The role of invasive species on disturbed lands: Autumn olive in the Appalachian coal fields
The Appalachian region of the US is home to the most extensive temperate deciduous forest in the world, which provides many ecosystem services and economic benefits. However, it has undergone significant change due to surface mining, resulting in fragmentation and net loss of productive forests. Post-mining landscapes are reclaimed using the Forestry Reclamation Approach (FRA), which seeks to achieve high hardwood tree canopy cover following the establishment of a “tree-compatible ground cover” seed mixture. However, this approach suffers from inadequate ground cover, making reclaimed sites susceptible to invasion by exotic species. Autumn olive (Elaeagnus umbellata), a nitrogen-fixing shrub, is one of the most common invasive species in this region, and is commonly viewed as a major deterrent of reclamation success. At an active surface mine, we are characterizing the following: 1) the effect of substrate and reclamation vegetation on autumn olive establishment and performance 2) the effect of autumn olive on plant available nitrogen, and 3) whether a single-year mechanical removal of autumn olive is sufficient to both control autumn olive and to establish productive hardwoods.
In 2014, we sowed 6,800 autumn olive seeds into >160 plots with varied plant functional composition: bare ground, forbs only, grasses only, and standing community. To determine the effects of autumn olive on soil nitrogen, we collected samples near the trunk, under the drip line, and 10 m away for 10 established shrubs across a range of reclamation sites. We did not find any significant differences in the percent total nitrogen between areas directly underneath autumn olive versus neighboring areas with autumn olive. This suggests that despite the biological nitrogen fixation from autumn olive, it does not appear to be changing soil nitrogen pools. To further test the effects of autumn olive on hardwood establishment, we have managed autumn olive using mechanical and combination mechanical/chemical control. Three native tree species were planted in winter 2015, and will be followed for two years. Overall, autumn olive is viewed as reducing reclamation success, but the interaction with reclamation species remains unclear.