Coeur d'Alene, St. Joe, Clearwater, and Nez Perce), and 

 on forested lands of the Idaho Department of Lands and 

 private properties. 



Setting 



The physical settings of the region vary from low-lying 

 riverine valleys, 300 m above sea level, to glacial trenches, 

 550 m above sea level, to six major mountain ranges 

 (Selkirk, Purcell, Cabinet, Coeur d'Alene, Clearwater, 

 and Bitterroot Mountains) having elevations as high as 

 2,745 m. Sampling was mainly restricted to a mideleva- 

 tional zone in this region, ranging from 550 to 1,400 m 

 above sea level. 



The macroclimatic regime of northern Idaho is an in- 

 land expression of the Pacific Coast maritime climate 

 (Ross and Savage 1967). Estimates for precipitation at 

 sample locations range from 500 to 1,270 mm (Pacific 

 Northwest River Basin Commission 1969); the actual 

 values are dependent on elevation, north-south and east- 

 west location, and position relative to orographically influ- 

 enced precipitation patterns. Generally, precipitation 

 occurs between October and May. The June through 

 September period averages less than 25 mm rainfall per 

 month. The average monthly ambient temperatures for 

 these sites are equally variable. Mean summer tempera- 

 tures range from 29 to 36 °C and mean winter tempera- 

 tures range from -2 to -10 °C, with maximum extremes 

 that range from 41 to -50 °C (USDC NOAA 1985). Al- 

 though the aboveground climatic conditions are extremely 

 variable, the presence of complete snow cover during 

 winter months creates a moderate soil environment in 

 which soil temperature regimes (USDA SCS 1975) are 

 frigid or cryic and soil moisture regimes are generally udic 

 or ustic, with some drier sites having a xeric regime. 



Geology 



The study area includes two geological provinces. The 

 Columbia Intermontane Province (Thornbury 1965), from 

 the Seven Devils Mountains northward to Moscow, with 

 interfingering as far north as Coeur d'Alene, is character- 

 ized by variable thicknesses of wind-deposited silt (loess) 

 that overlies mid- to late-Tertiary Columbia River Plateau 

 basalts, which, in turn, overlie intrusions of early Tertiary 

 Idaho Batholith granite or Precambrian metasediments. 



The Northern Rocky Mountains Province covers the 

 remainder of the study area from the southeast and 

 south-central Nez Perce National Forest to the Canadian 

 border. The Clearwater and Coeur d'Alene Mountain 

 ranges are an undifferentiated mass of Precambrian Belt 

 Supergroup metasediments and Idaho Batholith granodi- 

 orites and quartz monzonites. The eastern boundary of 

 the study area is formed by the Bitterroot Range, also 

 quite variable in composition of granite, gneiss, and 

 metasediments. North of Pend Oreille Lake, the Selkirk 

 Mountains and the Cabinet Mountains are both composed 

 of Belt Supergroup metasediments. Tertiary and Quater- 

 nary gravel and glacial till deposits occur sporadically 

 throughout the region. Major deposition of till from Pleis- 

 tocene Epoch continental glaciation occurs at all 



elevations north of Sandpoint (Buol and others 1980; Ross 

 and Savage 1967). The geologic data collected for habitat 

 type classification in northern Idaho (Cooper and others 

 1987) identify over two dozen different parent materials. 



The region has been subjected to periodic, violent erup- 

 tions of volcanos and subsequent deposition of ejecta over 

 wide areas of the Northern Rocky Mountains. Of the 

 three most recent eruptions — Glacier Peak, Mount 

 Mazama, and Mount St. Helens — the most significant was 

 the creation of Crater Lake with the climactic eruption of 

 Mount Mazama about 6,700 years ago. Ash from this 

 event is an important material we now find in both rela- 

 tively pure and mixed upper soil horizons, as deep as 

 1 meter, in northern Idaho (Nimlos and Zuuring 1982). 



Vegetation 



In this study, habitat type is the taxonomic unit used to 

 decribe plant communities (Daubenmire 1968). Habitat 

 type is defined as follows: All the area that now supports, 

 or within recent time has supported, and is still capable of 

 supporting one plant association. A habitat type may 

 encompass quite variable physical characteristics of 

 topography, climate, and soils, yet the effective environ- 

 ment for plant growth and reproduction remains rela- 

 tively constant. The diagnostic climax plant community 

 (association) acts as an integrator of climate, relief, and 

 soil through factor compensation, allowing for identifica- 

 tion of equivalent environments by means of simple floris- 

 tic lists of diagnostic species. 



In the Northern Rocky Mountains, contiguous stands of 

 mesic maritime forests are unique to northern Idaho 

 (Cooper and others 1987; Daubenmire and Daubenmire 

 1968). These stands are characterized by the climax 

 dominance of the coastal species Tsuga heterophylla (Raf.) 

 Sarg. and Thuja plicata Donn. ex D. Don. This interpre- 

 tation of Pacific maritime climatic influence is supported 

 by numerous studies of coastal disjunct species found spo- 

 radically throughout northern Idaho (Johnson 1968; 

 Johnson and Steele 1978; Steele 1971). The six habitat 

 types chosen for this study represent the modal environ- 

 mental conditions for the three overstory species (T. 

 heterophylla, T. plicata, and Abies grandis [Dougl. ex D. 

 Don] (Lindl.) most directly associated with this maritime 



climatic anomaly. 



METHODS 

 Sampling Procedures 



Vegetation Data — A set of 89 sample plots was se- 

 lected from those sampled by Cooper and others (1987) as 

 the data base for this study. Because similar studies have 

 shown that a large amount of variation can be expected in 

 the data (Base and Fosberg 1971; Monserud and others 

 1986; Sondheim and Klinka 1983), sample selection was 

 restricted to six similar habitat types: Abies grandis/ 

 Clintonia uniflora habitat type-Clintonia uniflora phase 

 (ABGR/CLUN-CLUN); Abies grandis /Asarum caudatum 

 habitat type-Asarum caudatum phase (ABGR/ASCA- 

 ASCA); Thuja plicata I Clintonia uniflora habitat type- 

 Clintonia uniflora phase (THPL/CLUN-CLUN); Thuja 



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