Great Basin Naturalist Volume 46 Number 2 Article 16 4-30-1986 Estimates of site potential for Douglas-fir based on site index for several southwestern habitat types Robert L. Mathiasen Northern Arizona University, Flagstaff, Arizona Elizabeth A. Blake Northern Arizona University, Flagstaff, Arizona Carleton B. Edminster Northern Arizona University, School of Forestry, Flagstaff, Arizona Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Mathiasen, Robert L.; Blake, Elizabeth A.; and Edminster, Carleton B. (1986) "Estimates of site potential for Douglas-fir based on site index for several southwestern habitat types," Great Basin Naturalist: Vol. 46 : No. 2 , Article 16. Available at: https://scholarsarchive.byu.edu/gbn/vol46/iss2/16 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. ESTIMATES OF SITE POTENTIAL FOR DOUGLAS-FIR BASED ON SITE INDEX FOR SEVERAL SOUTHWESTERN HABITAT TYPES Robert L. Mathiasen', Elizabeth A. Blake', and Carleton B. Edminster^ Abstract. — Estimates of site potential for Douglas-fir based on measured site indexes in 450 stands are compared between 10 southwestern habitat types. Significant differences in site potential are found between the habitat types studied. Site index is currently the most widely used curves and normal yield tables to estimate method of evaluating site quality or potential yield capability for habitat types in Montana productivity of forest lands in the United and Idaho. States (Jones 1969, Husch et al. 1972, Southwestern forests are becoming more Daubenmire 1976). Site index is based on the intensively managed for timber production average heights of dominant and codominant than in the past. However, growth and pro- trees at a specified index age (usually 50 or 100 ductivity data are presently limited (Gottfried years). Because stands of the index age are 1978). Habitat type classifications are recog- seldom encountered, site index curves are nized for these forests, but little information is constructed to allow for estimation of site in- available on the timber productivity potential dex for stands older or younger than the index for these habitat types (Moir and Ludwig age by interpolation between the curves. Site 1979, Hanks et al' 1983, Alexander et al. index curves describe the height growth of 1984). Jones (1974) provides a summary of the hypothetical trees of specified site indexes. silviculture of southwestern mixed conifer The use of habitat types (Daubenmire 1952) forests and emphasizes a need for improving to classify forest vegetation is gaining accep- their management based on the application of tance by land managers and researchers in the habitat types or stand types. This study pro- western United States (Layser 1974, Pfister vides additional quantitative data on site po- 1976, Pfister and Arno 1980). One of the pri- tential based on site index measurements for mary uses of habitat types is in timber man- Douglas-fir for several recognized southwest- agement. Habitat types are used to compare ern forest habitat types. regeneration success, succession patterns, cutting methods, and timber productivity and Methods to develop guidelines for collecting seed and planting nursery stock (Pfister and Arno Total height and age at diameter breast 1980). height were measured for two to six vigor- The use of habitat types to predict forest ously growing dominant or codominant Dou- site productivity potential is proposed by sev- glas-firs in 450 uneven-aged southwestern eral investigators. Differences in the rate of spruce-fir (31) or mixed conifer (419) stands height growth by habitat type are demon- from 1979 to 1985. Trees with visible signs of strated for several tree species (Daubenmire abiotic, insect, or disease damage were not 1961, Deitschman and Greene 1965, Stanek selected as site trees in the stands. The follow- 1966, Stage 1975, Hoffman 1976). Significant ing information was recorded for each stand: differences between site indexes are also national forest, location (township, range, and shown for habitat types (Stanek 1966, Stage section), elevation (nearest 100 feet), aspect 1975, Hoffman 1976). Pfister et al. (1971, (four cardinal directions), slope (nearest 5%), 1977) and Steele et al. (1981) use site index slope position (flat, bottom, ridge, slope) and Northern Arizona University, School of Forestry, Flagstaff, Arizona 86011. ^USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado i 111 ' 278 Great Basin Naturalist Vol. 46, No. 2 Table 1. Southwestern spruce-fir and mixed conifer habitat types sampled. Spruce-fir Habitat Types ABLA/LIBO: Abies lastocarpalLinnaea