Can Carbon and Phosphorous Amendments Increase Native Forbs in a Restoration Process? A Case Study in the Northern Tall-grass Prairie (U.S.A.).

In the northern Great Plains (United States), sites with less than 20% of native species are difficult to restore. We have experimented with a restoration method that shows some promise. It consists of systematically installing simulated small-scale patches (8.0 m² in size) over 25% of an old field and then seeding these patches with native species. The working hypothesis is that these patches will generate a constant source of propagules which in time will lead to increases in native species diversity within the surrounding grass matrix. The objective of this paper was to determine whether soil amendments should be used to facilitate the establishment and persistence of native species (primarily forbs) within these patches. We seeded the patches with a mixture of native grass and forb species and applied four soil treatments: P fertilization, C additions, C + P, and a control (no amendments). Results for the first 5 years were as follows: (1) seeded forb richness was mostly unaffected by soil amendments; (2) seeded and nonseeded forb biomass and density were substantially reduced by C additions, whereas they were unaffected or increased under P additions; (3) both seeded and non-native grass biomass substantially increased with C additions; and (4) there was an inverse relationship between native seeded forbs and non-native grass biomass. Our conclusions are that: (1) P amendments are a potential tool for enhancing native seeded forb biomass in simulated small-scale disturbance patches; and (2) C additions, although enhancing seeded grass biomass do not reduce the biomass of non-native grasses. [ABSTRACT FROM AUTHOR]