AP BIOLOGY

Detailed explanation-1: -The trees do not replace grasses as they require more water than grasses and this would lead to water scarcity for other species. Also, trees are prone to catch fire and the fire spreads swiftly. Due to these reasons, trees do not replace the grasses as a part of ecological succession.

Detailed explanation-2: -Pioneer species are replaced by climax species, such as trees, in the processes of ecological succession because the pioneer species transform the environment to make it suitable for climax species, but the climax species change the environment to be unsuitable for the pioneer species.

Detailed explanation-3: -Thus, disturbance can initiate successional change. Species that are well adapted for exploiting disturbance sites are referred to as pioneers or early successional species. In forests, these shade-intolerant species are able to photosynthesize at high rates and, as a result, grow quickly.

Detailed explanation-4: -During primary succession, organisms must start from scratch. First, lichens might attach themselves to rocks, and a few small plants able to live without much soil might appear. These are known as “pioneer species.”