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Cygnus (2013) 2: 29-37 DOI [20763492, 21308666, 21327567, 21294472] RESEARCH ARTICLE__________________________________ Forward shift in flowering periods of Leptospermum laevegatum due to rising temperatures caused by Climate Change Jessie Georgiades • Katrina Schleicher • Amelia Waters • Nicolas Watkins Received: 23 May 2013 / Accepted: 28 May 2013 Subject Editor: Hammad Khan, Manuscript Editor: Susan Barker Abstract Climate change is affecting a number of different aspects of the environment including the extant species. The purpose of this study was to examine whether increases in temperature as a result of climate change are affecting the phenological phases of Leptospermum laevigatum. This study hypothesised that increased temperatures would cause L. laevigatum to flower earlier than its historical flowering season. Data obtained from the ClimateWatch website was analysed and compared with historical data to determine whether the flowering stages had changed. The data was graphically represented in order to identify patterns of flowering. Comparisons were also made to temperature maps from the Australian Bureau of Meteorology in order to determine whether temperature was a determining factor in triggering different phenophases. This analysis has led to suggest the flowering of L. laevigatum is occurring earlier in the year due to increasing temperatures caused by climate change. Key words - Leptospermum laevigatum, phenology, Climate Change, temperature increase, flowering 1 Introduction Climate change is altering the way species interact and the phenological events that occur (Keeling et al. 2010). One of the more notable effects of climate change has been increased temperatures which has occurred on a global scale (CSIRO 2009). The average surface temperature of Earth has risen by 0.74°C over the past century. Australia has seen an increase in temperatures of more than double the rate of the historical records post 1950, with an average increase of slightly less than 1°C in the period 1910-2009 (Dunlop and Brown 2008; 29 CSIRO 2011). It is estimated that temperatures will increase by approximately 2.0 °C by 2030, and that by 2070 temperatures could increase by 6 °C (Hughes 2003), which would result in a cascade of effects in the biological environment. The long-term impact of climate change can be observed in a wide number of species, altering patterns in physiology, abundance, distribution and the timing of seasonal events (Howden et al. 2003). Research suggests that the phenological events of species could be affected by the increasing global temperatures (Walther et al. 2002). Each species has certain phenological phases which are the periodically occurring natural phenomena such as shooting and flowering in plants, migration of birds, egg laying and hatching of oviparous animals, and frog calling. Phenological cycles can be influenced by seasonal temperature and therefore changes in the cycles serve as a useful biological indicator of climate change (Rumpff et al. 2010; Richardson et al. 2013). Studies conducted by Parmesan and Yohe (2003) endorse this relationship through findings of a range of species (including birds, shrubs, trees, butterflies, herbs and amphibians) showing phenological changes as a result of climate change in recent times. Much of this data, however, is limited to the Northern Hemisphere (Keatley and Hudson 2007). L. laevigatum, commonly known as the Coastal Tea Tree, Victorian Tea Tree or Australian Tea Tree, displays periodically occurring events in its life cycle, and is an indicator of climate change in Australia. This plant is a large leafy shrub which is part of the Myrtaceae family (Wrigley and Fagg 1993). On average it grows around 6m tall with white flowers, which are approximately 20mm in diameter (Flora Base 2009). The tree also contains woody fruits which are semi fleshy and semi permeable, that contain the seeds for the tree (Andersen and New 1987). The phenological phases of L. laevigatum include no flower, first flower, full flower, last flowering, no flowers and fruits (Ladiges et al. 2010). L. laevigatum is native to South Australia, New South Wales, Victoria and Tasmania, typically located on coastal heathlands, sand dunes and cliffs. It has been introduced to Western Australia and in the South West it is an established environmental weed (Australian National Plant Society 2010). L. laevigatum is known to be capable of adapting to various soil conditions, although it is predominantly found in saline soils (Wrigley and Fagg 1993). Climate change affects the amount of sunlight plants are exposed to, the soil nutrients, moisture and subsequently their seasonal events. Extensive research on other Australian flora, which also flower during spring season, indicate characteristic changes to the timing of phenological events due to recent climate change (Walther et al. 2002). A study conducted by Walther et al. (2002) proposed plants that flower in spring have been flowering earlier over the past decades, due to the change in climate. The authors suggest that numerous plant species over the past 30-68 years have started flowering earlier by 1.2-3.8 days per decade. In agreement with studies showing many species’ response to recent changes in climate, it can be expected that a parallel change will be observed in L. laevigatum phenological events (Parmesan and Yohe 2003). ClimateWatch (www.climatewatch.org.au) states that L. laevigatum typically flowers from August to October, however historical records indicate it 30 previously flowered as late as December. Fruiting should also occur after the flowering phase. The purpose of this study is to further research the ecological responses to climate change. The aim was to examine the changes of the flowering phenophases of L. laevigatum from recent observational data from a two-year period (2011-2012) in comparison to historical data, in order to determine whether the changes observed in the data sets are correlated to temperature related climate change. The effect of climate change on most individual species is yet to be defined (Dunlop and Brown 2008). This study will provide greater understanding and knowledge on the effects of climate change on the plants that dominate the coasts of Australia. Based on the knowledge of climate change and research into the predicted effects on plant phenology, it was hypothesised that, due to temperature increases, flowering of L. laevigatum will occur earlier now than indicated in historical records. 