Water table dynamics and soil texture of three riparian plant communities
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Restoration of degraded riparian plant communities must consider relationships among water table dynamics, soil texture, and plant species. Water table dynamics, soil texture, and slope were compared among riparian plant communities dominated by: (1) beaked sedge (Carex rostrata), (2) Geyer's willow (Salix geyeriana [S. geyerana]), and (3) black cottonwood (Populus trichocarpa [Populus balsamifera subsp. trichocarpa]) occurring on recent alluvial bars. Six sites in western Montana (USA) were examined for each plant community type. Mean bimonthly fluctuation in water table depth did not differ among the 3 plant communities (P=0.67), but mean depth to water table was greatest (P=0.004) in the cottonwood community (62.8 cm), intermediate for the willow (32.0 cm) and least for sedge communities (20.7 cm). Soil texture differed among the 3 plant communities for sand (P=0.0004), silt (P=0.0002), and clay (P=0.003). Cottonwood communities occurred on soils that averaged 78% sand, whereas sedge and willow sites averaged 47% sand and 35% sand, respectively. Silt content was 40% beneath willow, 35% beneath sedge and 15% beneath cottonwood communities. Soils of the willow sites averaged 25% clay compared with 18% and 7% for sedge and cottonwood communities, respectively. Soils beneath all 3 plant communities differed in coarse fragment percentage (P=0.01), averaging 46% in cottonwood, 22% in willow, and 15% in sedge sites. No differences were found in slope among the 3 plant communities, either parallel to the stream (P=0.76) or perpendicular to the stream (P=0.29). Thus, these plant species exhibit a more narrow affinity for soil texture, coarse fragment content and water table depth than previously reported.