Prescribed fire and herbicide effects on soil processes during barrens restoration

Prescribed fire has become a common tool of natural area managers for removal of non-indigenous invasive species and maintenance of barrens plant communities. Certain non-native species, such as tall fescue (Festuca arundinacea), tolerate fire and may require additional removal treatments. We studied changes in soil N and C dynamics after prescribed fire and herbicide application in remnant barrens in west central Kentucky. The effects of a single spring burn post-emergence herbicide, combined fire and herbicide treatments, and an unburned no-herbicide control were compared on five replicate blocks. In fire-plus-herbicide plots, fescue averaged 8% at the end of the growing season compared with 46% fescue cover in control plots. The extent of bare soil increased from near 0 in control to 11% in burned plots and 25% in fire-plus-herbicide plots. Over the course of the growing season, fire had little effect on soil N pools or processes. Fire caused a decline in soil CO2 flux in parallel to decreased soil moisture. When applied alone, herbicide increased plant-available soil N slightly but had no effect on soil respiration, moisture, or temperature. Fire-plus-herbicide significantly increased plant-available soil N and net N transformation rates; soil respiration declined by 33%. Removal of non-native plants modified the chemical, physical, and biological soil conditions that control availability of plant nutrients and influence plant species performance and community composition.