4: Percentage of native species in the canopy

What information does the survey provide and why does it matter?

In every native woodland area, an estimate was made of the overall percentage cover of the upper canopy which was made up of native species. This was assessed for the uppermost layer present at any part of the wood, which included any areas of established regeneration or shrub layers where there were no larger trees above them.

A value of at least 90% native species in any canopy layer has been taken as a reasonable average measure of good condition for biodiversity and has been included in the native woodland condition indicator (see Native Woodland Condition Indicator).

Moving to a more completely native composition is usually preferable for biodiversity. However sometimes it is not feasible to aim for total removal of non-native species, e.g. on inaccessible sites. And in some situations it can be better for biodiversity to retain specific mature non-native trees at least in the short term, e.g. to maintain canopy structure and shade or a supply of dead wood and tree holes, especially where the non-native species are not actively regenerating.

The various objectives of management of woodland need to be factored in and site management planning should assess what is the suitable composition of non-natives for each woodland, as well as the pace of change where they are to be phased out.

Policy relevance

Classifying woods as native requires 50% or more of canopy cover to be composed of native species. Targets for improving condition for native woods include removing or reducing the non-native tree and shrub species share.

How can the NWSS data be used?

Type of useNationalRegional/local authorityLandscape/site scale
Overall assessment of nativeness of composition to include in regional/national analyses and condition indicator Yes Yes Yes