Trade-off's in restoration: using soil amendments to address restoration challenges for plants.
Addressing soil quality problems in restoration is primarily done by adding amendments to the soil but improving soil conditions could simultaneously promote both native and exotic plant species. Therefore, understanding the trade-off between the benefit of amendments for native and exotic species is necessary before being implemented in a restoration project. One potential soil problem encountered in restoration is soil salinization, which can be caused by many processes such as poor irrigation practices. The goal of this study was to explore how effective three amendments (gypsum, biochar and mulch) were at reducing salinity levels in a former golf course that had been irrigated. Elevated salinity was a problem for this project because some of the target communities, native grassland and coastal sage scrub, are intolerant to saline soils. We were also interested in how the amendments, as well as fertilizer, affected native and exotic species. Of the three amendments, only gypsum reduced salinity levels, but it did not have any positive impacts on native growth. The other two amendments all benefited native species, with a combination of mulch and fertilizer also reducing exotic species. When applied alone, fertilizer promoted the growth of exotic species. While we found that soil amendments could reduce salinity and promote native species, different amendments were needed to achieve these different goals. This suggests that the most cost-efficient way to use amendments is in a targeted manner, as opposed to a single amendment for use across the entire restoration site.