PS 23-69 - Promoting oviposition habitat for Oregon spotted frog using targeted seasonal grazing strategies

Abstract: The alteration of wetland habitat by non-native species is a primary driver in the decline of Oregon spotted frog (Rana pretiosa; OSF). Oregon spotted frogs require short-statured vegetation in seasonally inundated wetlands for oviposition. Reed canary grass (Phalaris arundinacea) can degrade breeding habitat by forming dense monocultures of tall vegetation, which can eliminate open areas and low-statured plants preferred by OSF. Current practice for reed canary grass management in OSF oviposition habitat includes fall mowing to reduce vegetation height. However, mowing is labor intensive and may not be feasible when access by heavy equipment is limited. Managed cattle grazing may be a viable alternative for improving OSF habitat, as targeted grazing can create openings in vegetation and shift the plant community composition, favoring native sedges and rushes over more palatable, non-native grasses. We compared the effects of continuous and rotational summer-fall grazing, relative to ungrazed controls, on vegetation height, thatch depth, reed canary grass cover, plant composition, water quality, and soil nutrients.



After two years, vegetation height and thatch depth decreased in the grazed treatments, but not in the control. Reed canary grass cover remained consistent across all treatments over the study period. Both grazing treatments showed an initial decline in species richness in the first year but rebounded over time. Finally, grazing appeared to have minimal negative impacts on soil or water quality. Corresponding to oviposition habitat improvements, OSF egg mass numbers increased in the continuously grazed area and were found in the rotationally grazed area for the first time.