The silviculture of mixed coniferous continuous cover stands in the Lowlands is now developing with the assistance of the large volume of experience and data available from central Europe and the increasing direct experience which is being gained in the UK. Data on stand structure and increment is beginning to be collected, at Stourhead (Western) Estate, for example.
The situation with stands dominated by pedunculate oak and/or ash is very different. These stands, often on heavy clay soils or soils over chalk, are common in southern England and north-east France but are virtually absent from the areas of central Europe where CCF has been developed. The classic oak forests of north central France are very different: sessile oak stands growing on sandy sites regenerated naturally but essentially even-aged in structure.
There is, therefore, little long term European experience and recent management of these stands in the UK consists of neglect or the haphazard application of a small-scale clear-fell and re-plant approach. The theoretical basis for management of these stands exists, however, and at Melbury and Rushmore Estates Andy Poore (SelectFor) has been undertaking transformations of oak and ash dominated stands to CCF on a range of soil types over the last 10 years.
The impetus behind the application of Continuous Cover principles to these stands are many:
- The need to achieve cost-effective regeneration - current small scale plantation techniques are very expensive.
- A desire to improve stand performance - closed mature oak and ash stands often have very low timber increment.
- The need to create more structurally diverse stands for biodiversity objectives incorporating the use of natural regeneration and low to moderate degrees of change.
- The necessity of regenerating these stands without major disruption to the landscape or to the sporting value of the woods. This is a particular challenge with small stands which make up the majority of the resource.
The major question which this project aims to address is whether permanently irregular structures can be created with these species and what such structures might look like. (The alternative would be some form of irregular shelterwood but on rich lowland sites the difficulty of such an approach should not be underestimated).
The aim of the first part of the project, which was completed in spring 2004, was to put in place a series of research areas which will produce information on stand structure and stand performance in terms of timber increment. There are few examples of systematically managed, irregular stands of these species in the UK, but a range of stands on the Melbury Estate in north-west Dorset have been subject to interventions over the last 10 years designed to move the structure towards a structure likely to achieve permanent irregularity.
Part 2 of the project will consider the silviculture of Continuous Cover oak/ash stands in detail in the light of recent experience and research in north-eastern France. Recently a major project into the silviculture of irregular oak stands has been established in the Franche-Compte Region by ENGREF, the leading forest research institute in Nancy, PRO SILVA France and the AFI (the ‘Association of Irregular High Forest’). A visit is being arranged next spring with the major participants in this project and we will be able to match the site types with those we are looking at in Southern England.