a montane kobresia myosuroides fen community type in the southern rocky mountains of colorado, u.s.a

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A Montane Kobresia myosuroides Fen Community Type in the Southern Rocky Mountains ofColorado, U.S.A.Author(s): David J. Cooper and John S. SandersonSource: Arctic and Alpine Research, Vol. 29, No. 3 (Aug., 1997), pp. 300-303Published by: INSTAAR, University of ColoradoStable URL: http://www.jstor.org/stable/1552144 .

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Arctic and Alpine Research, Vol. 29, No. 3, 1997, pp. 300-303

A Montane Kobresia myosuroides Fen Community Type in the Southern Rocky Mountains of Colorado, U.S.A.

David J. Cooper Department of Fishery and Wildlife Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado 80523, U.S.A.

John S. Sanderson Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado 80523, U.S.A.

Abstract Kobresia myosuroides is a well-known circumpolar taxon and an important com-

munity dominant in many arctic and alpine regions of the Holarctic. It typically occurs on xeric to mesic, windblown ridges, and in meadows and heaths. In this

paper we report on K. myosuroides populations more than 700 m below treeline in extreme rich fens in South Park, Colorado. The distinctive Thalictrum alpinum- K. myosuroides community type includes many wetland plant species and appears to be a unique fen community, endemic to South Park. The K. myosuroides populations in South Park are a well-marked race, or ecotype, forming tussocks up to 400 mm tall, with culms averaging 300 mm in height, and leaves more than 200 mm in length. These communities and populations are threatened by the peat mining industry.

Introduction Kobresia myosuroides is a circumpolar taxon (Hultdn 1964,

1968) that dominates communities in many arctic, arctic-alpine, and alpine regions of the Holarctic (Major and Bamberg, 1963;

Komtrkovd, 1979). From a physiological (Bell and Bliss, 1979) and syntaxonomic perspective (Ohba, 1974), K. myosuroides and the communities it dominates are relatively well known.

According to Braun-Blanquet (1948) the habitat occupied by K. myosuroides varies little in the Alps, Pyrenees, and Arctic, where it occupies windswept ridges. Kobresia myosuroides communities are also described from Scandinavia (Nordhagen, 1955), Siberia (Kuvaev, 1965; Epova 1965), Iceland (Steindors- son, 1945), Greenland (Bicher, 1954), eastern Canada (Polunin, 1940), western Canada (Hrapko and LaRoi, 1978), Alaska (Coo- per, 1986), and the Rocky Mountains of the United States, es-

pecially in Colorado (Cox, 1933; Marr, 1967; Komlirkov-i, 1979;

Willard, 1979). Throughout the world, K. myosuroides is re-

ported to occur almost entirely on xeric to mesic windblown

ridges, and in meadows and heaths. Cox (1933), Marr (1967), and Willard (1979) consider K. myosuroides communities to be the "climatic climax" of Colorado Rocky Mountain alpine tundra vegetation.

In this paper we document a K. myosuroides-dominated community type that forms stands in extreme rich fens in South Park, Colorado. We characterize the community type with stand data, compare it floristically with other K. myosuroides communities, and discuss its phytogeographic significance. We also characterize the morphological characteristics of this low-elevation K. myosuroides race and compare it with other arctic and alpine populations.

The Study Area South Park is one of Colorado's large intermontane basins

(Fig. 1). The floor of South Park ranges in elevation from 3050 m in the north to 2700 m in the south. It is surrounded on all sides by mountain ranges rising to over 4250 m. Mean annual precipitation varies from 30 cm in the north to 20 cm in the center and south. Due to the arid conditions, zonal vegetation in

South Park is short-grass steppe, dominated by Chondrosum (Bouteloua) gracile.

Rimming the northern and eastern sides of South Park are the Front and Taryall Ranges, composed of granite bedrock. To the west, the Mosquito Range contains significant outcrops of limestone and dolomite. The floor of South Park is covered by glacial outwash and Holocene alluvium derived from the Mos-

quito Range. Streams drain from west to east across the basin. From the toes of mountain front alluvial fans and glacial

outwash deposits in South Park, perennial discharges of calcar- eous ground water support extreme rich fen complexes. pH of these waters range from 7.5 to 8.5, and Ca2+, Mg2+, and CO3- are the dominant ions (Cooper, 1996). Ca2+ occurs in concentrations ranging from 30 to over 120 mg kg-'.

