Great Basin Naturalist

Volume 45 Number 1 Article 12

1-31-1985

Tundra vegetation of three cirque basins in the northern San Juan Mountains, Colorado

Mary Lou Rottman University of Colorado, Denver

Emily L. Hartman University of Colorado, Denver

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Recommended Citation Rottman, Mary Lou and Hartman, Emily L. (1985) "Tundra vegetation of three cirque basins in the northern San Juan Mountains, Colorado," Great Basin Naturalist: Vol. 45 : No. 1 , Article 12. Available at: https://scholarsarchive.byu.edu/gbn/vol45/iss1/12

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]. TUNDRA VEGETATION OF THREE CIRQUE BASINS IN THE NORTHERN SAN JUAN MOUNTAINS, COLORADO

Mary Lou RottmaiV and Emily L. Haitman'

Abstract.— The vegetation of three alpine cirque basins in the northern San Juan Mountains of southwestern Col- orado was inventoried and analyzed for the degree of specificity shown by vascular plant communities for certain types of habitats identified as representative of the basins. A total of 197 vascular plant species representing .31 fami- lies was inventoried. Growth forms of all species were noted and a growth form spectrum for all of the communities was derived. The caespitose monocot and erect dicot growth forms are the most important growth forms among the communitv dominants. The most common growth form among all species is the rosette dicot.

Since the early 1900s a number of ecologi- and Mather 1932). Sharp pinnacles, rounded cal studies have been undertaken in the al- crests, serrate ridges, and broad upland ero- pine tundra of the Front Range of Colorado sional surfaces characterize the alpine zone (Cooper 1908, Holm 1923, Cox 1933, Osburn of these mountains. The elevation of the San 1958, Marr 1961, Willard 1963, Komarkova Juans ranges from 1524 m in the southwest 1976, Flock 1978, May and Webber 1982). corner to 4358 m at the summit of Uncom- However, the alpine tundra of central and pahgre Peak. They are composed largely of southwestern Colorado remains relatively un- Tertiary volcanic tuffs and lavas that lie un- known (Langenheim 1962, Johnson 1969). A conformably over metamorphic sedimentary floristic study was done by Michener (1964) and volcanic intrusive rocks of Precambrian in the subalpine and alpine zones of the age as well as sediments of Paleozoic, Meso- Needle Mountains in the southern San Juan zoic, and early Cenozoic age (Casadwall and Moimtains. Another major study in the south- Ohmoto 1977). Broad regional ice fields and em San Juan Mountains, an analysis of snow- transection glaciers occurred during the pack augmentation by Steinhoff and Ives Pleistocene, producing cirques, basins, tarns, (1976), included the alpine zone as well as hanging valleys, and broad U-shaped valleys. the forest ecosystems below. There is no pub- Today periglacial features such as active pat- Hshed botanical work on the alpine vegeta- terned ground, active rock glaciers, and per- tion of the northern San Juan Mountains. In sistent ponds indicate the occurrence of spo- this study the vegetation of three alpine radic or discontinuous permafrost (Ives and cirque basins in the northern San Juans was Fahey 1971, Barsch 1978). inventoried and analyzed for the degree of Three alpine cirque basins, representative specificity shown by individual species and of the northern San Juan Mountain tundra, aggregations of species for certain types of were studied. American Basin, Hinsdale habitats. County, is characterized by a well-developed moist turf mantle interrupted by areas of Study Area bedrock outcrops, talus deposits, and pat- The San Juan Mountains are a dis- terned ground features. The vegetation in continuous section of the Southern Rocky this basin reflects a more moist climatic re- Mountains situated along the Continental Di- gime than in the other two basins, as evi- vide in southwestern Colorado. They are lo- denced by the predominance of moist mead- cated between 106 and 108 degrees west lon- ows, absence of dry meadows, and minimal gitude and 36 degrees 30 minutes and 38 occurrence of fell-fields. The elevational degrees 15 minutes north latitude (Atwood range of this basin is 3536-3962 m.

