Effects of initial irrigation, seeding date and directlyhauled topsoil on mined land community composition

This study was implemented to determine the effects of one, two, or three months of establishment irrigation, after spring or summer seeding on the long-term composition of mined land plant associations. While the treatment plots were seeded with the same diverse mixture of native species, floristic differences among treatment combinations were apparent after five growing seasons. Summer seeding enhanced the development of seeded warm-season grasses by retarding the initial development of seeded cool-season grasses and by limiting competitive effects of nonseeded species through seedbed tillage. Supplemental irrigation was substantially more important to the development of warm- than cool-season grasses. Seeded perennial forbs performed poorly on all treatments, presumably due to low seed viability, low germination, and/or competition from more water-responsive species. Despite drought conditions during plant establishment, supplemental irrigation was not critical to the ultimate development of nonseeded plant species when seedbed tillage occurred shortly after topsoil was applied. However, irrigation became more important to the long-term development of these species when tillage was delayed. Most forbs encountered were perennial natives that had volunteered from the direct-haul topsoil.Atriplex canescens was the only successful seeded shrub and performed particularly well on the summer seeded plot that received one month of initial irrigation.