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United States Department of Agriculture Forest Resources Forest Service Rocky Mountain of the Bitterroot Research Station May 2000 National Forest Tracey S. Frescino Bitterroot National Forest Montana Idaho About the author __________________________ Tracey S. Frescino is a Forester with the Interior West Resource Inventory, Monitoring, and Evaluation Program, Rocky Mountain Research Station in Ogden, Utah. Contents __________________________________ Page What forest resources are found on the Bitterroot National Forest? ............ 1 How does the forest change? ................................................................................. 7 Other information about the forest land of the Bitterroot .............................. 8 How much forest land is suitable for timber production? ............................... 8 How was the inventory conducted? ................................................................... 10 Documentation ....................................................................................................... 13 For further information ......................................................................................... 13 Rocky Mountain Research Station 324 25th Street Ogden, UT 84401 Forest Resources of the Bitterroot National Forest Tracey S. Frescino The Interior West Resource Inventory, Monitoring, single predominant species concept is in stands where and Evaluation (IWRIME) Program of the USDA Forest Engelmann spruce and subalpine fir occur together. If Service, Rocky Mountain Research Station (formerly in combination they constitute the stocking plurality for the Intermountain Research Station), as part of its na- a stand, forest type will be computed using the follow- tional Forest Inventory and Analysis (FIA) duties, en- ing criteria: for a stand to be classified as Engelmann tered into a cooperative agreement with the Northern spruce type, Engelmann spruce must be greater than or Region for the inventory of the National Forests in equal to 20 percent of the stocking, and subalpine fir Region 1. This report presents the highlights of the Bit- must be less than 20 percent of the stocking. In other terroot National Forest 1995 inventory, using commonly requested variables and summaries. The information presented in this report is based solely on the IWRIME inventory sample. Additional data collected by the Bit- terroot National Forest and used separately or in com- bination with IWRIME data will produce varying results. What forest resources are found on the Bitterroot National Forest? The 1,580,550 acre (USDA 1995b) Bitterroot National Forest is 92 percent forest land and 8 percent nonforest or water (fig. 1). Forty-seven percent of the total area of the Bitterroot is in a reserved designation such as Wil- derness. The first part of this report will present forest resources on all forest land on the Bitterroot, including reserved lands. Lands not reserved from tree utiliza- tion, some of which would be considered suitable for timber production, will be addressed in a later section. Forest type—Forest land tree resources are often de- scribed using a forest type classification. Forest type re- fers to the single predominant tree species in a stand, based on plurality of live tree stocking. Stocking is an expression of the extent to which growing space is ef- fectively utilized by live trees. One exception to this 8% Nonreserved forest land Reserved forest land Nonforest and Water 50% 42% Figure 1—Area by land class, Bitterroot National Forest. 1 Douglas-fir terms of their potential to produce similar plant communities at successional climax. Spruce-fir More than 100 forest habitat types and phases Lodgepole pine were described for Montana by Pfister and Ponderosa pine others, 1977. To assist with sub-regional and Whitebark pine landscape level assessments, habitat types from the Northern Region have subsequently Forest type Larch Engelmann spruce been summarized into Westside and Eastside groups based on similarities in natural distur- Grand fir bance regimes, successional patterns, and 0 1020304050structural characteristics of mature stands Percent of forest land area (Jones 1997; USDA 1995a). These habitat type groups serve as integrators of the moisture Figure 2—Percent of forest land area by forest type, Bitterroot National Forest. availability and temperature gradients of the biophysi- cal environment (Jones 1997). The Bitterroot has more than 60 unique forest habitat situations where subalpine fir and Engelmann spruce types that have been grouped into Westside habitat together have plurality, the classification would be classes. Figure 3 shows area of forest land by forest spruce-fir type. type and habitat type group on the Bitterroot. The most The most common forest