Soil Characteristics as an Aid to 

 Identifying Forest Habitat Types 

 in Northern Idaho 



Kenneth E. Neiman, Jr. 



INTRODUCTION 



Habitat types (after Daubenmire 1968) and other 

 vegetation-based land classification systems (Cooper and 

 others 1987; Daubenmire and Daubenmire 1968; Hall 

 1973; Hironaka and others 1983; Mueggler and Stewart 

 1980; Pfister and others 1977; Steele and others 1981, 

 1983; Tisdale 1979) have been adopted for use throughout 

 the Northern Rocky Mountains by the U.S. Department of 

 Agriculture, Forest Service, and other Federal and State 

 agencies. These systems rely on knowledge of the existing 

 floristics for identification of "climax" or long-term stable 

 plant associations. On forested lands that have not been 

 severely disturbed, habitat types can be identified with 

 relative ease by use of species presence lists. But as land 

 is disrupted by forest management, habitat types will 

 have to be identified from a secondary successional plant 

 community, often having little floristic similarity to its 

 climax community. Even highly trained plant ecologists 

 find this to be a speculative and frustrating task. Land 

 managers and scientists need to classify serai communi- 

 ties and also to develop a means for extrapolating serai 

 community types to their respective habitat types with 

 the aid of both biotic and abiotic factors. 



In studies of abiotic site factors, Jenny (1941, 1980) 

 theorized that soil development is a function of climate, 

 parent material, relief, and potential organisms interact- 

 ing over time. Major (1951) felt that species composition 

 of vegetation is a similar function of the same five factors. 

 Although soil and vegetation both appear to respond to 

 the same "functional factors," this relationship cannot be 

 extended to indicate that soil and vegetation are corre- 

 lated on a one-to-one basis. Although we find sites with 

 similar vegetational composition, often these do not have 

 similar site characteristics, parent material, or age 

 (Barnes and others 1982; Daubenmire 1968; McCune and 

 Allen 1985; Pfister and Arno 1980). Vegetation responds 

 to both long-term and short-term environmental changes 

 (Daubenmire 1956), but is particularly responsive to ex- 

 tremes of temperature and moisture. Climatic pulses 

 tend to have a minor effect on soil formation processes. 

 Thus, different soils often develop beneath similar plant 

 communities and, conversely, different plant communities 

 occur on what outwardly appear to be similar soils. 



In most physical systems, both internal and external 

 sets of independent factors determine the development of 

 individual characteristics. Nowhere is this more observ- 



able than in the wide variety of soil horizonations. 

 Whether viewed regionally or locally no two cross sections 

 of soil are exactly alike. Yet, in an attempt to understand 

 this variability, taxonomic systems are devised that iden- 

 tify individuals as members of classification units. Soil 

 taxonomy (USDA SCS 1975), a soil classification system, 

 is based on differentiating characteristics assumed to be 

 the result of independent factors. 



Jenny (1941, 1980) described five elements critical to all 

 soil development: climate, in the sense of regional macro- 

 climate; parent material, the basement rock or deposi- 

 tion^ material from which the soil originates; relief 

 (topography), the slope, aspect, elevation, landform, and 

 related ground water conditions; organisms, the micro- 

 and macro-organisms of plant and animal species poten- 

 tially available for site occupancy; and time, the zero point 

 being calculated from the initiation of soil formation or 

 since major disturbance to existing conditions. 



Jenny (1958, 1980) further described plants as being 

 both dependent and independent variables. The species 

 that dominate the vegetational community will exert their 

 own particular influence on both plant community and 

 soil-forming processes. Thus, with all factors remaining 

 constant except time and natural succession, soil develop- 

 ment continues as a reaction to both independent and 

 dependent biotic components. 



Many taxonomies have been developed for both plant 

 communities and soils, but little direct analysis of their 

 interrelationships has been attempted. In the Northern 

 Rocky Mountains, only one climax community classifica- 

 tion (Tisdale and Bramble-Brodahl 1983) and one succes- 

 sional community classification (Hann 1982) have aggres- 

 sively attempted to correlate specific plant communities 

 with specific soil and site characteristics. 



In two of the major plant community classifications 

 developed for the Inland Northwest (Daubenmire 1970; 

 Daubenmire and Daubenmire 1968) extensive soil profile 

 data were collected in hopes of defining a soil-vegetation 

 relationship. But all such attempts failed due to multiple 

 soil series occurring in one habitat type. Further confu- 

 sion arose when soil families and Great Groups also did 

 not correlate with plant communities. Daubenmire (1970) 

 recognized the importance of soil factors to vegetation and 

 strongly emphasized "those soil properties suspected of 

 playing important roles in vegetation differentiation are 

 not among the characteristics emphasized in soil classifi- 

 cation." Soil moisture and temperature regimes, aeration. 



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