Project 2.5ii.3

Understanding the climate change threat to tropical forests

Project Leader: Dr David Hilbert, CSIRO

MTSRF-funded researchers used an artificial neural network classifier to investigate the large expansions, contractions and spatial shifts of the environments of structural forest types in the Wet Tropics bioregion over the last 18-20,000 years, as well as likely changes due to future warming. In the worst-case scenario (IPCC A1FI: rapid warming (5 °C) accompanied by reduced rainfall (-23%) by 2080), results indicate that there will be substantial changes - mostly decreases - in the areas suitable for many rainforest types. As mean annual temperature increases, forest basal area decreases and tree species endemism decreases, although tree species richness and tree density do not change along the temperature/altitudinal gradient. While it is not possible to say exactly where and when changes in forest structure and plant species composition will occur, the region’s forests will be in a substantial disequilibrium with their environment. Large changes in the ecological environments of the bioregion will stress existing forest communities and ecosystems. Some areas may remain suitable for a certain vegetation type despite rather large changes in regional climate, due to physical features such as soils and landforms. Our results indicate that these climate refugia are not likely to be important at regional scales in the A1FI scenario, except for some areas of Mesophyll Vine Forest ecosystems in the central Wet Tropics.

These observations suggest a number of likely responses to global warming in the Wet Tropics’ forests, including reduced basal area (carbon stocks) and possible expansion of generalist lowland species with concomitant decreases in more cool-climate adapted upland endemics. Our preliminary analysis indicates that relatively few Wet Tropics tree species (~10%) are altitudinal generalists; many species may be restricted to narrow altitudinal ranges (200 m, which is equivalent to a 1°C range of mean annual temperature). This suggests that, as the climate changes, many Wet Tropics tree species will rapidly be exposed to mean annual temperatures that are beyond their normal tolerances.


Climate change and avian malaria

Project Leader: Dr David Hilbert, CSIRO

Mosquitoes are important vectors of wildlife and human diseases - how will their distribution and disease vectoring capacity be affected by climate change? To begin to answer this question, MTSRF-funded researchers captured mosquitoes and birds at a range of different altitudes in the Wet Tropics, at three heights relative to the forest canopy and in three seasons over three years. They found that both the abundance and diversity of mosquitoes increased with estimated mean annual temperature. Genetic tests identified the presence of avian malaria in the most common lowland mosquito that was captured, Coquillettidia crassipes. This genus was recently reported to be a vector of avian malaria in Africa but had not previously been implicated as a vector in Australia. DNA analyses of bird blood samples showed that Haemoproteus was a more common haemosporidian infection than Plasmodium, and peak infection rates were observed at intermediate temperatures and elevations. By contrast, infection rates of avian malaria (Plasmodium relictum) were highest in the warmer sites and declined to an average of ~3% at mean annual temperatures below about 22.5°C.





Project 2.5ii.3 CSIRO Hilbert, D. (2010) ‘Threats to ecosystems in the Wet Tropics due to climate change and implications for management’

Summary: This report summarises recent research that suggests several likely changes and threats to biodiversity and ecosystem processes in the Wet Tropics Bioregion, and briefly discusses the implication of these changes for management.