Recently abandoned croplands provide opportunities for establishment of biodiverse grasslands; however, the question remains as to what extent uniform soil conditions caused by decades of tillage (soil homogenization) limit plant diversity and primary productivity in newly established sites. Addition of soil patches (microsites) with distinct composition compared to surrounding soil has been attempted to increase diversity with mixed success, leaving uncertainty regarding the linkages between early successional plant communities and belowground soil patterns and processes. We propose the novel concept of microsite edges (microedges), which may function at small scales analogously to plant community ecotones by providing unique microsites for increased plant diversity. A field experiment was initiated in 2015 to determine if heterogeneous soils and microedges have increased productivity and diversity compared to homogeneous soils. Soils with added sand and woodchips patches were compared with soils where sand and woodchips were added and mixed to mimic homogenization, and soils with hummocks and hollows were compared to level, tilled soil. Each treatment was assigned to a plot within 28 randomized complete blocks in a former agricultural field and each plot was seeded equally. Quadrats overlaid in each plot were used to survey density and percent canopy cover of each plant species present.
Overall plant species richness, Shannon index of species diversity and productivity (canopy cover) were similar among treatments with the exception of the woodchip plots, which were sparsely vegetated compared to the other treatments. However, interestingly, within functional groups, canopy cover and richness differed, suggesting compositional differences among microsites and microedges compensate to reach the same overall levels of diversity and biomass in plots. Cover of adventive legumes and grasses was greater in woodchip homogeneous plots and hollows (grasses only) than other treatments, whereas adventive forbs and native grasses had greater cover in woodchip heterogeneous plots. Both homogeneous and heterogeneous sand treatments had much greater native grass and forb richness compared to other treatments, and hollows had the greatest adventive forb richness. These functional group differences, combined with supressed growth in woodchip plots, suggest human addition of microsites and microedges leads to greater diversity of functional groups, including their distribution across sites, with the potential to alter plant community successional trajectories.