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Commonwealth
Forests | | |
 Insects and disease
Damage to trees and forests from insects and disease has received much less attention,
either from foresters or the general public, than damage from fires – with two possible
Commonwealth exceptions. The first was the almost universal elimination of elms (Ulmus)
in
the United Kingdom in the 1970s, from Dutch elm disease (Ophiostoma ulmi) spread by elm
bark beetle Scolytus scolytus and S. multistriatus. The second is more recent: the
infestation
of mountain pine beetle (Dendroctonus ponderosae) in British Columbia, which attacks all
pines. Since 1994 an estimated 240 M m3 of timber has been lost, spread over 11.3 M
ha at
an estimated cost of $1.7 M yearly. The invasion has spread to Alberta and the USA, and now
threatens the jack pine of the boreal forest FAO 2006.
Figures from New Zealand put the threat from pests and diseases into perspective. Forest
industry in that country spends $0.6 per hectare on monitoring pest and disease outbreaks,
but $3.50 on fire protection. Yet the average yearly losses due to pests and disease is $137
M, compared with losses of $682,000 from fire (Hocking, 2003). Other serious, but less-noticed disease
and insect attacks have affected pines and cypress in eastern and southern
Africa. The earliest, dating from the 1950s, was the fungus Dothistroma pini, a needle
blight
which affected Pinus radiata grown in Kenya, Tanzania and Uganda, which ultimately spread
to New Zealand. They were accidentally introduced in the 1970s, illustrating the threat from
invasive species that may be spread by increasing passenger and freight air traffic. They
include the pine woolly aphid (Pineus boerneri), the pine needle aphid (Eulachnus rileyi)
and
the cypress aphid (Cinara cupressivora). By 1990 it was estimated that the last-named had
caused damage worth $44 M and was continuing to cause loss of increment valued at $14.6 M
yearly (FAO, 2006).
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