Regulation: Sites of Special Scientific Interest (SSSIs)
This is a statutory designation, which means that unlike “Nature Reserve” and “Area of Outstanding Natural Beauty” it does actually affect what you are allowed to do in your woodland. It is intended to protect particular features of your land which are unusual, or unique, and/or particular living organisms which are threatened species. On the Natural England website you can discover which features of your own woodland are important. In the case of woods, these are very often near streams or boggy areas.
As with TPOs, it is wise to have a management plan agreed with the Forestry Commission to define the limits of what you are allowed to do. This is a bit of trouble (but without cost) but it is quite satisfying to know that your wood is special, and that in caring for it you are making a very significant contribution to conservation.