Rainforests and bell miner associated dieback in natural ecosystems
In the age known as the Anthropocene Era for the great number of human-caused extinctions, it is alarming to see stands of forest dying. Across southern Australia, fragmentation and degradation of woodlands has led to dieback of eucalypts, loss of understory and decline in species populations. Chronic decline and dieback, including bell miner associated dieback (BMAD), is predicted to impact on 790,000ha or 18% of forests in coastal New South Wales.
This study assessed BMAD in coastal gullies between Eden and Bermagui, on the far-south coast of NSW. The gullies were in excellent natural condition, with weeds occupying just 0.03% of the plots. This study is unique in assessing vegetation within BMAD sites in a natural environment, contrasting for example with studies in northern NSW that are affected by Lantana camara. Vegetation assessments were conducted in 58 plots within 8 bell miner colonies, producing 1098 individual flora records of 164 species. A list is compiled of species found to be susceptible to BMAD.
A conceptual model compiles literature to identify understory density, sparse canopy, water availability, a level of soil moisture content and the presence of bell miners as the key elements for managing BMAD. Monitoring of tree health 5 years after an experiment which removed one of the prerequisite conditions, the presence of bell miners, found that this maintained tree health.
The questions answered by this study are a) does BMAD lead to an increase in rainforest, and b) can the resultant ecosystems be classified as rainforest? The scientific result of this study, is that BMAD does not lead to rainforest, and is not a form of succession. Warm Temperate Rainforest communities were found at 5 of the 8 sites, and included examples of Littoral Rainforest. The lack of significant increase in proportion of rainforest species and in understory density, suggest a common cause leads to any increase in rainforest, understory density and BMAD. The most likely cause is an absence of fire.
PDF download of thesis (3.5mb), “Rainforests and bell miner associated dieback in natural ecosystems”