Ecological Interpretations 



Even though soil -vegetation relationships were identi- 

 fied, the ecological interpretations are extremely hypo- 

 thetical. The habitat types used to define the study envi- 

 ronment are positioned along a continuous moisture- 

 temperature gradient. Tsuga heterophylla can maintain 

 viable populations only in the most moderate moisture 

 and temperature regimes found in northern Idaho. Sites 

 adjacent to T. heterophylla, but either too dry, too wet, too 

 hot, or too cold for it to successfully reproduce are gener- 

 ally dominated by Thuja plicata. The harshest environ- 

 ments within this continuum, sites too hot and dry or too 

 cold for T. plicata, are dominated by Abies grandis. The 

 two understory unions likewise respond to environmental 

 gradients, which generally can be described as warm- 

 moist sites supporting both climax Asarum caudatum and 

 Clintonia uniflora, while the colder and/or drier sites 

 support only C. uniflora. Within the theorized functions 

 for soil (Jenny 1941) and vegetation properties (Major 

 1951), these environmental relations are incorporated in 

 the climate, relief, and parent material factors. If a 

 change in vegetation is related to changing environmental 

 factors, then a concurrent, but not necessarily convergent, 

 shift in soil properties should occur. 



Within the data used for this study no statistically or 

 ecologically significant correlation could be found between 

 habitat types and taxonomic soil units. Reasons for this 

 failure are probably related to: the restricted amount of 

 available data and its nonconformity to statistical con- 

 straints; the relatively narrow environmental gradient 

 encompassed by the habitat types studied; and the broad 

 geographic region included within the data base. 



Interpretation of ecological relationships between habi- 

 tat types and soil characteristics appears to be related 

 directly to and confounded by climatic conditions that 

 control soil genesis and species composition of the plant 

 community. The cooler and wetter climatic regimes af- 

 fecting northern Idaho are so recent (Mehringer 1985) 

 that most of the vegetation-soil ecosystems are still in a 

 state of flux. Primary successional development of plant 

 communities and soil horizonation are proceeding at dif- 

 ferent rates. Duchaufour (1982) refers to short-cycle and 

 long-cycle patterns of soil formation, with the dominant 

 functional factors being vegetation and climate, respec- 

 tively. The vegetation of northern Idaho has responded 

 rapidly to the climatic change, whereas the soils are im- 

 mature relative to the current conditions of climate and 

 vegetation. This could account for the high variance val- 

 ues for soil characteristics when viewed from the perspec- 

 tive of a narrow vegetational continuum. I hypothesize 

 that the habitat types used in this study are relatively 

 stable in composition given the current climate, but the 

 soils associated with these habitat types have not yet 

 stabilized. 



CONCLUSIONS 



For the geographic area studied, there appear to be no 

 universal soil variables or sets of variables that can be 

 used to predict the climax plant communities. The rela- 



tionships between vegetation and soils are multifactorial 

 and dynamic; the effect upon plant growth or reproduc- 

 tion of any one soil variable changes quantitatively and/or 

 qualitatively with every variation in the complex of envi- 

 ronmental factors. Yet, identifiable relationships do exist 

 between a stratified set of soils and vegetation. This 

 study was able to identify soil characteristics usable for 

 differentiating pairs or groups of habitat types occurring 

 on specific groupings of parent materials in northern 

 Idaho. The concepts explored herein should be widely 

 useful. But they should be applied only to northern Idaho 

 ecosystems; only to the typal phase of the six habitat 

 types discussed; and only to soils developed from the 

 group of coarse-textured parent materials previously 

 defined. 



The importance of these findings for forest managers is 

 twofold. First, with a large sample size and sufficient 

 insight, a unique set of soils can be correlated with indi- 

 vidual habitat types. Within a habitat type each set of 

 functional soil-forming factors will develop a soil specific 

 to that set of environmental conditions. Second, and 

 probably more important, a silvicultural prescription may 

 not produce a uniform vegetational response when ap- 

 plied to a specific habitat type or habitat type-phase occu- 

 pying more than one type of soil. The use of universal 

 guidelines for prescribed silvicultural treatments, site 

 preparation, selection of regeneration species, stocking 

 levels, and many other management activities has often 

 resulted in failure. Many of these failures were the result 

 of an inappropriate prescription chosen because of insuffi- 

 cient knowledge about these highly complex ecosystems. 

 Effective management requires an individualistic pre- 

 scription for each stand based on knowledge of its unique 

 features, particularly its soils. 



REFERENCES 



Barnes, B. V.; Pregitzer, K. S.; Spies, T. A.; Spooner, V. H. 



1982. Ecological forest site classification. Journal of 



Forestry. 80: 493-498. 

 Base, S. R.; Fosberg, M. A. 1971. Soil-woodland correla- 

 tion in northern Idaho. Northwest Science. 45: 1-6. 

 Bray, J. R.; Curtis, J. T. 1957. An ordination of the upland 



forest communities of southern Wisconsin. Ecological 



Monographs. 27: 325-349. 

 Buol, S. W.; Hole, F. D.; McCracken, R. J. 1980. Soil 



genesis and classification. 2d ed. Ames, IA: Iowa State 



University Press. 404 p. 

 Bunting, S. C. 1978. The vegetation of the Guadalupe 



Mountains. Lubbock, TX: Texas Tech University. 183 p. 



Dissertation. 



Cooper, S. V.; Neiman, K. E.; Steele, R.; Roberts, D. W. 

 1987. Forest habitat types of northern Idaho: a second 

 approximation. Gen. Tech. Rep. INT-236. Ogden UT: 

 U.S. Department of Agriculture, Forest Service, 

 Intermountain Research Station. 135 p. 



Daubenmire, R. 1956. Climate as a determinant of 

 vegetation distribution in eastern Washington and 

 northern Idaho. Ecological Monographs. 26: 131-154. 



Daubenmire, R. 1968. Plant communities: a textbook of 

 plant synecology. New York: Harper Row. 300 p. 



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