ill., maps (1 col.); Typescript (photocopy); Thesis (M.S.)--Oregon State University, 1980; Includes bibliographical references
AN ABSTRACT OF THE THESIS OF Susan Cornelia Sever for the degree of Master of Science in Botany and Plant Pathology presented on December 14, 1979 Title: VEGETATIVE ECOLOGY OF A MONTANE MIRE, CRATER LAKE NATIONAL PARK, OREGON Abstract approved: Jerry F. Franklin Mires, or peat-producing ecosystems, dominated by sedges, shrubs, and brown mosses, are common features in Cascade subalpine regions, occurring where moisture accumulates in small basins or on poorly-drained slopes. Although descriptions and classifications have been developed for mire vegetation in much of the world, there is little information of even a descriptive nature for these montane mires in Oregon and Washington. This thesis reports on phytosociological structure, environmental relations, and successional trends in one such mire in the Oregon Cascade mountains. To characterize the general phytosociological structure of the mire vegetation at Sphagnum Bog, Crater Lake National Park, quantitative species cover data were used in conjunction with a Braun-Blanquet tabular analysis and two-dimensional stand ordinations, reciprocal averaging and a Bray-Curtis polar ordination. Defined community types correspond to physiognomic types as follows: Carex rostrata (reedswamp); Eleocharis pauciflora-Carex limosa, Eleocharis pauciflora/bryophvtes (low sedge fens); Carex sitchensis (tall sedge fen); Vaccinium/ Aulacomnium palustre, Vaccinium occidentale/Carex sitchensis (shrub thickets; Alnus incana/Brachythecium sp. and Salix barclayi (marginal carrs).Phases were defined when appropriate. A vegetation map was made to illustrate the locations and extent of the various communities. Comparisons with other montane mires in the area determined that the physiognomic units defined are repeatable when appropriate habitat conditions are present, and that they usually include many of the same characteristic species, the dominant mosses being particularly constant. Relationships of the vegetative patterns to the following environmental factors were investigated: topographic position, pH, water table depth, and nutrient concentrations. Concentration gradients of the nutrients calcium, magnesium, potassium, and phsophorus proved to be the most important in determining vegetation, 2 with R values ranging from .6 to .7. The role of topographic position was illustrated in several cross-sectional profiles. Water table measurements and, to a lesser degree, pH exhibit low correlation with the floristic gradients. It is suggested that the gradient determining vegetation patterns in this mire is a complex gradinet, dominated by nutrient regime, but also involving water table depths, water mobility, and topographic position. Some interaction of these factors is suggested. Complete succession to terrestrial forest seems unlikely in these spring-fed, water-logged soils. Peat cores sampled show that little succession, even of the mire types has taken place within the peatland, where peat, sometimes greater than 2 m deep is underlain by pumice. Limited invasion by Pinus contorta and Picea engelmannii is evident, however, in two drier community types—Vaccinium/Carex sitchensis, and Carex sitchensis (Aster occidentalis phase), as well as in a transitional meadow area. Establishment of these trees probably corresponds to favorable climatic periods 34 to 50 years ago, but some more recent establishment is also evident. Comparison with pre-existing mire classification systems developed elsewhere in the world, indicates that Sphagnum Bog corresponds with moderately rich fen vegetation or Philonotis fontana-Pohlia albicans spring vegetation, on the bases of floristics, pH, and nutrient concentrations. 126 SUMMARY AND CONCLUSIONS 1) The vegetation pattern at Sphagnum Bog consists of a complex mosaic of species associations, with only the extreme groups sharply distinguished from the rest. Gradual variation of species composition and structure is evident for the intermediate types. 2) The species associations, defined as communities and phases, were classed into four physiognomic types: reedswamp, sedge fen, decid uous shrub thicket, and deciduous fen carr. The Carex rostrata community corresponds to reedswamp; Eleocharis-Carex limosa to a low sedge fen with no moss layer; Eleocharis pauciflora/bryophyte with Philonotis fontana and Meesia triquetra phases to low sedge fens with a more or less continuous moss layer; Carex sitchensis community, with Hypericum anagalloides and Aster occidentalis phases to tall sedge fens lacking a moss carpet; Vaccinium Occidentale/Aulacomnium palustre community to a dwarf shrub thicket with a dense moss ground layer; Vaccinium occidentale/ Carex sitchensis to a shrub thicket, with no moss ground layer; and the Alnus incana/Brachythecium sp. community and Salix barclayi community correspond to deciduous fen carr types. A transitional type, intermediate between shrub thickets and low sedge/moss fens was also defined, the Vaccinium—Eleocharis/ bryophyte type. 3) One strong vegetation gradient was displayed by these community types when the stands were ordinated by reciprocal averaging. Stands were arrayed such that the wettest communities, i.e., 1) 127 reedswamp and low sedge fens lay at one end, the marginal carr types at the other, and sedge and shrub thickets in the center. 