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Pollination ecology of Eucalyptus globulus subsp. globulus and Eucalyptus nitens (Myrtaceae)


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Hingston, AB 2002 , 'Pollination ecology of Eucalyptus globulus subsp. globulus and Eucalyptus nitens (Myrtaceae)', PhD thesis, University of Tasmania.

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Tasmanian native blue gum Eucalyptus globulus subsp. globulus and its closely
related southeastern Australian mainland congener E. nitens are the major
trees grown in eucalypt plantations in temperate regions of the world.
Plantation stock are mostly grown from seeds, that are increasingly being
collected from seed orchards of trees selected for characters desired by the
forest industry. Seed production and fitness of the resultant trees are
dependent largely upon pollen transfer between flowers on different trees,
because of the partial self-incompatibility in these two species. The
unsuitability of the pollen to transfer by wind necessitates the harnessing of
animals to transfer pollen as they forage at flowers. This research aimed to
determine which animals were effective pollinators of these tree species in
These two species have contrasting floral forms, associated with enormous
differences in nectar production, that resulted in their flowers being used by
different animals as food sources. The small flowers of E. nitens produced
only 0.3 - 0.6 mg of nectar sugar per day and, accordingly, were visited
exclusively by small, mostly native, insects. Introduced honey bees (Apis
mellifera) and bumble bees (Bombus terrestris), being larger, more energy
demanding insects, were rarely seen visiting flowers of E. nitens, and birds
were never seen attempting to feed from these flowers. In contrast, the large
flowers of E. globulus produced 37- 56 mg of nectar sugar per day, rendering
them attractive to energy demanding birds and exotic bees, as well as the less
energy demanding smaller insects.
Single visits to flowers of E. globulus by swift parrots (Latham us discolor)
resulted in statistically significant increases in seed production above the
levels occurring in unvisited flowers. Although other bird species were not
sufficiently assessed by this method to determine whether they are also
effective pollinators, analyses of their foraging behaviour and pollen loads
suggest they are. In contrast, experiments indicated that insects were poor
pollinators of E. globulus. Single visits to flowers by insects, including honey bees and bumble bees, did not result in statistically significant increases in
seed production above the levels occurring in unvisited flowers. Even
prolonged exposure to insects throughout the life of a flower failed to result
in the production of as many seeds as that following a single swift parrot
visit, despite insects often consuming all of the daily nectar production.
Hence, seed production and the fitness of plantation trees should be
enhanced by management practices that benefit populations of native flowervisiting
insects in seed orchards of E. nitens and birds in orchards of E.

Item Type: Thesis - PhD
Authors/Creators:Hingston, AB
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