The London Plane Tree (Platanus x acerifolia) as a climate change indicator species in Australia

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1 Cygnus (2012) 1: DOI , , , RESEARCH ARTICLE The London Plane Tree (Platanus x acerifolia) as a climate change indicator species in Australia Charlotte Patrick Lui Yi Ling Elaine Mark Eley Meng-Hsuan Lin Received: 23 May 2012 / Accepted: 29 May 2012 Abstract The purpose of this study was to analyse the London Plane Tree (Platanus x acerifolia) as an indicator species for climate change in Australia. The hypotheses of the study are that the distribution of the Plane Tree is expected to shift into cooler, more temperate regions, as the Australian climate grows more extreme. Furthermore, flowering and fruiting timings of the tree are expected to become increasingly early as temperature increases, because temperature is the main variable that determines the budburst timing of most temperate tree species (Chuine et al. 1999). Hence the London Plane tree is expected to be a valuable indicator species for changes in Australian climate. Distribution data from the ClimateWatch online database was manipulated and analysed alongside citizen s observations of tree phenophases. This data was interpreted and compared to climate data supplied by the Australian Bureau of Meteorology. In this study, it was found that the London Plane Tree is affected by climate in Australia, which has a strong impact on the species phenology and distribution. Distribution was found to be limited by climatic conditions, while phenophases were found to be limited and determined predominantly by seasonal temperatures. It was concluded that early flowering of tree species has been observed in previous international studies, and may be recorded in the near future in plane trees in Australia. For this reason the London Plane Tree is a valuable indicator species for climate change and we recommend continual observation through ClimateWatch. Keywords London Plane Tree (Platanus x acerifolia), citizen science, indicator species, climate change, ClimateWatch, phenology 1 Introduction The London Plane Tree (Platanus x acerifolia) originates from temperate regions of the Northern Hemisphere (Gilman and Watson 1994), yet is frequently used in temperate regions 112

2 worldwide as an ornamental plant in parks, gardens and urban streets (Iglesias 2007). As part of the Australian ClimateWatch program (ClimateWatch 2012), this species serves as an indicator species for expected anthropogenic-related climate changes around Australia. Plane tree flowering occurs in spring, described as short and intense by Iglesias et al. (2007). In the Northern hemisphere this period occurs in April and May, whilst in Australia it occurs in September and October. The species is deciduous, with leaves changing colour during the autumn months of March, April and May in Australia, while the earliest flowering and leaf colour changes observed occur in preceding months which are warmest (Iglesias 2007). As seen in previous studies, higher temperatures have led to earlier flowering and fruiting of the plane tree (Walter et al. 2002). Observations of the timing of these phenological occurrences in Australia will allow for a representation of climate change in areas where this species occurs. The distribution of the plane tree is expected to shift into cooler, more temperate regions as the Australian climate grows more extreme, with flowering and fruiting timings of the tree expected to become increasingly early as temperature increases. As temperature is the main variable in determining the budburst timing of most temperate tree species (Chuine et al. 1999), the London Plane tree is expected to be a valuable indicator species for temperature change in Australia. These are the hypotheses of this research article, and will be examined throughout the content of the paper. The purpose of this study is to investigate recent London Plane Tree distribution data and records of the species phenophases to attain a greater understanding of the way climate effects the tree s distribution and phenology. Through use of data supplied by ClimateWatch (2012), and from information gathered from previous studies, this study will aim to produce a broader understanding of the Platanus x acerifolia in Australia and how climate change may affect this species. Distribution maps have been cross-examined with climate maps (provided by the Australian Bureau of Meteorology) to explain where and why the plane tree is growing in Australia. The ClimateWatch distribution data are the result of the increasingly important branch of data collection known as citizen science. By involving the Australian public with projects such as Climate Watch, citizens may gain an awareness of climate change, nature, endangered species and the great biodiversity that exists in Australia. Although there is a large margin for error in citizen science (which will be discussed in this study) invaluable data can be recorded over time in a great variety of locations by Australian citizens making use of the ClimateWatch online site, allowing phenological behaviour in flora and fauna across Australia to be observed and interpreted. 2 Materials and Methods The data presented in this study originates from the ClimateWatch online database (ClimateWatch 2012) for Australian species displaying phenological behaviours or cycles. 113

