Deforestation for cattle ranching in the Brazilian Amazon emits carbon, and reforestation absorbs carbon. The social productivities for these alternative activities vary across locations. We analyze a spatial/dynamic model of efficient land allocation to establish a benchmark for policies. We treat cattle prices as stochastic and location-specific productivities as uncertain when assessing the consequences of imposing alternative prices of carbon emissions. Modest carbon price increases would incentivize Brazil to choose policies that capture a significant amount of greenhouse gases in the next 30 years. Our analysis pinpoints tropical forest management as an important contributor to climate change mitigation.