A major threat to human well-being is the accelerated rate of ecosystem degradation. Restoration of degraded ecosystems, including harmful species control, entails cooperation among multiple agents such as land-owners, agencies and sometimes countries. These agents may have incentives to contribute less, leaving the job for other agents (free-ride), which may lead to inefficient or incomplete treatment. Ecosystem restoration is a dynamical process that may span over many years, particularly due to life histories of both harmful and native species. A major question is what factors facilitate or impede long-term cooperation among agents. In my talk, I will introduce a game theoretical approach to study how to restore ecosystems by multiple agents, taking into account the costs of both treatment and degradation over time. I assume no enforcement mechanisms and no binding agreements (namely, each agent cooperates only for its selfish interests). I will show that, under certain conditions, there exists a solution (Markovian Nash equilibrium) where all agents contribute, albeit slowly enough, and no agent has an incentive to further free-ride. Nevertheless, several factors affect the efficiency or the solution, some of which are counterintuitive and seem ‘paradoxical’. First, agents with fewer incentives to contribute, such as agents that are less affected by the harmful species, may nonetheless contribute more than the others at equilibrium. Second, monitoring agents’ actions (to know how much each agent really contributes) may impede cooperation and incentivize less contribution. Third, incomplete information about agents’ true objectives may increase cooperation. The results emphasize the importance of further using game theory to study how to manage ecosystems by multiple agents.