'Department of Biology, University of Colorado, Denv , Colorado 80202.

87 Great Basin Naturalist Vol. 45, No. 1

Burns Basin, San Juan County, has a north- occurs in scattered instances, and its presence west-southeast orientation. The convex or absence is inconsequential to the character slopes forming the perimeter of the main ba- of the commmiity in which it may occur. It is sin present an interesting contrast of moisture occasional in abundance and has a low con- regimes. The southwest-facing slope is char- stancy (20.1%-40%). A rare species is both acterized by a dry turf alternating with fell- rare in abundance and rare in constancy fields and imvegetated talus. The northwest- (1.0%-20%). facing slope consists of a series of tiers of The term habitat type in this study refers massive moist and wet ledges with adjacent to all of the area (sum of discrete units) that moist meadows. Midsection of the basin con- support one plant community. A habitat type sists of moist and wet meadows. The eleva- may be considered as the abiotic equivalent tional range of this basin is 3634-3932 m. of the stand-type in that the habitat type is a Both Bums and American basins have rock synthetic unit whose characteristics are ob- glacier complexes composed of tongue and tained by combining all the samples of a par- lobate units. ticular habitat. The habitat types defined are: Stony Basin, San County, is formed of Juan dry ledge, moist-wet ledge, rock crevice, three broad turf-mantled steps, each sepa- talus slope, patterned ground, fell-field, dry rated by a bedrock escarpment. Because of meadow, moist meadow, wet meadow, shrub its topographic position, the basin is contin- tundra, and krummholz. Nomenclature fol- ually buffeted by strong wind resulting in a lows Kartesz and Kartesz (1980). more severe climatic regime than is found in the other two basins. Islands of dry meadows and fell-fields interrupt the moist meadow of Results the upper two steps of the basin. The latter In the following description of habitat have an abundance of frost-associated fea- types and associated communities, only the tures including frost boils, patterned ground, dominant and secondary or more important ephemeral ponds, and rock debris islands. species are listed. The lower step is characterized by a shallow lake and hummocky wet meadow. The eleva- Habitat tional range of Stony Basin is 3764-3926 m. Ledge Type

The rock ledge habitat consists of the bed- Methods rock outcrops which, as a result of jointing and weathering, form benches and channels Three field seasons, 1981-1983, were in- where windborne fines are deposited and or- volved in the study. One hundred ninety-nine ganic debris is accumulated to form a sub- habitats and their associated vascular plant strate for vegetation. The orientation of the commimities were sampled. The abundance bedrock and amount of protection provided of each species was estimated using the stan- by rock overhang are controlling factors in dard abimdance classes of Daubenmire the microenvironment of this habitat type (1968). As data from multiple samples of a (Younkin 1970). For purposes of vegetation particular habitat type accumulated, the in- ventoried species and their abundance ratings analysis, the ledge habitat is divided along a were analyzed on the basis of constancy of moisture gradient and includes dry ledges occurrence between samples (Mueller-Dom- and moist-wet ledges. Two communities are bois and Ellenberg 1974). The terms used in found in the dry ledge habitat and three in describing the species within a community, the moist-wet ledge habitat. dominant, secondary, frequent, occasional, Geinn rossii var. turbinattim and Selagi- and rare, are defined as follows. A dominant nella densa are frequent species in one of the species is very abimdant (abundance class) dry ledge communities. Other important spe- and occurs with a high constancy cies include Aquilegia coerulea, Cystopteris

(80.1%- 100%). A frequent species is frequent fmgilis, Draha crassa, PotcntiUa subjuga var. in abundance and has an intermediate con- subjiiga, Silene acaulis var. subacauUs, and stancy (40.1%- 60%). An occasional species Smelowskia cah/rina. The other dry ledge January 1985 ROTTMAN, HaRTMAN: COLORADO TuNDRA VEGETATION 89

community is characterized by Carex hay- species show a high constancy for this habi- deniana, Cerastiitm earlei, Dmba crassa, Fes- tat: Angelica grayi, Aquilegia coerulea, Ceras- tuca brachyphyUa, Potentilla nivea, P. rubri- tium earlei, Claytonia megarhiza, Polemo- caulis, Saxifraga fkigellaris ssp. platysepala, nium viscosum, Senecio amplectens var. am- and Trifolium naniim. plectens, S. amplectens var. holmii, S.

