Assessing the economic and conservation impacts of the pine marten, a recovering predator, non-native grey squirrels, and forest land management

Grey squirrels have proved to be one of the world's most damaging invasive alien species. Grey squirrels cause profound damage to forestry by eating bark from trees, and have driven native red squirrels to extinction in much of the UK through a combination of competition and transmission of squirrel pox virus. The impact on the UK forestry industry and conservation efforts is substantial. The annual cost of the damage to forests, and associated control efforts amounts to an estimated £ 40-50 million with at least and a further £ 1 million spent on red squirrel conservation in northern England and Scotland where red squirrels have not yet been driven to extinction.

To date, there has been no successful method developed for the long-term control (nor indeed eradication) of grey squirrel populations. Hitherto, prevention of damage to trees has relied largely on the use of warfarin, however approval for the use of warfarin as a plant protection product will be withdrawn in September 2015. The large and growing economic damage to commercial deciduous forestry has major long term implications for the makeup of the UK's landscape and rural economic activity. As a result of the combination of threats posed by grey squirrels, Chalara on ash and climate change, woodland owners (including CONFOR members, project partner #1) are now questioning the viability of attempting to grow any of the principle hardwood species in Britain.

The loss of red squirrels from most of England deprives much of the UK public from experiencing the interactions with a species with which they have strong cultural ties. Indeed, with the exception of a few, small, intensively managed red squirrel populations the red squirrel is now almost entirely absent from England and Wales. Its future relies on ongoing expenditure by the public purse and the activities of committed NGOs (in particular RSNE, project partner #2). A major concern is that the progress in red squirrel conservation achieved by the trapping and shooting of grey squirrels to date will be lost, if funding to maintain grey squirrel control cannot be sustained.

The recent discovery by Dr Sheehy that the recovery and spread of the native pine marten in Ireland has led to a major decline in grey, but not red, squirrels offers both hope of a solution and an exceptional cross-disciplinary training opportunity for a PhD student to tackle fundamental ecological issues with profound relevance to the forestry industry, rural economy and conservation.
The pine marten population was practically extinct, the Scottish population have recovered spectacularly in recent years, and are now just miles away from the English border, meaning natural recolonisation of England from the north is imminent. Conservation efforts in Wales are also underway by the VWT (project partner #3). The recovery and spread of the pine marten on mainland Britain offers unprecedented hope of a solution to the problems caused by grey squirrels. However, the recovery of a carnivore population will inevitably present challenges, especially when a species returns after an absence of many years. Land managers have become accustomed over generations to living in a predator-poor environment, in which certain practices can be easily maintained because predators are scarce, absent or can be legally controlled. Similarly, wild prey populations can become 'predator-naive', developing patterns of behaviour and reproductive output that are unsustainable in the presence of their natural predators. In this context, as pine martens are encouraged to recover, a period of adjustment will be required during which both human and wildlife populations adapt to a more natural environment. Inevitably conflicts will arise where the recovery of the predator population causes or threatens to cause loss to other stakeholders, or requires land-managers to undergo change in practices.