Concern about the impacts of two invasive annual brome grasses (cheatgrass and Japanese brome, Bromus tectorum L. and B. japonicus Thunb. ex Murray) on the mixed-grass prairie of North America's northern Great Plains (NGP) is growing. Cheatgrass is well known west of the NGP, where replacement of fire-intolerant, native sagebrush steppe by fire-prone, exotic annual grasslands is widespread. Consequently, fire is often not considered as a tool for controlling annual bromes. This should not be the case in the NGP, where mixed-grass prairie is adapted to frequent fires. Fire's efficacy may vary with the degree of invasion, though; suppressing postfire annual brome populations or enhancing the native plant community may improve postfire annual brome control in highly invaded areas. To test this, we performed an experiment at two sites to evaluate the relative effectiveness of prescribed fire alone, fire followed by imazapic application and fire followed by native seeding across a pretreatment invasion gradient of annual brome-to-native species cover ranging from 0.05 to 2.35. Fall-prescribed fire alone greatly reduced annual bromes, but by the second yr after treatment the effect was significant only at invasion ratios < 1.2. Postfire imazapic application reduced annual bromes even further than fire alone, but only for 1 yr at the less invaded site and only at invasion ratios > 1.2 in yr 2 at the other site. Native species cover and total species richness responded positively to all treatments, but the degree of their response varied along the invasion gradient, between sites, with time since treatment and among treatments. Also, at one site, fire yielded a lagged stimulation of short-lived, exotic forbs. Seeding had little effect. Fire is an effective tool for reducing annual bromes in the NGP at lower invasion levels, but more tools are needed for long-term, effective control at highly invaded sites.

对两种侵入性一年生金枪鱼草（草和日本金枪鱼，Bromus tectorum L.和B. japonicus）的影响表示关注图恩 北美北部大平原（NGP）的混合草大草原上生长着。Cheatgrass在NGP西部广为人知，那里易生火灾的异国草场取代了耐火的本地鼠尾草草原。因此，火灾通常不被认为是控制年生溴的工具。在NGP中，情况并非如此，因为混合草草原适合于频繁发生火灾。但是，火的功效可能随入侵的程度而变化。抑制火后一年生溴的种群或增加原生植物群落可改善高度入侵地区的火后一年生溴的控制。为了对此进行测试，我们在两个地点进行了一项实验，以评估仅处方火的相对有效性，先进行火烧，然后进行伊马扎比施放，先进行火烧，然后再进行自然播种，以覆盖从年度溴到本地物种的预处理入侵梯度，范围从0.05至2.35。仅秋季规定的火灾就大大减少了一年生的溴，但到处理后的第二年，这种影响仅在入侵比<1.2时才显着。火灾后的马扎比虫施用使每年的溴减少量甚至比单独的火灾减少得更多，但是在入侵较少的地点仅减少了1年，而在其他地点的仅增加了2年的入侵率。本地物种的覆盖度和总物种丰富度对所有处理均产生积极响应，但其响应程度随入侵梯度，站点之间，处理以来的时间和处理之间的变化而变化。同样，在一个地点，大火对短暂的异国情调的前叉产生了滞后的刺激。播种效果不明显。