Effectiveness of herbicide, mechanical scraping, and native seed sowing as restoration tools in a disturbed pine rockland

Background/Question/Methods

South Florida is home to several unique and globally imperiled ecosystems. Outside Everglades National Park, less than 2% of the historic area covered by native pine rockland and rockland hammocks remains, and many of the plant species found in these community types are globally imperiled. Protecting South Florida’s pine rockland communities is becoming increasingly essential with the continued spread of development. However, land managers are limited in what management techniques can be employed within fragments surrounded by an urban setting. Management efforts to conserve this ecosystem would benefit from a comprehensive study examining different methods for restoring native plant cover to a disturbed or managed area. With this goal in mind, we examined the effectiveness of different site treatments (herbicide, mechanical scraping and control) and the application of native seeds as restoration tools within a disturbed pine rockland. We monitored native and exotic species abundances and richness within 180 quadrats distributed within 9 replicate site treatment plots over 2 years in the presence and absence of native grass seed sowing. 

Results/Conclusions

Mean % native grass cover increased significantly only within scraped seeded plots, and native grass richness was significantly higher for scraped seeded plots than for all other treatment combinations.  Mean non-native grass cover was highest within control plots. We found no significant difference between herbicide and scraped plots in terms of non-native grass cover; however, a significant increase in total non-native grass cover occurred within both treatments during the course of the study. Applying herbicide resulted in a significantly lower non-native grass richness than all but one treatment combination (scraped + seeded); however, by the end of the study no differences in non-native grass richness existed between any of the treatments. Furthermore, seeding had no significant effect on non-native grass abundances or richness. Although seed sowing may be an effective restoration tool within disturbed pine rocklands by increasing native species abundances and richness, our results suggest it is only effective when applied in combination with mechanical scraping. However, the encroachment of non-natives from surrounding areas poses a potential problem if scraping is used as a management tool in pine rockland restoration.  Land managers should consider treating for some exotic species in areas surrounding a target restoration site prior to scraping.