Woody weeds are less harmful than grasses to the growth of young trees. A continuous cover of vigorous woody shrubs will, however, compete strongly with young trees if the soil is very poor, as water and nutrients will be in short supply.
In woodland planting schemes where the primary aim is conservation and amenity, any native shrubs and trees which colonise the planted area are usually desirable, as they provide greater variety of species, structure and cover. It may be necessary, however, to control them for several reasons. These include keeping glades and rides open, allowing the more desirable trees to thrive, maintaining a full range of woodland structure, and allowing access for management and recreation. Too dense regeneration will result in spindly, unstable trees, heavy shade and a poor ground flora.
Certain invasive introduced species such as sycamore and rhododendron, and invasive native species such as birch, willow, elder and wayfaring tree, may need controlling. Rhododendron can be a huge problem in woodlands on acid soils, as it propagates vigorously, both thrives in and casts heavy shade, and creates toxic conditions in the soil when its leaves rot and fall.
If you cut woody weeds by hand, you will normally need to remove the stump or treat it to prevent regrowth. you can remove the stump by hand or winch, or kill it with a herbicide. Where deer populations are high, you may find that by protecting the desired species against deer, the unwanted sycamore, birch or willow regrowth is heavily browsed, so reducing its competitiveness.
Saplings and other unwanted woody growth can be killed by ring-barking the stem. This will leave the dead growth in position, which may be undesirable, looks unattractive and may be unsafe. On the other hand, the dead growth can be useful in screening and protecting the desirable species, and also continues to provide some cover for wildlife. Regrowth of the ring-barked plants from the base is also less vigorous than if the stem is severed. Ring-barking is simple to do on single-stemmed saplings, but awkward on multi-stemmed shrubs. Ring-barking which is not thorough can stimulate the plant to produce an unusually large crop of seed.
Another alternative for controlling scrub, is to cut it at the base and then lay the cut stems over the stools. This can be done with hawthorn, blackthorn, willow or sycamore to make an informal laid barrier or thicket, to protect and screen new plantings. This will also suppress the scrub growth for a few years, by which time the desirable trees should have grown sufficiently to shade out the unwanted species. The procedure of cutting and laying is very much quicker than cutting and removing or burning plus stump removal. However, the unkempt and tangled appearance of the developing woodland may make it unsuitable for sites with public access.
The control of one year old seedlings by pulling or herbicide application, and removal of seeding trees, can also be useful measures.
Techniques for cutting smaller trees and shrubs are covered at the end of this chapter.
Herbicides for woody weeds
Herbicides can be applied direct to the foliage of shrubs which are in leaf, but this is not suitable work for volunteer groups. For details of professional products see The Use of Herbicides in the Forest (Willoughby and Dewar, 1995).
Herbicides can also be applied to the cut stump to prevent regrowth. This can be a useful technique as it only affects the treated stump, and there is no unsightly dead material left standing. It is labour intensive, as clearance still has to be done, and the cut material removed, stacked or burned. Stump treatment avoids the ground disturbance caused by stump removal, although the cut stumps may be a hazard for walkers. Where machinery is to be used, for example to mow woodland glades or edges, the cut stumps must be below the operating clearance of the machine.
Ammonium sulphamate (Amcide or Root-out), is an amateur herbicide which can be applied to cut stumps. Glyphosate (Roundup tough weed killer) is also effective on cut stumps. Follow the manufacturer ’s instructions regarding application.
