Firstly, for VAT purposes this is farming i.e. agricultural produce (Annex A explains what is agricultural produce and this includes forestry). Having income only from agricultural produce, you are treated as an unregistered farmer and claim VAT back as you stated for certain activities using Form 58.
You can of course elect to register, but technically this can't be backdated to before the current VAT period. However, this can be overcome by a good tax consultant. If you elect, you are treated the same as any other VAT registered person.
If you are selling to VAT registered businesses and you only have income from forestry, you should register. If you have sales from eg livestock you may want to keep that source of income unregistered. You may need to keep your forestry trade seperate.