3 Citizens of Australia have access to ClimateWatch via the internet and any citizen is able to become a ClimateWatch user. Once individuals had attained online membership, sightings of the London Plane Tree (and other species) were recorded in the database by these citizens from 2010, through 2011 and in early Citizens were prompted to use ClimateWatch through initiatives such as the BIOL1130 unit at the University of Western Australia, involving a mandatory 20 entries to the database from each biology student. Individual entries for the London Plane tree involved choice of phenophase by the Climate Watch user. These categories are listed below ( First fully open single flower Full flowering End of flowering (when 95% of the flowers have faded) First fully open leaf open First leaf to change colour changing colour First leaf to drop this year 50% or more leaves dropped No leaves Fruit fully ripened/turned brown Entries also included the date and time of sighting, latitude and longitude, name of location and additional comments from the user. The Climate Watch data was manipulated via Microsoft Excel to produce a data table and distribution map, and then entered into Microsoft Word. The data table (Table 2) was produced through extensive viewing and handling of the data on Excel to observe the most frequently recorded phenophase for each month in 2010, 2011 and 2012 (where data was available). This data was then interpreted in relation to the two hypotheses of the study. From the latitude and longitude entries for each sighting, a distribution map was also produced. The distribution map used both ClimateWatch and Atlas of Living Australia, entering sightings from both sites to create a reliable source of data while highlighting any possible outliers (Figure 1). Interpretation of the Climate Watch dataset was undertaken by comparisons with historic climate data. This climate data was sourced from the Australian Bureau of Meteorology (2012). The Bureau website section titled Climate and Past Weather provided maps to be compared against the distribution map of plane trees produced for this study. 3 Results Location The locations of tree observations coincide with temperate to sub-tropical regions of Australia, suggesting hot, arid environments are unsuitable for the species (Figure 2). Central and Northern Australia do not hold any recorded London Plane Trees. However, this is likely to be the result of a small human population in these areas, as the Plane tree is introduced for 114

4 ornamental purposes in urban environments. The low human population in arid, desert Australia may also result in few or no Climate Watch entries made from these regions. This is a potential source of error in the Climate Watch citizen science data. Lack of recorded sightings does not necessarily mean the species does not exist in particular regions, hence making the citizen science data collection method less reliable. Not all sections of the Australian environment have been examined for this particular species due to the Australian human population distribution, which is concentrated mostly in coastal cities. Hence the London Plane Tree distribution reflects the human distribution, with the majority of sightings recorded in capital cities along the coast. The lowest annual mean temperature at which the species is recorded is c. 12 C in Victoria, whilst the highest is 24 C in Queensland. This finding suggests that the optimum mean temperature at which the London Plane will thrive is C. Future distribution of the tree may indicate changes in climate based on this finding. Locations with a mean annual temperature which rise above 24 C (potentially Queensland) may see a reduced occurrence of plane trees. Vegetation Greenness and Rainfall The plane tree distribution also corresponds with relatively high greenness of vegetation as seen in Figure 3, and relatively high rainfall as seen in Figure 4. These two variables are interrelated as rainfall directly impacts vegetation greenness. The data suggest this species is intolerant to exceptionally low rainfall and has been recorded predominantly in coastal areas of high rainfall. However, Figure 3 is a mean annual rainfall representation, and the high concentration of plane tree sightings in Perth, Western Australia suggests that the tree is capable of surviving relatively hot, dry summers as are characteristic of the Perth region. However, if drought were to strike this region and the rainfall to fall below c. 1000mm/year (the driest condition in which plane trees are recorded), a decrease in plane tree sightings may be expected. Furthermore, this data originates from 12 years prior to present day, therefore extrapolating outside this data is an unreliable source of information for plane tree tolerance to rainfall. The findings of this study in relation to the past data do, however, support the original hypothesis in terms of the approximate climate conditions in which the tree will be found and be able to survive. Should climate alter outside of these stated boundaries, future distribution maps would be expected to consequently alter. London Plane Tree sightings would be expected further south, into higher rainfall and lower temperature regions. Humidity (Figure 5) correlates with the temperature, rainfall and greenness data in terms of distribution. High annual mean humidity levels are supported, with greatest sighted number of plane trees in the coastal temperate to sub-tropical regions of Australia. 115

