Priest River Experimental Forest

The Forest Service established the Priest River Experimental Forest (PREF) in 1911 as one of the first experimental forests set aside as a forestry research center. Early research produced foundational information on fire behavior, silviculture methods, site preparation, and tree genetics that are still being used today. For example, researchers at PREF in the early 1900s were developing a fire danger rating system, fire-weather forecasting capabilities, and the beginnings of research on predicting fire behavior. Many long-term studies and research plots continued to be monitored today, producing valuable long-term datasets. PREF also initially served as the headquarters for the District 1 (now Region 1) Investigative Program. PREF is currently administered by the Rocky Mountain Research Station from the Forestry Sciences Laboratory in Moscow, Idaho.  

Priest River Experimental Forest contains approximately 6,368 acres (2,758 ha) of mountainous forestland, with small areas of talus and alpine grassland. Situated on the westward slope of a spur of the Selkirk Mountains, PREF is an excellent representation of the diverse forested ecosystems of the Northern Rocky Mountains. PREF contains a variety of managed and reserve areas, including ecological sites that vary from wild to highly disturbed areas, and all of the significant forest types and habitat associations of the region. Within PREF are two Research Natural Areas: Canyon Creek, 977 acres (395 ha) and Wellner Cliffs, 310 acres (125 ha) to serve as unmanaged ecological reference sites. 

See the Priest River Experimental Forest Interactive Map below (or view full screen here) to learn more about the experimental forest history, research, and facilities.

The Northern Rocky Mountains are a diverse region in terms of climate, topography, flora, and fauna. Within this context, Priest River Experimental Forest is an excellent representation of the forested ecosystems that are common to an area west of the continental divide and north of the Snake River Plain.  

Climate and Weather

In general terms, the Priest River-Northern Rocky Mountain climate is transitional between a northern Pacific coastal type and a continental type. The Pacific influence is noted particularly by the late autumn and winter cloudiness and precipitation. The relatively moderate average winter temperatures, compared with areas east of the continental divide, also show the Pacific influence. Summer is characteristically sunny and dry, though July and August are the only distinct summer months.

The average annual (water year, Oct 1 – Sep 30) precipitation at the Forest headquarters is 32.17 inches (817 mm). The Benton Spring rain gauge at 4,774 feet-elevation (1455 m) receives an annual average of 36.42 inches (925 mm) of precipitation. The wettest months are November through March, which receive close to 60% of the annual total precipitation. Snowfall accounts for more than 50% of the total precipitation at elevations above 4,593 feet (1400 m). High-elevation snowpack can reach an average depth of 51.97 inches (132 cm) at the end of March and sometimes remain into June.

The monthly mean temperatures at the headquarters range from 25F (-4C) in January to 64F (18C) in July. The annual mean temperature is 45F (7C). Extreme temperatures have ranged from a high of 108F (42C) to a low of -36F (-38C). The climate at PREF provides a transition between the strong maritime influence on the coniferous forests of the coastal Pacific Northwest domain and the dryer, colder interior flora found east of the continental divide.  

PREF maintains long-term weather and snowpack records and data is summarized in the GTR publication: Climate, snowpack, and streamflow of Priest River Experimental Forest, revisited

Terrestrial Ecosystems

Vegetation and ecosystem types within PREF are best described as "complex" because of the extremely rapid changes in aspects and from wet to dry ecosystems as habitat transitions from riparian to upland conifer forests, grasslands, or cliffs. Flora and fauna diversity is extremely high due to the number of different habitat types that are intimately intermixed. Management also varies within the Experimental Forest and tree stands range from old-growth to recently harvested young stands. 

Over the past 100+ years, here have been extensive sampling efforts of the diverse suite of species for in Priest River Experimental Forest, Wellner Cliff's RNA, and Canyon Creek RNA. A comprehensive List of Vascular Plant Species, List of Fungi Species, and List of Lichen & Bryophyte Species has been compiled by James B. Donley using historical records, inventories, reports, and publications. Over 600 vascular plant species, 207 lichen species, 134 bryophyte (moss, hornwort, liverwort) species, and more than 700 species of fungi have been observed and recorded in Priest River to date.

