Social forestry is the practice of growing and managing useful plants on government-owned land. This approach aims to provide social, economic, and environmental benefits to the local community and the nation as a whole. Option 1, growing different types of plants together on private land, does not align with the concept of social forestry, as it focuses on government-owned land. Option 2, management of forest by cooperative societies, is not an accurate description of social forestry, as it does not specifically emphasize the ownership of the land by the government. Option 3, growing one type of plant in government-owned land, does not encompass the full scope of social forestry, as it typically involves the cultivation of multiple useful plant species. Therefore, option 4 is the correct answer.