Botanical Work in the Kimberley

MAIN CLUB April Meeting

Our speaker was Professor Kevin Kenneally AM, of the UWA School of Agriculture and Environment. Kevin has conducted research on the plants and animals of the Kimberley for more than 40 years. A Life Member of the WA Naturalists’ Club, he has been president of the WA Gould League for the past 35 years and is a past-President of the Kimberley Society. In 2005 he was awarded the Order of Australia for a lifetime of inspiring young people to take an interest in nature. Kevin is a recognised international authority on the vegetation and flora of the Kimberley, having pioneered research in the region for over 40 years.

Kevin describes the Kimberley rainforest as a “jungle jigsaw”, consisting of at least 1500 very small patches of deciduous monsoon rainforest embedded in savannah woodland. These patches occur mainly in areas where there are basaltic intrusions into the sandstone, often at the base of the sandstone cliffs. They are sometimes referred to as vine thickets, being rich in lianas or vines (many with spines). However, there are no epiphytes—as there are in evergreen rainforests—and there is only one orchid species. In contrast to the neighbouring savannah, there are few grasses. The Kimberley has a monsoonal climate with distinct Wet and Dry seasons. The El Niño Southern Oscillation (ENSO) herds moisture from the Pacific Ocean which can sometimes affect northern parts of WA. When there’s an El Niño, it causes less rainfall and fewer tropical cyclones. During La Niñas, greater amounts of moist tropical air flow across Australia and this causes more tropical cyclones.

Dead-looking patches in the Dry season green up as deciduous trees sprout their new leaves when the Wet season arrives. The rainforest patches are found generally along the coast and along the rivers, and are richest where there is protection from fire and where water seeps out of the sandstone. Coastal fogs add to the moisture available. Overall, they are richest in the Mitchell Plateau region, where the rainfall is highest. Mangroves form another type of closed forest, fringing the sea and inlets.

Rainforest on eastern side of Mitchell Plateau

Occurring as they do in isolated pockets, the vine thickets are rich in plants that can disperse readily from one pocket to another. Many of those plants enclose their seeds in bright-coloured soft fruits which are eaten by birds and have the seeds dispersed by them. Different colours attract different birds. These plants include Gubbinge (Terminalia ferdinandiana) and Cluster Fig (Ficus racemosa). Many of the birds rely for their survival on these closed canopy communities and the monsoon rains. Some plants such as Australian Nutmeg have a colourful aril or fleshy seed attachment, which is attractive to certain birds or animals.

Some of the other Kimberley rainforest plants are Ebony, Canary Beech, Love Vine, Lacewing Vine, Itchy Vine, Loofa Vine, Crab’s Eye Bean, Banyan Fig, Monsoon Hibiscus, Climbing Wattle, Indian Prickly Ash (fruit left), and a mistletoe Amyema benthamii.
Many of the plants are pan-tropical. Some of the mammals found in these patches are the Blossom Bat, the Black Flying Fox, the Scaly-tailed Possum, the Golden Bandicoot, the Sugar Glider and the Golden-backed Tree Rat.

None of these mammals are endemic to these rainforest patches. The reptiles include the Carpet Python and the rare Rough-scaled Python, and two skinks: the Giant Slender Blue-tongue and Johnstone’s Carlia. The pythons have a wide gape and eat bats and birds. Some species of snail are endemic to single patches. This suggests that some of these vine thickets have been refugia for a very long time.

Fungi include species of Amanita, Boletus and Panus. There are also the bracket fungi Ganoderma, some of which are used as medicines in South-east Asia. The fungi include mycorrhizal species.

Kevin described some of the hazards of working in these environments, such as the difficulty of hacking one’s way through the thorny tangle of vines, and the “hot needle” pain of the bite of the ferocious Green Tree Ants, which stitch leaves together to form nests (right). His work has included sending specimens of Kimberley rainforest plants to herbaria around the world, to help “get the Kimberley on the map” botanically, and to clear up some discrepancies in plant taxonomy.

The Indigenous people of the Kimberley – its traditional owners – have always practised “eco-harvesting”, using their detailed knowledge of the biota and knowing when, where and how to collect food. Examples are Gubbinge fruits and the tubers of the yam Dioscoria bulbifera. Yams and Boabs feature commonly in ancient rock paintings of the Kimberley. Aboriginal people have been of great assistance to Kevin and other researchers while carrying out botanical surveys.

The rainforest pockets of the Kimberley are embedded in areas of fire-prone and fire-adapted eucalypts. This makes them particularly vulnerable. Without the traditional burning regime, fires in the surrounding savannah, with its 3m-high sorghum grass are uncontrolled, too hot and too frequent. They often burn for months, and each fire burns further into the rainforest patch. Cattle often encroach on rainforest pockets, searching for shade. As they do so, they trample the vegetation, compact the soil and bring weeds in their dung.

Speaking of the importance of conserving these environments and of documenting their biota, Kevin emphasised that every patch of rainforest in the Kimberley is different. For that reason, the loss of even one patch is the loss of biological diversity and of a unique ecosystem. A book, The Natural World of the Kimberley, published recently by the Kimberley Society, was on sale at the meeting.

Mike Gregson