Soils & Geology

Soil surface horizons have formed in aeolian loess and volcanic ash. Surface textures are mostly silt loams, relatively fine-textured soils with low rock contents and high water-holding capacity. The soils of the mountain slopes are underlain by granite, gneiss, and schist, with the primary parent material being gneiss. The schist contains prominent biotite and muscovite mica, and is thinner bedded than the gneiss.

Soils at elevations up to 3,280 feet (1,000 m) on southerly aspects are associated with shallow Saltese soils with minor amounts of deeper Jughandle soils on concave slopes of the drainages. Above this threshold, the Jughandle soils and associated phases of exposure, except the subalpine phase above 4,593 feet (1400 m), are mapped in the zone of maximum soil moisture and soil temperature effectiveness. Fertility is high on these sites. Above 4,593 feet (1,400 m), the colder soils predominate, though moisture is near maximum. South-facing slopes near this elevation and above contain the Horsehead soils, which represent a prairie-forest transition to the subalpine environment.

Forest Productivity

Moisture usually limits high timber production on soils of the river terraces and lacustrine benches, and the south-facing slopes at lower elevations. Relatively high evaporation from prevailing southwest winds helps make these sites dry. The stream terraces and fans of Benton and Canyon Creeks have favorable run-in moisture from side slopes, and fertility and productivity are near maximum in the area. Soils of the middle elevations, and on northerly, easterly, and westerly slopes have highest fertility and productivity associated with favorable moisture-temperature relationships. Fertilizer experiments have demonstrated that nitrogen and, on metamorphic bedrocks, potassium deficiencies, may co-limit productivity. Soils of the high elevations have less favorable soil temperature and lowest fertility.

Hydrology & Stream Ecology

Priest River Experimental Forest includes Benton Creek, Canyon Creek, Big Creek, and Fox Creek, which drain into Priest River. Priest River defines the western boundary of the Experimental Forest. A survey and analysis of lower Canyon Creek water quality and macroinvertebrate taxa was conducted by Fred Rabe in 1995 within the Canyon Creek RNA.    

PREF conference building.

Priest River Experimental Forest has facilities available for research and educational purposes. The headquarters site consists of an office/lab building, conference building, three residential buildings, a bunkhouse/mess hall, and a modest shop. A full-time employee occupies a fourth residence. All were constructed by the Civilian Conservation Corps between 1934 and 1939 and are listed in the National Register of Historic Places. The Gisborne Fire Lookout is listed on the National Historic Lookout Register. A conference building, with a capacity of 50, was added in 1998.

During the field season, the Experimental Forest averages 1000 use-days by Forest Service personnel and their cooperators. The residential buildings and bunkhouse have a capacity of 20 beds. During the winter months, a cabin and the bunkhouse/mess hall are shut down, reducing bed space to 12. The residential buildings are ADA compliant and provide visitors with full kitchen facilities and linens.  

Road access to Priest River Experimental Forest is by State Highway 2 from Spokane, Washington to Priest River, Idaho. From Priest River, drive north on State Highway 57 for 3 miles, then north on Peninsula Road (9 miles pavement and then 1 miles of gravel) to reach the Experimental Forest. Within PREF, the entry and forest roads are surfaced with gravel or native soils.

Researcher Russ Graham measures the impacts of site preparation treatments on the growth of a one-year old seedling.

Historical Research 

Since the Priest River Experimental Forest was established, numerous educators, Forest Service researchers, and state and private forestry personnel have used the site. Research conducted by J.A. Larsen, Harry Gisborne, Ken Davis, Charles Wellner, and Irvine Haig provided information on basic forestry and fire principles still used today for managing Rocky Mountain forests. These and other researchers throughout PREF's history have made it a key location for conducting studies on forest ecosystems of the Northern Rocky Mountains. Research topics conducted on the PREF have included forest fuels management, genetics of various tree species, forest ecology, mycology, forest soils, timber harvest practices (e.g. slash disposal, site preparation, alternative timber species), and impacts of for management practices on hydrologic and soil processes.  

Research at Priest River Experimental Forest has contributed to many major scientific findings, including:

• Research on rust-resistant western white pine;
• Development of methods of site preparation for timber harvest;
• Development of the Prognosis computer model, forerunner to the present Forest Vegetation Simulator (FVS), used today as a forest management tool;
• Beginnings of fire behavior, fire danger rating, and fire effects information;
• Influence of forest structure on water yield and quantity;  
• Importance of coarse woody debris in maintaining forest productivity;
• Development of the Free Selection silvicultural system 

Ongoing Research

In addition to continuing to monitoring long-term, permanent research plots, researchers are conducting new studies on forest ecosystem processes, management, and restoration. Research topics include: the effects of management activities on long-term soil productivity, coarse woody debris function, atmospheric deposition, western white pine seedling development in canopy gaps, landscape silviculture, whitebark pine restoration, and site preparation treatments.

