Adaptive restoration of sand-mined areas for biological conservation

Abstract

1. Adaptive management approaches to ecological restoration are current best practice. The usefulness of such an approach was tested in this study by implementing repeated experiments that examined restoration options for derelict sand mine sites dominated by 'Imperata cylindrica'. Reclamation of degraded land that is dominated by 'I. cylindrica' is a common problem throughout the tropics. 2. Initially, the hypothesized barrier to regeneration was limited seedling establishment because of 'I. cylindrica' competition. After burning the grassland, woody weed control and planting of seedlings were implemented in factorial combination. 3. Seedling survival 28 months after planting averaged 26%, with < 1% of all seedlings establishing to a height > 1 m. The hypothesis that a transition barrier comprising solely biotic interactions restricted regeneration of native woody cover was rejected after seedlings and natural regeneration failed to thrive in this experiment. 4. A revised hypothesis, that the transition barrier comprised a combination of abiotic limitations (soil deficiencies) and biotic interactions ('Wallabia bicolor' browsing and 'I. cylindrica' competition), was developed. A second experiment tested this hypothesis by removing 'W. bicolor' (fencing), slashing the 'I. cylindrica', adding organic mulch and planting a mixture of native pioneer and secondary successional woody species in factorial combination. 5. Seedling survival was 61% in the second experiment and mulching significantly enhanced the survival and growth of all planted species. Planting alone reduced the regeneration of 'I. cylindrica' after slashing. Native woody cover establishment was maximized by planting seedlings in mulched treatments. 6. Synthesis and applications. Taken together, these experiments support the hypothesis that there is a barrier restricting regeneration of native woody cover, and the barrier probably comprises both abiotic and biotic components. By adopting an adaptive management approach to the ecological restoration of sites, significant insights into their management requirements have been gained, supporting the current best practice restoration framework. Insights gained through monitoring and adaptation will be used to update the reserve plan of management, enhancing restoration of this severely degraded area and promoting connectivity of native woody cover within the conservation estate.