Factors influencing the flowering of the Tarengo Leek ...

FACTORS INFLUENCING THE FLOWERING OF THE TARENGO LEEK ORCHID (PRASOPHYLLUM PETILUM)

Nicholas Wilson, Julian Seddon and Greg Baines Conservation Research Technical Report 36 November 2016

Technical Report 36

Factors influencing the flowering of the Tarengo Leek Orchid (Prasophyllum petilum)

Nicholas Wilson, Julian Seddon and Greg Baines

Conservation Research Environment Division

Environment, Planning and Sustainable Development Directorate November 2016

ISBN: 978-1-921117-52-7 © Environment, Planning and Sustainable Development Directorate, Canberra, 2016 Information contained in this publication may be copied or reproduced for study, research, information or educational purposes, subject to appropriate referencing of the source. This document should be cited as: Wilson, N., Seddon, J. And Baines, G. 2016. Factors Influencing The Flowering Of The Tarengo Leek Orchid (Prasophyllum petilum). Technical Report 36. Environment, Planning and Sustainable Development Directorate, ACT Government, Canberra. http://www.environment.act.gov.au Telephone: Access Canberra 13 22 81 Disclaimer The views and opinions expressed in this report are those of the authors and do not necessarily represent the views, opinions or policy of funding bodies or participating member agencies or organisations. Front cover: Prasophylum petilum and the Hall Cemetery. All photographs: Conservation Research.

Factors Influencing The Flowering Of The Tarengo Leek Orchid (Prasophyllum petilum) i

Contents Executive Summary .................................................................................................................... ii

1 Introduction ........................................................................................................................ 1

2 Methods .............................................................................................................................. 2

2.1 Data Collection ................................................................................................................. 2

2.2 Statistical Analysis ............................................................................................................ 3

3 Results ..................................................................................................................................... 4

3.1 Total flowering individuals over 25 years ........................................................................ 4

3.2 Total flowering individuals over 21 years by patch ......................................................... 6

3.3 Frequency of flowering in individuals over 21 years ....................................................... 8

4 Discussion ................................................................................................................................ 9

4.1 Warm winters favour flowering ....................................................................................... 9

4.2 Complex temporal variation .......................................................................................... 10

4.3 Implications and further research ................................................................................. 11

4.4 Conclusion ...................................................................................................................... 12

Acknowledgments.................................................................................................................... 12

References ............................................................................................................................... 12

Appendix 1 ............................................................................................................................... 14

Appendix 2 ............................................................................................................................... 15

ii Factors Influencing The Flowering Of The Tarengo Leek Orchid (Prasophyllum petilum)

Executive Summary The Hall Cemetery, on the northern border of the Australian Capital Territory, is host to the second largest population of the endangered Tarengo Leek Orchid (Prasophyllum petilum). Since the Hall Cemetery population was identified in 1991, it has been monitored annually, providing 25 years of population statistics. The population at the Hall Cemetery has fluctuated substantially from year to year, particularly during the earlier surveys. Fluctuations in the population have often been attributed to climatic variation, though no specific associations have been suggested. There has also been spatial variation in the number of P. petilum counted during annual surveys of the Hall Cemetery population. The 25 years of P. petilum monitoring data were analysed to determine how the population has changed temporally and spatially, and what climatic variables might have influenced these changes. We used generalised additive models (GAMs) to predict the total population at Hall Cemetery, the population by location within the Hall Cemetery, and the probability of counting an individual plant. In addition to the monitoring data containing the date and location where a plant was observed, basic climatic variables including maximum and minimum temperature, and rainfall over one, three, six and twelve month periods prior to each survey were used as explanatory variables. Nights ≤ 0oC and ≤ -4oC in the preceding calendar year were also used as explanatory variables. The total number of P. petilum counted at the Hall Cemetery generally increased until the late 1990s, after which it remained relatively stable. However, the population appears to be changing differently within different parts of the site. There has been a general decline in most parts of the Hall Cemetery, however, the population in some locations has increased. Part of this variation appears to be explained by the number of nights ≤ -4oC which have a strong negative association with the number of P. petilum counted across the site, and within different parts of the site. The proposed mechanism for this association is that frost damages the aboveground parts of the plant before it flowers, resulting in the plant not being counted during the survey. The probability of counting a plant after it has first been identified declined rapidly to less than 0.1 within the first three years – a useful statistic when interpreting the findings of annual monitoring surveys. This research indicates that the Hall Cemetery P. petilum population is stable. Understanding how the number of nights ≤ -4oC affects the number of individuals present will help to inform management and conserve the species.