Methods

We studied 31 fens across the northern and central portion of South Park and found Thalictrum alpinum-Kobresia myosuroides communities in 13 of them. Stands of T. alpinum-K. myosuroides were inventoried using the relev6 method (Westhoff and van der Maarel, 1978) and a stand table is presented (Table 1). Plant nomenclature follows Weber and Wittmann (1992).

To document the morphological characteristics of K. myosuroides populations in South Park, we compared our specimens with populations represented by collections in the University of Colorado, Boulder, Herbarium (COLO). We chose three west Greenland and three north slope of Alaska populations to represent northern regions, and three alpine populations each from Colorado's eastern and western slopes. We also chose collections from Convict Creek Basin, California, where the only other non- alpine U.S. populations of K. myosuroides are known to occur (Major and Bamberg, 1963; Major and Bamberg, 1967). We measured leaf length, culm length, inflorescence length, and the number of florets on all plants on the herbarium sheets.

Data from the collections were analyzed using the General Linear Models Procedure with SAS (SAS Institute, 1993) fol- lowed by Tukey-Kramer multiple comparisons test to analyze for differences among the measured populations.

300 / ARCTIC AND ALPINE RESEARCH



AA

Colorado, USA

S15 N

south Park

A Thalidrum alpinum -- Kobresia myosuroides stands 5 10 106.00 w i05?5 o"

FIGURE 1. Location of Thalictrum alpinum-Kobresia myosuroides stands in South Park, Colorado.

Results PHYTOSOCIOLOGY

Kobresia myosuroides-dominated stands were found throughout the northern and central portion of South Park. Ko- bresia myosuroides dominates the vegetation forming tussocks up to 400 mm tall. Although standing water was never observed, the soils were saturated due to a high water table.

The stand table (Table 1) indicates that the calciphile Thal- ictrum alpinum and the wetland plant Juncus arcticus have high constancy and cover in all stands. The community, T. alpinum-K. myosuroides is named for the two prominent taxa. Pti- lagrostis porteri, a caespitose grass endemic to the northern por-

tion of South Park (Weber and Wittmann, 1996), reaches its op- timum in this community type (Cooper, 1996).

PLANT MORPHOLOGY

South Park and Convict Creek K. myosuroides populations had significantly longer leaf lengths than other populations (ANOVA, f = 26.92, P = 0.0001, df = 6) examined (Fig. 2), and were nearly twice as long as Colorado alpine populations. South Park and Convict Creek culms were significantly longer (in general two to three times longer) than other populations (f = 32.81, P = 0.0001, df = 6). Flowering spikes of South Park

populations were more than twice as long as any other population (f = 57.18, P = 0.0001, df = 6), and the South Park plants had significantly more perigynia per spike than other populations (f = 24.03, P = 0.0001, df = 6).

Discussion The only previously described wetland community domi-

nated by Kobresia myosuroides, the Carex subnigricans--Pedi- cularis attolens community, occurs just below treeline in the Convict Creek basin, California (Major and Taylor, 1988). The Convict Creek and South Park communities share only Muhlen- bergia richardsonis, Thalictrum alpinum, and Kobresia myosuroides, indicating distinct difference between the Sierra Nevada and Rocky Mountain floras.

The associations Selaginello densae-Kobresietum myosuroidis and Campanulo uniflorae-Kobresietum myosuroidis described for the Colorado Front Range alpine tundra by Komar-

kov, (1979) and Willard (1979), respectively, share only Bistorta

vivipara, Deschampsia cespitosa, and Thalictrum alpinum with

TABLE 1

Thalictrum alpinum-Kobresia myosuroides stands in South Park, Colorado

Species Percent cover

Stand number 52 135 153 168 201 210 216 222 228 244 253 Constancya

Kobresia myosuroides 40 40 60 50 40 40 40 40 60 60 60 V Thalictrum alpinum 5 5 7 10 5 15 20 5 5 15 10 V Juncus arcticus 10 10 10 10 5 15 30 25 15 10 15 V Carex capillaris 5 . + 3 1 5 1 2 IV Antennaria microphylla + 5 1 5 . 7 . III Bistorta vivipara 1 5 1 2 5 2 III

Deschampsia cespitosa 5 7 10 5 2 III Dodecatheon pulchellum + 1 + . + . + III

Muhlenbergia richardsonis 20 7 25 15 + 2 III Packera pauciflora 1 + 1 + I + 1 III Parnassia parviflora 2 1 1 + 1 III

