This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. DO~SOaFORMATION PROCESSES AND PROPERTIES IN WESTERN-MONTANE FOREST TYPES AND LANDSCAPES-SOME IMPLICATIONS FOR PRODUCTIVITY AND MANAGEMENT Robert T. Meurisse Wayne A. Robbie Jerry Niehoff Gary Ford ABSTRACT Soil is the primary medium for regulating movement and storage of energy and water and for regulating The principal soil orders in western-montane forests cycles and availability of plant nutrients. Soil also pro­ are Inceptisols, Alfisols, Andisols, and Mollisols. Soil vides anchorage, aeration, heat for roots, and is home moisture and temperature regimes strongly influence for many decomposers and element-transforming organ­ forest type distribution and productivity. The most pro­ isms. Informed inquiry and understanding are critical ductive and resilient forests are on soils with udic mois­ for making sound decisions about effective and efficient ture and frigid temperature regimes. Soils with low use and management of these vital resources. The objec­ water-holding capacity in us tic, xeric, and aridic mois­ tives of this paper are to: (1) characterize the dominant ture regimes and those with cryic temperature regimes soil-formation processes and properties in the principal are least productive and resilient. Soil organic carbon western-montane forest types and landscapes; (2) illus­ and nitrogen contents range from about 20,000 to more trate the major soil moisture and temperature regime than 100,000 and 1,200 to 9,000 pounds per acre. gradients of these forest types; and (3) discuss some implications for ecosystem function, productivity, and INTRODUCTION management. The western-montane forests occupy a vast area of the WESTERN·MONTANE FOREST western United States in which active mountain build­ ing, erosion processes, and weathering regimes interact TYPES AND EXTENT to produce landscapes and ecosystems of great diversity, The focus of this paper is on the western-montane grandeur, and degrees of resilience to land disturbance. forest types as described by Burns (1983) and the soils Geologically, land surfaces vary from very recent (sev­ that support them. The principal forest types, their eral thousands of years) to very old (millions of years). extent, and symbolic codes are in table 1. For further Soil-forming processes operating on these diverse land­ information about each of these types, refer to Agricul­ scapes have formed heterogeneous soils with highly ture Handbook 445. Additional information about the variant properties. The resulting soil-forest ecosystems forest types particular to the Inland North west and their are likewise heterogeneous in character and function productivity, processes, and properties is provided by and require site-specific understanding for making man­ Harvey and others (1989). agement interpretations that provide for ecosystem sustainability and health. Nevertheless, some important principles and concepts can be established to serve as PRINCIPAL KINDS OF SOILS guides for forest resource management. The most direct way to characterize the kinds of soil occurring in western-montane forests is to discuss the occurrence of soil orders. Soil orders are the highest taxonomic class in the United States system of soil clas­ sification (Soil Survey Staff 1975). They are differenti­ Paper presented at the Symposium on Management and Productivity ated by the presence or absence of diagnostic horizons of Western-Montane Forest Soils, Boise, 10, April 10-12, 1990. or features that reflect differences in the dominant soil­ Robert T. Meurisse is Regional Soil Scientist, Pacific Northwest Region, Forest Service, U.S. Department of Agriculture, Portland, OR 97208. forming processes that occurred. The recent amendment Wayne A. Robbie is Supemsory Soil Scientist, Southwestern Region, to the National Soil Taxonomy Handbook established a Forest Service, U.S. Department of Agriculture, Albuquerque, NM. Jerry new soil order-Andisols (Soil Survey Staff 1989), mak­ Niehoff and Gary Ford are Soil Scientists, Idaho Panhandle National Forests, Forest Service, U.S. Department of Agriculture, Coeur d'Alene, ID. ing 11 soil orders. Hausenbuiller (1978) provides a more 7 Table 1-Western-montane forest types and extent and their domi­ complete description of soil orders and the other truco­ nant soil moisture and temperature regimes nomic levels. Within the vast western-montane region, Code Name nine of the 11 soil orders occur, though several are rare. Only the highly weathered and leached Ultisols and Oxisols Million acres apparently are absent. Data are unavailable for precise USTIC·UDIC Moisture Regime estimates of the extent of soil orders. However, a review M ESIC·FRIGI D·CRYIC Temperature Regime