Juniper at Porton Down
Juniper is now almost confined to chalk and limestone soils in southern
England and Porton Down is the most important site within this area,
containing about 20% of the population. An invertebrate fauna of 20
species specific to juniper occurs in southern England. Fifteen of these
species have been found at Porton Down, more than on any other single
site.
Juniper occurs in two distinct age groups at Porton Down. The oldest,
now dead or dying, arose when sheep grazing pressure was reduced at
the turn of the 20th century. This allowed juniper to establish on the
grasslands.
The younger age group arose during the myxomatosis outbreaks of the
1950s and 60s when grazing pressure by rabbits was severely reduced.
Prior to 1969 most juniper seedlings had been grazed off but for ten
or twenty years afterwards juniper were able to establish. By the mid-1970s
rabbit grazing pressure was again very high and establishment has not
occurred since.
There are 19 species of invertebrate which live only on juniper, 14
of these have been found at Porton Down. The very large population of
juniper at Porton Down is crucial to the survival of these species.
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