Net Primary Productivity (NPP) quantifies the amount of plant biomass produced each year, per unit area, in an ecosystem or a landscape.  NPP is a central concept in ecology, conservation, and sustainability science.  It is used to quantify the amount of crop produced on a cropland, forage on a rangeland, timber produced in a managed forest, or feedstock produced for a bioenergy cropping system.  It is used to understand how much carbon is stored on the landscape and how that changes over time.  In ecology it is also used to measure the total input of energy to the ecosystem because it measures the annual energy captured by photosynthesis (minus plant respiration), which supplies energy through food webs to all of the consumers and predators — i.e. all of the wildlife — in an ecosystem.  Another important feature of NPP is that we have developed methods to measure it (with some uncertainty) from satellites, in particular the MODIS NPP product provided by NASA.

Humans remove NPP when we extract food, fiber, and fuel (biomass) from the land as natural resources.  Human Appropriation of NPP (HANPP) measures the amount of NPP that is appropriated for human use in a particular area.  It is sometimes expressed as a percentage of the total NPP on a portion of the landscape; in other words, if humans appropriate 60% of the NPP in a certain area, then 40% of the total carbon and energy captured by nature is left behind after humans have extracted food, fiber, and fuel as natural resources.  Some researchers think HANPP is an important metric to measure because it has some important and useful characteristics.  Higher HANPP corresponds to more intensive human use of land, providing an additional metric that measures the intensity of the human footprint, to use alongside other metrics such as land use / land cover change, or percent tree canopy, or road density, and others.  Theoretically, since HANPP removes energy supply from food webs in the landscape, it should also impact wildlife and biodiversity that historically depended on that energy; using HANPP to better understand human impacts on biodiversity has been a topic of research in the scientific literature.

The figure above shows a modeling estimation of HANPP across the upper Midwest, from a global analysis conducted by Haberl et al. (2007, PNAS).

For her Master’s thesis in SEAS, graduate student Erin Barton worked with Prof. Bill Currie and Doug Pearsall (from the Nature Conservancy) to quantify and map HANPP at county-scale resolution across the US portion of the Great Lakes basin.  One goal was to improve on the Haberl et al. (2007) global analysis within our region by using data specific to forest types and crops of this region.  Having mapped HANPP, Erin then performed statistical analyses to explore how patterns of HANPP at the regional scale, in this area, are related to patterns of landscape physiographic heterogeneity, a key indicator of the potential for particular areas to support wildlife biodiversity.  The ultimate goal of this research is to provide and to assess an additional landscape- to regional-scale tool for conservation science.  We are currently working on a manuscript reporting the results to submit to a peer-review journal — check back for updates and results as this work moves forward to publication.