Pioneer plant species could be described as those that

The answer is Pioneer plants are those that first colonize a particular place being the first settlers of a plant community.

Explanation:

The pioneer plants are the plants that first colonize a particular place, or that the human being has introduced into a physical place, being one of the first settlers of a plant community. Pioneer plants are more resistant to environmental changes since they need to be resistant and fast growing in order to survive in the frequently unfavorable conditions found in recently altered areas.

stress fractures occur largely in the feet and legs and are common in sports that require repetitive impact, primarily running/jumping sports such as gymnastics or track and field.

a covalent bond, specfically triple bond