In 2012 the Swedish Environmental Protection Agency was provided with 100,000 ha of productive forest land. The Agency swapped the land to obtain conservation-worthy forests, and these were turned into natural reserves. Conservation without reference to both benefits and cost typically results in inefficient solutions. In this paper we discuss how to select the forest stands to preserve in a cost-effective manner. We also discuss how to design a cost-benefit analysis of the swapping program. We provide several new results regarding the economics of preservation, when land swaps is a viable instrument.