Permanent Plots in the HJ Andrews Experimental Forest

Report Number 2
Reference Stands in or near
H.J. Andrews Experimental Forest

C. T. Dyrness and Steven A. Acker
April 1999


Link to Andrews Experimental Forest website (



Citation: Dyrness C. T.; Acker, Steven A. 1999. Reference Stands in or near the H.J. Andrews Experimental Forest. Permanent Plots of the Pacific Northwest. Report Number 2. (



This report describes key characteristics of 38 permanent vegetation plots (Reference Stands) within and around the H. J. Andrews Experimental Forest, western Oregon. These plots were established to provide typical examples of many major forest communities commonly found in the Tsuga heterophylla, transition, and Abies amabilis zones of Oregon's central-western Cascade Mountains. The sites serve as references for scientists of many disciplines in their studies of these and similar forest communities in the Pacific Norhtwest (Acker et al. 1998).


Thirty of the 38 Reference Stands are located in the H. J. Andrews Experimental Forest (AEF), a 6,400-ha watershed located in the central-western Cascade Range of Oregon, approximately 40 miles east of Eugene. Three Reference Stands are located 4 miles north of AEF in Wildcat Mountain Research Natural Area (RNA). Three stands are situated 7 miles west of AEF in the Hagan RNA. One stand is located 20 miles north of AEF in the Middle Santiam RNA. And one stand was situated 5.5 miles west of AEF on Cone Creek.

Study Areas

The H.J.Andrews Experimental Forest was established as an experimental forest in 1948 and is representative of dense coniferous forests of Douglas-fir, western hemlock, and common true firs typical of the Western Cascade Range. Forest age is variable but old-growth stands, with trees older than 400 years, are common. Phytosociological studies have identified 23 major forest communities within AEF (Dyrness et al. 1974). Reference Stands were selected to represent typical examples of many of the important forest communities which were identified and described by the phytosociological studies. Forest zones which are well represented by Reference Stands are the Tsuga heterophylla zone (from about 500 to 1,000 m in elevation) and Abies amabilis zone (from about 1,000 to 1,550 m elevation). The AEF encompasses steep, mountainous terrain with landforms ranging from ridgetops, smooth and uneven sideslopes, and benches in uplands, to terraces and flood plains along major streams. Soil parent materials are largely pyroclastic rocks (tuffs and breccias) at lower elevations and andesite, aerially deposited volcanic ash, and localized glacial deposits at higher elevations. Because of the pervasive infulence of volcanic ash, soils at AEF are uniformly low in bulk density and therefore very porous.

Reference Stands 13, 14, and 36 are located in Wildcat Mountain Research Natural Area, established to preserve prime examples of Abies procera stands on ridgetops in the Western Cascade Range of Oregon. Elevations range from about 1,160 m to 1,632 m at the top of Wildcat Mountain. Other tree species present in the Research Natural Area include Abies amabilis, Tsuga mertensiana, Pinus monticola, Chamaecyparis nootkatensis, Tsuga heterophylla, and Pseudotsuga menziesii. The dominant bedrock in the area is andesite; however, it is overlain by fairly thick deposits of volcanic ash. Soils are weakly developed primarily from volcanic ash and are very friable and porous.

Reference Stands 24 and 35 are located in the Hagan Research Natural Area which includes the north fork of Hagan Creek. R.S. 37 is situated a short distance south of the Research Natural Area on the south fork of Hagan Creek. The area is dominated by mature stands of Douglas-fir which came in following a fire in 1855. The elevation ranges from 520 m at the stream bottom to 1070 m on the ridgetops. The area is deeply dissected with steep slopes averaging about 66%. The climate is characteristic of Oregon's Western Cascade Range, with mild wet winters and relatively dry summers. Along with Douglas-fir, common tree species in the Research Natural Area include Tsuga heterophylla, Acer macrophyllum, Alnus rubra, Castanopsis chrysophylla, and Taxus brevifolia. Forest communities range from the very wet Tsuga heterophylla/Oplopanax horridum in riparian areas to Pseudotsuga menziesii/Holodiscus discolor/grass on very dry sites.

