Beyond the periphery

A National Environment Research Program (NERP) study has examined the important role that peripheral areas play in conserving Wet Tropics rainforest fauna. The study, undertaken by Dr Conrad Hoskin from James Cook University and Dr Robert Puschendorf from Plymouth University, has found that some endangered Wet Tropics frog species are persisting better in peripheral areas than in adjacent core rainforest habitat. The known range extent of several other vertebrate species was also substantially expanded during the study.

The research demonstrates the conservation significance of these areas both in their own right as well as for safeguarding the longterm viability of Wet Tropics biodiversity. Many of the peripheral areas surveyed occur outside of the Wet Tropics World Heritage Area, highlighting the need for ongoing collaborative management.

Core and peripheral areas

The Wet Topics World Heritage Area is recognised for its rich biodiversity and high number of endemic species. Many of these species are found in ‘core’ rainforest areas; cool, wet mountainous regions such as Thornton Peak and the Atherton and Carbine Tablelands.

Peripheral areas are hotter, drier habitats along watercourses of the western margins of the World Heritage Area and adjacent to the core areas, as well as some isolated rainforest patches to the north, south and west. Although the peripheral areas are poorly surveyed, they are known to be biologically rich with endemic species and vertebrate subspecies. These areas are generally located outside of the World Heritage Area.

About this study

Drs Hoskin and Puschendorf surveyed the core rainforest and peripheral areas of the Wet Tropics region. They assessed the health and population status of ‘missing’ stream frogs and recorded other vertebrate species found. They also undertook a reintroduction of the critically endangered Armoured Mistfrog (Litoria lorica) to establish a second wild population.

Endangered stream dwelling frogs

Amphibian chytrid fungus has severely impacted frog populations throughout the world with many species believed to have become extinct. Declines have been worse in higher elevation areas where chytrid thrives in damp, cool conditions.

In the Wet Tropics, it is the stream dwelling frogs from the ‘core’ rainforest areas that have been hardest hit by the fungus with a number of species severely declining since the initial outbreaks of the late 1980s and early 1990s. One of these species, the Armoured Mistfrog, was rediscovered by Dr Puschendorf in 2008 after being missing for sixteen years. Surprisingly, rather than being found in the core rainforest habitat it had disappeared from, it was rediscovered in dry sclerophyll forest in an area that it was not known to previously occupy. It was also found to be coexisting with chytrid.

This rediscovery supported observations that some other endangered Wet Tropics frogs also appeared to be persisting better in hotter, drier peripheral areas, suggesting more ‘missing’ frogs may be surviving beyond their core rainforest habitats. One of the aims of Drs Hoskin and Puschendorf’s NERP study was to test this theory.

Status of the missing frogs

The study found that several of the Wet Tropics endangered frog species were enduring well in the peripheral areas, with some persisting in higher densities in upland dry forest than in core rainforest. There was evidence of population recovery for two species, the Waterfall Frog and the Common Mistfrog, which were found in upland rainforest sites that they are known to have previously disappeared from. Encouragingly, peripheral populations appear to be living with chytrid, probably as a result of higher environmental temperatures in these areas being less conducive to the fungus.

The researchers noted the following peripheral areas for particular mention: the western slopes of Carbine Tableland, Lamb Range and Atherton Tableland; the periphery of Windsor Tableland; and Blencoe Falls.

Discouragingly, two of the Wet Tropics ‘missing’ frog species are now believed to be extinct with targeted surveys failing to detect their presence either in the core rainforest sites or peripheral areas. A third frog, the Northern Tinker Frog, is also likely extinct, pending results from currently deployed call recorders.

Based on their research findings, Dr Hoskin and Dr Puschendorf have recommended updated legislative status for the Wet Tropics missing frogs as per Table 1. 

Table 1 – Present and recommended legislative conservation status of ‘missing’ frogs of the Wet Tropics.

Key: Ex – Extinct, CE – Critically endangered, E – Endangered, V - Vulnerable