The Impact of Seeding Method on Diversity and Plant Distribution in Two Restored Grasslands

Abstract

Previous studies have compared grassland restoration techniques based on resulting species richness and composition. However, none have determined if different techniques generate different plant distributions in space, which may further impact restoration success. This study tests if there are quadrat-scale (1 m 2 ) differences between paired drilled and broadcast plantings in diversity, composition, and plant distributions. Higher competition intensity in and more contiguous spaces between rows in drill-seeded restorations were hypothesized to result in larger patches of native grasses and exotic species. Two paired drill- and broadcast-seeded plantings were sampled in June 2007 in Iowa, U.S.A. Within 10 quadrats in each planting, we measured species abundance with point intercept sampling and plant distributions by dividing the quadrat into 64 cells and recording the most abundant species in each cell. Drilled and broadcast plantings at both sites had similar Simpson’s diversity and evenness. However, the effect of planting type on species richness, composition, and plant distribution was site dependent. Native warm-season grasses in one site, and exotic species in the second, occupied more space and were distributed in larger patches in drilled plantings. Furthermore, drilled canopies consistently captured more light than broadcast canopies. This suggests that initial differences in seed placement can affect resulting plant distributions, resource use, and potentially long-term species turnover. Mechanisms structuring vegetation in these communities need to be further investigated to determine if this approach can provide more information on long-term diversity maintenance in restorations than traditional measures.