Reference Stand 25 is located in the Middle Santiam Research Natural Area, made up primarily of forests of old-growth Douglas- fir and western hemlock occupying the Middle Santiam River drainage. Slopes in the Research Natural Area are steep and elevations range from 457 to 1433 m. The Reference Stand, however, is situated on a terrace adjacent to the river. Bedrock in the Research Natural Area consists of lava flows, pyroclastic rocks, and water-reworked volcanic rocks. The area is geomorphologically active with numerous shallow and deep-seated mass movements. Climate is maritime, with dry and warm summers and cool and wet winters. The Research Natural Area has a variety of forest communities mostly dominated by old-growth Pseudotsuga menziesii and Tsuga heterophylla except at higher elevations where Abies amabilis is the dominant tree species.

History of the Reference Stands

The first 19 Reference Stands (RS) were established between 1971 and 1973 as a part of the International Biological Program (Hawk et al. 1978). With the exception of RS 9, all were originally 0.25 ha in size. Subsequently, RS 1 through 3 were increased in size to 1 ha and RS 13 to 4.69 ha. Reference Stands 20 through 26 were established in 1977, RS 27 through 33 in 1978, RS 34 in 1979, RS 35 and 36 in 1980, RS 37 in 1981, and RS 38 was established in 1990. Stands established after the initial cohort of 19 are, for the most part, 1 ha in size. Exceptions are RS 32 and 33 (0.25 ha), RS 34 (2.0 ha), RS 35 (2.13 ha), and RS 38 (2.44 ha). Since their establishment, these stands have all been remeasured at approximately 5-year intervals until 1989 when remeasurements were shifted to every 6 years.


For the original cohort of Reference Stands (1 through 19) the establishment procedure was described by Hawk et al. (1978). Each Reference Stand was surveyed and slope-corrected to a 0.25 ha area (50 x 50 m). Metal stakes were installed at 10-m intervals on the perimeter of each plot and at the corners of an interior 30 x 30 m plot. The entire stand was then divided into a 10 x 10 m grid, and all trees larger than 5 cm dbh (diameter at breast height) were mapped and tagged with numbered aluminum tags.

Data recorded on each Reference Stand included tree location by X and Y coordinates, tree tag number, tree species, and dbh in cm. Vigor, crown condition, and bole condition were also recorded for each tree. The location of downed logs and dead trees was also included on maps of each stand. Accuracy of mapped locations of trees was estimated to be plus or minus 1 m.

Tree saplings (>0.5 m tall, but <5 cm. dbh) were tallied within the 30 x 30 m interior plot by a total count. Tree seedlings (<0.5 m tall) were tallied in 4, 1 x 30 m strip transects. Cover and frequency of shrub species were tallied along 60 m of line- intercept at the top and bottom of each 30 x 30 m plot. Cover and frequency of herb and moss species were tallied in 60 microplots (2 x 5 dm) placed at 1 m intervals along the two central lines within the 30 x 30 m plot.

Plots established in 1977 and later (RS 20 - 38) were almost all 1 ha or larger in size at the time of establishment. RS 32 and 33, 0.25 ha in size, were the exceptions. Plots were 100 m x 100 m and were divided into 4 25 m x 25 m sub-blocks. Upon completion of surveying outer boundaries, the boundaries of interior 25 x 25 m blocks were surveyed. Within each of these blocks fine cotton line was strung in a 5-meter grid pattern. The use of the grid pattern afforded a maximum of accuracy in mapping with a minimum of expended time. The tree inventory and mapping followed procedures used for the original 19 Reference Stands.

Several methods were used to inventory understory vegetation in Reference Stands 20 through 33. In most stands understory vegetation was sampled by use of 4 to 7 circular plots. These plots were 12.6 m in radius and marked in the center by a permanent metal stake. Shrub and tree sapling cover was measured along 40 m of line intercept (10 m along each of the 4 cardinal directions). Forty microplots (2 x 5 dm) were also placed at 1 m intervals along the 40 m of lines for estimation of herb and moss cover. Each circular plot also had 4 circular subplots 2 m in radius which were used to inventory tree seedlings. On several RS understory vegetation was sampled on only reconnaissance plots. On these plots crown cover of all plant species was ocularly estimated. Virtually no understory vegetation information has been collected on RS 34 through 38.

Remeasurements of Reference Stands were initially carried out at appoximately 5 year intervals and more recently at 6-year intervals. At each remeasurement any profound natural or human- caused disturbance was noted, tagged trees were checked for mortality, and tagged trees were remeasured. Occasionally tree heights were measured as well as tree dbh. In addition, canopy class, overall vigor, and crown ratio were recorded for each tagged tree. Ingrowth trees (those growing into the 5 cm dbh class) were also tagged, measured, and brought into the data set. Annual checks for tree mortality were performed on most stands up until the early 1990's. Annual mortality checks continue to be made on RS 34, 35, and 38 (riparian Reference Stands).