One of the moist-wet ledge communities is soldanella, and S. werneriifolitis. dominated by Geiim rossii var. turbinatum, heteroneura var. with Carex albonigra, C. Patterned Ground Habitat Type chalciolepis, Erigeron melanocephahis, and Saxifraga cespitosa ssp. delicatiila as impor- Washburn (1956) defines patterned ground tant associates. Another moist-wet ledge as, "a group term for the more or less sym- commimity has Salix reticulata ssp. nivalis as metrical forms, such as circles, polygons, dominant. Associated with this species are nets, steps and stripes, that are characteristic Carex albonigra, Salix arctica, Saxifraga ad- of, but not necessarily confined to, a mantle scendens ssp. oregonensis, and S. debilis. subject to intensive frost action." The forms Ledges with snowmelt water running of patterned ground found in the study basins through fissures in the rock constitute the are nonsorted circles (frost boils and frost third possible moist-wet ledge habitat. These hummocks), sorted polygons, and debris is- are dominated by Cardamine cordifolia at the lands. The centers of the sorted forms have base of the ledges and Salix reticulata ssp. ni- from little to no vegetation because of the as- valis on the benches. Caltha leptosepala, sociated frost action that keeps the soil suffi- Carex nova. Primula parryi, Sediim rhodan- ciently disturbed to prevent plant coloniza- thum, and Sibbaldia procumbens are present tion (Johnson and Billings 1962). The in this community. communities found in patterned ground habi- tats vary with the specific type of patterned are another example Rock Crevice Habitat Type ground form. Frost boils of a habitat for which the community con-

Tliis is a restrictive habitat type that only cept must be loosely applied. Several species includes soil-filled crevices on solitary boul- are repeatedly found associated with frost ders or contained crevices on rock outcrops boils: Cerastitim earlei, Draba crassifolia, or headwalls in the basins. The community Geum rossii var. turbinatum, Oreoxis bakeri, concept is loosely applied to the species in and Stellaria umbellata. Frost hummock these habitats. The only relationship that the areas are traversed by water-filled channels singly-occurring species have to one another in the wet meadows. The dominant species is their presence on the same boulder or bed- on the elevated portion of the hummock is rock substrate. Certain species are frequently Carex nigricans. Secondary species are Carex found in rock crevices: Androsace septentrio- pseudoscirpoidea and Festuca brachyphyUa. mdis, Artemisia scopulorum, Claytonia me- Dominant species in the saturated areas at garhiza, Draba crassa, D. crassifolia, Festuca the base of the hummocks are Carex aquatilis brachyphyUa, and Oreoxis bakeri. and C. vernacula. Caltha leptosepala and Carex nova are secondary species in these areas. Sorted polygons are characterized by Talus Slope Habitat Type lichenized rocks in the borders. The central Extensive talus slopes occur throughout the fines of the polygons support a Carex nigri- basins. White (1981) defines talus as an accu- cans-Sibbaldia procumbens community. Fre- mulation of rock debris of various sizes trans- quent associates in this community are Arte- ported from the source areas by gravity, rain- misia scopulorum, Erigeron melanocephalus, wash, snowmelt water, or snow avalanching and Juncus drummondii. Debris islands, a to a site below. Fine material may be present sorted form of patterned ground, occur as re- in the interstices of the rock material; these petitive units on talus debris. The vegetation fines provide a suitable substrate for vegeta- on these islands suggests a successional devel- tion. Although dominance within the talus opment from talus slope to meadow. Depend-

slope commimity is poorly defined, certain ing upon the serai stage of development. 90 Great Basin Naturalist Vol. 45, No. 1 dominant species may be either Salix reti- Trisetum .spicatum are secondary species in culata ssp. nivalis and Silene acaulis var. sub- this commmiity. acaulis, or Senecio amplectens var. holmii and S. soldanella. Moist Meadow Habitat Type