5 Table 1 Through comparison with the London Plane Tree Distribution Map (Figure 1), regions of minima and maxima for the following categories were established. This climatic data shows the range of temperatures, rainfall and humidity in which the London Plane Tree can survive in Australia. The relative vegetation greeness of the plane tree distrtibution in Australia has also been included for comparison of the plane tree against other vegetation in genera Annual mean Temperature ( C) Rainfall (mm/year) ( ) Relative Humidity at 9am (%) ( ) Relative Vegetation Greeness (NDVI) ( ) Minimum Maximum Range Table 2 Major citizen observations of phenophases for the London Plane Tree in Australian. Most frequenty recorded phases for a given month were used in this table. Missing data occurred due to span of data from mid 2010 to early Missing data also a result of citizens incorrectly entering data, or not entering data to full completion. Month and most frequently observed phenophase Jan Feb Mar June July Aug Sept Oct Nov changin g colour changin g colour droppin g, brown fruit droppin g changin g colour - - Fruit ripened, leaves droppin g, first flowers First fully opened leaves, not flowerin g open, not flowerin g, brown fruit open, not flowerin g, brown fruit 2012 open, brown fruit open, not flowerin g, brown fruit

Fig. 1 Citizen science (data collected by Australian citizens) allows for observations of species such as the London Plane Tree across a wide variety of locations and environment types.

6 Fig. 1 Citizen science (data collected by Australian citizens) allows for observations of species such as the London Plane Tree across a wide variety of locations and environment types. The distribution of the London Plane Tree (Platanus x acerifolia) is shown above, based on data collected and entered by Australians into Climate Watch online. Data collected is from Red and blue dots on the map indicate placement and concentration of Plane trees in Australia as witnessed and described by Australian citizens. This data can be cross examined with climate maps to suggest ideal temperatures in which this species can live, as well as give an understanding of how climate change may effect the distribution of the species. 117

Fig. 2 Australian Bureau of Meterology Mean Temperature Map. This figure depicts mean air temperatures ( C) of the period March 2011-February 2012 in Australia.

By comparing this recent annual average data with London Plane Tree distribution, the effects of climate change on this temperate tree species can be predicted. Source: http://www.bom.gov.au/ Fig.

7 Fig. 2 Australian Bureau of Meterology Mean Temperature Map. This figure depicts mean air temperatures ( C) of the period March 2011-February 2012 in Australia. Colour key on right side indicates temperatures as seen on the map. By comparing this recent annual average data with London Plane Tree distribution, the effects of climate change on this temperate tree species can be predicted. Source: Fig. 3 Australian Bureau of Meterology Vegetation Greeness Map. This figure depicts the relative greeness of vegetation across Australia during the warm period of September February Colour key on right side indicates normalised difference vegetation index, assignmning a number value to a relative greeness of vegetation. This data over the summer months in Australia allows for a comparison with the London Plane Tree disribution to draw conclusions about the hardiness and greeness of this species relative to other vegetation found in Australia. Source: 118

Fig. 4 Australian Bureau of Meterology Average Annual Rainfall Map (1961-1990). This figure represents average annual rainfall during this 30 year period in Australia.

