thumb|The [[Gloucester Tree]]

Eucalyptus diversicolor, commonly known as karri, but can reach as high as , making it the tallest tree in Western Australia and one of the tallest in the world. As of February 2019, the tallest known living karri is just over tall. A tree south of Pemberton, known as 'The Tyrant' is tall and in girth and contains approximately of wood in its trunk and is thought to be the largest karri by wood volume. A Eucalyptus diversicolor of height and of girth in Coimbra, Portugal, is the tallest reliably measured tree in Europe.

Karri do not form a lignotuber but do form epicormic buds located under the bark along the length of the stem. The bark sheds each year with the new white bark contrasting with the orange to yellow new bark contrasts against the recently exposed white bark. The bark becomes increasingly granulated with age.

The stems and branchlets are round in cross section, the branchlets have no oil glands in the pith.

Taxonomy

Eucalyptus diversicolor was first formally described in 1863 by the botanist Ferdinand von Mueller in his book Fragmenta Phytographiae Australiae. The type specimen was collected in 1860 by the botanist Augustus Frederick Oldfield near Wilson Inlet, the location given, in Latin, is In Australiae regionibus depressioribus quam Maxime austro occidentalibus, ubi Blue Gum-tree vocatur.

The botanical name diversicolor is taken from the Latin word diversus meaning to turn apart and color or "separate colours" and refers to the difference between the top of the leaf and its underside.

Karri is a part of the Symphyomyrtus subgenus, all of which have two opercula on the buds and have four rows of ovules. It is not closely related to any other members of the subgenus and is the sole species in the section Inclusae. The defining feature of this section is having inflexed stamens, flattened ovoid seed shape, enclosed valves of the fruit and the lack of pith glands in the branchlets. Although it has no closely related species it has some affinity with tall Eucalypts found the wet forests of eastern Australian including E.saligna and E.grandis all of which have discolorous adult leaves and seeds with a flattened-ovoid shape. It mostly occurs within the Warren biogeographic region, but there are some outlying populations including the Porongorup Ranges, Mount Manypeaks, Torbay, Rocky Gully all along the south coast and Karridale and Forest Grove to the north west

The total area covered by karri forest is less than which is about one fifth of its virgin growth.

The species is considered invasive in South Africa where it is a problem in the Western Cape region and is locally known a karie. It commonly invades clearings, fynbos, water courses and road sides often out competing local species and is spread easily by seed dispersal.

Ecology

Karri is regarded as one of the six forest giants found in Western Australia; the others being Corymbia calophylla (marri), Eucalyptus gomphocephala (tuart), Eucalyptus jacksonii (red tingle), Eucalyptus marginata (jarrah) and Eucalyptus patens (yarri).

Some karri specimens are thought to reach an age of up to 300 years.

Pollinators

Most Eucalypts achieve pollination through insects and birds rather than wind. Insects are far less active through the colder winter months so bird pollination is thought to be more important. The trees are often visited by nectar feeding birds, particularly Purple-crowned lorikeets. The lorikeets have a wide range and are quite active during winter and are thought to be dominant pollinators and able to cross pollinate over larger distances.

Uses

thumb|[[Deanmill, Western Australia|Deanmill karri logs on train]]

thumb|'Log and fallers.' Poole, C. E. L., Primer of Forestry 1922

The wood has a green density of around with an air-dried density of about .

Fire lookouts were established in the forests using the tallest Karri trees, giving the foresters a commanding view of the landscape.

The idea of using karri trees in this way was first suggested in 1937 by a young forester, Don Stewart, who later became Conservator of Forests. The first of these was built on a large marri (Corymbia calophylla) at Alco, near Nannup. Eight lookouts were established in the forests between 1937 and 1952. Spotter planes are now used and some of the trees are now used as tourist attractions.

Karri wood is a beautiful mahogany colour, lighter in colour than jarrah. It is used extensively in the building industry, particularly in roofs for the length and knot-free quality of the boards. The wood is also used for flooring, furniture, cabinetry and plywood. The heartwood is golden to reddish brown, often with an orange or purple cast, and tends to darken with age. It has an interlocked grain with a uniform medium-coarse texture. It has the reputation of being termite-prone, although it is nowhere near as susceptible to these insects as pine. It is durable against rot. It is also an excellent furniture wood.

Some of the main streets of early Sydney were paved with blocks of Karri but have been long since covered by asphalt. The wood was also sent to London for the same purpose.

Further reading

  • Boland, D. J., et al. (1984). Forest Trees of Australia (Fourth edition revised and enlarged), CSIRO Publishing, Collingwood, Victoria, Australia. .
  • Department of Conservation and Environment – information page.