Tropical Topics An interpretive newsletter for the tourism industry Wet sclerophyll forests No. 69 September 2001 Birds lose ground as forests vanish Notes from the Some eastern yellow robins are having trouble finding food. This species inhabits eastern and south-eastern Editor Australia, but those in the Wet Tropics, cut off from the rest by a dry corridor (the Burdekin Gap), appear to be evolving Just as the Great Barrier Reef World separately and are recognised as a distinct sub-species. Heritage Area is associated with coral reefs, so the Wet Tropics These eastern yellow robins in the sub-species, World Heritage Area is associated north frequent the tall open forests distinct from Eastern yellow robin with rainforest. However, this is not known as wet sclerophyll – a narrow those elsewhere the complete picture. Coral reefs band of forest which exists between in Australia, rely particularly make up only 6 percent of the GBR rainforest and dry sclerophyll (see heavily on flowering banksias. In WHA – many more diverse page 2). They find much of their food north Queensland, the stronghold of ecosystems are also included (see by clinging sideways to a tree trunk, a banksias (notably Banksia aquilonia) Tropical Topics 66). Similarly, metre or so above the ground, and is the wet sclerophyll zone. However, although rainforest covers a larger plunging down when they spot they are unable to regenerate in proportion of the WT WHA, as something good to eat – usually an rainforest and eventually disappear as much as a third of the Area is insect. For this strategy to be it invades. White-cheeked composed of non-rainforest successful they need to have a clear honeyeaters are also losing ground. vegetation types. This Tropical view of the ground – but undergrowth Topics is the first in an occasional is getting in the way. White-naped honeyeaters in north series on vegetation types outside Queensland are largely restricted to the rainforest. The wet sclerophyll is in danger of wet sclerophyll forest although they being swallowed up by its neighbour. are found in dry sclerophyll elsewhere Wet sclerophyll forest is fairly In just 50 years, approximately half of in Australia. Feeding on eucalyptus abundant in south-eastern this limited forest type has been nectar, they are at risk of losing their Australia, but in the north it is invaded by rainforest. These trees, food source if rainforest prevents restricted in area. Situated in the shrubs and vines form a dense these trees from growing. tropics it has a special character understorey in place of the normal with some special inhabitants. open grassy floor, concealing the Even rainforest birds depend on wet eastern yellow robins’ food. Eastern sclerophyll forests on a seasonal yellow robins do not frequent those basis. Bridled honeyeaters, for I would like to thank Rupert Russell, sections of wet sclerophyll forest example, feed on banksias in winter. QPWS, Daryn Storch, QPWS, and where rainforest has invaded – so as Angie Chapman for their valuable the rainforest front advances, the Much of this information came to light help with this issue. robins’ habitat shrinks. when Cooperative Research Centre (CRC) Rainforest researcher Angie Please note White-throated treecreepers are Chapman did a study of birds in the that you are welcome to photocopy similarly affected since their feeding wet sclerophyll forests. She found a Tropical Topics. However, if the strategy (see page 5) also requires a total of 100 species using the forest, at text is reproduced separately it must clear view of the tree trunks. Both least some of the time. One third of not be altered and must mature rainforest and uninvaded wet these are either endemic to the Wet acknowledge the Environmental sclerophyll provide suitable Tropics, or recognised as sub-species, Protection Agency as the source. conditions but these birds tend to distinct from those elsewhere in Illustrations must not be reused avoid invaded wet sclerophyll where Australia. While only a few are wet separately without permission. their view is obscured. sclerophyll specialists, it would seem Please contact the editor (details on that many use this rare forest type on the back page) if in doubt. White-cheeked honeyeaters depend a seasonal basis. Many bird species largely on nectar for food. Those in will be losers if the wet sclerophyll the Wet Tropics, also recognised as a forests disappear. Wet sclerophyll and the rainforest invasion Although tall open woodlands cover fairly large areas elsewhere in Australia, in the Wet Tropics they are limited to a narrow, broken strip, 400km long, bordering the western side of the rainforest. Situated above 600m, this strip is 4km wide at most but often it extends for just a few metres – the accompanying map necessarily exaggerates its extent in places. Known as the wet sclerophyll, this forest type needs a wetter climate than the adjacent dry sclerophyll, but is characterised by the presence of eucalypts