Current and ongoing research projects at the PREF include: 

Cones being collected from the "Inter-varietal Hybrid Douglas-Fir" plantation at the Benton Nursery

Kaniksu South Project: (planned project, 2023) The PREF portion of this project is being developed in order to meet two broad goals: 1. landscape-scale fuel reduction across the experimental forest, and 2. treating stands with high disease load, especially root disease. Specific studies will investigate the efficacy of different silvicultural prescriptions at meeting management goals, set up long-term studies of density in both retention and planting, examine the efficacy of tethered site prep methods, and compare whitebark pine establishment treatments.  

Hybrid Douglas-fir Trials: A plantation of Douglas-fir hybrids "Inter-varietal Hybrid Douglas-Fir"  -  hybrids between coastal and inland Douglas-fir to create cold hardy and drought resistant genetics - is located at the Benton nursery at PREF. This plantation is being used to conduct genomic studies, and several of these F1 trees have been sequenced already. Breeding efforts to produce F2 offspring are planned.

Canyon Creek Free Selection Study: This free selection study is one of two replicates of a landscape-scale implementation of the free selection silvicultural system - the other replicate being located at Deception Creek Experimental Forest. This study acts as an example of free selection as implemented in forests of the northern Rockies historically associated with western white pine. Overstory removal treatments were conducted in 2007. A wide variety of conditions were created as part of this project, with canopy openness ranging from 25-45% in some locations, to over 92% in others. This range of conditions allows us to study stand development across a variety of conditions.  

Ponderosa Pine Prescribed Fire and Shelterwood Study: This study was established in the mid 1980s with the goal of studying the use of prescribed fire and shelterwood cutting to regenerate seral ponderosa pine. A total of three replicates were created, with six treatment categories each. Two residual densities were created with basal areas of 80 and 40 sq ft/acre, and these densities were crossed with three prescribed burning treatments: a spring burn, a fall burn, and an unburned control. Early work on this experiment explored burn severity and mineral soil, as well as the understory response across treatments. The stands comprising this experiment are scheduled to be re-entered as part of the Kaniksu South project, and data will be collected before and after these entries.

Western White Pine Genetics and Restoration Research:

• Blister rust resistant western white pine vigor quality "VQ" plantation: In 1955 to 1959, some of the earliest plantings of white pine blister rust resistant western white pine developed by a group of Forest Service researchers led by R.T. Bingham. The results of the VQ plots have shown that many of the western white pines exhibiting rust resistant characteristics have exceeded the expected growth and productivity, validating the techniques being used by R.T. Bingham to develop the new genetic strains. The VQ plots continue to produce seed with a high degree of blister rust resistance that have been used to produce plantations located throughout the Northwest, thus protecting the forests from the previous devastation caused by this disease.
• Canyon Creek western white pine plantation: In 1971, western white pine seedling survivors of artificial white pine blister rust inoculations (numbering 12,414) were transported from the Moscow Forestry Sciences Lab and outplanted at PREF on a 17-acre area of the lower Canyon Creek drainage (3,100 feet elevation). This plantation provides a large reservoir of known genetic material for future experiments on traits of white pine blister rust resistance and for information on the relationships between seedling symptom history and long-term resistance. With the assistance of personnel from National Forests, the Priest Lake Ranger District, and other agencies, cones, pollen, and/or scion materials have been collected from trees at the Western White Pine Canyon Creek Tree Improvement Area almost annually since 1988. These materials have been used by universities, government agencies, and other cooperators for a variety of purposes, including reforestation, rust-resistance breeding programs, new seed orchards, and genetics research.
• Ida Creek western white pine plantation: The establishment of this plantation resulted from a provenance test as one of three areas established at PREF in 1971 to assess the variation in growth and survival among seed sources of western white pine from different elevations in the interior northwestern USA.  
• Pollen Cloud/Mass Selection study" plantation:  The "Pollen Cloud" study at PREF is examining the potential improvement in the resistance of white pine to white pine blister rust by the removal of infected trees. The resulting stand may have a lower incidence of infection, implying an improvement in the quality of western white pine pollen released in the area.
• WBP Restoration (Gisborne Mountain whitebark pine restoration project): A high-elevation whitebark pine restoration project is in the planning phase. This project will explore the efficacy of different planting strategies, including mulch mats, biochar amendment, and more.  

