N. Reid et al., IMPART OF MISTLETOES (AMYEMA-MIQUELII) ON HOST (EUCALYPTUS-BLAKELYI AND EUCALYPTUS-MELLIODORA) SURVIVAL AND GROWTH IN TEMPERATE AUSTRALIA, Forest ecology and management, 70(1-3), 1994, pp. 55-65
The damaging effects of mistletoes Amyema spp. on host eucalypts in ru
ral Australia concern many landholders, but few data are available to
evaluate mistletoe impacts or formulate management strategies. We used
an experimental disinfection approach to determine the effects of a p
utative pest mistletoe, Amyema miquelii, on its two principal hosts, B
lakely's red gum (Eucalyptus blakelyi) and yellow box (Eucalyptus mell
iodora), on pastoral properties in northern New South Wales. For each
host species, pairs of nearby trees were matched for height, diameter
at breast height, level of mistletoe infestation and distance to neigh
bouring trees. One tree per pair was chosen at random and all the mist
letoes pruned. After 33 months all treated trees were still alive, but
among control trees seven of 29 red gums and one of 20 yellow box tre
es had died. The difference in survival between treated and control tr
ees was significant for red gum. Among surviving pairs of trees, treat
ed trees of both species had significantly greater diameter increments
and significantly more foliage than untreated trees. After 33 months,
the average increase in relative host foliage biomass attributable to
removal of mistletoes was 22% in red gum and 24% in yellow box, compa
red with untreated controls. The average increase in radial growth att
ributable to mistletoe removal was 55% in red gum and 49% in yellow bo
x. Diameter increment was negatively and linearly related to mistletoe
infestation level in control trees of both species. The differences b
etween infected and disinfected trees in this experiment may underesti
mate the impact of Amyema miquelii on host growth because small amount
s of host biomass were unavoidably lost during disinfection. In a sepa
rate experiment, loss of host biomass had a significant negative impac
t on diameter increment. Although the results indicate that control of
serious Amyema miquelii infestation of individual trees will be worth
while in terms of immediate host survival and higher growth rate, prud
ent long-term management may well allow for the loss of small numbers
of farm trees to mistletoes when planning tree recruitment and utilisa
tion.