is the widespread habi- Fell-field Habitat Type This perhaps most tat type in the study basins and is most repre- The fell-field habitat type is characterized sentative of the tundra in the northern San rock by a high proportion of weathered ma- Juan Mountains. The moist meadows are situ- with little or- terial. Soils are coarse textured, ated on the lee slopes and in topographical only rudimentary profiles. ganic material and concavities protected from the winter cli- windward sites, with Fell-fields occur on mate by snow accumulation that may remain little or no snow cover, thus exposing the until mid-July. The moist meadow may be re- plants and soil to severe dessication. The garded as a complex of several communities, longest growing season in the tundra occurs each with a distinct spatial occurrence within in this habitat type. The high diversity found the complex. A Deschampsia caespi- in fell-field communities is contributed pri- tosa-Geum rossii var. turbinatum community marily by the frequent and occasional spe- is found in lower sites on basin slopes and in cies. One of the fell-field communities is concavities. Associated with these species dominated by Silene acaulis var. subacaulis are: Artemisia scopulorum, Carex albonigra, and Geum rossi var. tiirbinatum, with Minu- C. nova, Oreoxis bakeri. Polygonum bistor- artia obtusiloba, Potentilla diversifolia, Se- toides, and Saxifraga rhomboidea. In flat laginella densa, and Trifolinm nanum as sec- areas at midslope, a Carex nigricans- ondary species. Another fell-field community Sibbaldia procumbens community occurs has Carex elynoides and Geum rossii var. tur- with vernacula, Erigeron binatum as dominants. Secondary species in- Carex melanoce- clude Festuca brachyphylla, Minuartia ob- phalus, Juncus drummondii, Oreoxis bakeri. tusiloba, Selaginella densa, and Trifolium Polygonum viviparum, and Ranunculus ma- nanum. Carex elynoides and Trifolium na- cauleyi as secondary species. The third com- num are dominants in the fell-field commu- munity in the complex, dominated by Salix nity occurring on slopes and ridge tops. Asso- reticulata ssp. nivalis, is present on the high- ciated with these species are Festuca est moist meadow sites in the basins. Second- brachyphylla, Geum rossii var. turbinatum, ary species include Artemisia scopulorum, and Silene acaidis var. subacaulis. Erigeron simplex, Salix arctica, Sibbaldia pro- cumbens, and Sile7ie acaulis var. subacaulis. Dry Meadow Habitat Type Wet Meadow Habitat Type The dry meadow habitat type occurs on exposed windy slopes high in the basins, Wet meadows are situated on relatively where strong winds create snow-free condi- flat surfaces below late-lying snowbanks, in tions throughout much of the winter. The catchment areas in the basins, and adjacent vegetation in these sites reaches anthesis to ponds, lakes, and streams. Frequently dis- early in the season, thus completing the sected by rivulets, these areas are often asso- growth cycle before vegetation in more pro- ciated with the presence of sporadic per- tected areas reaches maturity. The most ex- mafrost (Johnson and Billings 1962, Ives tensive dry meadow community is dominated 1974). As a result of permafrost in the sub- by Carex elynoides. Secondary species in- strate and the runoff, the wet meadows are clude: Festuca brachyphylla, Geum rossi var. saturated throughout the growing season. ttirbinatum, Hymenoxys grandiflora, Poa Where shallow, standing water is present, a rupicola, and Trisetum spicatum. A minor Caltha leptosepala-Cardamine cordi folia- and highly restricted dry meadow commu- dominated community occurs. The secondary nity is dominated by Kobresia myosuroides. species are Carex nova, Juncus drummondii, Carex ebenea, C. heteroneura var. chalciole- Pedicularis groenlandica. Primula parryi, Se- pis, C. pseudoscirpoidea, Luzula spicata, and dum integrifolium, and Trifolium parryi. A January 1985 ROTTMAN, HaRTMAN: COLORADO TuNDRA VEGETATION 91 second commimity, dominated by Caltha lep- of protection from wind, amount and nature tosepaki and Juncus dmmmondii, is charac- of weathering, debris transport, and slope as- teristic of better drained sites. Associated spe- pect determine the occurrence of specifc cies include: Carex aqiiatilis, Festuca brachij- habitat types and associated communities in phijlla, Geiirn rossii var. tiirbinattnn, Primida terms of the dominant and secondary species. parryi, Sibbaldia prociimbens, and TrifoHum Minor variations are seen in the occurrence parnji. of occasional species. Rare species have a higher occurrence in the rock-predominating habitats, where competition appears to be Shrub Tundra Habitat Type less than in a closed turf meadow. dwarfing of The shrub tundra habitat type is made up A consistent tendency toward of shrub thickets of Salix brachijcarpa or S. species is noted in the Carex nigricans- prociimbens and Salix reticulata planifolia and associated vegetation. A minor Sibbaldia moist meadow com- constituent of the basins in this study, this ssp. niua/is-dominated munities. This appears to correlate with a habitat type is hmited to moist depressions pattern of late snow release. As noted by and drainage areas. The moist areas are dom- Owen (1976), plants of the same species un- inated by SaJix planifolia. Secondary species der conditions of higher elevation and later in this commimity are: Carex ebenea, C. het- snownielt mature and flower at a smaller size eroneura var. chalciolepis, C. nova, C. pseu- than plants not under these conditions. doscirpoidea, and Geum rossii var. turbina- The Kobresia myosuroides-dominsLted dry tum. A Salix brachycarpa-dominiLted meadow, which has long been recognized as community occurs on well-drained slopes. A the climatic climax of the Front Range (Cox drier environment is reflected in the associ- 1933, Osburn 1958, Bamberg 1961, Marr ated species: PhaceUa sericea, Polemonium 1961, Willard 1963), is highly restricted in its viscosiim, Pontentilla diversifolia, Sedum lan- occurrence in the northern San Juan Moun- ceolatiim, and Trifoliinn namim. tains and is replaced in importance by a Carex elynoides-domiimted dry meadow Krummholz Habitat Type community.

