Seedling growth and competition of a late-seral, native perennial grass and 2 early-seral, native forbs in the presence of 2 densities of the invasive annual grass Bromus tectorum L. (Poaceae)

AbstractForage kochia [Bassia prostrata(L.) A. J. Scott] is competitive with annual weeds and has potential for use in reclamation of disturbed land. However, land managers are reluctant to use forage kochia in revegetation programs due to lack of understanding of its compatibility with or invasiveness in the native plant community. We conducted two greenhouse experiments, one to compare the competitive effect of forage kochia versus perennial grasses on growth of cheatgrass (Bromus tectorumL.) and one to study the effect of forage kochia on growth of native perennial grasses. In the first experiment, a single seedling ofB. tectorumwas grown with increasing neighbor densities (0 to 5 seedlings pot−1) of either forage kochia, crested wheatgrass [Agropyron cristatum(L.) Gaertner ×A. desertorum(Fisch. ex Link) Schultes; nonnative perennial grass], or thickspike wheatgrass [Elymus lanceolatus(Scribn. & J. G. Sm.) Gould; native perennial grass].Bromus tectorumgrowth was reduced moderately by all three perennial neighbors, butA. cristatumandE. lanceolatushad more effect onB. tectorumwhen compared with forage kochia. This experiment was repeated and similar results were observed. In the second experiment, forage kochia was grown with each of four native cool-season grass species: basin wildrye [Leymus cinereus(Scribn. & Merr.) Á. Löve], bluebunch wheatgrass [Pseudoroegneria spicata(Pursh) Á. Löve],E. lanceolatus, and western wheatgrass [Pascopyrum smithii(Rydb.) Á. Löve]. Forage kochia had no effect on height, tiller number, and aboveground biomass of native grasses. Similarly, native grasses did not show a significant effect on forage kochia seedlings. This experiment was also repeated, and forage kochia somewhat reduced the aboveground biomass ofL. cinereusandP. spicata. However, all native grasses significantly reduced change in height, branching, and aboveground biomass of forage kochia. These results suggest that forage kochia interfered withB. tectorumseedling growth, but it showed little competitive effect on native grass seedlings.

Download Full-text

Invasive Grasses Increase Nitrogen Availability in California Grassland Soils

Invasive Plant Science and Management ◽

10.1614/ipsm-09-046.1 ◽

2010 ◽

Vol 3 (1) ◽

pp. 40-47 ◽

Cited By ~ 24

Author(s):

Sophie S. Parker ◽

Joshua P. Schimel

Keyword(s):

Nitrogen Availability ◽

Perennial Grass ◽

N Cycling ◽

Rooting Depth ◽

Grass Species ◽

Annual Grass ◽

Annual Grasses ◽

California Grassland ◽

Pool Sizes ◽

Native Perennial Grass

AbstractAs Europeans colonized California, they introduced annual grasses from the Mediterranean Basin. These exotic annual grasses eventually invaded grasslands throughout the state, some of which were once dominated by native perennial grass species. Annual grasses differ from perennials in their phenology, longevity, rooting depth, litter chemistry, and interaction with the microbial community. As these traits may influence plant nitrogen (N) use, it is likely that the invasion by annual species resulted in changes in the availability and cycling of N in California grassland systems. We addressed the question of how invasive annual grasses influence rates of N cycling by measuring N pool sizes and rates of net and gross mineralization and nitrification, gross immobilization, and the denitrification potential of soils from experimentally planted annual and perennial-dominated grasslands. With an increase in annual grass cover, we saw increases in ammonium (NH4+) pool sizes and rates of N mineralization, nitrification, and denitrification in soils. These differences in N status suggest that N cycling in California grasslands was altered at sites where native perennial bunchgrasses were invaded by nonnative annual grasses. One consequence of annual grass invasion may be a legacy of NH4+-enriched soils that hinder the reestablishment of native perennial grass species.

Download Full-text