Apopulation contains short plants and tall plants. the short plants are not able to compete with tall plants for sunight. the tall plants , however, are more susceptile to wind damage. which type of section are the plants experiencing

The plants are experiencing environmental competition. The larger plants are winning in the resource department in being able to hog the sunlight, but the smaller plants are succeeding in surviving the weather conditions. I suspect the larger plants will eventually die off leaving only the smaller plants if they grow in a particularly windy environment. 

Gravitational force i believe