Final answer:
Deforestation, urbanization, overgrazing, and agriculture expansion are human activities that lead to the formation of plagioclimax communities, impacting biodiversity and ecological succession.
Step-by-step explanation:
Human activities that contribute to the formation of plagioclimax communities can include deforestation, urbanization, overgrazing, and agriculture expansion. These activities alter the natural succession of ecosystems, leading to a biologically simplified community that maintains itself only with ongoing human intervention. For example, deforestation can lead to habitat loss which directly affects biodiversity and ecological balance. Similarly, urbanization replaces natural landscapes with cities and infrastructure, while overgrazing by livestock can degrade soil and vegetation to an extent that the original ecosystem cannot recover. Lastly, the expansion of agriculture, which is a significant cause of habitat destruction, transforms diverse ecosystems into monocultures or farm fields.