The Economic Value of Biodiversity in the Río de la Plata Natural Grasslands: Evidence on the Sensitivity of WTP to the SLOSS Choice and Other Program-Design Features

Estimates of the economic value of biodiversity conservation in natural grasslands remains virtually absent remain scarce worldwide and are virtually absent for the Río de la Plata region, one of the world's largest temperate grassland ecosystems. We use a contingent valuation survey to estimate Uruguayan households' willingness to pay (WTP) for a payment-for-ecosystem-services (PES) program targeting 320,500 hectares of natural grassland, combining a population-representative in-person probability sample (n=400) with a larger online non-probability sample (n=2,994). Using a referendum-style payment question, we experimentally vary the spatial configuration of the protected area—two large contiguous zones versus fourteen smaller, dispersed zones covering the same total hectares—bringing the ecological Single Large or Several Small (SLOSS) debate into stated-preference valuation for the first time. Within the online sample, we also vary the duration of the payment commitment (one, five, or ten years), and across the full sample we test the sensitivity of WTP estimates to respondents' self-reported certainty using asymmetric, symmetric, and semi-symmetric treatments. The median household is willing to pay approximately UYU 371.70 (USD 9) per month in the benchmark in-person sample. We find no statistically detectable difference in median WTP between the contiguous and fragmented configurations, across payment horizons, or between the in-person and online samples. The latter comparison cannot separate sampling design from survey mode and some of these differences are estimated imprecisely, so the results should not be read as evidence of equivalence. WTP estimates remain stable under moderate certainty corrections but weaken under more aggressive recoding. These findings point to substantial public support for financing grassland conservation, but limited sensitivity of stated preferences to spatial and temporal design features that were not explained to respondents. These results inform the design, communication and finance conservation programs.