San Francisco State University
Geography 316: Biogeography
The Biogeography of The Blue Gum Tree (Eucalyptus globulus)
Photo of Eucalyptus in Golden Gate Park
by Anne O'Connor, student in Geography 316, Fall 1999
Species: Eucalyptus globulus
(National Geographic Society Map 1998)
Description of Species
Eucalyptus is common in southern parts of Australia in the coastal areas and hilly locations (Gardner 64). It is not common in the arid central and central western dessert zones of Australia (Pryor 1976). The subspecies E. globulus biocata is the most drought resistant and will survive more into the interior of the Australian continent (Attiwill and Adams 1996). E. globulus has been introduced all over the world in climates similar to its native habitat: Mediterranean climates in Europe, Chile, and North America, also in India, Africa, and Algeria (DOmbrian 1944). California has the ideal climate for E. globulus and has adapted well here. Bay Area Counties are ideal climate for the Blue Gum. Precipitation and fog drip give it enough moisture to thrive in the area. (Sellers 910). The genus was first brought to California in 1853 for timber production (Sellers 1910).
The native habitat of the Blue Gum Tree, Eucalyptus globulus, is in southern and southeastern Tasmania and the islands of the Bass Straight between the continent of Australia and TasmaniaKing Island and Flinders Island (Gardner 1987). It also occurs in Victoria, and south-eastern New South Wales in Australia (DOmbrian 1944). First found in Tasmania, the full name given to the species is Tasmanian Blue Gum. The species name, E. globulus, comes from the shape of the fruit (Grimwade 1930). There are four subspecies: E. globulus maidenii, E. globulus pseudoglobulus, E. globulus bicostata, and E. globulus globulus, but are commonly referred to as species themselves (Williams and Woinarski 1997).
The native range for the Eucalyptus is between latitudes of 9 degrees North and 44 degrees South (Williams and Woinarski 1997). It can survive into latitudes up to 56 degrees along coastal regions in such places as Portugal, United Kingdom, and Ireland (Pryor 1976). In Tasmania, E. globulus thrives in the moderate climate. Tasmanias mean annual rainfall is 20 to 60 inches with dry hot summers and cool wet winters. The elevation range the E. globulus survives best in is between sea level and 1000 feet in Tasmania and up to 1500 feet in Victoria (Gardner 64). Elevations in California allow for the successful growth up to 3000 feet in the Sierra Nevada (Sellers 1910). Ideal temperatures range from a high of 110 degrees to no lower than 22 degrees F (Sellers 1910). The E. globulus is somewhat frost tolerant in adulthood but younger trees are damaged by frost (Sellers 1910). For example: in Tasmania, there is snowfall in winter but the ground never reaches temperatures below 32 degrees F, which would kill the trees (Pryor 1976). To the other extreme, wet tropical conditions are a limiting factor to the growth and survival of the Eucalyptus (Pryor 1976). On the western side of Tasmania and some parts of southern Victoria, temperate rain forests have prevented Eucalyptus growth (Pryor 1976).
The species E.globulus is one of the tallest of the genus-- it can reach 375 feet in heightone of the largest trees in the world (Williams and Woinarski 1997). Growth in the early years, between 12 and 20 years, is rapid and can reach up to 175 feet (Sellers 1910). With an extensive and spread-out root system, the Eucalyptus removes nutrients and water from the soil and the strong surface roots will compete with other vegetation (Poore and Fries 1987). In addition, the root system has lateral growth, which penetrates to depths up to 45 feet and spreads out 100 feet. (Sellers 1910). Root growth, toward water, has been problematic in arid and drought susceptible areas where it sucks the water table dry. This is one reason why introduction of the genus is dangerous to native species. In India, a Eucalyptus tree farm dried up a stream a village depended on the water their crops and cattle (Shiva and Bandyopadhyay 1987). Another reason it has been a problem as an exotic introduced species, is typically Eucalyptus is introduced as a seed to a new environment free of insects and therefor nothing to control its growth (Pryor 1976). The leaf eating insects: scarabs, chrysomelids, curculionids, and tenthredinids; sucking insects: syllids, jassids and coccids; and the wood borers: cerambycids and cossids moths (Pryor 1976). When introduced into a new habitat with insects, an added invasive species, there can be adverse effects on indigenous species (Pryor 1976).
