Late Successional-Old Growth (LSOG) forests are mature, structurally-complex forests that support a diverse habitat for a variety of species and have high carbon storage capacities. In Northern Maine, commercial timber harvesting threatens the few remaining LSOG forests. The current harvest rate is approximately twenty-five times higher than the current conservation rate, emphasizing the time-sensitive nature of protecting LSOG forests. To evaluate the effectiveness of conservation in reducing timber harvest and to inform future conservation efforts, I conducted a two-part study. First, by calculating harvest rates relative to the year of conservation, I determined that conservation significantly reduced the harvest rate by 86% and average harvest patch size by 57%. This result confirms that conservation can be an effective way to preserve LSOG from timber harvest. Second, to determine where new conservation efforts should be prioritized to best preserve LSOG forests, given time and funding constraints with competing goals, I used a multicriteria analysis incorporating cost, carbon stocks, ecological value, and threat risk for LSOG patches. The cost of conserving the top 20% of LSOG forests ranged from $85 million for the most cost-effective forests to $225 million for the forests with the highest carbon stocks. Given their high ecological value and the proven effectiveness of conservation, LSOG forests in Northern Maine require targeted, timely conservation. My results highlight the actions that can be taken to protect LSOG forests for future generations and provide a tool for identifying high-value forests to conserve first.