4) The vegetation gradient was most closely paralleled by nutrient concentrations: calcium, magnesium, potassium, and total 2 phosphorus, with R values ranging between 0.6 and 0.7. Peat chemistry is probably the single most important determinant of vegetation patterns at Sphagnum Bog. 5) Importance of other environmental factors, as they relate to vegetation and species distributions and nutrient status was illustrated. The distribution of carr communities on the vegetation map indicates the importance of proximity to mineral soil. Topographic profiles indicate a general correspondence between vegetation types and topographic position, determining, in part, the wetness of the habitat, its relative aeration, and supply of flowing water. The pH did not vary widely across the system, and was not very useful for distinguishing communities within the system, but rather for characterizing the area as a whole. 6) The environmental gradient underlying the vegetation pattern is complex, involving nutrient status, and probably also the related and interacting factors of wetness regimes, water flow rates and patterns, and distance from mineral soil. 7) The vegetation units defined at Sphagnum Bog are repeated, often with similar species, and with similar structure and physiognomy, at other sites in the Cascades of central Oregon, where there is appropriate habitat. 6) 128 8) Based on consideratioins of topography and hydrology, floristic affinities, nutrient status, and acidity, Sphagnum Bog and other similar areas in the central and southern Cascades of Oregon, do not represent bogs, i.e., ombrotrophic mires, but moderately rich, spring-fed fens, fed by mineral-influenced water via springs. Elevation measurements showed that the peat did not form a convex surface above the water table; the pH range of 5.5 to 6.75 is higher than the average for ombrotrophic bogs; the Cascade mire vegetation is dominated by brown mosses and sedges and shrubs, characteristic of minerotrophic fens, rather than by Sphagnum- dominated, species-poor vegetation typical of truly ombrotrophic mires; and the nutrient contents are too high to fit the definition of a nutrient-poor bog. 9) Succession has not progressed significantly at Sphagnum Bog. Peat production probably began on a gentle slope fen by springs where drainage was extremely poor, and water accumulated in irregular ities of the surface. Various sedge communities acted as invaders in the wetter habitats, and Vaccinium thickets probably became established around the edges. Dwarf Vaccinium was observed invading low sedge/bryophyte fens. Conifer invasion will probably proceed very slowly, with establishment occurring in isolated periods of unusually favorable climatic conditions coupled with high seed production. Harsh conditions continue to eliminate all but the strongest individuals, such that equilibrium is nearly maintained. Invasion that does proceed 8) 129 will be limited to the Vaccinium occidentale/Carex sitchensis and the Carex sitchensis (Aster occidentalis phase) community.
AN ABSTRACT OF THE THESIS OF Susan Cornelia Sever for the degree of Master of Science in Botany and Plant Pathology presented on December 14, 1979 Title: VEGETATIVE ECOLOGY OF A MONTANE MIRE, CRATER LAKE NATIONAL PARK, OREGON Abstract approved: Jerry F. Franklin Mires, or peat-producing ecosystems, dominated by sedges, shrubs, and brown mosses, are common features in Cascade subalpine regions, occurring where moisture accumulates in small basins or on poorly-drained slopes. Although descriptions and classifications have been developed for mire vegetation in much of the world, there is little information of even a descriptive nature for these montane mires in Oregon and Washington. This thesis reports on phytosociological structure, environmental relations, and successional trends in one such mire in the Oregon Cascade mountains. To characterize the general phytosociological structure of the mire vegetation at Sphagnum Bog, Crater Lake National Park, quantitative species cover data were used in conjunction with a Braun-Blanquet tabular analysis and two-dimensional stand ordinations, reciprocal averaging and a Bray-Curtis polar ordination. Defined community types correspond to physiognomic types as follows: Carex rostrata (reedswamp); Eleocharis pauciflora-Carex limosa, Eleocharis pauciflora/bryophvtes (low sedge fens); Carex sitchensis (tall sedge fen); Vaccinium/ Aulacomnium palustre, Vaccinium occidentale/Carex sitchensis (shrub thickets; Alnus incana/Brachythecium sp. and Salix barclayi (marginal carrs).Phases were defined when appropriate. A vegetation map was made to illustrate the locations and extent of the various communities. Comparisons with other montane mires in the area determined that the physiognomic units defined are repeatable when appropriate habitat conditions are present, and that they usually include many of the same characteristic species, the dominant mosses being particularly constant. Relationships of the vegetative patterns to the following environmental factors were investigated: topographic position, pH, water table depth, and nutrient concentrations. Concentration gradients of the nutrients calcium, magnesium, potassium, and phsophorus proved to be the most important in determining vegetation, 2 with R values ranging from .6 to .7. The role of topographic position was illustrated in several cross-sectional profiles. Water table measurements and, to a lesser degree, pH exhibit low correlation with the floristic gradients. It is suggested that the gradient determining vegetation patterns in this mire is a complex gradinet, dominated by nutrient regime, but also involving water table depths, water mobility, and topographic position. Some interaction of these factors is