United States Department of State

People and the Temperate RegionA Summary of Research from the United States Man and the Biosphere Program 1991

Editedby

Peter F. Ffolliott

School of Renewable Natural ResourcesUniversity of Arizona

Tucson, Arizona

and

Wayne T. Swank

Southeastern Forest Experiment StationUSDA Forest ServiceOtto, North Carolina

. ,,;

UnitedStatesManandtheBiosphereProgram tl~~

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Forest and Meadow Communities of the Three SisterBiosphere Reserve

Charles B. Halpern, Bradley G. Smith, and Jerry F. Franklin

TheThreeSistersBiosphere Reserveencompassesnearly 100squarekilometersof virtually undisturbed land stradling thecrest of the central CascadeMountains ofOregon. Although coniferous forestsdominate, an array of other ecosystemscreatesa diverse picturesquelandscape(Figure 1). The Three Sisters BiosphereReserve, established as a primitive area in1933, was selected in 1974 to serve as acontrol for the nearby experimentallyoriented H. J. Andrews Biosphere Reserve.Ecological information about the ThreeSisters Biosphere Reserve was needed toestablish a basis for future comparativeresearch with the intensively managed H. J.Andrews Biosphere Reserve.

Objectives

Theobjectives of this study were to:

-Describe the composition, struc-ture, and distribution of majorforest and meadow communities,as well as their principal environ-mental controls.

-Establish a series of permanentsample plots for examining long-term changes in the compositionand structure of these communi-ties.

FIGURE 1. Forest and meadow ecosystems in the Three Sisters Biosphere Reserve in the central Cascade Mountains ofOregon.

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Methods

Field sampling, conducted over a 3-year period staning in 1981, documentedthe composition, structure. and distributionof forest and meadow communities in theThree Sisters Biosphere Reserve. In thesummer of 1983, a series of permanenttransects were established to assess long-term changes in vegetative compositionand structure across boundaries betweenthese forest and meadow communities.

· Forest vegetation was sampledusing a reconnaissance method, inwhich compositional characteristicsof forest sample plots were assessedthrough estimates of canopy coverof each vascular plant species.Structural characteristics wereexamined throU!!hthe identificationof height and diameter size classdistributions for all tree species.

The age of forest stands was esti-mated with increment cores takenfrom one or two dominant seraltrees within each sample plot.Environmental features (elevation,slope and aspect, landform, andtopography) were recorded andimponant soil characteristics(panicle size distribution and littercomposition) were described.Additional observations on fire andgeomorphic disturbance, as well asother distinctive features not ad-dressed in the reconnaissance data,were recorded.

· Meadow communities, comprisedof bog, fen, pumice flat and "rockgarden" communities, were exam-ined using techniques similar tothose employed for forests.Sample plots were characterized interms of species composition andenvironmental features, with specialattention given to the mosaic ofvegetative types within eachmeadow.

· Baseline information for futureexamination of vegetative change,obtained from a series of perma-nently marked transects across the

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boundaries between forest andmeadow communities, was installed(Figure 2). Sites were selected torepresent a diversity of types and toencompass the variety of treeinvasion patterns observed.

· Along ecotone transects, four typesof data were collected:

-composition and structure,including in species frequencyand canopy cover;

-location, diameter, height, andaQ:eof all trees. Smaller treesthat could not be cored were agedby counting terminal bud scars.

-soil characteristics and environ-mental features;

-photographs taken at perma-nently located points for futurecomparison.

Reconnaissance data were utilized todevelop community classifications forforest and meadow vegetation, and toidentify environmental features influencingthe composition and distribution of thesecommunities. Cluster analysis and ordina-tion techniques were used for this purpose.

Analyses of ecotone transect datafocused on the spatial distribution of treespecies by size and age classes, and thecomposition of the corresponding forestunderstory and meadow vegetation.

