Newly established forestry plantations are particularly vulnerable to damage by livestock and wild animals. The main problems are caused by animals that like to browse on the shoots of young plants i.e. sheep, deer, rabbits, hares and occasionally wild goats. Animal damage can result in stunted, forked and dead trees causing failure of a plantation which is costly to replace. Cattle will browse young trees but can also cause serious damage by trampling.
Depending on the species, young trees can remain susceptible to browsing for many years after planting. Repeated browsing can seriously check growth and it can take many years before trees are robust and tall enough to overcome its effects.
Tree species vary in their susceptibility to browsing. Sitka spruce is perhaps the most resistant of the common species planted in Irish forests, having a vigorous growth habit and strong sharp needles. Other conifers, however, such as Douglas fir and larch are very susceptible. Broadleaved species are all very susceptible and must be protected from the outset.
While deer can cause serious damage to young plantations they can also affect trees in the thicket and pole stages. Bark stripping of tree trunks is a common occurrence where deer numbers are high. The wood exposed in the scars can become infected, and as they heal the damaged wood is included in the lower trunk. This leads to a reduction in wood quality in the most valuable part of the tree. Control measures are fencing, using high deer fences, to exclude the animals from plantations and/or culling to reduce the population numbers.
The grey squirrel was introduced into Ireland at Castle Forbs in Co. Longford in 1911. Several pairs were given as a wedding present from the Duke of Buckingham to one of the daughters of the house. Originating in the Eastern North America, the squirrels have multiplied and have spread to nearly all counties east of the River Shannon and are spreading south. They are more aggressive than the native red squirrel and compete for food, but more importantly, they carry the squirrel pox virus for which red squirrel does not have immunity. Today they are threatening the survival of the red squirrel and now have the status of an invasive alien species.
The grey squirrel causes severe damage to commercial broadleaved plantations through stripping bark on branches and main stems as the crops pass from thicket to pole stage. Multiple forking of the main stem can occur as a result of the tree top dying back. Damage can be so severe that an entire plantation can be ruined for commercial timber production leaving it only fit for low value firewood.
Grey squirrels have few natural predators in Ireland but it has been observed that where the pine marten occurs that the grey squirrel is absent. Pine martens are known to prey on the grey squirrel in America but this has still to be confirmed in this country.
The spread of the grey squirrel is of major concern to both foresters and nature conservationists alike and research is ongoing to monitor the spread of the species to help in developing strategies for its control.
Control measures currently consist of shooting, trapping and using hoppers baited with cereals treated with the chemical pesticide warfarin.
Further information at: Controlling grey squirrel damage