Standing deadwood is a fantastic habitat.
It is the start of the woodland eco-system. Many centipedes and millipedes are among the many thousands of insects and invertebrates that live on standing deadwood.
It is suggested that Oak are good trees to ring bark as their deadwood has greatest habitat value as it supports the greatest number of species. Birch also has good habitat value but it is not a long lasting. Ash on the other hand supports far less life. UKWAS (UK Woodland Assurance Standard) recommends stems greater than 20cm diameter.
It has been recommended to ring bark groups of trees in relative proximately as the creatures relying on this type of habitat are small and so may not easily travel larger distances.
I feel that there are many woodlands that are too small to qualify for Forestry Commission grants but that would benefit from more standing deadwood as they are relatively young woodlands or have been clearfelled in the relatively recent past.