type on the Bitterroot, in common habitat type group on the Bitterroot is the percentage of total forest land area, is Douglas-fir with moderately warm and dry group, representing most of 43 percent. Douglas-fir is followed in abundance by the Douglas-fir and ponderosa pine forest types in the spruce-fir at 22 percent, lodgepole pine at 18 percent, forest. By summarizing forest land area data by habitat ponderosa pine at 9 percent, whitebark pine at 3 per- type group, the Bitterroot can be categorized in a way cent, larch and Engelmann spruce types at 2 percent, that theoretically will not change with disturbance or and grand fir at 1 percent (fig. 2). advancing succession. Habitat type—Forest communities are similarly de- Number of live trees—Another way to analyze tree scribed using a habitat type classification. Habitat type resources is by examining the composition of trees on is generally influenced by site characteristics such as forest land by individual species. Figure 4 shows total slope, aspect, elevation, soils, and climate. Compared number of live trees by species in two categories 1.0 to forest types, which describe the species currently to 6.9 inches diameter and 7.0 inches diameter and occupying the site, habitat types describe lands in greater. Subalpine fir makes up 31 percent of the total 500 Forest type Douglas-fir 400 Spruce-fir Lodgepole pine 300 Ponderosa pine Whitebark pine Larch 200 Engelmann spruce Thousand acres Grand fir 100 0 Warm/dry Mod Mod Mod Mod Mod Cool/moist Cool/wet Cool/mod Cold/mod Cold Scree warm/dry warm/mod warm/moist cool/moist cool/wet dry dry dry Habitat type group Figure 3—Area of forest land by forest type and habitat type group, Bitterroot National Forest. 2 200 Size class 1.0-6.9" 150 7.0" and greater 100 Million trees 50 0 Subalpine Douglas-fir Lodgepole Whitebark Engelmann Ponderosa Grand fir Western Aspen Rocky Mtn Subalpine fir pine pine spruce pine larch maple larch Species Figure 4—Number of live trees 1 inch diameter and greater, by species and size class, Bitterroot National Forest. number of trees, Douglas-fir, 27 percent; lodgepole Figure 5 shows the number of live trees by species pine, 24 percent; whitebark pine, 7 percent; Engelmann and elevation class. Elevation, mentioned above as a spruce and ponderosa pine, both 4 percent; and grand site characteristic affecting habitat type, is associated fir, 2 percent. Western larch, subalpine larch, aspen, with variations in local climate. For example, precipita- and Rocky Mountain maple combined contribute a to- tion generally increases with rising elevation, while tal of another 1 percent. Species that are scarce may temperature decreases. These factors have a profound not be encountered with the extensive sampling strat- impact on a tree species’ ability to compete with other egy used for this inventory. Over 75 percent of all live species at various elevations. In the Bitterroot, the trees on the Bitterroot are between 1.0 and 6.9 inches ponderosa pine, Douglas-fir, and lodgepole compete at diameter, and about a third of those are subalpine fir. lower elevations and lodgepole pine, subalpine fir, Species 8000-8900 Lodgepole pine 7000-7900 Douglas-fir Subalpine fir 6000-6900 Engelmann spruce Ponderosa pine 5000-5900 Whitebark pine Grand fir Elevation class (feet) 4000-4900 Subalpine larch Western larch 3000-3900 010203040 50 60 70 80 90 100 Million trees Figure 5—Number of live trees 5.0 inches diameter and greater by species and elevation class, Bitterroot National Forest. 3 Engelmann spruce, and whitebark pine at higher Size—The size distribution of trees in a stand is an in- elevations. dicator of structural diversity. Figure 7 displays the tree size distribution by diameter class on the Bitterroot. Number of dead trees—Standing and down dead tree Overall, there are a higher number of small trees than resources are important contributors to forest land large trees. A classification of forest land based on the composition and diversity. Dead trees provide food and predominant size of trees contributing to the majority cover for wildlife, enrich and stabilize soils, and contrib- of the stocking is called stand-size class. Figure 8 dis- ute significantly to forest fuel load. There are roughly 35 plays a breakdown of forest land by stand-size classes. million standing dead trees (snags) 5.0 inches diameter This figure shows that the majority of stands on the Bit- and greater on the Bitterroot National Forest. Many terroot are stocked with predominantly large trees and wildlife species are dependent upon snags. The species, that relatively few stands are considered to be non- size, and density of snags required varies according to stocked, such as stands that have been recently har- the species of wildlife.

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