As you say that you are doing Preparation for Indian Forest Services (IFS). There are many books for Preparation for Indian Forest Services (IFS). Here I am providing you name of some of best reference books for Preparation for Indian Forest Services (IFS). These are as follows:

Indian Forestry : A Breakthrough Approach to Forest Service 3rd Revised Edition null
By Manikandan K

UPSCIFS ExamAgriculture (Including Paper I & II) Main Exam Guide (English) Paperback
By Gupta R

UPSCIFS Compulsory (Paper I & II) Main Exam Guide (English) Paperback
By R. Gupta's

UPSCIFS ExamBotany (Including Paper I & II) Main Exam Guide (English) Paperback
By Ramesh Publishing House


IFS Indian Forest Service Zoology (English) Paperback
By Gupta R


UPSCIFS Forestry Main Guide (English) Paperback
By RPH Editorial Board


UPSCIFS ExamMathematics (Including Paper I & II) Main Exam Guide (English) Paperback
By Gupta's, R.