and other sclerophyllous plants. The wet nature of the terrain occupied by wet sclerophyll is also suitable for rainforest – and rainforest is moving in. In many areas tall eucalypts, typical of wet sclerophyll forests, can be found towering above a younger rainforest understorey. Since the seeds of these eucalypts rarely germinate and seedlings do not thrive in the shady conditions created by the rainforest, there are no saplings coming up to replace their elders. It is therefore apparent that a change in vegetation type, from wet sclerophyll to rainforest, is taking place. CSIRO There has been no significant change in rainfall patterns to trigger this change. It is thought that in the past, fires sweeping in periodically from the dry sclerophyll forests further west kept the rainforest at bay. A change in burning regimes and fuel loads since the arrival of Europeans and the disruption of traditional Aboriginal land management practices is thought to be responsible. Banksia aquilonia flowers provide nectar for many wet sclerophyll animals. Fire and wet sclerophyll trees Sclerophyllous trees are adapted to fire. They often have thick fire-resistant bark but, in the event of serious damage, many are able to produce new shoots from under the bark or from the roots (lignotubers). These forests are prone to fire because their open canopies allow grass to grow below, their leaves and twigs have inflammable oils and the abundant litter they produce burns easily. Rainforest, on the other hand, is relatively fire-resistant, but if it does burn, maybe on dry margins or disturbed sites, it is easily damaged. Wet sclerophyll trees – between the two – are ambivalent about fire. Rose gums (Eucalyptus Red stringybark trees (E. grandis), the most typical of resinifera) are similar in many wet sclerophyll trees in north ways, with ash beds formed Queensland, are quite fire- after fire giving the young resistant over the age of about seedlings a good start in ten, although successive burns life. However, unlike the weaken and eventually penetrate rose gum, this tree has a the hollow trunks which develop in typically sclerophyll trick most mature trees. Fire also stimulates up its sleeve; it is able to germination. Some seeds sprout in the resprout from lignotubers if absence of fire (it is not required to release the top is burnt off. Although seed from capsules as is the case for many saplings are vulnerable, as an eucalypts) but a good burn – the hotter the adult this tree is fire resistant. better – greatly increases germination rates. Since dense undergrowth of rainforest shrubs, which grow in the absence of fire, inhibits germination, fire would appear to be Rose sheoak (Allocasuarina essential for these trees. On the other hand, torulosa) trees are often destroyed seedlings and saplings are vulnerable to fire. by fire, but frequently occur So this is a contradictory tree. Mass in clumps where the germination may follow fire, but, without a accumulation of lignotuber, young trees need a fire-free dropped needles period to become established. On the other suppresses the hand, fire is needed to keep the undergrowth growth of grasses, from smothering them. It would seem that the thereby reducing the intervals between fires in rose gum forests occurrence of fire. Rose are a critical factor for their survival. These trees do not sheoak occur within rainforest – they are unable to grow in shade. On the Rose gum Red other hand, their dense carpet of needles stringybark may stop potential rainforest invaders from germinating. 2 Bettongs, fungi and beagles Where are the bettongs? It seems that two apparently unlikely factors are the key to bettong distribution – infertile soils and fire. Studies have shown that distributions of northern bettongs their part in maintaining this useful relationship by are closely related to the poor, infertile soils derived from dispersing the spores from the truffles in their droppings. granite and metamorphic rock. This is in contrast to many These are not destroyed in the animal’s digestive tract. In other animals which do best on the better quality leaves and fact germination prospects are probably enhanced. fruit produced on fertile basalt soils (see Tropical Topics 63). In the case of bettongs, however, infertile soils – Fire plays another part in this complex relationship. Studies particularly those which are low in phosphorus – mean more have shown that there is a sharp increase in truffle food. production after fires. This means that bettongs are restricted to those forest areas where fire is still possible, The reason can be found by looking at ecosystem links. The not those which have been invaded by rainforest. trees which live in these nutrient-poor soils are particularly dependent on the contribution made by certain soil fungi. Since truffles are vital to the bettongs, their presence is seen These organisms, known as mycorrhizas and as the key to the survival of this endangered animal.