Is HANPP a Stressor of Bird Species Richness?

One of the leading drivers of biodiversity loss is land use change due to the ever-increasing demand for food, livestock feed, biofiber, and biofuel. The concept of human appropriation of net primary production (HANPP) was developed to measure the impact that humans have on the environment by accounting for biomass removed from the environment in the form of crops, timber, and grazing. The species–energy hypothesis is an established ecological hypothesis postulating that greater species diversity is correlated with higher levels of energy from plant productivity; this can be measured as net primary production minus harvested HANPP or NPPecological. Theoretically, a “biodiversity footprint” could be developed by estimating the reduction in species associated with a volume of biomass extraction, reducing NPPeco. Achieving this would be an advance in sustainability science. We used the USGS Gap Analysis Project (GAP) dataset for bird species diversity and a unique mapping of HANPPharvest (from crops, grazing, and timber harvests) at the scale of counties in the conterminous US to test whether HANPP reduces bird species richness. Negative binomial regression finds, however, that HANPPharvest is only a marginally statistically significant stressor of bird species richness. A secondary measure of NPPecological/HANPPharvest is similarly a marginally significant positive predictor. Consistent with recent literature emphasizing the need to account for spatial autocorrelation in ecological research, however, both HANPPharvest and NPPecological/HANPPharvest are insignificant predictors of bird diversity in the conterminous US at the county scale when spatial autocorrelation, along with county size and coastal adjacency, are accounted for. We conclude that species richness is determined by a complex set of factors that render using data on HANPP to develop a biodiversity footprint speculative and imprecise in the case of bird species richness in the US.