No, one has to clear these 4 papers..There is no optional subjects for Forest Ranger.
1.English. 2. General Mathematics 3. General Knowledge. 4. Islamic and Pakistan Studies.
P.S I had appeared for the post of Forest Ranger in September last year..All the papers were quite easy(for me mathematics was also difficult because i done Pre-Medical in Fsc although it was of Matric level) except General Knowledge..