BSBINews - BSBI Archive - Botanical Society of the British Isles

16 Notes - Squirrel-stripping of native, naturalised, plantation and exotic trees
pessimistic, with the exception of the opportunity
of total eradication of grey squirrels in
Anglesey. I suspect there could be dangers,
uncertainties and impracticabilities in the (re-)
introduction of arboreal predators, such as
beech and pine-martens. Our cat killed two
adult and three young grey squirrels in three
days by ambush and raiding a drey, but two
other local cats suffered injuries, including eye
damage, in tree raids.
Lure crops, (e.g. sycamores and Norway
maples) are of very limited value. The table
shows that 45 Aeer were not attacked, whereas
65-72 non-Aeer trees were damaged. In order
to protect some rare tree taxa against deer and
grey squirrels, I use a method which would be
commercially impractical, and aesthetically
inappropriate for specimen trees. Very closely
adjacent pear trees (best), apples (too spreading)
or hawthorns (too fiercely rampant) act as
guard trees and prevent ring-barking and
skeletonising. In response to the basal
gnawing and stripping by grey squirrels, I
have ceased clearing nettles and other tall
weeds from around trunk bases.
Summary
With the probable exception of densely thorny
species, no tree species can be considered
wholly immune from biting and stripping by
grey squirrels, which attack trees (over 2m in
height) of all ages, and at all levels. The best
that can be said is that genera such as Aeer and
Fagus tend to be more susceptible than Tilia
(inexplicably), Pyrus and Prunus. In this
study, the most vulnerable genus by total
numbers and percentage of trees damaged or
severely damaged was Populus. P. nigra ssp.
betulifolia (most trees about 17 years since
planting) was, by far, the species suffering the
highest number of harmed specimens, usually
at high levels. Eleven trees from two Aeer and
five Salix species were skeletonised, all eleven
recovering from the base; but lesser damage
could kill conifers. In 216 years, 39 different
types of tree were damaged, 19 severely so.
Postscript: bridging the gap? - a botanical
mystery
Total ring-barking cuts off the phloem and
cambium, and kills trees above the level of the
ring-barking, whether or not they re-sprout
from below. Depending on the weather, the
foliage of conifers so-damaged shows
evidence within 1-2 months. Ring-barked
broadleaved trees wither and die above the
ring-barked zone sooner. Sycamores so-damaged
show the evidence within days in spring,
summer or early autumn, following grey
squirrel stripping.
One tree in my arboretum has behaved
differently. A Cercidiphyllum japonicum
(Katsura) was severely stripped in or before
May 2008, with total ring-barking of the main
trunk for at least 50cm above the tree-guard.
An adjacent sister Katsura was also badly
stripped, but not wholly ring-barked. Both
trees are about 7m tall. There is no strip of
continuous bark linking the ring of branches at
the bottom of the photo ofthe ring-barked tree
to the peeled strips at the top. After 18
months, the foliage of the top Srn of both trees
looks identical and healthy. Not only that, but
attached strips and islands of bark above the
ring-barked zone show the slightly swollen
edges or lips of healing bark tissues, characteristic
of wounded tree trunks, or recovery
below ring-barked zones.
I still expect the top 5m of the tree to die
("absolutely no chance whatsoever" -
independent commentator), but after 18
months it is little different from the sister tree.
Acknowledgements:
My thanks for help from Katy Cena and Rob
Guest.
References:
FARS [Friends of the Anglesey Red Squirrel].
(2009). 'Grey squirrel damage to woodland'
(Web information: www.redsquirrels.info/
barkstripping .html Accessed 17/6/2009.
Mainly ch. 4.
FORESTRY AUTHORITY. (1996). Controlling
grey squirrel damage to woodlands. Forestry
Commission Research Information Note
180(1).
FROHNE, D. & PFiNDER, HJ. (1983). Colour
atlas of of poisonous plants. Wolfe Publishing
Ltd., London and Stuttgart.
PEPPER, H.W. (1990). Grey squirrel damage
control with waifarin. Forestry Commission
Research Information Note 180 (2).
PIGOTT, D. (2005). Lime. Sage Press, Rye.