Microsite utilization by Bromus tectorum L. and Poa pratensis L. in a meadow steppe community.

Emergence of Bromus tectorum L. and Poa pratensis L., two dominant alien grasses in eastern Washington, from 24 microsites was monitored in spring and autumn 1979. Spring emergence of B. tectorum reached a maximum on north-facing slopes of artificially constructed pocket gopher mounds and burrows while spring emergence of P. pratensis was maximized on both north-and southfacing slopes of mounds. Earliest autumn emergence of B. tectorum seedlings was in fissures of 0.5 cm, 1 cm, and 2 cm depth while earliest emergence of P. pratensis was 24 days later in fissures of 0.5 cm, 1 cm, 2 cm, and 5 cm depth. All B. tectorum seedlings had emerged within 44 days after first emergence on north-facing slopes of artificially constructed mounds. Maximum emergence of P. pratensis (37%) seedlings occurred on the same north-facing positions of mound slopes and also on the north-facing slope of the burrow, 24 days after first emergence. Both species exhibit broad microsite tolerance and are found on similar but temporally separated microsites.