MTSRF
Project 2.5ii.2
Increased process-based understanding of the likely impacts of climate change on Daintree lowland rainforest performance
Project Leader: Dr Michael Liddell, JCU
MTSRF funding has permitted the continuation of atmospheric flux studies at Cape Tribulation, building a nine-year dataset that can now be analysed. During this period a drought event in 2002-2003 allowed the influence of water stress on the carbon balance of the forest to be assessed, leading to the conclusion that wet season recharge is essential in maintaining photosynthetic productivity. Without at least 2 m of rainfall in the wet season full photosynthetic activity cannot be maintained throughout the year. Analyses of differences in cloud cover (= available solar radiation) indicates that a future increase in wet season cloud cover would result in a decrease in forest productivity. Although trace emissions of volatile organic compounds have been detected from the forest, and there are major aerosol formation events in the vicinity, the origin of these formation events has yet to be determined. Nonetheless they are undoubtedly important for ensuring cloud formation. Cyclonic damage to the ecosystem measurably increased forest respiration rates over the period 2000 - 2004. A predicted mean annual temperature increase of 3.6°C for the Daintree (CSIRO CMAR) and reduced rainfall in the wet season will place the rainforest in a highly stressed situation by 2080. Our field data show that mean annual temperature at the Cape Tribulation site has increased by 0.6°C over the past nine years.
Below-ground fluxes in water and carbon in lowland rainforest
Project Leader: Dr Michael Liddell, JCU
Despite a growing body of knowledge about the hydrology of tropical rainforests, little is known about temporal and spatial patterns of water uptake and carbon fluxes in soil. Water uptake will be an important factor in the response of forests to climate change. This MTSRF-funded project aimed to determine water uptake rates and identify some of the factors controlling them in lowland rainforest in the Daintree region. Soil water content and potential were measured at depths of 0.1, 0.75 and 1.5 m, over a two-year period. Water uptake was calculated from the change in soil water content during periods with no rainfall. Water uptake ranged from 0 to 12 mm d-1, and was closely related to mean soil profile water potential. These researchers also investigated carbon fluxes through the soil at the same location. Soil carbon content and fertility were measured by analysing topsoil (0-0.1 m) samples from across the site (5 x 5 grid across 1 ha, corresponding with litter collection traps) and samples to 1.5 m depth from a pit. Topsoil properties varied considerably across the site, and canopy cover was spatially correlated with soil fertility and depth/rockiness, as estimated by apparent electrical conductivity. Soil carbon was found to have a turnover rate of approximately 5% per year. Carbohydrate was the most abundant component of soil organic matter, but its concentration relative to other components decreased with depth. The rate of carbon cycling through the soil at this site is likely to be sensitive to perturbations in rainfall.
Long-term monitoring of flowering and fruiting in Wet Tropics rainforests
Project Leader: Dr Michael Liddell, JCU
MTSRF funding has permitted the commencement of a long-term project monitoring phenological shifts in rainforest flowering and fruiting in response to climatic variability. Two sites are being monitored: the Australian Canopy Crane Research Facility at Cape Tribulation (where presence/absence data are scored visually from the gondola of the crane) and in association with the SkyRail Rainforest Cableway near Smithfield (at which a d-SLR camera is used to continuously collect high-resolution images along both sides of the gondola carriageway; images are analysed later and species showing an event are identified). One year of data has been collected at both sites. Preliminary analyses of these new datasets, in combination with historical data from the SkyRail transect, indicate that these methods will enable us to successfully track changes in flowering/fruiting phenology in response to climatic variability.
Publications
Project 2.5ii.2 JCU Liddell, M. (2010) ‘Climate Change: Scaling from trees to ecosystems’
Final Report on Project Activities, June 2010. Project 2.5ii.2 set out to provide a detailed process-based understanding of the performance of lowland tropical rainforest in concert with climatic measurements, with a view to coupling this understanding with future climate scenarios provided by MTSRF Project 2.5ii.1 to predict possible influences of climate change on the Daintree lowland rainforest of far northern Queensland over the next century. This report includes summaries of outputs of each of the five key objectives of this project: (a) Atmospheric fluxes; (b) Plant physiology; (c) Fluxes of carbon and water; (d) flowering/fruiting phenology; and (e) Insect populations and biodiversity.