{2}\)yr\({}^{-1}\)) for Lyon County, Iowa in 2012 for (**a**) corn grain, (**b**) soybeans, (**c**) alfalfa, (**d**) livestock grazing and (**e**) total HANPP (harvest). limits when ecological realities are a sliding scale and are often more relevant locally than globally. At the national scale, variations in NPP, HANPP, and NPP (ecological) provide a different set of insights. The \"New World\" continents of Australia and the Americas appropriate a smaller percentage of NPPand enjoy higher levels of NPP (ecological) than the \"Old World\" continents of Asia, Africa and Europe, where basic needs for large human populations derived from ecosystems press harder against national and regional ecological endowments. Most trade in biomass products is from the former to the latter, for example, as virtual water studies indicate [4]. Yet much of densely populated Asia appropriates a very high percentage of NPP with little NPP (ecological) remaining, despite its low per capita HANPP consumption rates. These indicators illuminate time-honored issues of land use, land degradation, natural capital, and what may constitute overpopulation. At the county scale, as illustrated in the U.S. example, the critical importance of the \"mesoscale\" emerges, where ever-growing urban populations, and even urban regions (e.g., the Atlantic seaboard, coastal California, growing sunbelt metropolitan areas from Florida to Arizona) are reliant for their basic food and other biomass needs upon ever-specializing rural areas. These relationships, however, are not dominantly global, as most biomass products are uneconomical to transport huge distances, nor does each city have its own delineable \"hinterland.\" Rather, a network of interdependencies emerges where HANPP-exporting regions specializing in agriculture (e.g., the Midwestern crop belts, the lower Mississippi Valley, the Central Valley of California) or commercial forestry (Maine, the Pacific Northwest, parts of the southeast) supply broad, mostly domestic urban areas and regions with food, feed, biofiber and biofuel [30], while also exporting to meet the shortfalls of Eurasia. We leave it to future studies to explore the many nuanced environmental justice issues embedded in these networks of interdependencies. At the pixel scale, here chosen at 30 m to match the spatial resolution of the USDA/NASS Cropland Data Layer, additional narratives are illustrated.