Timberline elevations range from approx- Carex Indicators imately 3535 to 3720 m in the study basins. The ecotonal area characteristically has rep- Some members of the Cyperaceae, Carex resentative species from both the alpine and albonigra, C. arapahoensis, C. heteroneiira subalpine zones. Krummholz conifer species, var. chalciolepis, and C. pseudoscirpoidea, Abies lasiocarpa and Picea engehnannii, are have rather broad ecological tolerances that dominant and exert a primary influence on enable them to grow in both dry and moist the svirrounding environment and vegetation. habitats. Carex nova and C. vernacula occur The associated species are highly variable in moist as well as wet habitats. Other Carex from one krummholz habitat to another; species are more specific in their moisture re- however, a list of the more frequent species quirements or tolerances and are useful in- serves to illustrate the ecotonal nature of the dicators of substrate moisture conditions. In- commimity: Aquilegia coerulea. Arnica cordi- dicators of dry substrates are: Carex folia, Dugaldia hoopesii, Minuartia obtusi- elynoides, C. perglobosa, and C. phaeoceph- loba. Polygonum bistortoides, Ribes mon- ala. Indicators of moist substrates are: C. nel- tigeniim, Silene acaulis var. siibacaulis, and sonii, C. nigricans, C. norvegica, C. pyre- Thalictnim fendleri. naica, and C. nardina var. hepburnii. Carex

aqiiatilis is an indicator of wet substrates of- Discussion ten characterized by standing water.

