Woodland thinning on Putney Heath

A healthy woodland should contain the full range of structures in balance which would provide a ground layer, field layer, shrub layer and canopy. By providing openings within the woodland canopy and therefore allowing light to penetrate to the woodland floor, the provision of open space provides the opportunity for the growth of nectar bearing shrubs and flowering plants which are so vital for the development of invertebrate variety and biomass.

As much of the Commons’ woodland has developed through a process of natural succession, the result has been the establishment of large areas of even-aged trees that are tightly spaced together, and which therefore prevent the growth of new trees and the creation of a well-developed woodland structure. In order to create a more diverse age structure within the Commons woodland, there is a need for tree thinning to be carried out in the more heavily shaded areas from time to time.

One way to achieve this is through the reduction of the invasive non-native trees species.  These include Turkey oak (Quercus cerris), sycamore (Acer pseudoplatanus), Holm oak (Quercus ilex) and rhododendron (Rhododendron ponticum).

Turkey oak is a hardy, fast growing species of oak that was first introduced to the British Isles in 1735. Since then, it has aggressively colonized many parts of the countryside leading to the displacement of native flora. 

It is far less valuable to British wildlife than our native English oak (Quercus robur) and it is often considered to be a pest because:

·         it is so fast growing

·         it will hybridise with the English oak

·         it is host to the knopper gall wasp (Andricus quercuscalicis).

The knopper gall wasp is a recent introduction to the British Isles, first arriving in the 1960s and now found throughout England, Wales and Scotland.

_{Knopper gall on the acorn of an English oak tree on the Commons}

As part of its life-cycle, the knopper gall wasp migrates from its host tree, the Turkey oak, to English oak, where it lays eggs on the buds of the developing acorns leading to the formation of a sticky formation (gall) which can damage the acorns of the English oak and impact on its ability to reproduce successfully. According to Imperial College London, knopper galls can destroy about 50% of the annual acorn crop but in some years, up to 100% of the crop can be lost to these wasps.

Ring Barking

To help manage areas of the Commons which have suffered from the colonisation of a high number of Turkey oak, the Commons’ Maintenance Team have carried out “ring barking”, rather than felling, on selected trees in the woodland behind Curling Pond and the woodland adjacent to the top of Jerry’s Hill.

^{Location of ring barking marked in red}

^{Ring barking of invasive Turkey oak on Putney Heath}

Ring barking, which may sometimes be referred to as “girdling”, is the removal of a complete band of bark from around a trunk or branch of a tree.  It is a traditional method that has been used for centuries as a means of clearing woodland and is often actively encouraged by wildlife conservationists.  

Rather than our team going in and felling trees, potentially leaving a scarred area of woodland, this method creates a reservoir of dead standing trees which will disintegrate over time.  It is a natural process similar to a tree dying slowly of disease and it creates a rich and diverse habitat for a wide range of insects and fungi, as well as woodpeckers and other woodland birds.  In particular, dead wood is invaluable for the increasingly rare stag beetle (Lucanus cervus) – the presence of Stag beetles on the Commons is a primary reason for our designation as a Special Area of Conservation (SAC).

If you have any further queries, please contact the Ranger's Office