Rural FIA
Rural FIA
Program information
Data collected from FIA plot surveys supports a wide range of scientific research and is publicly available. U.S. Forest Service FIA analysts evaluate these data to produce state-level reports mandated by Congress, as well as estimation tools and downloadable datasets (FIA Data and Tools) for public use. FIA data contributes to research on:
- Potential wildfire hazards
- Wildlife habitat conditions
- Causes of tree mortality, including insects and diseases
- Biomass estimates and carbon storage
- Timber volume and resource estimates
- Numerous other scientific and management efforts across federal and state agencies, universities and private industry
The national FIA Program is organized into five regional units: Pacific Northwest, Interior West, Northern, Southern and the National Office. The Interior West FIA (IW-FIA) unit — part of the USFS Rocky Mountain Research Station — conducts and continuously updates a comprehensive inventory and analysis of current and future conditions of forest and rangeland resources across the region. This unit is responsible for inventories in Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah and Wyoming.
Program history
The USFS’s forest inventory programs have operated continuously since 1930. Originally known as the “Forest Survey,” the program completed periodic inventories of rural forests across the lower 48 states by the 1960s. It was later renamed “Renewable Resource Evaluation” in the mid-1970s and became the “Forest Inventory and Analysis (FIA)” program in the mid-1980s.
Notable milestones in the FIA Program include:
- 1980s: Forest inventories were conducted alongside the Forest Health Monitoring (FHM) program using different plot designs on a national grid, with periodic data collection and uneven remeasurement intervals
- 1992: The Colorado State Forest Service (CSFS) begins assisting the U.S. Forest Service with FHM plot measurements in Colorado
- 1995: FIA adopts the four-point plot design used by the FHM program
- 1999: FIA merges with the FHM program and begins transitioning to an annual inventory system in the early 2000s (with plots remeasured every 10 years in the Rocky Mountain Region)
- 2002: Annual inventory begins in Colorado, with CSFS staff conducting field data collection
- 2011: Annual inventory begins in Wyoming, with CSFS staff conducting field data collection
- 2017: CSFS initiates Urban FIA data collection in Colorado cities
Historically focused on rural forests, the program expanded following provisions in the 2014 Farm Bill to include urban forests. This addition provides a more comprehensive understanding of the nation’s forest resources and the wide-ranging benefits they offer. In 2014, FIA also extended inventory efforts to interior Alaska, Hawaii, and U.S. island territories.
For more background, see FIA: In Context and A History of the Forest Survey in the United States 1830-2004.
Methods for gathering data
The Forest Inventory and Analysis (FIA) program employs standardized, science-based methods to accurately measure and record forest plot data. Its data collection protocols include a core set of nationally consistent variables, along with region-specific variables designed to address critical scientific questions and meet the natural resource information needs of local and regional land managers and researchers.
Plot selection
The Farm Bill of 1998 mandated changes to inventory procedures and formally integrated the Forest Inventory and Analysis (FIA) program with the complementary Forest Health Monitoring (FHM) program. To reduce bias and ensure statistically robust data, a hexagonal lattice framework was established across the conterminous United States, providing a consistent and scientifically rigorous sampling design.
Each hexagon in the FIA framework is spaced 3.27 miles apart from its center and covers approximately 6,000 acres. A FIA plot is placed within each hexagon, regardless of landscape features or land ownership. To preserve historical data and track changes over time, FIA also incorporates older FHM plots into the hexagonal grid design. Once the plots are determined, the FIA program is conducted in two main phases:
Phase 1 (P1)
In this phase, office-based work is used to remotely identify plots that are potentially forested. Given the random placement of plots, some will fall in non-forested areas such as water bodies, agricultural fields, open meadows, or even parking lots. These non-forested plots are removed from the survey, while plots that are likely to be forested move on to the next phase.
Phase 2 (P2)
Plots that pass the P1 screening are visited by field crews. Upon arrival, experienced teams assess whether the plot qualifies as forested land. To meet the FIA definition of “forested,” the area must be at least one acre in size, 120 feet wide, and have a minimum of 10% canopy cover of qualifying tree species. If the plot meets these criteria, the crew proceeds with data collection on various forest attributes.
Phase 2 + Soils (P2 + Soils)
A subset of P2 plots, known as P2+Soils plots, undergoes additional data collection focused on soil characteristics. This includes measurements of soil depth to restrictive layers, soil texture, and the nutrient content of duff and litter.
Plot design
Each FIA plot represents a potential sample area of 2.47 acres and follows a nested sampling design, which includes several levels: a hectare plot (not shown), macroplot, subplot, microplot, and transects. The data collected from these smaller sample areas are then extrapolated to represent approximately 6,000 acres. This 4-point plot design was adopted nationwide by FIA in 1995 to ensure consistency and statistical reliability across the program.
Data collection
As part of the National FIA Program, each region collects a standard set of core variables to ensure consistency across the program. In addition, regions may gather supplementary data to address specific policy questions, research needs, or changes in ecosystem services.
Some of the key variables collected include, but are not limited to:
- Tree diameters and lengths (for trees 5 inches and greater in diameter)
- Sapling diameters and lengths (for trees between 1 inch and 5 inches in diameter)
- Seedling counts (for trees under 1 inch in diameter)
- Insect and disease damage
- Tree mortality causes
- Form defects (such as crooked or malformed trees)
- Crown ratios (the ratio of live crown to total tree height)
- Area of crown coverage
- Bare ground coverage
- Understory vegetation (species and area coverage)
- Vertical structure of vegetation (layers of vegetation within the forest)
- Duff & litter depths (organic material on the forest floor)
- Down woody materials (wildfire fuels like fallen branches and logs)
- Residue piles (from timber cutting activity)
- Soil composition, structure and compaction
These variables help assess a range of forest conditions, from tree health to soil structure, and provide valuable insights into forest management, health, and ecosystem services.