E. globulus in Golden Gate Park
E. globulus is a broad leaf
evergreen. Eucalyptus grows in a range of sizes from shrubs to trees. There are four
stages of growth of the Eucalyptus: seedling, juvenile, intermediate or mature and adult
(Williams and Woinarski 1997). There are two types of leaves: juvenile leaves grow
for the first 18 months: they are oval shaped leaves, powdery silver-gray in color and set
on opposite sides of the branch (DOmbrian, 1944). Adult leaves, dark green in color,
are falcate and oblique, alternate on the branches, and are the longest leaves of all the
species of Eucalyptus -- up to 15 inches long (DOmbrian 1944). The leaves are
leathery and hang vertically like pendulums (Pryor 1976). The typical leaf size is 4
to 12 inches long and 11/4 to 11/2 inches wide (Gardner 1987). Adult leaves gradually
begin to replace the juvenile leaves from the top down. During the metamorphosis the tree
will display both leaves until it looses the juvenile leaves (Grimwade1930).
E. globulus leaf (Boland, Brophy, and House 1991)
The leaves contain eucalyptol, an essential oil, making up 70% of the leaf volume (Botanical.com 1995). The oil is a cineole rich one, with medicinal qualities (Boland, Brophy, and House 1991). In 1854 the industry involving Eucalyptus oil began (Boland, Brophy, and House 1991). The oils were used during World War I to cure meningitis and the influenza epidemic in 1919 (Boland, Brophy, and House 1991). The high oil content make E. globulus undesirable to the Koala which are very particular as to which species of Eucalyptus it will eat. The Koala prefers species which do contain the oil cineol but at lower percentages such as E. viminalis in Victoria or E. tereticornis in New South Wales and Queensland (DOmbrian 1944).
Eucalyptus globulus (Grimwade 1930)
From species to species the color of the flowers vary from red, purple or pink, to green or yellow, but the most common is a white or cream color (Sellers 1910). Most species flowers are in groups or clusters, one exception is the flower on the E. globulus which are solitary (Pryor 1976). The flowers are white in color and vary in size from subspecies to subspecies. The subspecies E. globulus globulus has larger flowers and fruit compared to the E. globulus pseudoglobulus. The flowers are bisexual. (Williams and Woinarski 1997). The male element opens first followed by the female parts several days later. (Brooker and Kleinig 1990). Because of the differences in times, pollination occurs with other flowers on the tree rather than with in the same flower. The pollinators are insects, birds and small marsupials (Brooker and Kleinig 1990). Flowering occurs from June to November (DOmbrian 1944). After fertilization the flower becomes large, hard and turns to fruit (Brooker and Kleinig 1990). The ovules within the flower become the seeds within the fruit. (Brooker and Kleinig 1990). The spread of the seeds is mostly by the wind (Williams and Woinarski 1997).
Fruit of the E.globulus (Brooker and Kleinig 1990)
The bark of the E. globulus is a
smooth yellow brown, which sheds off in strips annually (DOmbrian 1944). The wood is
then exposed it is light in color, yellow or orange and then turns gray or white as
it is exposed to the environment (Williams and Woinarski 1997). The name
gum comes from the gum the tree extrudes from its bark (DOmbrian 1944).
Bark peeling from a tree in Golden Gate Park
The soils in the native habitat of Tasmania
and southeastern Australia are ultisols, derived from metamorphic materials,
in the oceanic region between 39 degrees South to 42 degrees South, and have a pH level
between 4.9 and 5.6 (Attiwill and Adams 1996). Soils ideal for the species are fertile
soils with lower levels of alkaline (Sellers 1910). The soils in the Bay Areaclay
loam and adobe soils promotes maximum growth (Sellers 1910). The trees
can also survive in swampy areas or in standing water but not in water with high salt
contents (Sellers 1910).
