Monitoring Agricultural Sustainability Using Remotely Sensed Net Primary Production over Time and Space.

Annual measure of Net Primary Production (NPP) provides estimates of the net amount of biomass (or vegetation) produced by plants each year. Biomass is the ultimate energy resource for all species on Earth; tracking the trend of biomass production is a critically important indicator for understanding energy flows in ecosystems. With increasingly available high-resolution remote sensing of vegetation from satellites, NPP is now monitored and made publicly available at global-scale with high spatial (about 10 km) and temporal (weekly) resolution. However it may not be straightforward to directly use NPP as a policy-relevant indicator. The Human Appropriation of NPP, or HANPP, on the other hand, is a method that aggregates additional indicators with NPP so that we can better understand the impact of human activity on the Earth’ ecosystems. The HANPP specifically measures to what extent land conversion and removal of biomass (e.g., harvests) change the availability of NPP in ecosystems. HANPP, therefore, attempts to measure the scale of human activities compared to natural processes. Reviewing two global-scale studies that illustrates how researchers interpret HANPP to answer questions about the sustainability of Earth’s ecosystem, we propose the status and trend of HANPP and its properties can be highly relevant for the measurement of farming systems’ site-specific sustainability. NPP can be combined with other geospatial information on agricultural production and technologies that provide more context (e.g., trends in spatially disaggregated crop production data and fertilizer use can be compared against HANPP to provide a proxy indicator for agricultural intensification). We propose to modify the methodology of calculating HANPP defined in earlier studies to keep the analysis more cost-effective and more specific to the sustainability of agriculture. As a pilot, this approach was tested in Kenya to compare the agricultural sustainability changes occurred between 2000 and 2010.