A total of 197 vascular plant species repre- Species Growth Forms sentative of 31 families was inventoried in the study basins (Rottman 1984). Basin orien- Each species found in the study basins was tation, variability of moisture regimes, degree assigned to a growth form category. The 92 Great Basin Naturalist Vol. 45, No. 1 growth forms of May and Webber (1982) types are physically discrete and recogniz- were used. Based primarily on the nature of able, a one-habitat type/one-commimity con- the shoot habit, these growth forms include: cept is not applicable. A similar finding is re- caespitose monocot, single-shooted monocot, ported by Douglas (1972). It was found that erect dicot, rosette dicot, mat dicot, cushion virtually all habitat types have more than one dicot, erect shnib, and dwarf shrub. potential community with different domi-

The caespitose monocot is a tufted grami- nants and that some dominants are repetitive, noid growth form. Graminoid sods are able to by themselves or in combination, in different modify tlie microenvironment to a greater habitat types. extent than any other growth form or pattern of spatial distribution (Billings 1974). When Literature Cited compared to other growth forms, the per- Atwood. W. a., and K. F. Mather. 1932. Physiography of caespitose species is rela- centage monocot and Quaternary geology of the San Juan Moun- tively small (9%); however, this growth form tains. Colorado'. U.S. Ge'ol. Surv. Prof. Pap. 166. contributes the greatest percentage of domi- Ba.mberc;, S. a. 1961. Plant ecology of alpine tundra areas in Montana and adjacent Wyoming. Un- nants in the commimities analyzed. published thesis. Univ. of Colorado, Boulder. 163 The single-shooted monocot growth form pp. is represented primarily by grasses and sedges Bars( H. D. 1978. Rock glaciers as indicators for dis- (25 species, 12% of total). Although this cate- continuous alpine permafrost. An example from the Swiss Alps. Pages 349-352 in National Re- gory has more species than the caespitose search Council of Canada, Ottawa, Proceedings it is never a monocot, dominant within of the Third International Conference on commimity. Permafrost. The highest percentage of species (38%) BiLLi.N(;s, E. D. 1974. .\rctic and alpine vegetation:

plant adaptations to cold summer climates. Pages j and the second highest percentage of domi- 404-443 in D. Ives R. Barry, eds., J. and C. Arc- nants in the communities are erect dicots. tic and alpine environments. Methuen, London. Since both the root and shoot systems of Casadvall, T., and H. Ohmoto. 1977. Sunnyside Mine, erect dicot plants require less space for later- Eureka Mining District, San Juan County, Colo- rado: geochemistry of gold and base metal ore al spread, this growth form is compatible deposition in a volcanic environment. Economic with extremely rocky habitats where only a Geology 72:1285-1.320. minimal amount of soil is available. Cooper, W. S. 1908. Alpine vegetation in the vicinit\ of The importance of the rosette dicot Longs Peak. Bot. Gaz. 45:319-337. Cox, C. F. 1933. .Alpine plant succession on James Peak, growth form (26%) is reflected in the fact Colorado. Ecol. Monog. 3:299-372. that approximately 70% of the species with Daubenmire, R. 1968. Plant communities: a textbook of ubiquitous occurrences in the study basins are plant svnecologv. Harper and Row, New York. in this category. This growth form is found in 300 pp.' all the habitat types studied and appears to DoicLAs, G. W. 1972. Subalpine plant comnumities of the western North Cascades, Washington, .\rctic be equally abundant in both meadow and and .\lpine Research 4:147-166. rock habitats. Fi.ocK, J. W. 1978. Lichen-bryophyte distribution along The mat (6%) and cushion dicot (2%) a snow-cover soil-moisture gradient, Niwot growth forms are minor in occurrence. Both Ridge, Colorado, .\rctic and .\lpino Research of these growth forms are considerably more 10:31-47. Hoi.M, T. 1923. The vegetation of the alpine region of important in tundras to the north, where the Rocky Mountains in Colorado. Memoirs of their greater occurrence is correlated with an the National Academv of Sciences 19:1-45. increased wind factor. IvEs, D. 1974. Permafrost.' Pages 159-194 in D. Ives The erect and dwarf J. J. shnib growth forms are another minor seg- and R. G. Barry, eds., Arctic and aliiinc Environ- ments, .Methuen, London. ment of the growth form spectrum account- IvEs, D,. J. AND B. D. Fahey. 1971. Permafrost occur- ing for a combined 7% of the total species. rence in the Front Range, C^olorado Rocky Moun- tains, .Vnu'iica. Glaciologv United States of J. 10:105-111. Community Specificity Johnson, K. L. 1969. Alpine vegetation and soils of Mesa Seco Plateau, San Juan Moimtains, Colorado. Un- The specificity of communities for particu- published dissertation. Univ. of Illinois. 225 pp. lar haliitat types was evaluated on the basis Johnson. P. L.. and W. D. Bh.i.incs. 1962. The alpine of conununity dominants. Although habitat vegetation ot tlic Be.utooth Plateau in relation to January 1985 ROTTMAN, HaRTMAN: COLORADO TuNDRA VEGETATION 93

