Managing riparian vegetation for multiple ecosystem benefits in agricultural landscapes of the Sacramento Valley

Historic degradation and destruction of riparian vegetation in California has resulted in a loss of wildlife habitat, biodiversity and associated ecosystem services. Riparian buffer zones in agricultural landscapes can be managed or restored in order to provide multiple benefits, but information is lacking on the tradeoffs involved in these management decisions. We examined the effects of land use (range vs. cropland), distance from the channel, and plant communities on above- and belowground diversity and ecosystem services in a survey of 20 sites along waterways in Yolo County. Riparian zones supported greater plant diversity and nearly twice as much total carbon (C) storage per hectare compared to adjacent land managed for agricultural uses, especially in rangelands, but had generally lower soil microbial and nematode diversity and abundance. When woody plant communities were present in the riparian zone, soil nitrate (NO3-) and plant-available phosphorus (P) levels were lower. Belowground diversity and community structure appeared to depend more on plant productivity (as inferred by vegetation cover) than plant diversity or species richness. Greater plant species richness, nematode food web structure, total microbial biomass, woody C storage and lower NO 3- and P loading were correlated with higher visual riparian health assessment scores, offering the possibility of managing these riparian habitats to provide multiple ecosystem functions. We then assessed the effects of revegetation, floodplain bench creation and grazing on selected ecosystem characteristics and services in a case study of a 7-year-old riparian restoration site in Yolo County. Restoration increased richness and cover of native plant species beneficial to wildlife. Some restored habitats had higher wood C storage, but slightly higher greenhouse gas emissions and lower microbial biomass carbon than the unrestored site. Ruminant grazing increased cover and richness of noxious weed species and decreased natives. Levee setback and creation of a floodplain bench increased bank stability, reduced flooding potential, and did not decrease soil C stocks or nematode abundance and diversity despite massive top soil disturbance during excavation and grading. These studies provide a resource for landowners and managers to consider the tradeoffs of different types of riparian restoration and management for multiple ecosystem benefits.