Guest blog by Nick Littlewood, Lecturer in Wildlife Conservation Management at SRUC, and Mark Hancock, Senior Conservation Scientist, RSPB
We’ve known for some time that planting non-native conifer trees on blanket bog is bad news for biodiversity. As well as the habitat directly impacted, the effects of plantations, and especially of the generalist predators that they support, extend out across unplanted peatland. What might explain these patterns? Might generalist predators be strongly influenced by abundance of key prey animals, like voles and other small mammals?
Thanks to research just published, studying small mammals in this habitat using a novel camera-trapping approach, we now know more about the link between plantations and the small mammal prey likely to underpin predator populations. This work helps to show what can be gained by restoring such deep-peat plantations back to blanket bog.
Effect of plantations on mammals
In a natural, undamaged state, extensive areas of blanket bog support few small mammals. The generalist mammalian predators that might consume small mammals, such as Foxes, Weasels, Stoats and Pine Martens, also struggle to survive here without shelter and year-round availability of prey.
Peatland restoration from conifer plantations is a long-term process. This is a 14-year-old ex-forestry restoration area at Forsinard Flows RSPB Reserve © Mark Hancock
Recently, RSPB researchers showed that conifer plantations at Forsinard Flows RSPB reserve, at the heart of the Flow Country in northern Scotland, supported increased populations of these predatory species. There was evidence suggesting that these mammals also travelled out across adjacent unplanted bog, where they might predate nests and broods of ground nesting birds, especially waders, for which the area is internationally important. The ecological footprint of the plantations could therefore extend well beyond the immediate area planted, as found in earlier wader studies in the area.
Now, through research just published in the European Journal of Wildlife Research, we have demonstrated that the remaining typical Flow Country plantations (of non-native conifers on deep peat) host far larger populations of small mammals, especially voles and mice, than does undamaged bog. Given that these are key prey animals, present year-round, it helps explain how mammalian predator populations are sustained in these forestry plantations.
We studied small mammals through a simple but novel camera trapping technique. This involves attaching a close-focus lens over the front of the camera and strapping it to an open-ended box into which small mammals were attracted by bait.
With simple adaptations, camera traps can obtain high-quality images and video of small mammals, such as this Field Vole © Nick Littlewood
Using this technique, we found that undamaged bog hosted some Pygmy and Common Shrews but we detected no voles or mice at all in this waterlogged habitat. On the other hand, in forestry plantations, we found small mammals in most of the sample sites, with detections dominated by Bank Voles and Wood Mice. Voles and mice are often favoured as prey items by predatory mammals. Shrews are far less important, being distasteful and really tiny (e.g. a pygmy shrew is perhaps only one eighth the weight of a vole). Therefore, we found that these deep-peat forestry plantations tended to host much more prey suitable for mammalian predators, than comparable open bog areas.
Small mammal camera trap box with camera trap attached at right hand end. The close focus lens, attached with blue-tac, is just visible here © Nick Littlewood
Restoration (tree removal)
Peatland restoration in ex-forestry sites in the Flow Country focusses on removing trees and reversing the drainage that had been installed as part of the tree planting process. In areas where trees had been removed between 2 and 17 years previously, we found that the chance of detecting small mammals was around half of that in plantation but still almost four times higher than in bog.
Thus, whilst tree removal reduced the availability of prey for predatory mammals, the level was nonetheless higher than in surrounding blanket bog, for several years after restoration began. We expect that small mammal communities in ex-forestry restoration areas will increasingly align with those of bogs, since the vegetation, which strongly influences small mammals, shows a gradual recovery towards bog-like conditions.
Camera trapping for small mammals
Studies of small mammals typically entail live trapping. This is time consuming, as it involves visiting traps every few hours, and entails welfare implications for the animals caught, including some mortality risk. The camera trapping technique demonstrated in this new study has minimal welfare issues and there is no requirement to retrieve cameras after a specific time period. This makes it ideal for use in remote and expansive sites, such as the Flow Country.
Generalist predators, such as Pine Martens, may be sustained in conifer plantations on deep peat by availability of voles and mice as prey © Nick Littlewood
Exploiting this new technique, we have shown that plantation removal should benefit ground nesting birds, by reducing resources available to sustain predatory mammals, but with some time-lag after restoration begins. This new camera-trapping approach has lots of potential for studying small mammals in other environments, such as surveying invasive species on seabird islands.
This small mammal camera trapping research was carried out by SRUC, the James Hutton Institute, North East Scotland Biodiversity Partnership, The Mammal Society, University of Cambridge and RSPB.
Nick Littlewood (SRUC) and Mark Hancock (RSPB)
Littlewood, N.A., Hancock, M.H., Newey, S., Shackelford, G. and Toney, T. (2021) Use of a novel camera trapping approach to measure small mammal responses to peatland restoration. European Journal of Wildlife Research, 67:12.
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Thanks for asking this great question. This is not something that we have looked at, so we don't know for sure, but we can speculate based on the situation at Forsinard. Spruce trees do sometimes produce abundant crops of seeds - the quantity varies each year but likely these will form a significant part of the diet in at least some winters. Some of the Forsinard plantations also have Lodgepole Pines, so again a source of seeds.
Additionally, plantation areas are bisected by grassy rides. These are much grassier than open bog areas, as the land is affected by drainage from when the plantation was established and by fertilizer application as part of the forestry process. So this too will provide some resources for rodents.
Nick
Very interesting, thank you. Shows how one plantation in the middle of blanket bog can reduce the birds nesting over a huge area. From what I remember of volunteering at Forsinard that will have a massive effect.
One question though: what do the rodents eat in a plantation? You would not have thought they provided year round food.
Great photo of the restoration site too, with all that bog cotton.