The Stewart Karri: Western Australia's tallest tree ⋆ Jinni Wilson

At 85 metres high, the Stewart Karri is Western Australia’s tallest known tree, and one of the twenty tallest in the world. Hidden away in a remote valley near Manjimup, it is now under threat from a water harvesting proposal.

The Stewart Tree was first named and measured in the 1940s during a search for tall Karris to turn into fire lookout towers. Other giants, like the Gloucester and the Dave Evans trees, eventually had spikes driven in and platforms built on top. But the Stewart remained pristine, left to grow in peace in a deep valley along Record Brook.

Karri forest is endemic to the wet south-west corner of Western Australia. Before logging in the 19th century, individual trees were known to grow over 90 metres high, making them one of the tallest tree species in the world. In a bizarre twist, the tallest tree in Europe is a Karri. The ‘Karri Knight’ was planted in Portugal in the 1890s, and measures in at 73 metres. Its fame means that the species is surprisingly well known outside of Australia. People come from across the globe to see them, marveling at their giant, ghostly white trunks gleaming amidst a cloak of green.

Very little old-growth Karri remains. Most of the natural forest has been logged and the remnant is becoming increasing stressed by declining rainfall. Karris require a vast amount of water, and only grow in the high rainfall zone along the south coast. But Australia has been a drying continent for millions of years, a long term trend now exacerbated by climate change and ironically, the over-clearing of forests.

The Stewart Tree grows in a valley on a tributary of the Donnelly River, one of the last wild rivers in southern Australia. While most other rivers have been dammed, the Donnelly has miraculously maintained its integrity. Until now.

Under the proposed Southern Forests Irrigation Scheme a 15GL dam would be built just downstream from the Stewart Tree. Close to 80 hectares of old-growth karri forest would be cleared for the dam footprint, and billions of litres of water pumped out of the Donnelly River system to fill it. Much of it would be used to water avocados, a notoriously water-hungry fruit. Instead of using commonsense to farm sustainably within the limitations of the water supply, a small select group seek to harvest water which belongs to nature. Water that the Karri giants depend on.

In Europe and the United States the over-exploitation of water resources has devastated whole ecologies. Now Governments are moving to rewild the rivers: dams are being removed, straightened banks ‘rebended,’ and ecologies restored.

We have already seen the damage that water harvesting has done on the East Coast of Australia, with the drying of the Murray-Darling system. While folks there work to reverse the damage and hold politicians to account, here in Western Australia we are planning to repeat the same mistakes all over again.

We are lucky to still have a few healthy rivers in the South-West. A very small number of them, like the Donnelly, are almost pristine. With their catchments maintained, wild and intact, they support our precious native forests. Not only are the forests valuable ecosystems in their own right, they support some of the largest trees in the world. The Stewart Tree and its whole forest ecosystem is surely a natural wonder of global significance. Far more precious than a harvest of avocados.

Take the water from a Karri forest and we will lose it forever. There is still time to prevent such a tragedy: just don’t dam the Donnelly!