Product-Specific human appropriation of net primary production in US counties

Abstract

Human appropriation of net primary production (HANPP) has been developed in the 21st century as an ecological indicator that may supersede ecological footprint due to its spatial specificity, precise measurement of land use intensity, and potential to be tied to trade in biomass-based products, thus enabling a consumption-based analysis. Fusing publicly available data sources, this paper presents a product-specific, county-level analysis of HANPP harvested from crops, timber and grazing in the conterminous United States in the years 1997, 2002, 2007 and 2012, the most recent dates for which all necessary data are available. Total HANPP(harvest) was 716–834 megatonnes (MT), including 514–615 MT from crops, 105–148 MT from timber and 64–76 MT grazed. Of this total, 432–512 MT, 60–66 percent, was a harvested commodity while the remainder was straw and forest slash; 83–84 percent was above-ground HANPP. Mean HANPP density varied from 92 − 107 gCm-2yr−1 in the years studied. With net primary production (NPP) varying from 558 − 610 gCm-2yr−1, this is 15–17 percent of NPP; NPP(ecological) thus varied from 466 − 577 gCm-2yr−1, 83–85 percent of NPP. The specific products with the largest proportions of HANPP were corn grain (26–32 %), soybeans (9–11 %), hardwood (6–10 %) and softwood (8–9 %) timber, grazing on private land (7–9 %), wheat (6–9 %), alfalfa (5–6 %) and aggregated minor crops (15–18 %). Among states, HANPP density varies from 7 gCm-2yr−1 in Nevada to 391 gCm-2yr−1 in Iowa and from 2 % of NPP in Massachusetts to 53 % in Iowa. Disaggregated analysis for 3101 counties shows even greater variation, from less than 1 to 726 gCm-2yr−1, and delineates regions carrying similar HANPP signatures. In the U.S. context, data availability and stoichiometry choices place only modest limitations on the accuracy of HANPP estimates making it a valuable ecological indicator for analyzing land use intensity, especially in agricultural ecosystems.