Findings

Imponant findings from the forestcommunities sampled in the Three SistersBiosphere Reserve included:

· A total of 162 vascular plantspecies were identified and 16major forest plant communitieswere defined. The plant communi-ties fell into five forest Series de-fined by the climax tree species-Pseudotsuga menziesii, Tsugaheterophylla, Tsugaheterophylla-

FIGURE 2. Baseline infonnation on vegetation was obtained from pennanently marked transects located across the forestand meadow community bolDldary.

Abies amabilis, Abies amabilis-Tsuga mertensiana, and Tsugamertensiana.

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· The distributions of the Series werecorrelated with environmentalchanges associated with increasingelevation, that is, decreasing tem-perature, increasing precipitation,greater snowpack, and shonergrowing season. Within eachSeries, secondary environmentalgradients, such as soil moisture andtemperature, influenced the compo-sition and distribution of plantcommunities.

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· The frequency and distribution ofdisturbances, such as wildfire, wereimponant in understanding thestructure of forest ecosystems.

The forests were relatively young,between 175 and 250 years of age, al-though there also were remnant old-growthforests of 400 to 500 years. Most of thestands at lower elevations have burned atleast once since the 1840s. Forests in-creased in average age with elevation.Old-growth forests were restricted largelyto the subalpine zone.

Findings in meadow communitiesincluded:

· A total of 384 vascular plant spe-cies were identified and 23 montaneand subalpine meadow communi-ties were defined.

· The composition, structUre,anddistribution of meadows werecorrelated with landform and

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topography, elevation, hydrologicalfeatures, and soil characteristics.For simplicity, meadow communi-ties can be grouped into threecategories:

-Meadows occurring on flatterrain or in basins-Meadowcommunities on these sitesexperience either a water tablepersisting at or above the soilsurface, or a deep and persistentsnowpack that keeps the soilsmoist through the short growingseason. These communitiestypically are graminoid-domi-nated.

-Meadows along steeply slopinglandforms-Here, soils rangefrom deep, loamy, and well-drained, to shallow, rocky, andpotentially droughty. Thesemeadows, which typify thehighly dissected terrain of thewestern portion of the ThreeSisters Biosphere Reserve, areforb-dominated communites.

-Meadows along the gentle slopesand rolling plains adjacent to thebase of the region flanking thebases of the Three Sisterspeaks-On these sites, soils varyfrom shallow and gravelly todeep and pumicey. Thesemeadows are dominated by adiversity of graminoids, forbs,and low shrubs.

· The patterns of tree invasion intothese meadows were diverse.Hydric, mesic, and xeric meadowcommunities have all experiencedencroachment. Forest-meadowboundaries range from abrupt todiffuse. Tree invasion has oc-curred in waves, in clumps, or asisolated individuals. A majority ofthese trees became establishedbetween 1930 to 1970.

Implications

Information from this study providedthe first extensive body of data on thecomposition, structure, and distribution ofecosystems in the Three Sisters BiosphereReserve. The study results included:

· a classification and a key to forestcommunities in the biospherereserve;

· a general description of the naturaldisturbance history in the forestedportion of the biosphere reserve;

· a classification of montane and sub-alpine meadow communities; and

· a series of permanent transects forexamining long-term changes in thecomposition and structure of forest-meadow communities.

Forest community and fire historyinformation from the relatively untouchedecosystems of the Three Sisters BiosphereReserve provided a baseline for compari-son with the experimentally-oriented H. J.Andrews Biosphere Reserve and with otherintensively managed areas along the west-ern slope of the Cascades. Furthermore,the forest community classification wascompatible with those developed by theUSDA Forest Service on adjacent natIOnalforest lands.

Despite their ubiquity and aestheticappeal, meadows in the Three SistersBiosphere Reserve, and in the PacificNorthwest in general, have not been de-scribed adequately. These communitystudies provide an extensive data base onthe composition, structure, and distributionof meadow communities in the centralCascade Range. Data obtained fromfuture remeasurements of forest andmeadow ecosystems will help in obtaininga better understanding of the dynamics ofthese and similar ecosystems that span theSierra-Cascade Axis.

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