2 Materials and Methods The data used in this study was provided to the University of Western Australia BIOL1130 students by ClimateWatch (2013). The data were collected by citizen scientists between 2011 and 2013, and downloaded as a Microsoft Excel spreadsheet. Observations that were defective or identified as an outlier were excluded from the count. The number of sightings for the first and full flowering phases in each month from 2011 and 2012 was calculated and used to produce two clustered bar graphs in Microsoft Excel. The latitude and longitude points for the processed ClimateWatch data were then isolated and imported into the mapping and analysis tool accessed on the Atlas of Living Australia (ALA) webpage (www.ala.org.au; Atlas of Living Australia, 2013). Those points were mapped and if proved to be inaccurate, such as unrealistic points would also be discounted, however all points appeared to be accurate. This data was then displayed as a distribution map of Australia. Once this data was placed on the map, historical data records from the ALA were also mapped. No changes were needed to be made to the historical data set as it was already verified. Analysis of these data provided knowledge of any distribution pattern or trend that would indicate changes in the timing of species’ phenological events. The Australian Bureau of Meteorology (www.bom.gov.au) database was utilised to source recent temperature trend maps of Australia (Australian Bureau of Meteorology, 2013). Analysis of these maps in conjunction with the distribution map of L. laevigatum from the ALA determined whether these factors are specifically key to the species and allowed assumptions to be made about the climatic changes occurring in the areas characteristic to the species. The annual mean temperature anomaly for Australia based on a 30 year climatology was obtained from the Australian Bureau of Meteorology(2013) to link with the distribution map – developing an understanding of the preferred temperature range of L. laevigatum and evident changes in temperature in its distribution range over a longer period of time. 31 Previous studies conducted with a similar method (Lacey et al. 2012; Wale et al. 2012) support the success of this approach. 3 Results The data for L. laevigatum provided by ClimateWatch reflects evidence of distinctive phenological events, specifically in the appearance of the first fully opened single flower and full flowering (i.e. more than 50% of flowers fully opened). Initial flowering dominated in the months of August and September in 2011, and was similarly observed in 2012 (Fig. 1a and 1b). In contrast, Fig. 1a shows L. laevigatum in full flowering occurred most frequently in August 2011, but the following year peaked in September. Flowering (i.e. from first fully opened single flower to full flowering) spans from August to October in 2011 (Figure 1a), whereas in 2012 a small number of flowers appear marginally earlier in July (Figure 1b). Despite these slight shifts in the occurrence of flowering events, October marked the end of the flowering period for both 2011 and 2012 (Fig. 1a and 1b). a) b) Fig. 1 Flowering periods for L. laevigatum in 2011 (a) and 2012 (b). This shows a slight shift in first and full flowering periods, with some trees flowering marginally earlier in 2012. Data sourced from ClimateWatch (2013) 32 Fig. 2 A map of historical data from 1770-2012 (Atlas of Living Australia 2013), with data from 2011- 2013 (ClimateWatch 2013). Comparison of the species distribution along the Australian coast shows that the distributions of the two data sets overlap. The majority of L. laevigatum are located on the south-western coast of Western Australia, south-eastern coast of South Australia, south and south-eastern coast of Victoria, northern and eastern coasts of Tasmania, and the eastern coast of New South Wales (Fig. 2). Fig. 3a demonstrates an overall increase in annual temperatures in 2011 from above average to highest on record temperatures in areas characteristic to L. laevigatum. Temperature patterns also display an increase in 2012 (Fig. 3b) with areas ranging from average to highest on record temperatures. a) Fig. 3 b) Mean temperature deciles in Australia (a) from 1 January to 31 December in 2011 showing very much above average to highest on record ranges in south-west Australia and above average to very much above average ranges in south-east Australia. (b) 2012 data reflects this increasing temperature trend in south-west Australia and ranges from average to very much above average temperatures in south-east Australia, with warmer temperatures also shifting into lower latitudes (Australian Bureau of Meteorology 2013). 