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Can an examination of the interactive effects of soil disturbance by rodents and landscape positions on vegetation response evaluate the ecological role of the keystone species (ecosystem engineers) at a broad scale, thereby providing good approaches to the management of the key engineers for healthy Mongolian steppes? To answer this question, we surveyed plants growing on and off the mounds created by Siberian marmots ( Marmota sibirica) among 14 landscape positions and within a single mountain slope in a forested steppe region of Mongolia. Significant interactions between landscape position and soil disturbance by marmots were seen in forb volume. The impact of soil disturbance on species composition was low in mountain areas and high on depositional plains. Soil disturbance may have changed microenvironments from xeric to more humid or from moist to more xeric, depending on the other site characteristics. Collectively, our results suggest that sedimentation and pre-existing water conditions modify the relationships between soil disturbance and landscape position. Because the landscapes can be divided clearly into those that received only positive influences and those that received only negative influence from the marmot disturbance, zoning becomes more meaningful. Our a priori evaluation of the influence of keystone engineers on ecosystems at a broad scale could provide insights into how to optimize the performance of ecosystem engineering in a way that is beneficial to ecosystem management. [ABSTRACT FROM AUTHOR]