a) The rationale for strongholds
We hope we will never need to rely on strongholds to conserve red squirrels. If the control of grey squirrels is as successful as we hope, then grey squirrels will largely be kept apart from red squirrels and the current distribution of red squirrels can at least be maintained, if not expanded.
Grey squirrels have not yet been recorded in any of the stronghold sites, but it is not possible to guarantee that we can prevent this very mobile and resourceful species from spreading beyond its current range. If we want to secure the future of red squirrels in mainland Scotland, it is important that, as well as making every effort to control grey squirrels, we put in place additional safeguards to protect red squirrels.
As well as being sites for the enhanced conservation of red squirrels, strongholds are a contingency plan in case grey squirrels spread further in Scotland. Under a scenario where containing natural dispersal had been shown not to work, strongholds would be the last refuges in which red squirrels are conserved, with grey squirrel control efforts being focussed in and around these sites to the exclusion of others.
b) How strongholds will work
Research has shown that in some habitats, red squirrels are able to sustain a population even in the presence of grey squirrels. In these forests, which are distinguished by their lack of large seeded broadleaves (especially oak, but also beech, chestnuts and hazel), grey squirrels cannot normally establish themselves. They may travel from nearby areas to these habitats to feed, but they do not stay to breed.
By selecting the largest and, where possible, most defendable of these forests we believe that we have identified a series of sites which give red squirrels the best possible chance under a Scotland-wide grey squirrel scenario.
To ensure that these sites remain relatively unattractive to grey squirrels, and to increase their value for red squirrels, we will work with land managers to support appropriate management activity over coming decades:
- We will encourage management which improves the carrying capacity of the site for red squirrels, for example:
- Retaining some conifers into old age, to provide additional food
- Diversifying the species and ages of trees to ensure that there is food for red squirrels every year (different species of conifers tend to cone at different times, with differing gaps between coning years)
- Making sure the woods are well connected so that red squirrels can use the whole habitat (though see Squirrelpox concerns, below)
- Using continuous cover forestry techniques (see What will strongholds mean for land management?).
- We will plan to prevent any future grey squirrel colonisation of the site by:
- Discouraging the establishment of large seeded broadleaves on or near the site where these could support resident grey squirrel populations
- Discouraging the development of woodland networks which could assist grey squirrels to reach the strongholds
- Identifying priority areas for grey squirrel control around the site, and within the site should this prove necessary
- Monitoring the presence of greys.
Anecdotal evidence from large conifer forests in south Scotland and northern England which have the characteristics of strongholds suggests that woods managed in this way can give red squirrels a competitive advantage over grey squirrels. More detail on the management of strongholds can be found in section 6, What will strongholds mean for land management?.
c) Squirrelpox concerns
Squirrelpox virus is an added complication for the functioning of strongholds. Most grey squirrels in England carry the virus and in recent years seropositive grey squirrels and red squirrels suffering from the symptoms of squirrelpox have been found in parts of south Scotland (see squirrelpox map).
It is not yet known how grey squirrels pass the virus to red squirrels, but we do know that infected red squirrels normally die within 15 days. The rate of displacement of red squirrels by grey squirrels in the presence of squirrelpox is some 15-20 times faster than in areas without the virus.
If current efforts do not prevent squirrelpox – currently only found in south Scotland – from spreading to the wider Scottish grey squirrel population, then over the long term red squirrels in strongholds will be at risk from the virus. Local control of grey squirrels is likely to be required to prevent infected grey squirrels from coming into contact with red squirrels.
In extremely large forests (such as Kielder forest in England) models suggest that the speed at which the virus kills red squirrels might, paradoxically, save much of the population from coming into contact with the virus. We do not yet know whether the stronghold woods will be large enough for this to happen. We propose to model the likely progress of the virus within those strongholds most at risk. This will enable us to see if the forest can be managed in such a way as to limit the spread of the virus.
d) Strongholds – not very good habitat for red squirrels?
Many of the stronghold sites do not currently hold very large populations of red squirrels; indeed, sites with higher populations of red squirrels are often found nearby. Some of these have been identified as Priority Woodlands in previous work (Poulsom et al, 2005), however, the very characteristics of sites which make them favourable for red squirrels (for example presence of hazel, beech, chestnut trees, supplementary feeding) may also make a site vulnerable to grey squirrel incursion, should grey squirrels reach the area.
e) Strongholds as ‘islands’?
If grey squirrels displace red squirrels throughout mainland Scotland, and red squirrels are only found in strongholds and on offshore islands such as Arran, then red squirrel populations will effectively be isolated from one another in island-like refuges.
In theory this could lead to problems of in-breeding and could leave individual populations vulnerable to local extinction. However, even a stronghold with a red squirrel population of only 0.25 animals per hectare would have a population of at least 500 red squirrels, a relatively large gene pool – and translocation of animals between strongholds would be possible.
f) Strongholds in a changing climate
The state of our knowledge on climate change has not allowed it to be a factor in selecting strongholds, but a changing climate will certainly affect their management. Research into the impacts of climate change on Scottish forestry (PDF) shows likely future climate scenarios and suggests how forestry will need to adapt in the future. In relation to strongholds:
- Continuous cover forestry techniques and greater use of mixtures of species (as recommended for strongholds) are central to the way that wider Scottish forestry should adapt to a changing climate
- The distribution of species such as oak and beech is likely to change, with the potential for more widespread natural regeneration of both of these species in some areas. It may become more difficult to prevent regeneration of these species within some strongholds
- Conversely, wetter summers in western Scotland may make acorn and beechmast years more infrequent and so reduce grey squirrels’ competitive ability
- Milder winters and longer growing seasons may increase over-winter survival of pests, and may increase the number of generations in one year. There is no evidence that these changes will favour one squirrel species over the other, but the more adaptable grey squirrel is unlikely to be disadvantaged.
g) If they are so good, why not have more of them?
It is appropriate to limit the total number and area of sites because of the potential conflict which some of the prescriptions (especially restriction on large seeded broadleaves) have with other management objectives, including management for other habitats and species.
Consultation questions relevant to this section:
1. Do you agree with the rationale and justification for strongholds? If not, why not?
2. Do you think that the management approach for strongholds is appropriate to achieve their objectives? If not, why not?
- Continue to 5. Where are the red squirrel strongholds?
