Introduction to the Forest Inventory and Analysis Program

by
Andrew J. R. Gillespie
W. Brad Smith
USDA Forest Service, National FIA Program Staff, Washington, DC

Introduction to FIA

The Forest Inventory and Analysis (FIA) program is the Forest Service's national program for collecting and reporting information on status and trends in forested ecosystems across all land ownerships ‑ public and private.  Managed through Forest Service Research and Development, the FIA program has been in continuous operation since the first inventory was completed in 1933.  The FIA mission as outlined in the Forest and Rangeland Renewable Resources Research Act of 1978 is to report periodically on all of the Nation's public and private forests.  This includes information on status and trends in area, location, growth, mortality, harvesting, composition, and structure of forests.  FIA also collects data from loggers on utilization efficiency; from wood processing mills on types of wood products made; and from private landowners on management goals, interests and demographics.   FIA operates at a strategic scale; with one field sample location approximately every 6,000 acres, FIA data are statistically useful from the National scale down to areas of about 200,000 acres.

FIA clients come from many groups including State and Federal forestry agencies, private industry, academia, environmental organizations, and anyone else who wants reliable information about the Nation's forests.  FIA data serve many internal Agency information needs such as the periodic Resource Planning Act (RPA) assessments, status reports on Criteria and Indicators, and special assessments such as the United Nation's Food and Agriculture Organization (FAO) Forest Resource Assessment.

Historically, FIA data were collected on state‑by‑state cycles within six different regions of the country.  The typical inventory process included a complete statewide stratification using aerial photography; field visits to collect ground data; visits to logging operations and wood processing facilities to track utilization  rates; data compilation, analysis, and reporting.   The cycle (time between remeasurements of a given state) has varied from 7‑10 years in the south to 12‑15 years in the north to 20+ years in the west.

A recent law is requiring FIA to make dramatic changes in our inventory approach.  FIA is switching to an annual system where 10% to 20% of the sample locations in each State will be visited each year, with all sample locations being visited over a 5‑10 year interval.  The law mandates consistent data collection and summarization across all land ownerships, including national Forest lands.  FIA will produce annual compilations of collected data as well as complete State analytical reports at 5 year intervals.  The new program will include subsampling of an extended suite of ecosystem attributes such as soil, lichen communities, total vegetative profiles, crown conditions, and surveys for ozone damage through incorporation of the plot portion of the Forest Health Monitoring Program.   A copy of the Strategic Plan describing these changes is available from the National FIA web site at fia.fs.fed.us/strategy.pdf

Relationship between FIA and National Forest Systems Inventory

In the early years there was minimal distinction between FIA inventories and NFS inventories.  Many of the methods and personnel involved were the same, only the intensity of sampling varied.  As time passed, NFS and FIA inventories have diverged in methods due to their different interests:  FIA is interested in making population estimates across larger areas independently of administrative boundaries, while NFS is interested in obtaining management information at the compartment or forest level within National Forest boundaries.  National Forest line officers have retained the authority and resources for gathering information within Forest boundaries, while FIA has been deemed responsible for all other lands.  However, external customers are indifferent to this division of labor:  all they want is complete coverage, in a consistent fashion, for all lands within a state.

Unfortunately, as methods have diverged, there has been no mechanism to ensure consistency between information from National Forests and from other lands.  Since FIA was never funded to conduct inventory on National Forest lands, FIA was forced to either attempt to crosswalk data provided from National Forests (often with unpredictable and unsatisfactory results), or to omit National Forest lands from our reports and databases.  This is confusing to many of the Agency's customers who cannot understand why the Forest Service cannot produce a simple consistent dataset across an entire state.  This has also detracted from the usefulness of FIA data for NFS analysts, who have no use for data which exclude their National Forest lands and which are based on different methods.  Many current FIA customers use tree level FIA data to perform their own analyses, so it is not sufficient to simply report aggregated estimates at the forest or plot level.

This situation has improved greatly in recent years as more Regions have voluntarily contracted with FIA, providing FIA with the funding needed to conduct strategic inventory on NFS lands using standard FIA procedures.  Everywhere outside of R‑5 and R‑6, FIA customers including NFS analysts have access to a consistent strategic level database that spans administrative boundaries with consistent, spatially referenced, complete datasets available at the tree and plot level.  Increasingly this database is being used to generate both tabular and spatial coverages for individual forests as well as for mixes of National Forest land and other ownerships.

Myths about FIA Data

There continues to be some debate about the relative roles of FIA and NFS with respect to conducting ‑ and funding ‑ strategic forest inventory on NFS lands.  In the course of this debate, there has been some confusion regarding what FIA is and whether or not it is relevant to NFS analysts.  Some of the  'myths', along with relevant facts, are included below:

MYTH #1:   “FIA data are collected at too gross a scale to be useful to National Forest planners.”

