Using ecological theory to guide the implementation of augmentative restoration

Abstract

Invasive organisms are now considered the second worst threat to native biological biodiversity, behind habitat loss and fragmentation. Successful control of invasive plants can have unexpected impacts on native plants and wildland systems. Therefore, it is important for managers of invasive species to become increasingly concerned with more than target invaders, but also ecological mechanisms and processes like invasion resistance, environmental heterogeneity, and succession that direct plant community dynamics. Augmentative restoration is a management approach that augments existing ecological processes by selectively repairing and replacing those processes that are damaged or missing thereby directing plant communities in a desirable direction. Our overall objective was to test the concept of augmentative restoration. Our overall hypothesis was that successional processes occurring at high levels could be augmented by selectively repairing or replacing successional processes that occur at low levels to increase desired species composition. In a split plot design with 4 replications at 3 sites, 8 factorial treatment combinations from 3 factors (shallow tilling, watering, and seeding) were applied to whole plots, and 2,4-D was applied to sub plots. Cover and density of seeded species, Centaurea maculosa, and Potentilla recta as well as existing native and exotic forbs and grasses were sampled in 2002 and 2003 to produce pretreatment and post-treatment data. ANCOVA was used to analyze cover and density data using pre-treatment data as a baseline covariate. Data indicated that areas with high percent bare ground required seeding and watering to increase seeded species and native forbs, while seeding and tilling increased seeded species and native forbs in areas of high soil moisture. C. maculosa, P. recta, and exotic forbs decreased in response to tilling and 2,4-D. Exotic and native grasses increased in response to tilling and 2,4-D indicating that grasses may have reproduced primarily vegetatively. This data provided evidence that augmentative restoration could provide managers with an ecological framework to develop restoration procedures that address invasion resistance, environmental heterogeneity, and succession in order to enhance native forbs and grasses as well as improve the emergence of seeded species to increase desired plant composition in wildlands damaged by invasive plants.