Modeling multiple ecosystem services and beneficiaries of riparian reforestation in Costa Rica

Riparian buffers—forests along rivers—generate many essential ecosystem services, and their protection and restoration are the focus of many policy efforts. Costa Rica is a global leader in this regard, where legislative and executive frameworks work in concert to conserve forests that deliver public benefits such as water qualityand carbon storage both locally and globally. Yet implementation and enforcement is an urgent challenge, and could benefit from high-resolution targeting with a quantitative understanding of expected benefits. Here, we undertake such an analysis, focusing on the benefits of implementing Forest Law 7575, which specifies the amount of forest to be preserved along rivers. We model changes in sediment retention, nutrient retention, and carbon sequestration from a baseline scenario based on current land use that is in partial compliance with the law. We contrast this with a simulated reforestation scenario, where riparian forest cover is increased to at least a minimum level of compliance (10 m buffers) everywhere. We find that targeted riparian reforestation—increasing national forest cover by 1.9 %—would substantially increase ecosystem services. Water quality regulation would be improved via an increase of 3.9 % in sediment retention (1.4 Mt/year), 81.4 % in nitrogen retention (0.012 Mt/year), and 85.9 % in phosphorus retention (0.0022 Mt/year). Moreover, riparian reforestation would increase the national carbon stock 1.4 % above current levels (7.0 Mt). Our analysis shows where riparian buffers are most beneficial—generally in steep, erosion-prone, and intensively fertilized landscapes. Through a canton-level analysis comparing potential increases in sediment and nutrient retention with demographic information, we find that these benefits would flow to communities that depend on rivers for drinking water and that are otherwise vulnerable. Small increases in riparian reforestation in Costa Rica, implemented via an existing law, could confer large benefits to rivers and all who depend on them.