Eucalyptus plantations are found all over the world (China, Portugal, Spain, Chile, South Africa, Swaziland) for a variety of reasons, but mostly they are commercial -- for the wood, oils, and pulp (Boland, Brophy, and House 1991). Various other purposes for planting Eucalyptus include fuel, wind breakers, and to dry up swampy areas.
There is great variation within the genus Eucalyptus. There are estimates of around 700 species of Eucalyptus (Williams and Woinarski 1997). With such diversity it is assumed that the Eucalyptus has evolved in isolation producing species with the greatest variety (Pryor 1976). The closet relatives are within the family Myrtacae and subfamily Leptospermoidae and include: Angophora, Syncarpia, Tristania, Melaleuca and Leptospermum (Williams and Woinarski 1997). The family, Myrtacae, have relatives, which also have capsular fruit, on nearby New Caledonia and New Zealand Melaleuca and Boronia but neither have native Eucalyptus occurring there (Pryor 1976). The earliest eucalyptus like fossils discovered in southeastern Queensland date back to the Paleocene or Eocene (Williams and Woinarski 1997).
During the Paleocene, 65 MYA, the southern coast of Australia was at 60 degrees South latitude still connected to Antarctica. The continent slowly drifted northward to its present location with the southern most extent at 35 degrees south latitude (Attiwill, Adams, and Andrew 1996).
Movement of the continents (Specht and Dettmann 1995)
Within Australia a barrier formed, the Nullarbor Plain, isolating species from the southwest and southeast sometime before the Miocene. There was adaptation of species from region to region where the eastern species are adapted to wet summers, the western species are adapted to wet winters (Pryor 1976) Western soils are newer and more fertile while the eastern soils are old soils with lower levels of nutrients. (Pryor 1976). The Australian continent became more arid and has undergone an increase in seasonal climate within the last 200,000 years (Williams and Woinarski 1997). It was at this time when fires became part of the Australian environment (Williams and Woinarski 1997). The fires are important to the Eucalyptus for the purpose of seed dispersal, survival, and production and helps in vegetative reproduction (Williams and Woinarski 1997).
E. globulus distribution (Brooker and Kleinig 1990)
Attiwill, Peter M. and Adams, Mark A.. (1996). Nutrition of Eucalypts. Ed. Emma Short. CSIRO Publishing. Australia.
Boland, D.J., Brophy, J.J., House, A.P.N.. (1991). Eucalyptus Leaf Oils: Use, Chemistry, Distillation and Marketing. Ed. D.J. Boland, J.J. Brophy, and A.P.N. House. Inkata Press, Melbourne, Australia.
Brooker, M.I.H. and Kleinig, D.A. (1990). Field Guide to Eucalypts: South-eastern Australia. Inkata Press, Melbourne, Australia.
DOmbrian, A.W. (1938). A Gallery of the Gum Trees. Australian Medical Publishing Co., Glebe, NSW.
Gardner, C.A. (1987). Eucalypts of Western Australia. Ed. T.E.H. Aplin. Australia.
Grimwade, Russell. (1920). An Anthography of the Eucalypts. Angus and Robertson Ltd.. Sydney, Australia.
Grimwade, Russell. (1930). An Anthography of the Eucalypts. Angus and Robertson Ltd.. Sydney, Australia.
Grieve, M. (1995). A Modern Herbal. Botanical.com.
(5 October 1999).
National Geographic Society. National Geographic Society Maps On CD-ROM 1998.
Poore, M.E.D. and Fries, C. (1987). The Ecological Effects of Eucalypts. Natraj Publishers. New Delhi.
Pryor, Lindsay D. (1976). The Biology of Eucalypts. Camelot Press Ltd.. London, England.
Shiva, Vandana and Bandyopadhyay, J. (1987). Biological Audit of Eucalypts Cultivation. Natraj Publishers. New Delhi.
Sellers, C.H. (1910). Eucalypts: Its History, Growth, and Utilization. A.J. Johnston Co. Sacramento, California.
Williams, Jann E. and Woinarski, John C.Z. (1997). Eucalypt Ecology:
Individuals to Ecosystems. Ed. Jann E. Williams. Cambridge University Press,
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