Here is the idea. This can be in different perspectives...
First off, farming is the production of living things to sell for profit. Usually dealing with plants or animals. Many things are considered farming. Examples: wool production, hay production, honey production, christmas tree growing, rice production, produce production, orchard growing, flower and ornamental plant production, and even some timber industries that grow trees for cutting purposes.
Logging is going into nature produced forests or woodlands to collect timber. The trees grow naturally and not by humans. This takes away from the farming perspective. This is basically taking advantage of nature's resources. This is just like coal mining, oil drilling, diamond mining, and salt industries. Even some fish production is like this too because the fish are taken from their natural habitat to be sold for profit.
Farming is raising and we are not harming nature by harvesting plants. Instead we are taking away natural places to benefit us and turn them into farm land. Logging is a once and done thing, we go in cut trees, sell timber, and keep moving.