What happens when you have too few deer?
The risks posed to woodland ecology by having too many deer are well publicised but what is less well known is that having too few deer is also very detrimental to biological diversity.
What are the damaging signs of having too few deer?
Typically a reduction in species diversity with fewer more vigorous species coming to dominate, habitats such as wood pasture and edge begin to disappear.
So how might this manifest itself on the Isle of Wight?
We can expect subtle long term changes to our woodland flora with vulnerable species being most at risk. One such plant, the Wood Calamint, which is unique to the island within the UK, has suffered due to mature over growths of Hazel, as a result it is now very much endangered. This rare plant does not enjoy being shaded by more vigorous vegetation, likewise the heathland habitat of the very scarce Reddish buff moth is threatened by woody encroachment, deer grazing is a natural process that helps to prevent this.
Are there any examples of damage to the island’s woodlands that has already occurred?
The Forestry Commission have said that in Parkhurst Forest “Rare, remnant pre-enclosure pasture woodland and open heath grassland species have hung on in the post-enclosure high forest but are under threat from the unchecked growth of vegetation.”
Parkhurst was originally a hunting preserve for the nobility, before the forest was enclosed in the early 19thcentury these pastures benefited by being grazed by around 200 deer.
So why are wood pasture habitats so important?
Wood pasture contains a diversity of flowering species, and are important feeding grounds for lepidoptera, whilst many of our woodland bats feed on invertebrates found there. One of our rarest, the Greater Horseshoe, benefits from feeding on the beetles found in deer dung. The very rare Pearl Bordered Fritillary butterfly thrives where deer grazing slows down natural regeneration and helps to maintain open areas of Bracken in canopy gaps and along woodland edges.
Is there any other evidence of long term damage caused by over growths of vegetation in Parkhurst Forest?
The Wessex Lichens group have reported that some areas are “desperately overgrown with even the rides lost to dense bramble with an under storey of Sycamore between the trees” and that “the forest’s lichen old woodland assemblages are suffering from increasing and dense shade”
Are any of the island’s birds being affected by the lack of sufficient deer grazing?
Three birds that are common in the New Forest but largely absent from the Isle of Wight are the Tawny Owl, Common Redstart and Nuthatch. Beetles such as those associated with deer dung can be an important part of these bird’s diet, the Tawny Owl also feeds on Wood Mice and Bank Voles. In order to catch these small mammals they require some of the habitat within woodlands to be more open without a large amount of dense cover. The Common Redstart also prefers these more open woodland areas that deer grazing and browsing helps to create. It would appear that our local woods are no longer suitable for these birds.
So what might be the best approach to managing deer in the Isle of Wight’s woodlands?
Trinity College, Dublin has recently published some interesting research Exclusion of large herbivores: Long-term changes within the plant community in which they found that excluding deer from Oak woods was harmful to biodiversity, to quote one of the authors, Dr Miles Newman ” Woodland ecology, it seems is a little like life- it’s often best to do things in moderation. If there is too much or too little grazing, these important habitats may lose valuable species for good.”
If you have seen some deer on the island please take part in the Isle of Wight Deer Survey locations will be treated with strictest confidence. For periodic updates please visit Isle of Wight Deer Conservation or email firstname.lastname@example.org
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For more photos of deer on the Isle of Wight please see the Isle of Wight Deer Album
For more photos of deer on the Isle of Wight please visit my Isle of Wight Deer Album