Graduate Thesis Or Dissertation
 

Revegetation with Carex nebrascensis and Carex utriculata following reconstruction in a NE Oregon meadow stream

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1r66j535w

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  • Riparian vegetation is an essential component for the maintenance and/or repair of channel stability and function. Sedges within low-gradient riparian systems provide the structure necessary for sediment trapping leading to channel narrowing through bank building processes. Planting success in riparian restoration projects has often failed due to inappropriate species selection, planting locations and/or methodologies. Stream restoration efforts utilizing channel reconstruction methods are increasing in number across the West thus emphasizing the need for knowledge on revegetation methods. Planting success in a recently constructed channel is essential because the lack of vegetation makes the channel highly susceptible to erosion. Sedges play an important role in the stability of low gradient, fine-textured stream channels. Two native sedges, Carex nebrascensis (Nebraska sedge) and Carex utriculata (beaked sedge) are often used in riparian restoration within the West because they have extensive root systems that can provide bank stability in fine-sediment channels. Survival and vegetative reproduction were evaluated on greenhouse grown plugs of these two sedge species following transplanting within a reconstructed NE Oregon meadow stream. Sedge plugs were planted on two fluvial surfaces along the stream: depositional (point bars) and erosional surfaces (straight) at or below bankfull level. A second study was performed to evaluate the effect of Cirsium arvense (Canada thistle) presence on sedge transplant survival and vegetative reproduction. This was performed only on erosional planting locations. Depths to groundwater and soil moisture were also recorded at each planting location. Survival at the end of the first growing season in the first study was the same for both species, but shoot numbers were greater for Carex nebrascensis (98 shoots/m²) compared with Carex utriculata (84 shoots/m²). No differences were observed between shoot numbers by species at the end of the second growing season. Greater shoot numbers also occurred on depositional planting locations (117 and 165 shoots/m²) compared to erosional planting locations (65 and 59 shoots/m²) at the end of the first and second growing seasons. Transplant loss due to scour from high flows was greater at erosional planting locations (48%) than at depositional planting surfaces (19%). Sedge transplant loss from scour during high flows was greater for Carex utriculata transplants (44%) than for Carex nebrascensis transplants (23%). Presence of Cirsium arvense was observed to be associated with a reduction in vegetative reproduction during the first growing season but not at the end of the second growing season. Carex nebrascensis produced more shoots than Carex utriculata regardless of thistle presence for both growing seasons probably due to depth to groundwater. Transplant loss due to scour from high flows was greater for Carex utriculata (55%) compared to Carex nebrascensis (28%). These results suggested that revegetation success will be increased if sedges are planted on depositional geomorphic surfaces within reconstructed meadow channels. Cirsium arvense may be controlled following sedge transplanting during the first growing season to increase vegetative growth. These results also suggested that Carex nebrascensis is an appropriate species for transplanting at sites with water tables deeper than 30 cm.
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