Tree and scrub control

To maintain open conditions in marshes, bogs and fens, control of woody growth may be necessary. Pine and birch can rapidly invade peat bogs. Water levels are reduced by evapo-transpiration, and the leaf litter adds unwanted nutrients to the bog. The trees also shade out bog species, and provide roosts for flocks of birds, whose droppings further enrich the bog. However, in other wetland areas, willow scrub, or carr, provides valuable habitat, and the need for clearance work should be carefully considered. An area of established, fairly stable carr should be left untouched, and control should only be undertaken if it is threatening remaining open areas.

There are various methods of controlling or removing trees on wetland areas. The softness of the ground and the fragility of the habitat are very significant factors which make clearance work difficult.

  1. Manual felling and extraction. Trees can be cut and the stumps grubbed up, using hand tools and winches. Alternatively, stumps can be killed with herbicide. The cut material can be left on site, burnt or removed for reuse or disposal. Techniques are described further below.
  2. Machine clearance. Various machines with low ground pressure have been developed for tree clearance and timber extraction on soft ground. Helicopters have also been used for lifting grubbed-up trees. This eliminates ground damage, but is expensive. See Bacon, John and Lord, Bob in Enact (Vol 4, No 3) for a summary of suitable machines and techniques.
  3. Ring-barking or chemical control. By removing a ring of bark, or injecting a suitable herbicide, trees can be killed while standing. Although quick to do, and causing no extraction damage, both techniques encourage the dying tree to produce masses of seed. The dead trees are unsightly and dangerous, remain as perches for roosting birds, and as they rot and fall, alter the surrounding habitat.

Cutting

  1. Follow basic safety precautions for use of hand tools. Only trained operators should use chain saws or brush cutters.
  2. Cutting after leaf-fall in autumn or winter is easier than working when trees are in leaf, and should minimise disturbance to birds and invertebrates. However, ground conditions are likely to be at their wettest, making access difficult and increasing damage to fragile ground. If possible, lower the water level to provide drier working conditions.
  3. Dispose of cut material according to management aims. Normally removal will be essential, to avoid the rotting material causing enrichment and suppressing the wetland flora. Great care must be taken during extraction that the habitat is not damaged by trampling and dragging. Where access is possible, a woodchipper will greatly reduce the bulk to be removed, so lessening the number of journeys required across the wetland habitat. If material has to be dragged or carried, confine trampling to the minimum of routes. Particularly vulnerable sections can be protected by laying a temporary track of poles and brushwood. Temporary boardwalks or trackways can also be hired from plant hire companies.
    Heaps of decaying wood are themselves good habitats if piled on ground of low conservation interest away from the wetland.
  4. If stumps are to be removed, cut them off about 1m (36″) high so they are easy to relocate and winch out.
  5. If stumps are to be treated with herbicide, this should be done immediately after cutting. If there is any delay, cut stumps to about 1m (36″) high so they can be relocated, and then cut again immediately before treating. Glyphosate is approved for stump treatment of woody plants.

Grubbing up

  1. Grubbing up trees and shrubs solves the stump problem without the use of herbicides, and, if whole trees can be removed and dragged away, may be quicker than cutting followed by stump treatment.
  2. Grubbing up may be difficult with larger trees, on very soft ground or at a distance from access and disposal points. In soft ground it will leave ‘craters’, which may make interesting habitats, although mowing or other later management work will be difficult. Depending on the soil, harrowing after tree removal will smooth the ground and encourage the quick regrowth of herbaceous plants, which can be maintained by periodic mowing.
  3. Use a sharp spade to grub up seedlings and small bushes. Use a mattock on slightly larger bushes or saplings, or an axe in deep peat which is free of stones. Cut all around the base and lever the stump out with mattocks and crowbars. Difficult stumps may require several people working together. It helps to use a winch which, if it does not enable you to pull a stump out directly, keeps it under strain and allows resisting roots to be cut through with a mattock or bow saw.

Wet grasslands

Wet grasslands are usually maintained by a combination of hydrological management, grazing and mowing. For further information see Burgess, Neil D and Hirons, Graham JM (1990) and Merritt, Anthony (1994).

Hydrological management

The alteration of water level by the use of sluices and channels is a traditional method of managing wet grasslands, which mimics the natural process of flooding but in a controlled way. Depending on the regime used, management of water level can be used to encourage growth of grass for grazing of stock, or to provide conditions for wading birds and wildfowl. Hydrological management can be used directly to control vegetation growth by flooding out unwanted species, or to provide conditions of bare mud on which a flush of annuals will grow. See the above references for further details.

Grazing

Grazing of stock is a useful method of managing larger areas of wet grassland, to maintain the mix of marginal, grassland and herbaceous species, and prevent the ingress of scrub. Grazing results in a patchy pattern of growth with areas of longer growth, together with short vegetation and bare, trampled and poached ground. This variety of habitat favours invertebrates and birds, and cannot be easily imitated by mowing. Cattle are the usual choice for wet grasslands, as sheep are prone to foot-rot if kept on wet ground. Grazing is only feasible if the land is fenced and has a water supply, and where there is a local farmer interested in using the land.

Mowing

Some wet grasslands were traditionally mown for hay in June or July. This provided a crop, and prevented the growth of unwanted woody species. The following flush of grass was then grazed in late summer.

Where the quality of the hay crop is not important, a later cut may be more beneficial for wildlife, after meadow plants have set seed and birds have fledged. Some strips can be left uncut each year in rotation to provide habitat for invertebrates and small mammals.

Even when the crop is not wanted, cuttings should be removed, to prevent the ground flora being suppressed. Small areas can be cut by hand with a scythe or strimmer, or using a rotary mower. Where ground conditions and access permit, larger areas can be cut by tractor and rotary or flail mower.

Chapters