The geomorphological impact of small fossorial mammals (adapted to digging and living underground), such as rodents can be significant, and both their direct and indirect effects may contribute to landscape formation. This thesis is based on empirical field studies of two burrowing rodent species in sub-polar environments, namely invasive House mice (Mus musculus) on sub-Antarctic Marion Island and Norwegian lemmings (Lemmus lemmus) in sub-Arctic Abisko. The spatial distribution, sediment displacements, impact on vegetation and microclimatic effects of the rodents are documented. Invasive mice and rats, introduced on sub-Antarctic Islands during the 19th century, lack natural enemies and are shown to have a significant direct and indirect geomorphic impact by direct sediment displacement, vegetation removal by burrowing, grazing and trampling and thereby exposing the sediments for rain, wind and frost processes.  The geomorphic impacts of lemmings are comparatively more limited as they rely on natural hollows and snow cover for protection and do not burrow to the same extent as other fossorial rodents in cold regions. Lemmings are thus suggested to have little impact on landform integrity, but can affect vegetation composition. A comparison of the findings from this study with published data on seven other rodent species and other physical mass transfer mechanisms in sub-polar and alpine environments suggests that fossorial rodents are a significant and sometimes dominant geomorphic force in sub-polar and alpine environments. The geomorphic work by ground squirrels, ice rats, plateau pikas and zokors is shown to be in the same order of magnitude as solifluction and rock falls. In alpine and periglacial environments these rodents are considered to act as key-stone species and ecosystem engineers through the creation of landforms by  dislocation and of soil and other impacts on soil properties, vegetation and ecosystem function

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Eight rodent species with fossorial activity differing in a number of characteristics such as ecology, climatic conditions, geographical distribution, or kinship were studied using infrared thermography in order to describe their surface temperature and its patterns. An attempt to describe the relation between surface temperature and varied social organisation in burrowing rodents was made.

The research in this thesis concerns with the ecology and behaviour of an endangered fossorial rodent, the giant root-rat (Tachyoryctes macrocephalus), in the Afroalpine ecosystem of the Bale Mountains, Ethiopia, and the results are discussed in relation with available ecological data on other fossorial/subterranean rodents. Firstly, this theses is focused on investigating the ecological role of the giant root-rat. The evaluation of root-rat's impact on various ecosystem features, in the first study, highly contributed to the knowledge not only about the species itself but also about the functioning of the ecosystem it inhabits. In fact, the results of the study indicated that the giant root-rat acts as an ecosystem engineer in the Afroalpine grasslands. Secondly, this thesis involves a pilot radio-telemetry study on the giant root-rat focusing on its temporal and spatial activity. Specifically, the results of the second study brought new light to giant root-rats' daily activity, its pattern, amount and seasonal change demonstrating the difference in activity patterns between strictly subterranean rodents and subterranean rodents with aboveground habits such as the giant root-rat. In the third study, we described the space-use patterns of the giant root-rat and revealed several trends in its spatial behaviour that can serve as a strategy to cope with the harsh and changeable environmental conditions in the Afroalpine ecosystem.