Factors Influencing The Flowering Of The Tarengo Leek Orchid (Prasophyllum petilum) 1

1 Introduction Prasophyllum petilum D.L.Jones & R.J.Bates (Tarengo Leek Orchid) was first described in 1991 and is only known to occur at five locations in south-eastern New South Wales (NSW) and the Australian Capital Territory (ACT) (Department of Environment 2010). Growing up to 400 mm tall, P. petilum produces 5-20 pale brown to green flowers on an inflorescence that develops within the folded leaf (Jones et al. 2008). The species is listed as endangered nationally as well as in the ACT and NSW. All of the known populations occur in lower parts of the landscape in grassy woodland or natural grassland (Department of Environment 2010). This is characteristic of the genus, which is known to commonly occur in moist depressions (Jones 1988). Prasphyllum petilum persists as a tuber during late summer and autumn, sprouting in May before flowering in late spring (Department of Environment 2010). Prasphyllum species are usually pollinated by bees and wasps, that are attracted by perfume and nectar produced by the flowers, though other insects are also attracted (Jones 1988). The number of flowering individuals (individuals cannot be identified unless flowering) at Hall Cemetery has fluctuated year to year (Environment and Planning 2016), a trend consistent with other populations (Department of Environment 2010). To date, little is known about the conditions that influence flowering (ACT Government 2003). Fire can have a range of effects on other species of the Prasphyllum genus (Jones 1988). However, fire has been consistently absent from the Hall Cemetery for some time – and is likely to remain so – indicating that P. petilum is not dependent on fire, and that fire has not played a role in influencing the observed fluctuations. Prasphyllum petilum is also considered to be sensitive to grazing (NSW OEH 2012), a disturbance that is in part replicated by mowing at the Hall Cemetery site. Although mowing is now managed to avoid damage to P. petilum before flowering is complete, this has not always been the case, and may explain some of the past variation in flowering individuals. Competition with other plants may also influence the number of flowering individuals (NSW OEH 2012). Coates et al. (2006) find that the emergence of Prasophyllum correctum – a species with a similar life cycle to P. petilum – was negatively associated with autumn/winter rainfall in the previous year. Fluctuations in the number of flowering plants have been similar between the Hall Cemetery and Tarengo Travelling Stock Reserve sites (Department of Environment 2010), indicating flowering may be influenced by climate rather than site specific environmental factors. The absence of information about the ecological requirements of P. petilum makes management and conservation of the species difficult. At the time of writing, there are data containing information about the number of flowering P. petilum at Hall Cemetery over the 25 years that observations have been recorded. This report explores the temporal, spatial and environmental factors that have influenced the number of flowering P. petilum at the Hall Cemetery. The nature of this analysis is exploratory and thus, no definitive hypotheses are suggested. Prior to the analysis it was expected that the overall population had shown an increasing trend over time, and that climate may explain part of the fluctuations around this trend. We also suspected that the temporal trend may be more variable at finer spatial scales within the Hall Cemetery, and there may be patterns in the occurrence of flowering within individuals plants.

2 Factors Influencing The Flowering Of The Tarengo Leek Orchid (Prasophyllum petilum)

2 Methods

2.1 Data Collection Surveys of the number of flowering P. petilum at the Hall cemetery began in 1991 and have since occurred annually. The Conservation Research unit took over responsibility for conducting surveys in 1995, at which point metal tags (pinned to the ground 5 cm to the south of the plant) were used to identify flowering individuals in subsequent years. From this point in time, clusters of P. petilum that were spatially separated from other clusters were also identified. The clusters were numbered and are referred to as patches from here on. The site is visited weekly from early spring to determine when flowering has commenced that year. Once flowering has begun, the site is surveyed once a week, for three weeks. Each individual plant is monitored, with individual plants being grouped by the patch of plants it is growing amongst (Table 1). Table 1 Data recorded during annual surveys of the number of flowering P. petilum individuals at the Hall Cemetery between 1991 and 2015.

