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Despite advances in post-mine sites reclamation methods in the recent years, restoration treatments are not always successful in creating self-sustaining ecosystems. Occasionally, vegetation remains in a state of arrested succession where conditions are hostile for many late-successional target species. An in-depth study of the environmental factors that control vegetation dynamics on reclaimed mined sites may, therefore, improve the methods for late-successional species introduction, rehabilitating the landscape effectively. In this context, using 12 reclaimed mines in northern Spain colonized mainly by two leguminous shrubs (Cytisus scoparius and Genista florida) we explored: (i) how organic-matter thickness, bryophyte cover and plant diversity and cover attributes change across a gradient of dominant shrub cover/volume, and (ii) how the understorey plant species were associated with these shrub canopies. We hypothesized that shrub growth modified the micro-climatic conditions and influenced the understorey plant species either by facilitation or competition. The results reveal an important positive effect of shrub volume on micro-environmental conditions, such as organic matter-thickness and bryophyte cover, creating environmental heterogeneity underneath larger shrub canopies. At the same time, the shrub volume gradient was also associated with species composition; there was a shift in plant composition from a greater abundance of annual, light-demanding species and legumes in open conditions towards water-requiring, shade-adapted, and broad-leaved species under greater shrub volumes. In contrast, there were no shrub effects in diversity and evenness. The analysis of individual species indicates that 18 out of the 40 most frequent species showed a significant association with shrub volume. Assessment of the species optima associated with shrub colonization allows the development of new species mixtures that are tailored to individual site conditions to favour desired plant communities. Moreover, it seems that shrubs acted as ecosystem engineers in these reclaimed mined sites. Natural shrub encroachment has been shown in this study as one means through which these ecosystems can be modified to create heterogeneity in micro-environmental conditions and hence inducing greater overall diversity. (C) 2014 Elsevier B.V. All rights reserved.