Final answer:
A forest that emerges on previously unforested land through the process of ecological succession is known as a secondary forest. These forests are formed through natural regeneration on land that has been cleared of original vegetation, often due to human activities such as agriculture.
Step-by-step explanation:
A forest that has grown up from unforested land is called a secondary forest. These forests commonly regenerate naturally on abandoned agricultural land when human disturbance declines.
Secondary forests are essential because they represent a significant portion of the world's forest cover, especially in places with extensive historical deforestation, such as the east coast of the USA, much of Western Europe, and densely populated areas like Singapore. Succession is the ecological process that leads to the formation of these forests. Over time, as intermediate species evolve and the ecosystem reaches its dynamic equilibrium, a climax community is established, characterizing the forest's mature state until the next disturbance.