Forestry is an activity that is exclusive to Farming Simulator 15. It offers a quick, large profit, but can be more labor intensive because you cannot hire a worker to help.
The cost of trees is the same on normal, $7000. But the profits per tree vary greatly from about a 50% loss ($3500 selling price) to a 65% profit ($11,500 selling price). If your on easy or hard this can vary greatly. From indications easy can net you over $100,000 for a tree to hard where you can barely get a profit at all buying trees to harvest.