of selected soil survey reports and interpretation of data from "Soils of the Western United States" (Washington SWPIPO Southwestern State University 1964) permits a reasonable estimate of ponderosa pine 11 relative occurrence (table 2). Probably the major differ­ PIPO/PSME v.gl Ponderosa ence between current estimates and the 1964 report is the pine-Rocky 20 relatively low occurrence of Spodosols. Many of the soils Mountain that were formerly thought to be Spodosols are now clas­ Douglas-fir sified as Andisols, Alfisols, and Inceptisols. MC/PI MO/TH PL Mixed conifer­ Inceptisols are a diverse group of soils of intermediate western white development in humid and subhumid regions. They are pine-western 5 mostly friable soils with moderate-to-high levels of or­ redcedar ganic carbon. Though many have high rock fragment PICO Lodgepole pine 13 content (more than 35 percent by volume) and have cryic temperature regimes, they usually are moderately deep PIEN/ABLA Engelmann and deep and are relatively fertile. Many are on unstable spruce-sub­ 10 and active fluvial slopes in the Idaho Batholith. alpine fir Alfisols occur on a variety oflandscapes, but most are XERIC·UDIC Moisture Regime stable or meta-stable surfaces. They support a wide range FRIGID·CRYIC Temperature Regime offorest types. Alfisols have relatively light-colored sur­ face horizons and the dominant feature is the presence of NWPIPO Northwest Ponderosa pine 7 an enriched subsurface clay layer. Most clays are the expanding 2:1 layer types. Ion exchange capacities are ABGRIPSME Grand fir­ moderate to high and the soils have relatively high fertil­ v.gl Douglas-fir ity. These soils dominate the Colorado Plateau in the (Rocky Mountain) 6 southern part of the western-montane forests (Meurisse LAOC Western larch 3 and others 1975). ABMAIABCO Red fir- Andisols are forming mostly in volcanic ejecta such as white fir 4 ash, pumice, cinders, and lava. These soils have a charac­ USTIC·ARIDIC Moisture Regime teristic layer of volcanic ash or pumice, 14 inches (35 cm) MESIC·FRIGID Temperature Regime to several feet thick over buried soils. These soils, and intergrades to other orders, are among the most produc­ P-J Pinjon-juniper 48 tive of western-montane forest soils (Meurisse 1985, 1987). Andisols occur mostly in the northwestern and Table 2-Estimated relative occurrence of soil orders in the western-montane forest region. The principal associated forest types are shown in their relative occurrence in each soil order Soil Relative order occurrence Principal associated forest types Inceptisols 3.0 PICO, PIEN/ABLA, PIPO/PSME, LAOC, ABMAIABCO, ABGRIPSME Alfisols 2.0 SW PI PO, PICO, PIPO/PSME, MC/PIMO/THPL, PIEN/ABLA, P-J, LAOC, ABMAIABCO Andisols 1.6 ABGRIPSME, MC/PIMOITHPL, NW PIPO, PICO, PIEN/ABLA, LAOC, SW PIPO Mollisols 1.3 PIPO/PSME, SW PIPO, P-J, NW PIPO Aridisols .8 P-J Entisols .6 PiCe, PIEN/ABLA, P-J Spocfosols .5 PIEN/ABLA, PICO Others .2 10.0 8 northern parts of the western-montane region, on pla­ SOIL MOISTURE AND teaus and gentle to moderately steep mountain slopes. TEMPERATURE REGIME Some are on steep and very steep slopes in northern Idaho and have a high erosion hazard. GRADIENTS OF FOREST TYPES Mollisols are characterized by thick, dark-colored sur­ Available soil moisture and soil temperature regimes are face horizons with at least 1 percent organic matter in two overriding variables affecting the distribution, species the surface mineral soil layers. They occur mostly in the mix, and productivity of western-montane forests. Soil relatively dry western-montane forests and often have moisture and temperature regimes are internal soil proper­ an abundance of grass and forbs in the understory. Many ties and are described in the Soil Taxonomy Handbook of the forests transitional to pinyon-juniper forests and (Soil Survey Staff 1975) and by Hausenbuiller (1978). grasslands occur on these soils. They occur mostly on Generalized descriptions of these regimes are in table 3. stable mountain slopes and high plateaus. The distribution of the principal western-montane forest The Aridisols occupy the driest parts of the region, and types, by soil moisture and temperature regimes, is the principal forest is the pinjon-juniper type. Entisols ill ustrated in figures 1 and 2. The size of the delineation are forming in parent materials of recent origin, in cold is proportional to the distribution of the forest type ac­ climates, and on some unstable land surfaces where ero­ cording to these regimes and mean annual precipitation. sion prevents development of diagnostic features. It does not necessarily relate to aerial extent. For ex­ Spodosols are strongly acid and have low levels of base ample, the ponderosa pine (Pinus