Structural diversity can be increased by incorporating open areas and through phased felling and restocking to ensure that, over time, a varied woodland develops. As part of this, some trees can be left as long-term forest cover to produce standing and fallen deadwood. For woods of less than 10 hectares, internal diversity is less important – in these situations diversity can be considered in the context of the landscape setting. There are also some woodlands that derive their particular landscape character or biodiversity value from a principal species and in these situations a case for divergence from the Guidelines can be made.

Restocking
There is a presumption against the removal of woodland and the loss of forest cover in the UK, and it is normally the case that felling approval is granted subject to restocking. Restocking is required as a policy priority linked to a number of national and international commitments to prevent forest losses worldwide and to mitigate the effects of climate change. In Great Britain, the Forestry Commission in England and Scotland, and Natural Resources Wales, may serve a Restocking Notice, which requires restocking and establishment to take place.

https://www.forestry.gov.uk/pdf/FCFC001.pdf/$FILE/FCFC001.pdf

Restocking of harvested plantations should be far more carefully planned to rebalance the species mix and ensure delivery of public benefits for the public funding involved. This is also crucial as insurance against emerging pest and diseases (where undue dominance of one species comprises an unacceptable risk).

http://www.forestpolicygroup.org/wp-content/uploads/2014/08/...

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Note added at 1 hr (2018-02-18 14:06:19 GMT)
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- When an owner or tenant is convicted of an illegal felling, Forestry Commission Scotland can serve a Restocking Notice to restock the land concerned, or any other land as may be agreed;
- The owner or tenant must also maintain the replacement trees to acceptable standards for up to 10 years;
- If the conditions of a Felling Licence or a Restocking Notice are not complied with, Forestry Commission Scotland may issue an Enforcement Notice demanding you take action to meet the conditions;
- It is an offence not to obey an Enforcement Notice and can mean a possible fine of up to £5,000.

nd.forestry.gov.uk/supporting/grants-and-regulations/felling-licences/penalties