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Results from the Guisachan Wild Boar Project

Boar create excellent seedbeds for tree regeneration, and by feeding on bracken rhizomes, reduce the ability of bracken to dominate the woodland understorey. Boar compare favourably with other methods of controlling bracken.

The Guisachan Wild Boar Project, in which Trees for Life is a partner, officially drew to a close last year, when the final report was submitted to the funders in June. That was by no means the end of the story, but first here's a summary of some of the key results from the project:

  • Adult wild boar preferred to root in the bracken-dominated areas rather then areas with grasses/rushes/moss, and least preferred were areas dominated with a heather/blaeberry/cowberry mix.
  • Wild boar impacted on bracken by digging up and eating the rhizomes at all times of the year and by grazing on the young crosiers and by eating mature fronds if other vegetation was in short supply. After one year there was a significant reduction in the frond height and frond density of bracken and there was a downward trend in the underground rhizome store.
  • Wild boar were not observed to graze on heather or blaeberry leaves and shoots, but would tear tussocks of heather out of the ground and carry them away as nesting material.
  • In the test plots left to recover for one year after the boar were in them, the vegetation communities were returning to their previous composition, with some suggestion that grasses were replacing mosses. Where old tussocks of heather had been removed, heather seedling regeneration was high.
  • Tree seedling regeneration was high in boar-disturbed areas. Pine seedling regeneration was virtually zero in the control and pre-boar plots and averaged 0.1 - 1.4 seedlings / m2 after disturbance by boar. Birch seedling regeneration also increased as a result of the boar.
  • At high densities (>6 /ha) of young boar and adult boar, damage to mature pine trees was considerable with some being uprooted and many killed by bark stripping of roots and trunks. Damage at 1 sow per hectare was dramatically reduced and very few pines had severe damage after one year, while damage to birch and rowan was minimal.
  • Birch and rowan seedlings above 50cm had a good chance of survival in the presence of boar, particularly when sited amongst heather and blaeberry. However Scots pine saplings were still vulnerable to being uprooted at over 3m in height.
  • Wild boar do not seem to particularly target wood ants' nests, as many disturbed nests were successfully re-built and nest disturbance was at a similar level to that of general ground disturbance.

We continued with bracken sampling last autumn (2007), and with the help of Trees for Life volunteers, all 70 bracken rhizome samples were dug up, washed and weighed in a matter of weeks. We are delighted to report that the downward trend in rhizome weights reported last year is now statistically significant. This compares favourably with other methods of controlling bracken, such as chemical spraying or manual cutting, whereby it takes 2 -3 years before depletion of the underground rhizome store becomes significant.

In conclusion: wild boar are undoubtedly ecosystem engineers.

  • In areas where they have rooted and exposed the soil, clearing away the moss layer and bracken litter, seedlings from trees and other species such as heather, grasses and herbs can proliferate.
  • In areas of dense bracken, the boar root intensively, thus reducing the ability of bracken to dominate the woodland understorey. They also graze on the bracken fronds, again reducing the competitive advantage of bracken.
  • It is also interesting to speculate about their role in coniferous versus deciduous woodland. Deciduous trees in the enclosures were sporadically browsed or the bark nibbled by the boar, but nothing serious. In contrast, they had a real preference for Scots pines, particularly for bark-stripping and exposing the trees' shallow surface roots. The very large trees with tougher, thicker bark were safe, but saplings were extremely vulnerable, particularly on wet ground where rooting was easier. I wonder, if, on the edges of the ancient Caledonian pinewood, wild boar used to give the upper hand to oak, hazel, birch etc by preferentially rooting out pine saplings?

The boar will all be removed from Guisachan by late summer 2008, and homes found elsewhere for our sows and Boris (the male boar). We expect to get excellent regeneration of pine and birch again in the summer. This time, with no boar to gradually root them out, the young seedlings should be able to thrive.

Liz Balharry


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Sow in heather

Bracken July 2005
Photo by Liz Balharry

 


Bracken September 2007

The effectiveness of the boar in clearing bracken is shown by these two photographs, taken in July 2005 and September 2007 respectively.
Photo by Liz Balharry

 


Wild boar sow amongst heather
at the Guisachan project site.

Trees for Life is an award winning conservation charity working to restore the Caledonian Forest
and all its species to a large contiguous area in the Highlands of Scotland.

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