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Population pressure increasingly endangers high-mountain ecosystems such as the pastures in the Eastern Pamirs and the mountain forests on Mt. Kilimanjaro. At the same time, these ecosystems constitute the economic basis for millions of people living there. In our study, we, therefore, aimed at characterising the land-use effects on soil degradation and N-cycling by determining the natural abundance of 15N. A short review displays that δ15N of plant–soil systems may often serve as an integrated indicator of N-cycles with more positive δ15N values pointing towards N-losses. Results for the high-mountain pastures in the Eastern Pamirs show that intensively grazed pastures are significantly enriched in 15N compared to the less-exploited pastures by 3.5 ‰, on average. This can be attributed to soil organic matter degradation, volatile nitrogen losses, nitrogen leaching and a general opening of the N-cycle. Similarly, the intensively degraded savanna soils, the cultivated soils and the soils under disturbed forests on the foothill of Mt. Kilimanjaro reveal very positive δ15N values around 6.5 ‰. In contrast, the undisturbed forest soils in the montane zone are more depleted in 15N, indicating that here the N-cycle is relatively closed. However, significantly higher δ15N values characterise the upper montane forest zone at the transition to the subalpine zone. We suggest that this reflects N-losses by the recently monitored and climate change and antropogenically induced increasing fire frequency pushing the upper montane rainforest boundary rapidly downhill. Overall, we conclude that the analysis of the 15N natural abundance in high-mountain ecosystems is a purposeful tool for detecting land-use- or climate change-induced soil degradation and N-cycle opening. [ABSTRACT FROM AUTHOR]