Which of the following is considered a pioneer species in primary succession?

Mosses and lichens are considered pioneer species in primary succession because they are among the first organisms to colonize bare rock or land that has been disrupted by events such as volcanic eruptions or glacial retreats. These organisms are well-adapted to harsh conditions where soil is absent, and they play a critical role in the ecological process of soil formation.

As they grow, mosses and lichens contribute organic matter when they die, slowly breaking down rock surfaces and creating a thin layer of soil. This initial soil layer enables more complex plants to establish themselves in the area over time. By enhancing soil quality and stabilizing the substrate, these pioneer species pave the way for other species to succeed them, eventually leading to a more biodiverse ecosystem.

In contrast, while weeds and grasses can thrive in disturbed environments, they are typically associated with secondary succession and not primary. Oak and pine trees, being later successional organisms that require more developed soil, do not play a role in the very initial stages of primary succession.