By Heather Haines
Historical trends in temperature and rainfall are fundamental to our understanding of Australia’s climate, yet we lack records that extend beyond 100 years into the past. Recently, we reviewed the use of tree rings for studying Australia’s historical climate.
Australia is a continent known for experiencing prolonged periods of floods and droughts. These extreme conditions are important for our biota and society. Yet both can have substantial impacts including heavy environmental and economic costs. Knowing how often droughts and floods occur helps us to understand how they are changing through time so we can predict them in the future and prepare for their consequences.
Unfortunately, historical climate records across the Australian continent are sparse and very few extend beyond 100 years. The lack of records means it is difficult to assess the long-term significance of climate variability on our environment and economy.
The analysis of tree rings has been a popular tool used to develop long-term climate records in North America and Europe. Tree growth is sensitive to environmental conditions and we can infer past climate by looking at variability within the rings. This type of study is termed dendroclimatology, and in Australia its application has been limited. A recent review paper published in Science of the Total Environment describes the current status of Dendroclimatology in Australia and outlines the potential for future use of this technique in different Australian climate zones.
The review covers the four major climate zones of Australia; temperate, arid, sub-tropical and tropical. It shows that all of these zones contain tree and shrub species which have the potential to provide high quality records of past climate.
Despite this potential only four dendroclimatic reconstructions have been published for Australia, one from each of the climate zones: A 3592 year temperature record for the SE-temperate zone, a 350 year rainfall record for the Western arid zone, a 140 year rainfall record for the northern tropics and a 146 year rainfall record for SE-subtropics (Figure 1).
We report on the spatial distribution of the past tree-ring studies and identify the key challenges in using tree-ring records for climate reconstruction in the future. Many Australian species have yet to be tested for use in dendroclimatology, this is due mainly to the difficulty in annual ring identification in Australian trees. Species from this region are known to exhibit both false (more than annual) and missing (less than annual) rings, exhibit faint unclear ring boundaries, and they may be highly sensitive to localized factors such as insects and competition.
New techniques may help us overcome these limitations. For instance using the ratio of carbon and oxygen isotopes or wood density patterns to establish annual rings, dating of rings to confirm age using radiocarbon analysis, and identifying ring boundaries based on their wood anatomy and properties. Combining these methods with traditional ring width measurements will enable more species to be used for dendroclimatological analysis across the entire continent.
Development of tree-ring chronologies across Australia will provide long-term climate records for areas with no other source of such climate data. A better understanding of the environmental conditions that have existed in the past will allow for stronger predicted conditions for the future. Such knowledge will allow environmental and economic planning to be directed towards the regions most in need of protection and mitigation under future flood and drought scenarios. This will help us to predict the effects of future climate change on the Australian economy and its biodiversity. Following on from this review, ARI researchers are attempting to use such mixed technique methods to develop long-term climate records from several sites across Australia.