borealis~ (Abies lasiocarpalVacciniwn scoparium-Linnaca borealis^) ABLA/ EREX; Abies lasiocarpa/Erigeron eximius^'^ (Abies lasiocarpa/Erigeron superbus*) Mixed Conifer Habitat Types PIEN/SECA: Picea engebnanniilSenecio cardaminc^ (Picea pungens-Picea engelmanniilSenecio cardamine ) PIEN/EREX; Picea cngcbnanniilErigcron cximius^ (Picea pungens-Picea cngebnannii/Erigeron superbiis^) PIPU/EREX: Picea pungens/Erigeron exiniius' (Picea pungens-Pseiidotsiiga menziesii ) ABCO/ACGL; Abies concolorlAcer glabrum^'^ (Abies concolor-Pseudofsttga menziesiilAcer glabrum ^) ABCO/FEAR: Abies concolorlFestuca arizonica^^ (Abies concolor-Pseudotsuga menziesii /Poafendleriana^) ^ ABCO/QUGA: Abies concolorlQuercus gambelii ' ~ (Abies concolor-Pseudotsuga menziesii/Qucrcus gambeUi*) ABCO/BERE; Abies concoIor/Berberis repcns (Abies concolor-Pseudotsuga »u'»iz;r.su7[sparse]^) ABCO/EREX; Abies concolorlErigeron eximius'^ (Abies concolor-Pseudotsuga menziesiilErigeron superbus^) . classsification forest ts-pes 'Ale.xander, B G . Jr , F Ronco. Jr E L Fitzhugh. and J A Ludwic 1984. A of habitat of the Lincoln National Forest, New Mexico. USDA Forest Service, Gen. Tech. Rep. RM-104, 29 pp. In preparation. classification of forest habitat types of southern "DeVelice. R L , J A LUDWIG. W H Moir, and F Ronco. Jr A northern New Mexico and Colorado. USDA Forest Service, Gen. Tech. Rep. RM. ^Fitzhugh, E L , W H Moir, J A Ludwig. and F Ronco Forest habitat types in the Apache, Gila, and part of the Cibola national forests, Arizona and New Mexico. In preparation. nii.xed conifer habitat Service, Res. *MoiR, W H . AND J A Li'Dwic 1979. A classification of spruce-fir and types of Arizona and New Mexico. USDA Forest Pap. RM-207. 47 pp. ^he Abies concolor-Pseudotsuga menziesii/Poa fendleriana habitat type originally described by Moir and Ludwig (1979) is now considered to represent a phase of the Abies concolorlFestuca arizonica habitat type described by Moir and Ludwig (1979). Personal communication with W. B. Moir, 1985. nfOUNCBLOOD. A P In press. Coniferous forest habitat types of central and southern Utah. USD.^ Forest Service, Gen. Tech. Rep. INT. Table 2. Mean Douglas-fir site inde.xes and standard deviations by habitat type. April 1986 Mathiasen etal.: Douglas-fir Ecology 279 (89.5), and ABCO/FEAR (87.6) habitat types pret these data as representing moderate to are classified as high site potential habitat high site (juality for the Southwest. Our site types for Douglas-fir. The ABLA/LIBO index data for this habitat type basically corre- (niean-67.7) is classified as the low potential spond to that of Moir and Ludwig's, except habitat type. The moderate site potential class the range of site indexes is wider in our study. includes the remaining six habitat types stud- Moir and Ludwig (1979) do not present ied with mean site indexes ranging from 82.6 Douglas-fir site quality estimates for three of (PIPU-EREX) to 73.6 (ABLA/EREX). Mean the habitat types sampled in this study. Based site indexes for the ABLA/EREX and ABLA/ on our site index data, site quality for Dou- LI BO habitat types were not significantly dif- glas-fir is moderate for the ABCO/EREX and ferent, but they were classified into different ABLA/EREX habitat types and high for the site potential classes because the mean for the ABCO/FEAR habitat type. ABLA/LIBO habitat type was below 70 feet. Several investigators discuss the difficulties of using site index for estimating site potential in uneven-aged stands (Stage 1963, Jones Discussion 1969, Curtis 1976, Daubenmire 1976). Steele et al. (1981, 1983) use site indexes and normal Site index is currently the most widely used yield tables to estimate productivity potential method of evaluating site quality in the for habitat types in Montana and Idaho. How- United States (Jones 1969, Husch et al. 1972). ever, normal yield tables for Douglas-fir in the Several investigators note significant differ- Southwest are not available, and we do not ences in site index between habitat types for feel the use of yield tables from other regions several tree species (Stanek 1966, Roe 1967, would be valid for the Southwest. The devel- Hoffman 1976). However, Daubenmire opment of separate site curves for different (1961) rejects the use of ponderosa pine site habitat types should improve the accuracy of index curves for predicting potential produc- site index as an estimate of site quality. How- tivity of habitat types in eastern Washington. ever, this approach may not solve the prob- Our results indicate that the southwestern lems related to using site index in uneven- spruce-fir