Question

what is the role of pioneer species in secondary succession?
to better the environment to allow other species to take over
to establish a climax community
to create harsh environmental conditions

Explanation:

Pioneer species in secondary succession improve the environment. They break down soil, add nutrients, and make it more habitable. This allows other species to colonize and succeed them. A climax community is the final stable stage, not the role of pioneer species. They do not create harsh conditions; instead, they ameliorate them.

Answer:

to better the environment to allow other species to take over