The trees that have grown in the cleared country generally have
heavy branches and it is only in the steep ravines, in the residual forest
or where a fence has allowed the development of a group of pines, that
the trees show the branch-free stems recorded by the early settlers.
Over the years trees have died apparently from old age and little
concern was expressed by the islanders. Seedlings have regenerated
following the good seed years which occur every 4 to 6 years and there
appears to be adequate replacement material if they are protected from
grazing animals. There has been some planting on the forest reserves and
common areas, however, little planting or encouragement of seedling
regeneration has been carried out by private landholders.
Approximately six years ago local people and visitors became con-
cerned by the fact that significant areas of the island had no regener-
ation and that many of the older trees, and some of the younger ones, were
showing signs of ill health. The trees gradually developed thin crowns,
sometimes produced secondary epicormic growth and eventually died. At no
stage was there a dramatic loss of trees.
A number of theories were advanced including infestation by a root-
rotting fungus, Phythophthora einnamomi which was causing widespread
damage in native eucalypt forests in Australia. It was also thought that
the disorder might be similar to that affecting planted specimens of
Norfolk Island pine in a number of oceanfront suburbs in Sydney on the
east coast of Australia.
Early in 1972 Heather (A.N.U. Dept For. pers. comm.) analysed samples
of soil taken from beneath affected trees on the island. These were
subjected to culture tests and examinations in an attempt to isolate the
root-rot fungus. As only one of the 40 samples was found to contain
Phythophthora cinnamomi this approach was considered inconclusive as an
explanation of the disorder although it was accepted that the fungus was
present on the island.
At the same time the problem involving the dieback of pines in Sydney
was being actively investigated. The symptoms were similar, however,
in Sydney only coastal plantings were affected and specimens sheltered
from the on-shore prevailing wind survived. On Norfolk, pines in the
centre of the island were dying as well as some on exposed coastal sites.
The Sydney disorder was reported by Hartigan (1970) and he concluded
that the evidence pointed to some phytotoxic agent being carried by the
wind onto the oceanfront trees. The investigation established that the
disorder could not be attributed to overmaturity, disease, insects, soil
impoverishment or lack of water. Later work by Hartigan (N.S.W. For.
Comm. pers. comm.) and others identified the causal agent as the sus-
pension in the aerosol of detergent particles from sewerage effluent
emptied into the sea and swept back to shore by the prevailing winds. The
detergent apparently dissolved the waxy layer on the scale-like leaves
sufficiently to allow the salt in the spray to dessicate the leaf. The
natural salt tolerance mechanism of the species was being broken down by
the other components in the salt spray.