The effect of common soil amendments on the germination and growth of native plants frequently used in restoration in coastal southern California
A common practice in habitat restoration is to amend soil to help promote the growth and establishment of native plants. However, there is often little research done to determine the germinate rate of native species in field soil and how those germination rates are affected by soil amendment. This is particularly important to understand when direct seeding is being planned for a restoration site and to understand how plants will establish in an area after restoration has concluded. In 2017, restoration began on the site of an old golf course near the University of California Santa Barbara (UCSB). Surveys of the former golf course have shown that the soil quality is generally poor, with low levels of nutrients and high salinity. Consequently, the restoration plan will incorporate the addition of amendments to the soil to help with the establishment of native plants. To better understand how the soil amendments will impact the germination rate of native plants that are being targeted for restoration, a greenhouse experiment was undertaken on seven locally sourced plants that are native to the coastal Santa Barbara region. Species were grown in soil collected from the former Ocean Meadows Golf Course at the Cheadle Center for Biodiversity and Ecological Restoration (CCBER) native plant greenhouse and nursery. Seeds were planted in four different potential soil amendments (biochar, gypsum, mulch, and untreated), and their germination and growth measured in early 2017. Six of the seven species germinated in all soil treatments, except for one shrub, which did not germinate in any soil treatment. Growth rates were similar across species, with greater growth rates observed in the greenhouse potting soil for all species. Soil pH and salinity did not have a significant effect on the germination or growth rate of any species. Future studies should look at soil structure, the concentration of nitrogen and other nutrients, and other soil characteristics to determine why some soil amendments promoted plant growth and establishment more than others for native plants. This experiment was undertaken by UCSB undergraduate research interns Anne-Marie Parkinson and Danielle Gantar, who were sponsored by the UCSB Associated Students Coastal Fund.