Many of the Reference Stands have been equipped with thermographs which record air temperature and soil temperatures at depths of 10, 20, and 30 cm. These temperature data are available in the AEF Climatic Data Set. In addition, other information such as snow depth, litter fall, and phenology has been collected on selected Reference Stands.

Research Conducted on H. J. Andrews Experimental Forest Reference Stands

Many research projects have used the AEF Reference Stands as study areas. Much of the early work in defining and characterizing old- growth Douglas-fir was carried out on the Reference Stands. Another tree species which has been intensively studied on the reference stands is Pacific Yew. Animals which have received attention included small mammals and northern spotted owl. In addition, Reference Stands have been extensively used as sites to determine the environmental characteristics of the major forest communities of the H. J. Andrews.

Detailed Description of Reference Stands

The Reference Stands, their sizes, and the plant communities they represent are listed in Table 1. Detailed descriptions of the vegetation and soils of the individual Reference Stands are accessible from the links in Table 1.

Directly Related Publications

Acker, S.A., W.A. McKee, M.E. Harmon, and J.F. Franklin. 1998. Long-term research on forest dynamics in the Pacific Northwest: a network of permanent plots. Pp. 93-106 in F. Dallmeier and J.A. Comiskey, eds. Forest biodiversity in North, Central and South America, and the Caribbean: Research and monitoring. UNESCO, Paris.

Busing, R.T., and T.A. Spies. 1995. Modeling the population dynamics of Pacific yew. Res. Note PNW-RN-515. USDA Pacific Northwest Research Station, Portland, OR 13 p.

Busing, R.T., C.B. Halpern, and T.A. Spies. 1995. Ecology of Pacific yew (Taxus brevifolia) in western Oregon and Washington: the role of old-growth forests. Conservation Biology, in press.

Dyrness, C.T., J.F. Franklin, and W.H. Moir. 1974. A preliminary classification of forest communities in the central portion of the western Cascades in Oregon. Coniferous Forest Biome Bull. No. 4. Univ. of Washington, Seattle. 123 p.

Franklin, J.F., K. Cromack, Jr., W. Denison, A. McKee, C. Maser, J. Sedell, F. Swanson, and G. Juday. 1981. Ecological characteristics of old-growth Douglas-fir forests. USFS Gen. Tech. Rep. PNW-118. USDA Forest Service, PNW Forest and Range Exp. Sta., Portland OR. 48 p.

Franklin, J.F., H.H. Shugart, and M.E. Harmon. 1987. Tree death as an ecological process. BioScience 37: 550-556.

Hawk, G.M., J.F. Franklin, W.A. McKee, and R.B. Brown. 1978. H.J. Andrews Experimental Forest reference stand system: establishment and use history. Coniferous Forest Biome Bull. No. 12. Univ. of Washington, Seattle. 79 p.

Klopsch, Mark Warren. 1985. Structure of mature Douglas-fir stands in a western Oregon watershed and implications for interpretation of disturbance history and succession. M.S. Thesis, OSU Dept. of Forest Science. 52 p.

Old-growth Definition Task Group. 1986. Interim definitions for old-growth Douglas-fir and mixed-conifer forests in the Pacific Northwest and California. Res. Note PNW-447. USDA Forest Service, PNW Research Sta. Portland, OR. 7 p.

Spies, T.A., J.F. Franklin, and M. Klopsch. 1990. Canopy gaps in Douglas-fir forests of the Cascade Mountains. Can. J. For. Res. 20: 649-658.

Zobel, D.B., A. McKee, G.M. Hawk, and C.T. Dyrness. 1976. Relationships of environment to composition, structure, and diversity of forest communities of the central western Cascades of Oregon. Ecol. Monogr. 46: 135-156.

Other Publications Using Data and/or Sites

Binkley, D., and R.L. Graham. 1981. Biomass, production, and nutrient cycling of mosses in an old-growth Dougals-fir forest. Ecology 62: 1387-1389.

Dale, V.H., M. Hemstrom, and J.F. Franklin. 1987. Modeling the long-term effects of disturbances on forest succession, Olympic Peninsula, Washington. Can. J. For. Res. 16: 56-67.