cryopedogenic processes and patterns. Ecol. der County, Colorado. Unpublished dissertation. Monog. 32:105-135. Univ. of Colorado, Boulder. 76 pp. T., R. Kabtesz. 1980. A synonym ized Owen, H. E. 1976. Phenological development of her- Kartesz, J. AND checklist of the vascular flora of the United baceous plants in relationship to snowmelt date.

II. Pages 323-342 in H. W. Steinhoff and Ives, States, Canada, and Greenland. Volume The J. D. biota of North America. Univ. of North Carolina eds.. Ecological impacts of snowpack augmenta- Press, Chapel Hill. 498 pp. tion in the San Juan Mountains, Colorado. San KoMARKOVA, V. 1976. Alpine vegetation of the Indian Juan Ecology Project, Final Report, Fort Collins, Peaks area, Colorado Rocky Moimtains. Unpub- Colorado State Univ. Publications. lished dissertation. Univ. of Colorado, Boulder. RoTTMAN, M. L. 1984. A floristic analysis of three alpine 655 pp. basins in the northern San Juan iMountains, Colo- 1962. Vegetation environmental rado. Unpublished dissertation. Univ. of Colo- Lan(;enheim, J. H. and patterns in the Crested Butte area, Gunnison rado, Boulder. 311 pp. 32:249-285. Ives. 1976. Ecological County, Colorado. Ecol. Monog. Steinhoff, H. W., and J. D. im- W. 1961. Ecosystems of the East Slope of the pact of snowpack augmentation in the San Juan Mark, J. Front Range in Colorado. Univ. of Colorado Mountains, Colorado. San Juan Ecology Project, Studies, Series in Biology 8:1-134. Final Report, Fort Collins, Colorado State Univ. P. 1982. Spatial and Publications. 489 May, D. E., and J. Webber. tem- pp. poral variation of the vegetation in its productiv- Washburn, A. L. 1956. Unusual patterned grovmd in Pages 35-62 in Greenland. Geo). Soc. of America Bull. ity on Niwot Ridge, Colorado. J. C. Halfpenny, ed.. Ecological studies in the Colo- 67:823-865. rado Alpine: a festschrift for John W. IVlarr. Univ. White, S. E. 1981. Alpine mass movement forms (non- of Colorado Institute of .\rctic and Alpine Re- catastrophic) classification, description and sig- search. Occasional Paper 37. nificance. Arctic and Alpine Research 1964. high altitude vegetation of 13:127-1.37. MicHENER, M. J. The the Needle Mountains of southwestern Colorado. Willard, B. E. 1963. Phytosociology of the alpine tun- Unpublished thesis. I'niv. of Colorado, Boulder. dra of Trail Ridge, Rocky Mountain National 77 pp. Park, Colorado. Unpublished dissertation. Univ. Mueller-Dombois, D., and H. Ellenberg. 1974. Aims of Colorado, Boidder. 245 pp. and methods of vegetation ecology. John Wiley, YouNKiN, W. E., Jr. 1970. A study of the vegetation of New York. 547 pp. alpine rock outcrops in northern Colorado. Un- OsBURN, W. S., Jr. 1958. Ecology of winter snow-free published thesis. Colorado State Univ., Fort Col- areas of the alpine tundra of Niwot Ridge, Boul- lins. 109 pp.