Tree work specifications list: basic guide to the common terms.
There is great variability amongst tree species in their capacity to tolerate various pruning treatments.

Crown reduction British Standards recommend a maximum percentage at any one time of 30% in volume to re- shape outline of the tree crown in height and spread,normally preserving the tree’s natural form. These cuts are normally small and should retain enough foliage to continue the photosynthetic task and healthy growth to defend against dysfunction.

Pollarding – To remove growth from a previously pollarded crown only scaffolding limbs remain or main stem. Can be done on early mature trees to create this growth form.

Crown Thinning – To thin the crown by reducing the volume by a max of 30% in volume not changing the structural outline of the tree crown.

Crown Lift – to remove lower branches from crown area to a desired height back to limbs or parent stem.

Dead wood – to remove dead and diseased growth/wood in the crown area.

Tree felling – tree removal to stump level.

There is UK law which protects trees and hedges; it must be ascertained whether the site is protected (conservation area) or the individual tree is by a Tree Preservation Order.

Large volumes of timber will require a forestry felling licence (normally woodland areas).

UK law also provides protection of bird species and their nest habitats alongside bats.

Particular attention must be given around sensitive times of nesting and breeding seasons and importance of deadwood, decay pocket habitats.

I have not provided an exhaustive list but these are the ones helpful for the most common enquiries.