Fact 1: Erosion of soil has a negative impact on the environment. Fact 2: Forest environments collapse. Given the two facts above, what has a negative impact on forests?

Available choices:
[1]. local fauna.
[2]. local flora.
[3]. humans disturb it.
[4]. deforestation.
[5]. erosion of soil.
[6]. smallpox.
[7]. local wildlife.
[8]. vehicles.
The answer is:
[5].