Ecological Relations of Bromus inermis and Festuca altaica subsp. hallii
Grilz, Perry L.
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This study was designed to elucidate the ecological relations of Bromus inermis and Festuca altaica subsp. hallii. Germination ecology, water relations and growth following spring or fall burning, glyphosate application on B. inermis, F. hallii seedling survival, and seedbank composition were studied in a F. hallii grassland in central Saskatchewan where B. inermis is an agressive invader. Bromus inermis had greater and more rapid germination over a broader range of temperatures and water stress than F. hallii. Germination was lower for F. ballii under decreasing temperatures and similar for B. inermis under decreasing and increasing temperature regimes. Light did not influence germination in F. hallii; however, germination of B. inermis was higher under darkness. Osmotic potentials, relative water content and stomatal conductance were lower for B. inermis in Fall burns in 1987, but similar to Control and Spring burns in 1988. Fall burns reduced tiller densities of native graminoids and F. hallii. Tiller densities of native graminoids were not affected by spring burning, but F. hallii tillered 40% more after spring burns. There was a burn x glyphosate interaction for the reduction of B. inermis; spring burning and glyphosate combined reduced B. inermis most. species richness and diversity were similar between treatments in F. hallii and B. inermis stands. Tiller densities of B. inermis were higher on burned plots in 1987. In 1988, burning had no impact on tillering and growth of B. inermis. Leaf area indices and biomass following burning were generally higher in Spring than in Fall burns and Control. The seedbank composition was similar between B.· inermis and F. hallii stands averaging 1,900 seeds per m2• B. inermis seeds were found only in B. inermis stands, representing less than 1% of the total seedbank. Seedling survival of F. hallii was higher with early spring planting than late spring with vesicular-arbuscular mycorrhizae (VAM) improving survival. Burning alone did not control B. inermis in F. hallii grassland. However, spring burning combined with a wicking of glyphosate reduced B. inermis and increased tillering of F. hallii. Festuca hallii should be seeded in the spring when soil temperatures are increasing and soil moisture is favorable. Seedlings of this native perennial should be inoculated with VAM and planted early in the spring. Reduced germination of B. inermis under high water stress and in the presence of light suggests that prescribed burning may reduce the availability of "safe sites" for germination. Bromus inermis is well adapted to grassland dominated by F. hallii and it apparently can outcompete the dominant specie. Therefore, if grasslands dominated by F. hallii are to be preserved for future generations, proactive management strategies must be employed to limit invasions by B. inermis and enhance the vigor of F. hallii.