The Karri tree is one of four tree species that dominate the forest areas of south west Western Australia. The majestic karri is the tallest of Western Australia’s native trees and grows up to 90 metres in height. It is one of the world’s tallest hardwood trees. The karri (Eucalyptus diversicolor) is smooth-barked.
It gets its botanical name of ‘diversicolor’ from changes in the colour of the bark. The bark is white to cream but changes to brown as the bark matures. When the bark is shed, the mainly white trunk is then exposed and takes on a patina of colours from white to deep brown. The single trunk grows long and straight. Once the tree is mature, there will be no branches on the lower two thirds of the tree. The natural colour variation of dressed karri ranges from pale pink to a rich reddish brown. It is highly regarded by architects for its high density and durability. One downfall of the karri is that it has not as resistant to termites as jarrah.
The karri typically grows in the wetter parts of the extreme south west and within the Warren biogeographical region. There are small pockets of karri in other locations notably in the Porongorup Ranges. The karri often grows in poorer type soils. The bark collects at the base of the trunk to a depth of some metres. Combustion of the bark and other forest litter from bushfires causes nutrients to be released. Flowering is stimulated by fire.
The leaves are dark green on top and lighter underneath. The leaves are 90 to 120mm long and 20 to 30mm broad. The cream-coloured flowers occur in groups of seven, each one being 18 to 28mm diameter. Flowering takes place in spring and summer. The fruits are squat and barrel-shaped and contain many small dry seeds.
Areas of karri are a great tourist attraction. The Valley of the Giants lies within the Walpole Nornalup National Park and is west of the township of Denmark. The scenic drive is spectacular with giant karris towering up to the skies.
In years gone by, fire lookouts were erected in the tops of tall karris. These lookouts were manned throughout the summer to aid in the detection and control of bushfires. Although no longer used for their original purpose, there are still three forest lookouts that can be climbed by those tourists with a head for heights. The trees used as lookout trees are believed to be over 250 years old.
The Gloucester tree in the Shire of Manjimup, Western Australia is the world’s tallest fire-lookout tree. In 1946, forester Jack Watson took six hours to climb 58 metres using climbing boots and a belt. George Reynolds pegged the ladder and lopped branches to ease the effort required to climb the tree and a wooden lookout was built 58 metres above the ground. The lookout was demolished in 1973, being replaced with a steel and aluminium cabin. Nowadays tourists can climb the 153 spikes that snake around the tree. A flimsy chain connects the outside of the spikes. Only 20% make it to the top of the tree. In 2002, the 1 millionth person made the climb to the top.
The Diamond Tree is also in the Shire of Manjimup just 10 km south of the town on South Western Highway. The wooden viewing platform was built in 1939 and is 52 metres above the ground. It is the oldest platform of its type still in use. After being used every summer from 1941 to 1973, it is still occasionally used to support aerial surveillance.
The Dave Evans Bicentennial Tree is the tallest of the three ‘climbing trees’. The platform is 75m above ground, weighs two tonnes and can sway up to 1.5m in the wind.
Karri is used extensively in the building industry where its length and knot-free wood make it especially useful in the construction of rooves. It is keenly sought as a furniture wood having a beautiful mahogany colour. Karri honey is popular being light in colour with a delicate flavour.