Garman, S.L., A.J. Hansen, D.L. Urban, and P.F. Lee. 1992. Alternative silvicultural practices and diversity of animal habitat in western Oregon: A computer simulation approach. Pp. 777-781 in P. Luker, ed., Proc. 1992 Summer Simulation Conference. The Society for Computer Sumulation, Reno, NV

Garman, S.L., S.A. Acker, J.L. Ohmann, and T.A. Spies. 1995. Asymptotic height-diameter equations for twenty-four tree species in western Oregon. Research Contrib. 10, OSU Forest Research Lab., Corvallis, OR. 62 p.

Gholz, H.L., F.K. Fitz, and R.H. Waring. 1976. Leaf area differences associated with old-growth forest communtities in the western Oregon Cascades. Can. J. For. Res. 6: 49-57.

Gregory, S.V., and L. Ashkenas. 1990. Riparian Management Guide, Willamette National Forest. USDA Forest Service, Pacific Northwest Region, Willamette National Forest, Oregon. 119 p.

Gregory, S.V., F.J. Swanson, W.A. McKee, and K.W. Cummins. 1991. An ecosystem perspective of riparian zones. BioScience 41: 540-557.

Harmon, M.E., and H. Chen. 1991. Coarse woody debris dynamics in two old-growth ecosystems. BioScience 41: 604-610.

Harmon, M.E., J.F. Franklin, F.J. Swanson, P. Sollins, S.V. Gregory, J.D. Lattin, N.H. Anderson, S.P. Cline, N.G. Aumen, J.R. Sedell, G.W. Lienkaemper, K. Cromack, Jr., and K.W. Cummins. 1986. Ecology of coarse woody debris in temperate ecosystems. Adv. Ecol. Res. 15: 133-302.

Krankina, O.N., and M.E. Harmon. 1994. The impact of intensive forest management on carbon stores in forest ecosystems. World Resource Review 6 (2): 161-177.

Kuiper, L.C. 1988. The structure of natural Douglas-fir forests in western Washington and western Oregon. Agricultural University Wageningen Papers 88-5: 1-47.

Lorensen, T., C. Andrus, and J. Runyon. 1994. The Oregon Forest Pracitices Act Water Protection Rules: scientific and policy considerations. Oregon Department of Forestry, Forest Pracitices Policy Unit, Salem, OR. 39 p.+ appendices.

McDade, M.H. 1987. The source area for coarse woody debris in small streams in western Oregon and Washington. M.S. Thesis, Dept. of Botany and Plant Pathology, Oregon State Univ., Corvallis.

McDade, M.H., F.J. Swanson, W.A. McKee, J.F. Franklin, and J. Van Sickle. 1990. Source distances for coarse woody debris entering small streams in western Oregon and Washington. Can. J. For. Res. 20: 326-330.

Peck, J.E., S.A. Acker, and W.A. McKee. 1995. Autecology of mosses in mature and old-growth forests in the central Western Cascades of Oregon. Northwest Science 69: 184-190.

Swanson, F.J., and A. McKee. 1990. Old-growth research at the H.J. Andrews Experimental Forest. NW Env. J. 6: 420-421.

Swanson, F.J., A. McKee, and S.V. Gregory. 1990. Managing riparian zones as ecosystems. Watershed Management Council Newsletter 4(3): 1-5.

Van Sickle, J., and S.V. Gregory. 1990. Modeling inputs of large coarse debris to streams from falling trees. Can. J. For. Res. 20: 1593-1601.

Wilson, M.V. 1991. Age structure patterns in Abies amabilis stands of the Cascade Mountains. Amer. Midl. Nat. 125: 331-339.

Literature Cited

Acker, S.A., W.A. McKee, M.E. Harmon, and J.F. Franklin. 1998. Long-term research on forest dynamics in the Pacific Northwest: a network of permanent plots. Pp. 93-106 in F. Dallmeier and J.A. Comiskey, eds. Forest biodiversity in North, Central, and South America, and the Caribbean: Research and monitoring. UNESCO, Paris.

Dyrness, C.T., J.F. Franklin, and W.H. Moir. 1974. A preliminary classification of forest communities in the central portion of the western Cascades in Oregon. Coniferous Forest Biome Bull. No. 4. Univ. of Washington, Seattle. 123 p.

Hawk, G.M., J.F. Franklin, W.A. McKee, and R.B. Brown. 1978. H.J. Andrews Experimental Forest Reference Stand system: establishment and use history. Coniferous Forest Biome Bull. No. 12. Univ. of Washington, Seattle. 79 p.