Ptilagrostis porteri 10 10 3 2 10 III

Elymus trachycaulus 5 . 1 + . II Festuca arizonica . 5 . . 1 10 II

Gentianopsis thermalis + + . . . 3 II Kobresia simpliciuscula 5 5 3 . . II Pedicularis crenulata 1 1 + . II Primula incana + + . . + . II

Sisyrinchium pallidum + + + + . II

Additional species not shown in table. Species are listed by stand, percent cover is in parentheses, and all have a constancy of I: Stand 52: Argentina anserina

(3). Stand 135: Carex praegracilis (5); Carex simulata (3); Eleocharis quinqueflora (10); Hippochaete variegata (2). Stand 153: Carex scirpoidea (1). Stand 168: Campylium stellatum (5). Stand 201: Carex praegracilis (+); Erigeron lonchophyllus (1); Psilochenia runcinata (+); Triglochin palustris (+). Stand 216: Aster spathulatus (+); Lomatogonium rotatum (+); Primula egaliksensis (+); Psilochenia runcinata (+). Stand 222: Carex microglochin (1); Erigeron loncho-

phyllus (+). Stand 228: Triglochin palustris (1). Stand 244: Argentina anserina (5); Carex scirpoidea (3); Primula egaliksensis (+). Stand 253: Lomatogonium rotatum (1).

aConstancy Classes follow Westhoff and van der Maarel (1973).

D. J. COOPER AND J. S. SANDERSON / 301



LEAF LENGTH 300

250 A A

250

200

150

100

50

0 n 33 27 30 30 37 28 max 314 294 162 151 286 180

CULM HEIGHT

400 --A --- A

350 300 250

200 B

150I B 100

50

0 n 26 16 30 30 24 24 max 448 405 135 206 208 180

INFLORESCENCE LENGTH 30 A 25 20 B B B B B

15

10

5 5

i I 1 1 0

n 27 17 30 31 22 24 max 31 22 21 18 27 18

NUMBER OF FLORETS

20 A

B 15

B B B

B 10

5

n 27 13 30 6 20 22 max 18 16 12 12 15 11

SP CC ES WS WG AK

FIGURE 2. Mean leaf length, culm height, inflorescence length, and number of florets for six populations of Kobresia myosuroides: South Park (SP), Clear Creek, California (CC), East Slope, Colorado (ES), West Slope, Colorado (WS), west Greenland (WG), North Slope AK (AK). "A " and "B" indicate populations with equivalent means. Error bars show one stan- dard error deviation.

our South Park community. This lack of similarity may reflect the differences between the alpine and montane floras as well as the differences in habitats; the alpine communities occupy dry sites with shallow mineral soil while the South Park community occupies wet sites with organic soils. Alpine meadow communities on limestone and dolomite in Eurasia, for example in Mac- edonia (Grebenshehikov, 1965), share Kobresia myosuroides and

Bistorta vivipara, and appear as closely related floristically to the South Park Thalictrum alpinum-Kobresia myosuroides community as the Colorado alpine association described by KomBr- kovai (1979).

The South Park populations of Kobresia myosuroides are the most robust that we have seen. The only other population containing leaves and culms as tall occurs in Convict Creek, California. Large plant size may be due to the longer and warmer growing season of lower elevation sites relative to either alpine or arctic locations. Since these populations of K. myosuroides are apparently adapted to anaerobic soil conditions, their large size may also result from the wet, nutrient-rich soils of the extreme rich fens.

The South Park and Convict Creek populations are closely related in size and habitat and most likely represent a low-elevation ecotype occurring at K. myosuroides' southern range limit in North America. This well-marked race is tussock forming, adapted for wetland conditions, and tolerant of high soluble soil salt concentrations. The Thalictrum alpinum-Kobresia myosuroides community appears to be the most rare fen community type in the Rocky Mountains. It has not been reported from other fen complexes in Colorado (Cooper, 1990, 1996), Wyoming (Cooper and Andrus, 1994; Fertig and Jones, 1995), Montana (Lesica, 1986; Chadde and Shelly, 1995), Utah (Padgett et al., 1989), or Idaho (Bursik and Henderson, 1995), and may be endemic to South Park.

A significant commercial peat mining industry has been ac- tive for several decades in South Park, providing horticultural products for the Denver, Colorado, and other regional markets. Mining occurs almost entirely in extreme rich fens, and many areas that once supported these communities appear to have been destroyed. We suggest that significant conservation action is need to protect this community type and its populations of Ko- bresia myosuroides.

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D. J. COOPER AND J. S. SANDERSON / 303



a montane kobresia myosuroides fen community type in the southern rocky mountains of colorado, u.s.a

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