suggested. Complete succession to terrestrial forest seems unlikely in these spring-fed, water-logged soils. Peat cores sampled show that little succession, even of the mire types has taken place within the peatland, where peat, sometimes greater than 2 m deep is underlain by pumice. Limited invasion by Pinus contorta and Picea engelmannii is evident, however, in two drier community types—Vaccinium/Carex sitchensis, and Carex sitchensis (Aster occidentalis phase), as well as in a transitional meadow area. Establishment of these trees probably corresponds to favorable climatic periods 34 to 50 years ago, but some more recent establishment is also evident. Comparison with pre-existing mire classification systems developed elsewhere in the world, indicates that Sphagnum Bog corresponds with moderately rich fen vegetation or Philonotis fontana-Pohlia albicans spring vegetation, on the bases of floristics, pH, and nutrient concentrations. 126 SUMMARY AND CONCLUSIONS 1) The vegetation pattern at Sphagnum Bog consists of a complex mosaic of species associations, with only the extreme groups sharply distinguished from the rest. Gradual variation of species composition and structure is evident for the intermediate types. 2) The species associations, defined as communities and phases, were classed into four physiognomic types: reedswamp, sedge fen, decid uous shrub thicket, and deciduous fen carr. The Carex rostrata community corresponds to reedswamp; Eleocharis-Carex limosa to a low sedge fen with no moss layer; Eleocharis pauciflora/bryophyte with Philonotis fontana and Meesia triquetra phases to low sedge fens with a more or less continuous moss layer; Carex sitchensis community, with Hypericum anagalloides and Aster occidentalis phases to tall sedge fens lacking a moss carpet; Vaccinium Occidentale/Aulacomnium palustre community to a dwarf shrub thicket with a dense moss ground layer; Vaccinium occidentale/ Carex sitchensis to a shrub thicket, with no moss ground layer; and the Alnus incana/Brachythecium sp. community and Salix barclayi community correspond to deciduous fen carr types. A transitional type, intermediate between shrub thickets and low sedge/moss fens was also defined, the Vaccinium—Eleocharis/ bryophyte type. 3) One strong vegetation gradient was displayed by these community types when the stands were ordinated by reciprocal averaging. Stands were arrayed such that the wettest communities, i.e., 1) 127 reedswamp and low sedge fens lay at one end, the marginal carr types at the other, and sedge and shrub thickets in the center. 4) The vegetation gradient was most closely paralleled by nutrient concentrations: calcium, magnesium, potassium, and total 2 phosphorus, with R values ranging between 0.6 and 0.7. Peat chemistry is probably the single most important determinant of vegetation patterns at Sphagnum Bog. 5) Importance of other environmental factors, as they relate to vegetation and species distributions and nutrient status was illustrated. The distribution of carr communities on the vegetation map indicates the importance of proximity to mineral soil. Topographic profiles indicate a general correspondence between vegetation types and topographic position, determining, in part, the wetness of the habitat, its relative aeration, and supply of flowing water. The pH did not vary widely across the system, and was not very useful for distinguishing communities within the system, but rather for characterizing the area as a whole. 6) The environmental gradient underlying the vegetation pattern is complex, involving nutrient status, and probably also the related and interacting factors of wetness regimes, water flow rates and patterns, and distance from mineral soil. 7) The vegetation units defined at Sphagnum Bog are repeated, often with similar species, and with similar structure and physiognomy, at other sites in the Cascades of central Oregon, where there is appropriate habitat. 6) 128 8) Based on consideratioins of topography and hydrology, floristic affinities, nutrient status, and acidity, Sphagnum Bog and other similar areas in the central and southern Cascades of Oregon, do not represent bogs, i.e., ombrotrophic mires, but moderately rich, spring-fed fens, fed by mineral-influenced water via springs. Elevation measurements showed that the peat did not form a convex surface above the water table; the pH range of 5.5 to 6.75 is higher than the average for ombrotrophic bogs; the Cascade mire vegetation is dominated by brown mosses and sedges and shrubs, characteristic of minerotrophic fens, rather than by Sphagnum- dominated, species-poor vegetation typical of truly ombrotrophic mires; and the nutrient contents are too high to fit the definition of a nutrient-poor bog. 9) Succession has not progressed significantly at Sphagnum Bog. Peat production probably began on a gentle slope fen by springs where drainage was extremely poor, and water accumulated in irregular ities of the surface. Various sedge communities acted as invaders in the wetter habitats, and Vaccinium thickets probably became established around the edges. Dwarf Vaccinium was observed invading low sedge/bryophyte fens. Conifer invasion will probably proceed very slowly, with establishment occurring in isolated periods of unusually favorable climatic conditions coupled with high seed production. Harsh conditions continue to eliminate all but the strongest individuals, such that equilibrium is nearly maintained. Invasion that does proceed 8) 129 will be limited to the Vaccinium occidentale/Carex sitchensis and the Carex sitchensis (Aster occidentalis phase) community.