The role of soil fertility in restoring Louisiana's coastal prairie

Studies have shown that soil nutrients, especially nitrogen (N), play an important role in the reestablishment of native prairie plant species. Soil N favors early succession species while long-lived native perennials compete favorably in N poor soils and numerous restoration studies have employed carbon additions in the form of sawdust and/or sucrose to immobilize soil nitrogen. However, this technique poses financial and logistical challenges when reconstructing coastal prairie in former agricultural fields. In this study the germination and survival of native prairie species were studied along a nutrient gradient established in an old rice field in Gueydan, Louisiana. Fifty plots, planted with seeds of 22 native prairie species, received one of five treatments: a low or high rate of nitrogen, no addition, and a low or high rate of carbon (sawdust and sucrose).  Vegetation coverage by species was sampled every September from 2004 - 2007. Precipitation was well below normal from 2003 to the middle of 2006 except for April - June 2004. Above ground productivity showed a strong response to nitrogen levels as measured by the percentage of available sunlight reaching the ground. Species richness increased with increasing fertility, but despite the increase in biomass as fertility increased there was no statistical difference in species conservatism values with conservative species germinating and surviving in all treatments. These results suggest that factors other than N may influence the outcome of succession in coastal prairie. It is hypothesized that drought adapted prairie perennials are superior competitors in heavy clay prairie soils when receiving low levels of precipitation.