Masters Thesis

Wet meadow vegetation community along a hydrologic gradient after passive restoration, Southen Cascades, CA

I examined the vegetation community and structure of a wet meadow from 2013-2017 across ecological, temporal and spatial scales, immediately following hydrologic restoration. I set out to determine if the natural seedbank can act as a primary source for passive revegetation. I collected soils from 20 vegetation plots across a hydrologic gradient and germinated potential seeds in a greenhouse. Obligate (OBL) and facultative wetland (FACW) seedbank species germinated in all plots along the hydrologic gradient. I compared seedbank composition with emergent vegetation using Sorensen’s similarity index and found a higher similarity with OBL and FACW species (35-55%) than with facultative upland (FACU) and upland (UPL) species (17-29%) across all years. Annual vegetation surveys demonstrated that FACU species cover decreased gradually in drier plots by 2017, whereas the wettest plots were dominated exclusively by OBL and FACW species across all years. FACW species cover increased in plots between the hydrologic extremes, while UPL and facultative (FAC) species cover decreased. The regeneration of OBL and FACW species was not constrained to only seed-producing species. The relative frequency of rhizomatous species Carex simulata and Juncus balticus remained stable throughout 2013-2017, and both species were able to propagate across a wide-range of hydrologic conditions. Vegetation community composition was driven predominantly by depth to water (r2 = 0.444), soil moisture (r2 = 0.231), organic matter (r2 = 0.408), and organic carbon (r2 = 0.414). These results provide evidence that passive revegetation can be a successful strategy after hydrologic restoration.

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