During primary succession, which organisms are the first to colonize the barren environment?

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In primary succession the first organisms to establish themselves are pioneer species. These organisms are able to survive in very harsh, barren conditions with little or no soil. They begin the process of soil formation by breaking down rock and adding organic matter as they grow and die, which gradually makes the environment more hospitable for other species. This initial colonization sets the stage for subsequent ecological development, leading to greater biodiversity over time.

The other terms don’t describe the first colonizers. Trophic cascade refers to how changes at one level of the food web affect other levels, not who first colonizes an area. Phase shift is a large, rapid change in ecosystem structure or function, rather than the identity of the organisms that start colonizing. Biomass is simply the total mass of living matter in an area, a measure, not a type of organism.