Abstract
<title>Abstract</title> <p>Understanding cooperation in rural communities requires examining how norms and enforcement arrangements jointly shape collective action under constrained governance. This study provides behavioural diagnostics from a frontier region in East Kalimantan, Indonesia, building on Ostromian commons-governance theory. Villagers (n = 45) completed a one-shot Trust Game measuring interpersonal trust and reciprocity, and a repeated Public Good Game with sequential exposure to four institutional regimes: baseline voluntary provision, government co-contribution, a threshold with shortfall penalty, and peer punishment. Because regimes were introduced sequentially rather than randomly assigned, the analysis documents contribution patterns and norm–institution associations rather than causal treatment effects. Three patterns emerge consistently. First, contributions are higher during sanctioning phases than during baseline. Second, reciprocity is a stable predictor of public-good contributions across all regimes. Third, phase differences under sanctioning are more pronounced among lower-trust participants, consistent with institutional substitution, though causal identification is precluded. Government co-contribution is not reliably associated with higher contributions. The shortfall-penalty estimate shows considerable uncertainty under Bayesian inference, with a credible interval overlapping zero even at the 80% level. These findings highlight how enforcement and reciprocal norms jointly support cooperation where formal authority is uneven.</p>