Download Forward shift in flowering periods of Leptospermum laevegatum due

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. Accessed 6 April
2013 CSIRO, 2011, 'Science and Solutions for Australia- Climate change' . Available from: http://www.csiro.au/
Accessed 12 April 2013 CSIRO & Australian Bureau Of Meteorology, 2012, 'State of the Climate' CSIRO Publications, 3-4. Dunlop M & Brown P, 2008, 'Implications of climate change for Australia's National Reserve System: A
preliminary assesment'. In: Department of Climate Change (ed.). Canberra, Australia. Flora Base, 2009, Leptospermum laevigatum (Gaertn.) F.Muell. Department of Environment and Conservation:
Western Australian Herbarium
Hoffmann AA & Sgrò CM, 2011, 'Climate change and evolutionary adaptation', Nature, vol. 470, pp. 479-485
Howden M, Hughes L, Dunlop MIZ, Hilbert D & Chilcott C, 2003, 'Climate Change impacts on biodiversity in
Australia'. Available from: <http://www.csiro.au>. Accessed 10 April 2013]
Hughes L, 2003, 'Climate Change and Australia: Trends Projections and Impacts', Ecology vol. 28, no. 4, pp.
423-443
Keatley M & Hudson I, 2007, 'Shift in Flowering Dates of Australian Plants Related to Climate: 1983-2006',
Modism 2007: International Congress on Modelling and Simulation: Land, Water and Environmental
Management: Integrated Systems for Sustainability, pp 504-510 Keeling RF, Kortzinger A &GruberG, 2010, 'Ocean deoxygenation in a warming world', Annual Review of
Marine Science, vol. 2, pp. 199-229
Lacey E, Bassan S, Dai Vo T & Ryan K, 2012, 'The phenology of the Cabbage White Butterfly - the effect of
climate change', Cygnus, vol. 1, pp. 31-44
Ladiges P, Evans B, Saint R & Knox B, 2010, 'Biology: An Australian focus', McGraw Hill Publications
36 Law B, Mackowski C, Schoer L & Tweedie T, 2000, 'Flowering phenology of myrtaceous trees and their
relation to climatic, environmental, and disturbance variables in northern New South Wales', Austral
Ecology, vol. 25, pp. 160-178 Parmesan C & Yohe G, 2003, 'A globally coherent fingerprint of climate change impacts across natural
systems', Nature, vol. 421, pp. 37-41 Richardson AD, Keenan TF, Migliavacca M, Ryu Y, Sonnentag O & Toomey M, 2013, 'Climate change
phenology and phenological control of vegetation feedbacks to the climate system', Agriculture and
Forest Meteorology, vol. 169, pp. 156-173 Rumpff L, Coates F & Morgan J, 2010, 'Biological indicators of climate change: evidence from long-term
flowering records of plants along the Victorian coast, Australia', Australian Journal of Botany, vol. 58,
pp. 428-439
Wale J, Hooper S & Hand M, 2012, 'The commencement of flowering of the Marri tree shifts earlier in response
to the increase in temperature and alteration of seasonal timing', Cygnus, vol. 1, pp. 172-178
Walther G, Post E, Convey P, Menzel A, Parmesa, ., Beebee TJC, Fromentin J, Hoegh-Guldberg O & Bairlein
F, 2002, 'Ecological responses to recent climate change', Nature, vol. 416, pp. 389-395
Wrigley JW & Fagg M, 1993, 'Bottlebrushes Paperbacks and Tea Tree and all other plants in the
Leptospermum alliance', Angus and Robertson Publications 37