This data over the summer months in Australia allows for a comparison with the London Plane Tree disribution to draw conclusions about the hardiness and greeness of this species relative to other

8 Fig. 4 Australian Bureau of Meterology Average Annual Rainfall Map ( ). This figure represents average annual rainfall during this 30 year period in Australia. It is the most recent, complete data for average rainfall across Australia. The colour key on right side indicates rainfall level in millimetres as seen on the map. This data over the summer months in Australia allows for a comparison with the London Plane Tree disribution to draw conclusions about the hardiness and greeness of this species relative to other vegetation found in Australia. Source: Fig. 5 Australian Bureau of Meterology Average Humidity Map (9am ). This figure depicts the average daily humidity at 9am during this 30 year period in Australia. Colour key on right side indicates the relative humidity percentage. This data allows for a comparison with the London Plane tree disribution map to draw conclusions about the effect of humidity of distribution of this species across Australia. Source: 119

9 4 Discussion The original hypotheses of this study were that the distribution of the London Plane Tree will shift into cooler, more temperate regions as the Australian climate becomes warmer, and that the flowering and fruiting timings of the species are expected to occur earlier in the year. Through examination of a species distribution map and several Bureau of Meteorology climate maps, several conclusions were made on the occurrence of Platanus x acerifolia across Australia. Phenophase timing Phenophase timing of the London Plane tree was based solely on the ClimateWatch citizen science data. The period in which the tree flowers is short, lasting only 48 days in 2011 in Perth, Western Australia from first recorded flowering to the first recorded end of flowering. The flowering period in Table 2 correlates with the spring months of September and October, as was predicted. However, comparison with other years would be necessary to make an accurate conclusion about the flowering period of this species and whether it has changed in recent years. This data, therefore, does not conclusively support the hypothesis that flowering will occur earlier due to increasing temperatures. Further data from ClimateWatch will be needed in coming years to compare against the data seen in this study. However, a study conducted by Walter et al. (2002) concluded that flowering of numerous plant species in North America and Europe has been occurring earlier each year. From 1954 to 1972 flowering and leaf unfolding has been observed to occur 1.4 to 3.1 days earlier each decade (Walter et al. 2002). Similar observations in Australia may be made with continued citizen involvement in Climate Watch. The fruiting period in Platanus x acerifolia is long. The fruit becomes ripe and brown in the winter months, with the first recorded ripe fruit in June 2010 in Melbourne. The data available also suggests that fruit ripening occurred later in 2011, as the first recorded ripening of fruit was in September 2011 in Perth. However, as Perth has a warmer climate and lower rainfall than Melbourne, climate variations between the two locations may be responsible for this difference. Based on these observations, it would appear that the plane tree fruit ripens later in a warmer climate, rather than earlier. This data therefore does not support the hypothesis, as it was predicted that fruit ripening would occur earlier in warmer temperatures. Further data is needed to come to a full conclusion for the effect of temperature on fruiting. Climate analysis For the purpose of this study, the Australian Bureau of Meteorology climate map for average Australian rainfall has been used (Figure 4). This data ranges from 1961 to The distribution data ranges from 2010 to 2012 (Figure 1), and therefore a time gap exists between these two figures. As this rainfall data is averaged over a longer period of time, the age of the data in relation to the age of the ClimateWatch data was not considered a major source of error. Furthermore, as the plane tree lifecycle is relatively long, it is assumed that 120

