Trees support a wide variety of other organisms, ranging from bacteria and viruses to birds and insects. Although these may affect individual trees in terms of health and lifespan, they rarely pose a threat to entire woodlands, due to the natural system of checks and balances present in a woodland ecosystem. Individual trees within a woodland which die from fungal attack or other causes provide habitats which are essential for the survival of many other organisms.
Treatment of pests and diseases is very important in commercial woodlands, orchards and for some amenity trees. Detailed information on pests and diseases are available in publications from the Forestry Commission, and immediate advice is available over the phone from the Tree Advice Trust, who also issue an occasional series of ‘Tree Damage Alerts’, which contain topical advice on many aspects of tree care.
The Asian longhorn Beetle (see below) is currently causing concern.
Pests
Mammals
Voles, rabbits, hares, deer and domestic stock can all severely damage young trees, including newly planted trees, naturally regenerated trees, and coppice shoots. Methods of protection are given here.
The main threat to established trees is from the grey squirrel, which can severely damage or kill trees between 5 and 40 years old, by stripping the bark anywhere on the main stem from the base to the crown. Woodlands dominated by beech, oak, sycamore and sweet chestnut are most vulnerable. Woodlands containing these species, but which are dominated by less vulnerable species are less likely to be attacked. Damage occurs between the end of April and the end of July, with the worst damage occurring about the third week in June. Damage is thought to be caused by frustrated young males with insufficient territory.
Where populations of squirrels reach 12 or more per hectare, control measures need to be taken. The aim should be to reduce the population to about 2 dominant males per hectare, who will keep out invaders. If the entire population is destroyed, other squirrels will quickly move in. Squirrels have no natural predators, and the only effective method of control is to use hoppers baited with grain treated with Warfarin. control should start from March 15th, well before damage commences. There are strict regulations regarding the use of Warfarin and a national proficiency Test certificate is required for its use. advice should be sought from the local office of the Forestry Commission, who will also have details of any local Grey Squirrel Management Group.
Deer populations have increased rapidly in the last few decades, and they are over-abundant in many areas. Deer can cause damage to young trees through browsing of foliage and fraying of the bark. Muntjac deer can also cause significant damage to woodland flora. Although newly planted trees can be protected, the only way to ensure the success of natural regeneration, coppicing and the development of woodland flora is by culling of the deer population. This will only be effective if neighbouring areas are similarly managed, as deer can range over large areas. contact your local office of the Forestry commission for advice.
Insects
Most outbreaks of insect pests collapse as parasites and predators reach effective population levels. Insects and insect borne diseases are rarely a problem in mixed woodlands, although particular species may be vulnerable. Dutch Elm Disease, which caused the loss of most elms in England in the mid-1970s, was caused by a pathogen carried by the elm bark beetle.
The Asian longhorn Beetle is currently causing concern as it can attack and kill healthy trees. The larvae feed under the bark and then burrow into the wood, and most hardwood species are at risk. Symptoms include foliage turning yellow and/or red, and premature leaf drop. Also look for piles of coarse sawdust at the base of the tree or where branches meet the trunk. Plant Health Regulations were brought into force in 1999 to try and stop further import of this beetle via wood packaging from China and elsewhere. Contact your local tree officer, Forestry Commission office or the Tree Advice Trust for advice.
The best way to keep insect populations in balance is to encourage insect-eating birds through provision of habitat within the woodland. Nesting boxes are a useful way to encourage bird species, especially when the woodland is young and lacks natural nest sites.
