Effects of Nutrient Manipulations and Grass Removal on Cover, Species Composition, and Invasibility of a Novel Grassland in Colorado

Abstract

Cover and richness of a 5-year revegetation effort were studied with ,respect to small-scale disturbance and nutrient manipulations. The site, originally a relict tallgrass prairie mined for gravel, was replanted to native grasses using a seed mixture of tall-, mixed-, and short-grass species. Following one wet and three relatively dry years, a community emerged, dominated by species common in saline soils not found along the Colorado Front Range. A single species, Alkali sacaton (Sporobolus airoides), composed nearly 50% of relative vegetation cover in control plots exhibiting a negative relationship between cover and richness. Seeded species composed approximately 92% of vegetation cover. The remaining 8% was composed of weeds from nearby areas, seed bank survivors, or mix contaminants. Three years of soil nutrient amendments, which lowered plantavailable nitrogen and phosphorus, significantly increased relative cover of seeded species to 97.5%. Fertilizer additions of phosphate enhanced abundance of introduced annual grasses (Bromus spp.) but did not significantly alter cover in control plots. Unmanipulated 4-m 2 plots contained an average of 4.7 planted species and 3.9 nonplanted species during the 5-year period, whereas plots that received grass herbicide averaged 5.4 nonplanted species. Species richness ranged from an average 6.9 species in low-nutrient, undisturbed plots to 10.9 species in the relatively high-nutrient, disturbed plots. The use of stockpiled soils, applied sparingly, in conjunction with a native seed mix containing species uncommon to the preexisting community generated a species-depauperate, novel plant community that appears resistant to invasion by ruderal species.

Response of a mixed grass prairie to an extreme precipitation event

“…Those results are in agreement with our measurements of N in soil beneath cheatgrass compared with those beneath the native Pascopryum smithii, suggesting that cheatgrass may have initiated a similar plant-soil N feedback at out site. We also know from previous studies that nutrient limitation can inhibit the ability of introduced annual species to exploit opportunities created by disturbances (Paschke et al 2000, James et al 2008, Cherwin et al 2009). Finally, we found that cheatgrass was one of the only species that responded to fertilizer additions with increased productivity (hence the only species to exhibit N-limitation in our experiment).…”

Management of novel ecosystems: are novel approaches required?

“…The fact that much of this soil had been stockpiled for an unknown interval meant that what was returned and spread over the surface was very different from what had originally been removed. Measurements of organic matter and organic nitrogen indicated that the soils on the revegetated site were more characteristic of arid shortgrass steppe than of a mesic, bottomland tallgrass prairie (Cherwin et al . in press).…”

“…Other warm‐season grasses common in mixed‐grass and shortgrass steppe provided another 25% of relative vegetation cover. Particularly remarkable was the fact that planted species constituted over 90% of the vegetation cover and the site appeared largely resistant to invasions by other native and non‐native plants (Cherwin et al . in press).…”

Assembly of root‐associated bacteria communities: interactions between abiotic and biotic factors

“…A shift in RAB community composition could affect host fitness, especially if involving mutualist/pathogen abundance. Increasing N availability causes shifts in dominance between plant species (Pennings et al ., ; Suding et al ., ), reductions in plant species diversity (Strengbom et al ., ; Bobbink, ; Suding et al ., ; Clark and Tilman, ) and increased vulnerability of systems to invasion (Bobbink, ; Cherwin et al ., ). Describing root associated microbial response to N is important to understanding plant community response to N enrichment.…”