FACT:  FIA data are relevant for areas as small as 200,000 acres.  An area this size will on average include about 33 ground plots, which is a sufficiently large sample size to estimate ‑ with known precision ‑ basic parameters such as the average structure, composition, growth, mortality and removals for the forest in question.  This will of course not address project level planning needs; but this certainly would suffice for many forest‑wide analyses needs consistent with forest planning.  Additionally, FIA data are the only data which exist outside of the National Forests to support the information needs of planners interested in considering a landscape context of ecosystem management planning.

MYTH #2:   “FIA data are not spatial, and cannot be used to analyze spatial patterns.”

FACT:  FIA data are in fact spatial in that the sample locations are known and can be used by FIA analysts to produce a variety of mapped products using modern spatial statistical tools.  These data, alone or combined with other data layers, can be used to produce contour maps of almost any measured variable including species presence/absence, volume, growth, mortality, tree grade, or health status.  Estimates can also be produced for any ecosystem stratification by overlaying FIA plot locations with the ecosystem coverage to associate plots with ecosystem classes.  Given the sample intensity of FIA, this makes most sense when the ecosystem classes are sufficiently large (200,000 acres or more) to include sufficient sample locations.

Because of the statistical design of the FIA system, it is also possible to generate maps of confidence or reliability which show where a statistically generated map can be considered reliable or not.  Maps should always be studied in pairs:  one showing the response of interest (say volume per acre), and another map of the same area showing the confidence (standard error or confidence interval) associated with the spatial representation of the response of interest.

It is true that historically FIA has not been a great producer of maps.  That is changing now, as FIA analysts take advantage of modern analysis technology and statistical approaches to produce a variety of strategic‑scale map products which span administrative boundaries.  For some examples of recent applications of FIA data within National Forests, see the FIA Virtual Scrapbook at
fia.fs.fed.us/scrapbook/ scrapbook.htm.  This web‑based collection of sample maps shows how FIA data have been used to generate data layers which are very relevant to forest planning needs.

MYTH #3:   “FIA data are of no use for riparian zones or other linear features.”

FACT:  FIA sample locations are randomly located within a systematic cell grid, with 1 plot per approximately 6000 acres.  As such, it is true that they will not focus excessively on high priority areas such as riparian zones.  However, there is no bias; riparian areas or other similar features will still be sampled in proportion to their occurrence within the landscape.  If 12% of your Forest is riparian, you can expect about 12% of your FIA plots to be riparian.  This may not be sufficient for many analysis needs; yet it can at least be counted on to provide some information for all covered areas without a need for an expensive additional study.  FIA data can be also be used as the basis for designing more intense surveys to answer more specific questions, and the FIA sample frame provides one alternative for intensifying sampling.

How are FIA data used by NFS analysts?

FIA data have been used in many ways by NFS analysts to obtain information relevant to NFS objectives.  Some examples include:

*	Validation monitoring.  Since FIA uses permanent plots measured at periodic intervals spread across the landscape, they provide an ideal independent data set for validating the models and assumptions used to project future forest conditions and to assess the effects of past management practices.   For example, FIA data have been used as an independent data set to validate and, in some cases, to adjust annual allowable harvest rates, to assure sustainable levels of management.

*	Forest scale statistical summaries.  The average National Forest of 1.2 million acres can be expected to have approximately 200 FIA sample locations, with each location having multiple observations in some cases going back decades.  This is more than sufficient information to derive forest‑level estimates of basic parameters such as total acres of forest land as well as rates of growth, harvest and mortality.  There will likely also be enough information to stratify by a few basic categories such as broad ecosystem classes or administrative units.  This information constitutes an independent,  constantly updated baseline of status and trends of gross conditions within National Forest boundaries.

*	Combination of FIA data with other spatial data can provide modelled coverages of derived products unattainable elsewhere.  Vegetation information from FIA can be combined with satellite imagery, digital elevation models, and other coverages to develop models for estimating information in areas or at smaller scales where information may be lacking. 

Our National FIA web site will soon include more case studies showing how FIA data have been used successfully by NFS analysts to address their information needs.

Summary:  Using FIA Data for National Forest Analyses

The FIA program considers NFS analysts to be a potentially large ‑ and presently under served ‑ customer group.  We believe that FIA data are extremely relevant to Forest or Regional information needs, not as a replacement to traditional stand exam project level data but rather as a strategic forest inventory suitable for forest planning, and as an information base allowing analysts to look outside forest boundaries and across larger scales for purposes of managing forests  in a landscape context.  

FIA is committed to making our information and analysis products useful and accessible to NFS planners and analysts.  FIA analysts are ready to collaborate on a personal basis with NFS analysts to help you make the best use of Agency data, or to provide on‑site training for NFS staff interested in accessing and using FIA data.  For information about the status and availability of FIA data for your Forest or Region, please contact your regional FIA Program Manager who can be found on our National homepage at 
fia.fs.fed.us