The National Resource Inventory (NRI) is a statistical survey of land use and natural resource conditions and trends on all U.S. non-federal lands. The NRI program serves as the Federal Government’s principle source of information on natural resources in the United States. Every 5 years, the NRI assesses the current status and trend in land cover/use, erosion rates, wetlands, and conservation practices. The program is administered by Natural Resource Conservation Service (NRCS) in cooperation with Iowa State University Statistical Laboratory.
Collection of natural resource data began in the 1930s in response to drought and severe soil erosion on American farms. Over the years, the program has evolved in complexity, statistical considerations, and resources monitored. The NRI has increased in scope to include data on ecological communities and environmental quality in addition to data specifically on agricultural.
Table adapted from Nusser and Goebel 1997
Most sampling throughout the country uses the Public Land Survey (PLS) system. The national sample is a stratified two-stage unequal probability area sample. The first stage is selecting primary sampling units (PSU) which are usually quarter-sections (0.5 x 0.5 miles, 64.75 ha). Six quarter-sections are selected in each township (6 miles x 6 miles) as PSUs. The second stage of sampling is selecting 3 sample points in each PSU which is conducted according to restricted randomization. In parts of the country where the PLS was not implemented, other grid systems such as latitude and longitude or universal transverse mercator are used. Sampling across the USA generally ranges from 2 to 6% of non-federal lands. The 1992 survey sampled 307,468 PSUs and 800,000 points.
Figure from Nusser and Goebel 1997
Methods for data collection have evolved over the years with the changing needs of the program. Currently the program relies heavily on aerial photo interpretation, other remote sensing materials, county office records, soil survey maps, and wetland inventory maps. Field studies are conducted to obtain data not easily gathered using remote sensing techniques. Different land cover/use categories have different resources and thus require different methods to measure them. Specific protocols for the survey can be found here.
Rangeland Plot Schematic
NRI homepage: http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/technical/nra/nri/
Iowa State University Statistical Laboratory http://www.cssm.iastate.edu/index.php?option=com_content&view=article&id=41&Itemid=50
Goebel, J. J. (1998). The National Resources Inventory and its Role in U.S. Agriculture, Agriculture Statistics 2000, Proceedings of the conference on agricultural statistics organized by the National Agricultural Statistics Service of the US Department of Agriculture, under the auspices of the International Statistical Institute.
Herrick, J. E., V. Lessard, K. E. Spaeth, P. Shaver, R. S. Dayton, D. A. Pyke, L. Jolley, and J. J. Goebel (2010). National ecosystem assessments supported by scientific and local knowledge. Frontiers of Ecology and the Environment, 8(8), 403-408.
Nusser, S. M. and J. J. Goebel (1997). The national resource inventory: a long-term multi-resource monitoring programme. Environmental and Ecological Statistics, 4(3): 181-204.