10 many of the observed specimens have been exposed to these previous rainfall conditions in 1961 to The largest populations of London Plane Trees were observed in temperate climate conditions. Hot, dry summers occur in several of these regions, yet a minimum rainfall appears to be necessary for the growth of plane tree populations. Furthermore, a temperature range for these regions of plane tree growth exists. However in examining these patterns of distribution in relation to climate, it must be taken into consideration the human populations in the regions. As the plane tree is an introduced species in Australia, human cities and establishments dictate where the trees will be distributed. The intentional planting of the trees in urban areas is a major part of where the tree populations are located. They are predominantly concentrated around coastal major cities. Had the species been native and growing wild, the distribution would be a much more accurate representation of the climatic prerequisites for the plants growth. However, irrigation systems and shelter in urban areas reduces the reliability of the distribution data of plane trees in comparison to climate data. Climate is not the only variable dictating the location of the plane tree in Australia. However, the distribution of the plane tree does correlate with original predictions for this study. Extreme, hot and arid climates were not inhabited by plane trees according to ClimateWatch data. Similarly, very cold regions and tropical northern regions were uninhabited by the species in Australia. If, in future years, the species is recorded in these different climatic regions, the species may indicate climate change. Potential issues in ClimateWatch data analysis Chuine et al. (1999) made use of the London Plane Tree as an experimental group for predicting the flowering period of temperate tree species across different locations. From examinations and recordings of the varied European tree populations, the authors of the study were able to come to conclusions about the reliance of Platanus x acerifolia on climate for timing budburst and flowering. The results support the hypothesis of this Climate Watch study. The London Plane Tree flowering is affected by climatic variables (Chuine et al. 1999). However it was also found in this past study by Chuine et al (1999) that genetic variations between populations must be taken into account when comparing phenological events or distribution. The results of this previous study apply to the Climate Watch data, as it involves citizens in locations across the whole of Australia. Slight genetic variations between individuals in a population may produce varied data across Australia as populations have adapted over time to differing climatic conditions. While the results of this study were useful, comparison between genetically different populations in different climates may be a source of error in data relating to the phenological events of this plant across Australia. Averaging or compiling of phenology-related data from across Australia may not be entirely valid, as flowering and budburst timing may alter slightly between individuals and between populations. Genetic variation is an uncontrolled variable in the Climate Watch study, introducing another source of difference in phenology across Australia other than the climatic variables upon which this study focused. However, the London Plane tree has a relatively low 121

11 genetic diversity between individual trees (Chuine et al. 1999) when compared to other plant species. Therefore, phenology and distribution of the species has been examined in this study assuming minimal difference resulting from genetic variation. Acknowledgements Climate Watch must be acknowledged for the data used throughout this study, which was provided for the University of Western Australia. From this data Table 1 and Figure 1 were produced and analysed. The Australian Bureau of Meteorology must also be acknowledged for the climate and weather maps used throughout this study as a comparison to ClimateWatch data (Figure 2, 3, 4, and 5). Thanks goes to Shannon Brandt, Michael Millman, Laura Wells and Lauren Sumner for providing feedback in the drafting stages of this report. References Atlas of Living Australia (2012) Australian Bureau of Meteorology (2012) Botany of London Plane Trees (2009) Chuine PC, Cour P, Rousseau DD (1999) Selecting models to predict the timing of flowering of temperate trees: implications for tree phenology modelling, Plant, Cell and Environment 22: 1 13 Climate Watch (2012) Flora of Australia Online (2007) Gilman E, Watson G (1994) Platanus x acerifolia Bloodgood, fact sheet distributed by Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL Iglesias I, Rodríguez-Rajo FJ, Méndez J (2007) Behavior of Platanus hispanica Pollen, an important spring aeroallergen in northwestern Spain, J Investig Allergol Clin Immunol 17: Chakraborty S, Luck J, Hollaway G, Freeman A, Norton R, Garrett KA, Percy K, Hopkins A, Davis C, Karnosky DF (2008) Impacts of global change on diseases of agricultural crops and forest trees CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources 3:

Weather and Climate of the Rogue Valley By Gregory V. Jones, Ph.D., Southern Oregon University

Weather and Climate of the Rogue Valley By Gregory V. Jones, Ph.D., Southern Oregon University The Rogue Valley region is one of many intermountain valley areas along the west coast of the United States.