Habitat degradation, fragmentation, and destruction are today the leading causes of species extinction on Earth. A major challenge for environmental managers, hence, is to efficiently balance land usebetween economic development and conservation of natural habitats. In New Caledonia, the smallestbiodiversity hotspot in the world, finding this trade-off is tedious. In particular, the conservation ofits highly diverse forest ecosystems, distinguished by high rates of endemism, can be conflicting withmining activity, the major economic sector of New Caledonia. Managers are willing to study howto refine decisional processes through the use of systematic conservation planning and computationalsustainability. To this end, we considered the project ”Cote Oublíee” started in 2016 by the environ-mental managers of the South Province of New Caledonia. It aims at delineating a complex reservesystem (including about 1200 km2 of terrestrial and 950 km2 of marine reserve) in the southeast of NewCaledonia in an area with rich biodiversity and overlapping with different socioeconomic interests (suchas 238 mining concessions, private and cultural lands, and fisheries) as well as 135 km2of area to berestored. Our objective was to identify how the reserve could be efficiently delineated while respecting socio economic constraints. More precisely, we focused on the biodiversity representation as much ason the spatial configuration of the reserve. Additionally, we aimed at reducing fragmentation throughthe identification of areas suitable for ecological restoration. Relying on a constraint-based reserveselection model, we iteratively considered operational scenarios and produced maps providing the basisfor decision support. The model was then refined according to a feedback loop between managers andscientists. Through this iterative process, we could suggest a delineation of the reserve that maximizedthe representation of biodiversity features while satisfying managers constraints. We also highlightedkey areas for reducing fragmentation through ecological restoration. This real-world pilot study showedhow systematic conservation planning can provide the basis of a decision support framework for conservation, through reserve selection models. Beyond that, it showed how the iterative use of such aframework could help to reduce the gap that can sometimes exist between scientists and managers.