Cost-effectiveness of management strategies in a nucleation experiment in a tropical dry forest

Cost-effective, large-scale strategies are needed to restore degraded ecosystems worldwide. Applied nucleation is one technique that can accelerate succession in tropical forests. However, the effectiveness of irrigation and fertilization in the context of large-scale applied nucleation in tropical dry forests (TDFs) has not yet been tested. To this end, we established a large-scale experiment in southwestern Colombia on abandoned pastures. We planted 11,382 seedlings of 11 native species coupled with six management treatments that varied in the amounts of fertilizer and water. We monitored survival, height, and resprouting ability seedlings over 2 years. We also estimated the cost of seedling production, planting procedures, management, and monitoring, and assessed their cost-effectiveness using seedling survival as an indication of effectiveness. After 2 years, 73% (8,266) of seedlings planted survived, and species survival ranged from 5 to 99%. Individuals that received the lowest amount of fertilizer (25 g of Nitrogen, Phosphorus, and Potassium [NPK]) with additional irrigation had the highest survival rates (>76%). Final height ranged from 52 to 330 cm across species. Seedlings that received the highest amount of fertilizer (50 g of NPK) without additional irrigation had the highest mean final height (174 ± 9.0 cm). The control was cheapest ($7313/ha) and the most cost-effective method in terms of seedling survival. Our findings suggest that the best way to establish cost-effective, large-scale restoration projects in TDFs is to plant native species mixtures of locally adapted species without fertilization and irrigation and to invest in long-term monitoring.