Well.. First you should go through the past papers, jot down important/repetitive questions of both subjects.
For Forestry,
I havent started my preparation yet.. I am collecting data by surfing internet ( Journals, Reports,Research papers etc)
I haven't bought any book but my senior suggested me to buy
1. Forestry by Salman Hameed Kazmi
2. Agriculture and Forestry 2017 Edition By Muhammad Asif Malik

For Zoology,you should start preparation by consulting Msc books and also BSc books (for revising basic concepts).
Some of the best Zoology books are :
1. Zoology by Miller-Harley
2. Integrated principles of zoology,
3. Campbell Biology
4. Invertebrate zoology by P.S.Verma
5. Cell Biology, Genetics, Molecular Biology, Evolution and Ecology by P.S.Verma & V.K Agarwal

Most of them are easily available in soft form. I have a few of them,Let me know if you need.