As programs with payments for ecosystem services (PES) have become more numerous, raising the need for and also the opportunity for rigorous evidence on their contributions, we examine shifts within Costa Rica's Pagos por Servicios Ambientales (PSA) program. The PSA was heralded from its initiation, despite demonstrations of low early impacts. We study shifts in impact over time across early periods and whether further adjustments could raise contributions. Looking over time, we find that PSA contracts signed for the 2000–2005 period had higher impacts than contracts for the program's initial time period, 1997–1999 found in previous research. Looking over space, we find that PSA payments have higher impacts for lower slopes and lower market distances. Linking these results, the rise in impact for 2000–2005 occurred alongside a shift in the targeting of PSA, which was along ecological dimensions (limiting effects of owners offering unprofitable lands). Yet the spatial variations in impacts we document suggest that explicitly targeting impact offers the potential to further raise PES impacts in Costa Rica, as well as in other nations.

随着为生态系统服务 (PES) 付费的计划越来越多，增加了对其贡献的严格证据的需求和机会，我们研究了哥斯达黎加Pagos por Servicios Ambientales 内部的变化(PSA) 计划。尽管表明早期影响很小，但 PSA 从一开始就受到了预示。我们研究了早期影响随时间的变化，以及进一步的调整是否会增加贡献。随着时间的推移，我们发现 2000 年至 2005 年期间签署的 PSA 合同比先前研究中发现的该计划最初时期（1997 年至 1999 年）的合同具有更大的影响。纵观空间，我们发现 PSA 支付对较低的斜率和较短的市场距离有更大的影响。将这些结果联系起来，2000-2005 年影响的增加与 PSA 目标的转变同时发生，这是沿着生态维度（限制所有者提供无利可图的土地的影响）。