The use of statistically valid sample designs for selecting monitoring locations enables one to report on the condition and trend of all monitored renewable resources within an area of interest with known levels of precision and accuracy. Additionally, by using similar field methods among monitoring efforts, data can be combined among monitoring efforts and used to inform land management decisions at multiple spatial scales and across data needs. However, to realize these benefits, sample designs must be done in a consistent, compatible manner including the geospatial layers used to define the study area.
Figure 1. Two million terrestrial (left) and 67,000 lotic (right) master sample points for potential sampling.
Prior to 2016, individual sample designs were developed for each unique AIM project, requiring the compilation of geospatial data layers, statistical expertise, and specialized software packages. Consequently, the development of individual designs was both time and resource intensive. Furthermore, the merging of data from individual projects to produce estimates at larger scales or to improve estimates at smaller scales was complicated.
With the increased application of AIM to meet BLM monitoring and assessment needs, the AIM team sought to streamline and standardize the sample design process to increase consistency, reduce the required time and expertise, and to more efficiently assist field offices. The result is a ‘Master Sample’ for the sampling of terrestrial vegetative (i.e., upland) and lotic aquatic (streams and rivers) resources on BLM lands within the contiguous U.S.
A master sample consists of a very large number of potential sample locations (see details below) from which project-level sample designs can be selected for specific monitoring needs. Potential sampling locations in the master sample are attributed with many different geospatial layers (e.g., BLM administrative boundaries, watersheds, topography, soils) to facilitate the selection and stratification of monitoring locations for specific projects. Because the geospatial data layers used in the master sample are standardized, as well as the process for selecting the sample points, the resulting monitoring sample designs and subsequent data can be more easily shared, integrated, and used for other applications.
A list of all standardized geospatial data layers are found below
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Example applications of the AIM Aquatic and Terrestrial Master Samples
- Project effectiveness monitoring (> ~250 acres or ~5 stream kilometers)
- Grazing permit renewals (> ~250 acres or ~5 stream kilometers)
- Watershed assessments
- Resource management plan effectiveness monitoring
- State level reporting
- Ecoregional or national level reporting
Benefits of using a master sample
- Increased efficiency and standardization of sample designs
- More efficient and effective field office assistance with survey designs
- Easier and more defensible applications of resource conditions across spatial scales
- Increased ease and defensibility of analyses that combine data from multiple AIM monitoring efforts
Terrestrial master sample details
- Spatial extent: BLM lands within the 13 contiguous western states
- Base layers used to identify BLM lands: Surface Management Agency (SMA) database published July 2015 by the National Operations Center (NOC)
- Survey design approach: generalized random tessellation stratified sampling (GRTS); unweighted point selection with no a priori stratification
- Point density: 1 point per 35 hectares for a total of 2 million possible sample locations
- Example stratum to be used for survey designs: BLM Field/District Offices, BLM Allotments, Landfire Biophysical Settings, Greater Sage-grouse PHMA/GHMA, EPA Ecoregions, SSURGO Soil Map Units
Aquatic master sample details
- Spatial extent: 13 contiguous western states with BLM land
- Base layers used to identify BLM streams and rivers: USGS National Hydrography Dataset (NHD) version 2.0, medium resolution (1:100,000) and Surface Management Agency (SMA) data layer published July 2015 by the National Operations Center (NOC)
- Survey design approach: generalized random tessellation stratified sampling (GRTS); unweighted point selection with no a priori stratification
- Point density: one point per 0.5 km of perennial stream for a total of over 67,000 possible sample locations
- Example stratum to be used for survey designs: Strahler stream order categories, hydrologic unit codes, BLM field office boundaries, BLM districts, Greater Sage-grouse PHMA/GHMA
For more information contact
Scott W. Miller, AIM Aquatic Development and Implementation Lead
BLM-National Operations Center, Branch of Assessment and Monitoring
Cell: 720.545.8367
E-mail: swmiller@blm.gov
Emily Kachergis, AIM Terrestrial Implementation Lead
BLM-National Operations Center, Branch of Assessment and Monitoring
Phone: 303.236.0071
E-mail: ekachergis@blm.gov