Permanent Plot re-measurements: Used to study long-term (now at ~110 years) forest stand demography and dynamics, many permanent plots at PREF are continued to be monitored. Tree measurements common to all permanent plots include species, diameter at breast height, total height, percent live crown, crown class, tree status, tree class, and damage to the trees. Some permanent plots also have measurements of shrub cover, height of shrubs, and photographs. Researchers are setting up new permanent plots to add to the network.  

Assisted Migration Adaptation Trial (AMAT): A crew from the British Columbia Ministry of Forests planted seedlings in 2012 at a site in the Benton Creek drainage at PREF for the AMAT. This project will track the progress of the seedlings as part of a long-term study of climate warming and its effect on the range of native and non-native conifer species. The crew also installed a weather station to monitor the conditions at the site

Long-term soil productivity study: In 1991 a study to evaluate the effects of timber harvesting and site preparation on changes in the bulk density of forest soils in northern Idaho was initiated at PREF. This site was a as part of a world-wide cooperative Long-Term Soil Productivity (LTSP) network designed to provide a controlled and extensively replicated experiment to isolate and study the soil disturbance effects of compaction and organic matter removal. Treatments involving three levels of residual organic matter and three levels of site preparation/soil compaction during tree harvest were tested at the PREF LTSP plots. Data at these plots has been collected and analyzed regularly over the following 30-year period together with data collected at more than 100 LTSP and affiliated sites across North America and at several other international locations, including New Zealand, China, and Chile.

Bedding Experiment plantations: A study to evaluate the effects of site-preparation treatments on the long-term growth and productivity of interior Douglas-Fir and western white pine was started at PREF in 1982 (named the "Great North Idaho Bedding Experiment" or "GNIBE"). The PREF GNIBE study site-preparation treatments, made on replicates of 30-meter long by 1.5-meter wide planting-beds, included: (a) no site preparation, (b) scalping organic matter and mineral topsoil, (c) mounded bedding with competition not removed, and (d) mounded bedding plus three years of competition control with herbicide. The results of the PREF GNIBE study sites have so far been analyzed in 1986 after three years of growth, and in 2017 at 34 years of age.

Benton Watershed Fuels Reduction study: In 2003 a large study was initiated at PREF to determine the effects of prescribed fire and mechanical alternatives for forest fuel reduction on runoff and soil erosion. Ten sub-drainages were selected for fuel reduction treatments (thinning followed by prescribed fire; thinning followed by mastication; simulated wildfire; simulated wildfire followed by salvage logging; and no treatment control). Several study plots were established at each of the ten small drainages/study areas to collect pretreatment data (including estimates of percentage litter, fine and coarse woody debris, grass, forbs, and shrubs) and to monitor and record the post-treatment effects. The long-term effect of the forest fuel reduction treatment applications on forest structures and on disease and insect infestation are being observed on the Benton watershed study-units. 

Research Infrastructure

The Control Weather Station: The control weather station has been operating since 1911 and collects daily minimum and maximum temperatures, daily precipitation totals (rain and snow), hourly timing of precipitation, and general conditions (e.g., "overcast", "windy", etc.). This weather station is supplemented with a digital Atmos 41 all-in-one weather station, manufactured by METER Group. This weather station collects data every 15 minutes.

High Elevation Weather Station: Data will be available from a newly-installed high elevation (5,000 ft) weather station beginning in June 2023.

Benton Creek gaging dam: The Benton Creek gaging dam measures streamflow for the entire Benton Creek drainage, and has been operating since 1941.

Snow Course measurements: PREF has an upper and a lower snow course, on which snowpack data have been collected since 1937. These snow courses measure snow depth and snow-water equivalent.

Benton Nursery: The Benton Nursery at PREF is approximately 15 acres and has been home to a number of seedling and genetic studies over the years. The nursery has irrigation infrastructure, a storage shed for garden tools, and an eight foot tall fence to exclude herbivores.

PREF Headquarters: Includes an office/laboratory space as well as a conference room that can accommodate up to 50 people. 

