Cost‐effectiveness of water‐saving technologies for restoration of tropical dry forest: a case study from the Galapagos Islands, Ecuador

Tropical dry forests are among the most threatened of ecosystems globally, especially on islands, where two key challenges face efforts to restore them: (1) dealing with water scarcity and (2) reliably predicting costs and benefits of alternative approaches given limited resources available for restoration. In this study, we evaluated the cost‐effectiveness of using water‐saving technologies (WSTs) that increase available water during tropical dry forest restoration efforts. Between 2014 and 2018, 4,983 seedlings of 29 woody species were planted across 16 sites in the Galapagos Islands, Ecuador. Seedlings were randomly assigned to a combination of four WST treatments as well as a “no technology” control treatment; seedling survival and all planting costs were subsequently monitored. When analyzing all species together we found that Groasis, Groasis + Hydrogel, and Cocoon WST treatments generally had a significant and cost‐effective positive effect on 2‐year plant survival (95% credible highest density interval > 0). However, the extent of these effects on plant survival and cost‐effectiveness varied by species and site due to differences in plant survival. For example, Groasis or Groasis + Hydrogel were the most cost‐effective restoration methods for eight of the nine species analyzed independently, while the control treatment was most cost‐effective for Opuntia echios var. echios on Baltra Island. Overall, we found that despite their initial costs, WSTs can reduce costs by at least 34% when restoring tropical dry forests in remote sites such as the Galapagos Islands and likely elsewhere in the arid tropics where water availability limits plant growth.