The invasion of exotic plants into coastal sage scrub (CSS) has caused large scale habitat conversion associated with increased displacement of rare and endangered species, fire, and alteration of ecosystem function. Few studies have looked at restoration of invaded soil. Therefore, the level of alterations caused by the non-native plants is little known, or the extent or rate of recovery of soil processes from exotic plant invasions once invaders have been removed and native plants restored. Our hypotheses are: (1) Presence of exotic plant species changes the characteristics of the soils beneath them by altering soil inputs via litter and root exudates. (2) If exotics are controlled and natives restored, soil characteristics will return to pre-invaded conditions because the soil inputs of the native plants will be restored.
Results/Conclusions Soil nitrogen, carbon and phosphorus to 10cm depth, plant species richness, and percent cover were recorded three times during the growing season from two coastal sage scrub locations. Nitrogen mineralization rates were determined in lab incubations and plant litter decomposition rates determined using litter bags located in both restored and invaded areas. Contrary to our predictions, plants invading CSS did not alter the total carbon and nitrogen pools or nitrogen mineralization rates to a significant level. However, invaded soils appear to experience greater NO3 drawdown earlier in the season than do soils of native and restored areas. By summer, differences in extractable N decreased in invaded soils, whereas NO3 decreased in restored plots. Because total N and N-mineralization rates were not significantly different, changes in NO3-N during the growing season may be controlled more by uptake than by supply. Implications of varying plant litter decomposition rates among species and in response to reciprocal transplants will be discussed.