Research Natural Areas 

The Forest Service Research Natural Areas (RNAs) network protects some of the finest examples of natural ecosystems for the purposes of scientific study and education and for maintenance of biological diversity. There are two RNAs within the PREF footprint.

Canyon Creek RNA: 977 acres (395 ha), established in 1937. Canyon Creek is located adjacent to Priest River and was established as a reference site typical of western white pine and spruce-fir climax forests.

Wellner Cliffs Research Natural Area: 310 acres (125 ha), established in 2006. Wellner Cliffs is located along lower Canyon Creek on the Priest River Experimental Forest and contains a diverse matrix of habitat types, including mid-elevation mixed conifer forests, dry open ponderosa pine forests, grasslands, and riparian habitat with exposed rocky cliffs and high lichen diversity. 

The Forest Service has collected and archived long-term datasets of daily weather (1911), snow pack (1937), tree growth (1914) and streamflow (1938). Priest River Experimental Forest supplies climate data for external websites; these data sets are public domain. The Experimental Forest and Range network encourages re-use of data from among its collaborators. We also recognize that it is important for scientists to receive proper credit for the contribution their data make to other projects. Thus, the data user must properly cite the data publication in any other publications or in the metadata of any derived products developed using Forest Service data (Conditions of Use).   

Daily Weather Records

• The NCDC website has the complete record of daily weather observations (11/27/1911 to present) in txt or pdf formats. Searching using Priest River Experimental Forest or Station, ID # 107386. The data set consists of daily maximum and minimum temperature, precipitation, daily snowfall and accumulated snow fall.
• A reformatted version of the NCDC data, with gaps filled from PREF records, is available as an xlsx document at the Moscow Forestry Sciences Lab, available by request.
• Benton Spring (elev. 4725 ft, 1440 m), monthly observations, transcribed into Excel spreadsheets from 1961 to present, available by request
• Benton gauging dam (elev. 2640 ft, 805 m) spreadsheet format of daily and monthly totals from 1941 to present, available by request
• The Western Regional Climate Center maintains monthly averages and metadata taken at Priest River Experimental Forest.

Snow Pack Datasets 

Snowpack data is collected from Benton Meadow (elev. 2,380 ft, 725 m) and Benton Spring (elev. 4,775 ft, 1,455 m) snowcourses. The Natural Resource Conservation Service (NRCS) has the full record for both snowcourses. Visit the NRCS National Water and Climate Center website and select the snow course of interest (Benton Meadow or Benton Spring). Snowpack has been recorded at PREF since 1937.

Surface, Terrain, and Canopy Height Models

These data publications  (found in the USFS Research Data Archive) each contain three raster datasets with a spatial resolution of one meter: 1) a digital surface model (DSM), which represents the highest lidar return in each grid cell; 2) a digital terrain model (DTM), a representation of the ground surface with vegetation and other non-ground returns removed; and 3) a canopy height model (CHM), a representation of the height of vegetation above the ground surface.

Atmospheric Chemistry

On December 31, 2002, a National Atmospheric Deposition Program (NADP) site was established in Priest River Experimental Forest. Data for Priest River can be found at the NADP webpage interactive map using the site designation reference ID02.

Streamflow Data

Streamflow has been recorded from Benton Gaging Dam since 1937. Digitized gauge heights from 1955 to present are available from the Moscow Forestry Sciences Lab. This data will eventually be archived in the Rocky Mountain Research Station database.

Tree Growth Data

Tree growth has been recorded, derived from permanent growth and yield plots, from 1914 to present. Data is available at the Moscow Lab.

Archaeological data

A detailed archaeological survey of PREF was conducted in 1978 and is on file at the Moscow Forestry Sciences Lab.

Data for Priest River Experimental Forest available through  the USFS Research Data Archive

• Canopy effects from biomass utilization on the Priest River Experimental Forest, 2021
• Runoff and erosion from small forest watersheds on the Priest River Experimental Forest, 2021
• Digital surface, terrain, and canopy height models for Priest River Experimental Forest in 2011
• Priest River Experimental Forest weekly precipitation chemistry data: ID02, 2016
• Priest River Experimental Forest daily weather data: GHCND:USC00107386 - Priest River Experiment Station, ID US, 2016
• Streamflow data for the Priest River Experimental Forest , 2015