Influence of Water Repellency On Post-Fire Revegetation Success.

Ecosystems that have been encroached by juniper woodlands pose a significant challenge to land managers in restoring desired plant communities after a fire. In an effort to restore and maintain ecological function these systems are often reseeded; however, these efforts are not always successful. When reseeding efforts fail, sites become susceptible to increased soil erosion and invasion by annual weeds that out-compete native species, degrade ecological processes, and modify natural fire patterns. The development or enhancement of a water repellent (WR) layer, as a result of the fire, is a common occurrence in these communities. We have hypothesized that post-fire reseeding failure may be due to soil WR limiting seedling moisture availability. Newly-developed wetting agents may provide an innovative post-fire restoration technique by improving ecohydrologic properties required for plant growth, by overcoming soil WR and increasing the amount and duration of available water for seedlings. The primary objective of this study was to compare seedling emergence and survival of desirable native species, to the weed species cheatgrass (Bromus tectorum), planted in post-fire WR soil, with or without wetting agent application. Results showed that soils treated with wetting agent had significantly higher infiltration rates and soil water content. Treated soils produced significantly higher plant densities, above and below ground biomass, and root depth, regardless of species. Seeds that germinate in soils without wetting agent typically desiccated, as a result of the WR layer disconnecting the seedlings from the underlying soil moisture reserves. These results indicate that for juniper ecosystems wetting agents have the potential to be used as a post-fire restoration treatment. However, if these soils are not managed, within subsequent years the lack of seedling establishment of desired species may allow for the invasion of annual weeds, once WR has diminished.