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How to balance forestry and biodiversity conservation – A view across Europe
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Re-introducing pine marten to English woodlands – regulating grey squirrel populations
A. Schuck
European Forest Institute, Bonn, Germany
Once a common small predator in English wood- lands, the pine marten (Martes martes) numbers declined dramatically during the nineteenth and
early twentieth century. This resulted from the combined impact of continued habitat loss, their valued fur, and an increase in predator control associated with the growth in Victorian game shooting estates. The pine marten thus became one of Britain’s rarest predators and considered func- tionally extinct in England. They did survive in small numbers but were not able to recolonise the land- scape even when their persecution stopped. The pine marten was given protected status in Ireland in the 1970s. Britain placed martens under protec- tion in the 1980s.
Fig. 1. Red squirrel (Sciurus vulgaris), affected by the spread of the squirrel pox virus, which is carried and dispersed by the introduced grey squirrel (Photo: Ulrich Wasem).
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Grey squirrels (Sciurus carolinensis) were first introduced to England from North America in the 1870s, i.e. during the period when pine martens were persecuted and populations were in dramatic decline. Owing to the lack of predators, the grey squirrel populations rapidly increased and by the early- to mid-twentieth century had spread across the whole of Great Britain. The first reports of grey squirrels introduced to continental Europe date to 1948 in Italy, where a population has become established.
In addition to habitat loss, the grey squirrel is one main reason for the decline of the endemic red squirrel (Sciurus vulgaris). The squirrel pox virus, carried by grey squirrels without causing them harm, is fatal to red squirrels and leads to severe decline in populations once present. Evidence also suggests that grey squirrels competitively exclude red squirrels, not by occupying or driving them out of an area, but rather by monopolising food resources. Thus, the red squirrel is officially classed as near threatened in England, Wales, and North- ern Ireland.
There have been numerous attempts to exter- minate grey squirrels from prime red squirrel habi- tats, but such measures are costly, need to be applied over the long term, and have very often failed. Because of conservation efforts and an increasing population of pine marten, the fortunes for the red squirrels have shifted. Studies in the Central and Highland regions of Scotland are con- firming that grey squirrel populations tend to col- lapse if there is a sufficient number of pine martens in a particular habitat. Grey squirrels, which often feed on the ground, are not very agile and thus easy prey for pine martens. Red squirrels are lighter and more agile, and can more effectively escape their predators. The decline of grey squirrels in turn releases red squirrels from the pressures of food competition and reduces the probability of disease infection. Consequently, their population numbers are increasing.
Currently substantial funds are spent on meas- ures for grey squirrel suppression. The re-introduc- tion of the pine marten provides a viable option to support these measures, and not only for red squir- rel recovery, but also for limiting damages caused to broadleaved trees by the grey squirrel. However, there are costs to be weighed against these bene- fits. As pine martens are good climbers they may enter pheasant or poultry pens and cause consider-
able damage. So, it will be important to ensure that the benefits they bring to forests and their support to preserving endemic species is in balance with other interests.
A balanced strategy is needed that builds on scientific evidence while taking into consideration the concerns and demands put forward by differ- ent stakeholders. Well-designed, equal partner- ships between landowners, foresters, conservation bodies, and other parties will surely positively affect the attitudes towards re-introducing the pine mar- ten. Allowing predators such as the pine marten to re-establish as an integral part of forest ecosystems will contribute also to making woodlands more resilient in the years to come.
Consulted literature
Bertolino, S.; Piero, G., 2003: Spread and attempted erad- ication of the grey squirrel (Sciurus carolinensis) in Italy, and consequences for the red squirrel (Sciurus vulgaris) in Eurasia. Biological Conservation 109: 351–358.
https://doi.org/10.1016/S0006-3207(02)00161-1 CABI 2020: Sciurus carolinensis. In: Invasive Species Com-
pendium. CAB International, Wallingford, UK.
https://www.cabi.org/isc
Sheehy, E.; Sutherland, C.; O’Reilly, C.; Lambin, X., 2018:
The enemy of my enemy is my friend: native pine mar- ten recovery reverses the decline of the red squirrel by suppressing grey squirrel populations. Proceedings of the Royal Society B: Biological Sciences 285: 20172603.
https://doi.org/10.1098/rspb.2017.2603
Spencer, J.; Stringer, A.P.; Sheehy, E., 2018: Martens, squir- rels and forestry – The return of the pine marten to low- land England and Wales. Quarterly Journal of Forestry 112, 4: 257–261.
Stringer, A.P.; MacPherson, J.; Carter, S.; Gill, R.; Ambro- se-Oji, B.; Wilson, R.; Kelsall, P.; Feirn, W.G.; Galbraith, L.C.; Hilário, C.M.; Parry, G.; Taylor, A., 2018: The feasi- bility of reintroducing pine martens (Martes martes) to the Forest of Dean and lower Wye Valley. Forestry Com- mission England; The Wildlife Trusts – Gloucestershire;
Vincent Wildlife Trust. 107 p.
