Wild boar, through disturbing the soil, have a significant effect on forest ecosystems throughout their natural range in Europe and Asia. They cycle nutrients and minerals, expose subsoil invertebrates to predation by birds and other animals, create patches of bare soil used by invertebrates for burrows (e.g. mining bees, some species of beetles) and, in our own Caledonian Forest, create ideal conditions for germination of seedlings, especially Scots pine but also birch and other species.
They can also help to disperse tree seeds, through pushing them into the soil while rooting, or by eating them and “depositing” them elsewhere. At low densities they contribute to higher plant biodiversity by producing small scale disturbance across large areas which can be colonised by annual plants for instance.
There has been interest in using wild boar to control bracken, and this was one of the original drivers behind our introducing several captive wild boar to our Conservation Estate at Dundreggan in November 2009. Prior to this we were partners in the Giusachan Wild Boar Project in Glen Affric.
Initially we had 6 animals (all female) from two locations (Aigas and Highland Wildlife Park). They were in a 5.5ha enclosure, giving a density of 1.1 boar/ha (equivalent to 110/km2) for 2 years. The surviving four animals were moved in January 2012 to an adjacent area of 6.8ha (0.6 boar/ha or 60/km2). One animal died in February 2015 and in April 2015, the three remaining boar were given the freedom of the whole 12.3ha enclosure.
Our monitoring of the impact of our wild boar showed that their effect on dense stands of bracken was temporary and less than clear-cut. They also suggested that boar at higher than natural density may have a negative impact on some aspects of forest biodiversity. So in 2014 we decided not to pursue a breeding programme and to reduce the density that we kept our boar at by allowing the 4 sows access to the whole 11 ha enclosure. This was still a high density compared to more natural situations on the European continent but we felt it would enable us to look in detail at some of the subtle effects of boar on soil nutrient cycling and other elements of the ecosystem.
However, in October 2016 two of the boar died of natural causes, possibly simply old age. Following advice, the remaining boar was humanely dispatched.
Boar are now roaming in several areas in Scotland, including in Glenmoriston. Their establishment in the wild has been independent of any licenced process which is not something that Trees for Life endorses. However, their presence restores a natural ecosystem function that has been missing from Scotland for centuries. They may one day be recognised as a native species to Scotland in the same way that beavers have been.