Shifts in the date of flowering commencement in some Australian plants

The impacts of climate change on natural systems have been documented in many parts of the world (e.g. Europe, Asia and the Americas) using phenological datasets which cover varying durations, but mostly over periods exceeding twenty years. Such data sets have been unavailable to date in Australia, and therefore impacts of climate change on natural systems (e.g. commencement of flowering) have not yet been documented. Without such long-term phenological data, it is very difficult to reliably predict the likely impacts of climate change on biodiversity.

The records used in this study come from the state of Victoria, Australia and have been collected between 1983 and the present. Records currently available for examination cover the period from 1983 to 2002. The dates of first flowering of 126 species from within one community have been recorded – approximately 45 species are currently suitable for examination (i.e. greater than 20 years of observation). This study reports the initial examination, via simple linear regression, of first flowering dates for four species from the data set.

Weather data (mean, minimum and maximum temperature) were obtained from the Bureau of Meteorology for the Scoresby weather station (station number 086104). Annual mean daily temperature was found to have increased significantly (P < 0.001) by 0.8ºC from 1965 to 2002. This observation is in broad agreement with reported increases in Australia's average temperature of 0.7ºC (over the much longer period from 1910 to 1999; however, the majority of this increase has occurred since 1950). Over the period of observation of flowering (1983 to 2002), temperature at the site has increased by 0.3ºC.

Two of the observed species (Glycine clandestina J.C. Wendl [Twining glycine] and Thysanotus tubersosus R. Br. [Tufted fringe lily]) have had significant shifts (P < 0.001 and P = 0.044, respectively) in their date of first flowering (Figure 1). This shift equates to 46 days later in twining glycine. The latest commencement of flowering was October 22nd (yearday 295) 2002 – the last year of observations currently being examined. Tufted fringe lily, however, has commenced flowering earlier (42 days); the earliest commencements of flowering were in 1985 and 2002 on the 9th of October (yearday 282).

The remaining two species (Dichondra repens J.R & G. Forst. [Kidney plant] and Wahlenbergia stricta (R. Br.) Sweet [Tall bluebell]) have not had significant shifts in their dates of first flowering (P < 0.829 and P = 0.192, respectively). Kidney plant has basically remained unchanged (0.39 days over the 20 years). For tall bluebell, although the shift is not significant, the negative trend would equate to flowering 15 days earlier.

The findings presented in this study suggest that climate change is likely to have a significant impact on the reproductive behaviour of plant species in south-eastern Australia. While the four species examined here have been arbitrarily chosen they demonstrate a diversity of responses occurring in Australian plants, similar to those recorded in other studies (e.g. Europe). A greater commitment to long-term data collection, and the collaboration of the climate-change and ecological modeling communities, is needed if greater understanding of climate change impacts on Australian biodiversity is to be achieved.