33 Fig. 4 indicates temperature anomalies in southern regions of Australia from the last hundred years (1910-2012). This shows evidence of a positive trend in average temperatures, both in the frequency of positive annual anomalies since the 1950s, and the degree to which mean annual temperatures deviate above average. Fig. 4 Annual mean temperature anomalies for southern regions of Australia inhabited by L. laevigatum. Based on a 30-year climatology, this shows a strongly positive trend in mean temperatures. Data sourced from Australian Bureau of Meteorology (2013) 4 Discussion The purpose of this study was to examine the changes of seasonal events for L. laevigatum based on recent and historical data, and to determine if these changes are correlated to climate change. Limited data was available. However, based on the available historical records on ClimateWatch the seasonal events of the tree appeared to have altered. It was established that L. laevigatum is affected by the change in climate as depicted in Fig. 1. In addition, ClimateWatch (2013) indicated that flowers started to develop on the L. laevigatum during the start of spring. This statement is supported, as Fig. 1 depicts in 2011 and 2012, the first flowers occurred in the months of August and September and full flowering was also intense in the months of August and September. However, flowering in 2012 was reported to have occurred in July, one month earlier than August. The increased temperature around the coastal areas where this tree locates itself 34 provides a possible reason for this result. In comparing Figs. 3 and 4, it is evident that there has been a significant increase in temperature over the past decades in their area. Therefore we assume that the warmer temperatures have had an overriding effect in some areas to initiate flowering in L. laevigatum that is not reflective of historical information (ClimateWatch 2013). Previous studies have illustrated a distinctive average advancement in the onset of spring timed phenological events by 2.3-5.2 days per decade (Richardson et al. 2013). Another study conducted by Keatley and Hudson (2007) investigated the timing of phenological events in flowering species, showing an advancing trend of 0.37 days per year. Therefore it is expected a very marginal forward shift in the appearance of flowers for L. laevigatum in 2011 and 2012 should be observed. This has been reinforced by the data found in the timing of the appearance of L. laevigatum in the flowering phase (i.e. between showing the first single fully opened flower through to full flowering). The small number of L. laevigatum blooming slightly earlier in July is assumed to be a gradual adaptive effect of the mean increase in temperature that has been observed over the 2011-2012 period. Interestingly this has also been reflective of the long-term change in temperature patterns associated with global climate change (CSIRO 2011). The dependence of L. laevigatum upon particular temperature to trigger flowering events is indicative of the influence of changes in climate on phenological cycles (Rumpff et al. 2010). Along the coastline of south-eastern Australia temperatures have shown an increasing trend since the early 1900’s (Rumpff et al. 2010), and national annual mean daily temperatures have risen by 0.9°C since 1910 (CSIRO & Australian Bureau Of Meteorology 2012). This agrees with the extrapolation, based on the data, that the timing of seasonal events in spring flowering plants such as L. laevigatum will shift forward in future years. There are however, limitations in the data that have consequently affected the validity of these conclusions. The data provided by ClimateWatch (2013) was obtained over a short period of time. Therefore this increases the undesired effect of unknown outliers or invalid data in the process of discovering a trend. As sightings have been conducted from August 2011 onwards, there is uncertainty in the true occurrence of first flowering in 2011 and whether there was a potentially high number of L. laevigatum in full flower prior to August. The accuracy of the recordings is also uncertain, due to the possibility of citizen scientists falsifying data, due to human error or lack of knowledge. Sightings were also inconsistent, with minimal data obtained for most months over the two-year period with the exception of August and September 2012. It was difficult to identify which flowering changes are due to climate change or have been influenced by other factors. It has been discovered that flowering should occur earlier due to the warmer weather, so we can predict the few out of place flowering events may be due to other influences on the tree, such as fires that can cause changes in flowering (Law et al., 2000) or insect predation (Andersen and New 1987). The changing of seasonal events could also be known as evolutionary adaption. This means that the trees have to adapt to the conditions by which they are surrounded. This has the potential to alter natural interactions 35 between species such as plant predation (Hoffmann and Sgrò 2011). However, it was revealed that there was no difference in distribution of L. laevigatum in comparison to historical data (Fig. 2); therefore this was not considered a force of change for the timing of its phenological events. This study creates an avenue for further inquisition of more frequent and accurate data over a longer period of time. It will then be possible to produce reliable results to support the expected forward shift in the timing of flowering in L. laevigatum, resulting from the longterm changes in weather patterns that are climate change. It is therefore recommended that citizen scientists continue to utilise ClimateWatch, as this will, over a longer period of time, prove to be a very historical and beneficial indicator of biological effects of climate change in Australia. Acknowledgements This study acknowledges the University of Western Australia for supplying the data for this research. We would also like to thank Climate Watch, Australian Bureau of Meteorology and Atlas of Living Australia for the resources they provided. We also appreciate the guidance from Sonja Jakob. References Andersen AN & New TR, 1987, 'Insect inhabitants of fruits of Leptospermum, Eucalyptus and Casuarina in South- Eastern Australia', Australian Journal of Zoology, vol. 35, pp. 327-336 Atlas of Living Australia, 2013. Available from: <http://www.ala.org.au>. Australian Bureau of Meteorology, 2013, Australian Climate change and variability. Available from: <http://www.bom.gov.au/climate/change/aus_cvac.shtml > Australian National Plant Society, 2010, 'Leptospermum laevigatum' Available from: <http://anpsa.org.au/llae.html> ClimateWatch, 2013. Available from: <http://www.climatewatch.org.au>. CSIRO, 2009, 'Our Climate is Changing' Available from: http://www.csiro.au/en/Outcomes/Climate/Understanding/Climate-is-changing.aspx. 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