Changes in ecosystem function and effects of environmental complexity on floristic diversity during tallgrass prairie restoration

Less than 5% of the tallgrass prairie remains intact, with the majority lost to intensive agricultural practices. The reduction in the historical extent of the tallgrass prairie represents the greatest loss of any ecosystem in North America, and underscores the need to understand the ecological principles underlying effective prairie restoration. The primary objectives of this research were (1) to determine the effects of grass re-establishment on former croplands on a suite of plant and soil properties and processes, and (2) to examine whether the manipulation of soil resource availability and heterogeneity affects the structure (i.e., diversity) and function (i.e., productivity) of restored prairie.; A 12-year chronosequence of grasslands restored through the Conservation Reserve Program was used to evaluate rates of change in soil and plant properties and ecosystem function during grassland restoration. Native grasses dominated the vegetation within 6–8 years. Root biomass, the C:N ratio of roots, and C storage in roots increased over time and approached values characteristic of native tallgrass prairie. Improved soil structure; increased soil carbon, and greater conservation of nitrogen occurred during the first 12 years of restoration. These results demonstrate important short-term changes in ecosystem structure and function in response to re-establishment of the dominant matrix grasses.; In order to assess resource constraints on diversity and productivity in newly restored prairie, a restoration experiment featuring 4 levels of soil heterogeneity was created by manipulating soil depth (deep vs. shallow) and nitrogen availability (reduced, ambient, and enriched). Aboveground net primary productivity (ANPP) was lower in shallow than deep soils, and fertilization increased ANPP relative to ambient and reduced nutrient treatments. Plant species diversity was positively correlated with variability in productivity and cover established through the soil treatments. Total plant diversity declined over time in all soil treatments and among all levels of soil heterogeneity as a result of the increasing dominance of Panicum virgatum. Diversity was negatively correlated with the photosynthetic rate of P. virgatum, which was positively correlated with soil nitrate levels and intercepted photosynthetically active radiation.; In summary, these studies demonstrate that the establishment of the matrix grasses can drive the recovery of ecosystem function in the trajectory of the original system. However, restoring the structure of tallgrass prairie plant communities may depend on the heterogeneity of the soil environment and the responses of the dominant species to resource variability.