Year Flowering Individuals

Survey Date

Plant ID Patch

1991 to 1994

Counted Recorded Not recorded Not recorded

1995 to 2015

Counted Recorded Plants identified and labelled with metal

tag

A spatially separated group of plants, that a plant is

recorded in Rainfall data (Table 2) were obtained from records of the Hall (Lochleigh) meteorological station (station number 070045) (BOM 2016). All temperature data (Table 2) prior to 2009 were obtained from the Canberra Airport Comparison station (station number 070014), while all data from 2009 onwards were obtained from the Canberra Airport Station (station number 070351) (BOM 2016). This change was due to the former station closing and being replaced by the latter. After initial exploratory analysis, a relationship was identified between the number of flowering individuals and various variables representing minimum temperature. It was hypothesised that frost may influence the number of flowering individuals. In the absence of freely available data on the number of days with frost, nights with minimum temperatures ≤ 0oC and ≤ -4oC were used as proxies for the occurrence of frost. These temperatures were arbitrarily chosen and do not necessarily represent critical thresholds.


Table 2 List of climatic explanatory variables and their respective observation periods used as part of the statistical analysis.

Climate variable Observation period Rainfall (total) 1 month 3 months 6 months 12 months Minimum temperature (average daily) 1 month 3 months 6 months 12 months Maximum temperature (average daily) 1 month 3 months 6 months 12 months Nights ≤ 0oC (count) Calendar year until surveys commenced Nights ≤ -4oC (count) Calendar year until surveys commenced

2.2 Statistical Analysis Generalised Additive Models (GAMs) and Generalised Additive Mixed effects Models (GAMMs) were used to determine how temporal, spatial and environmental factors have influenced P. petilum at the Hall Cemetery. After an initial exploration of the raw data, eight parameters were identified as displaying a relationship with the P. petilum observations: year, rainfall over the previous 6 months, minimum temperature of the previous 6 and 12 months, maximum temperature of the previous 12 months, nights ≤ 0oC in the preceding calendar year, nights ≤ -4oC in the preceding calendar year and the patch within the site a plant occurs in (Table 1, Table 2). An information theoretic approach was applied to develop multiple candidate models for three response variables: the number of flowering plants across the Hall Cemetery, the number of flowering plants within each patch of the Hall Cemetery, and the probability of an individual flowering. In contrast to analysing every possible combination of explanatory variables, the information theoretic approach requires that model structures make biological sense (Burnham and Anderson 2003). This process is more likely to produce biologically meaningful results. Initially models were developed using GAMs in the ‘mgcv’ package in R version 3.2.3 (R Core Team 2015). Patterns in the residuals indicated that temporal correlation may be affecting the model predictions for the analysis of flowering plants within patches. To account for this influence, GAMMs were used with year as an auto-correlation structure. Patch was used as a random effect in the analysis of flowering individuals by patch, and Plant ID was used as a random effect in the analysis of the probability of an individual flowering. These random effects were used as both variables were expected to influence the magnitude of the modelled relationship, but not the relationship itself. Relevant analyses were applied for the 21 years since plant locations were recorded (i.e. 1995 to 2015), as the patch location was not recorded for the first four years. Analysis of the total number of flowering individuals and flowering individuals within a given patch used a poisson distribution with a log link, and the analysis of the probability of flowering used a binomial distribution with a logit link.


Multiple candidate models were developed within each of the three analyses and were compared using the second order Akaike information criterion (AICc) using the ‘MuMIn’ package in R version 3.2.3 (R Core Team 2015). AICc was used instead of AIC as the ratio of samples to model parameters was <40 (Burnham and Anderson 2003). All models with delta values (AICc of the best model subtracted from that of a given model) less than or equal to two were considered to have empirical support (Burnham and Anderson 2003). QQ plots, residual distribution, residuals plotted against the linear predictor and response values plotted against fitted values were used for model validation.

3 Results

3.1 Total flowering individuals over 25 years The number of flowering P. petilum individuals counted over the 25 consecutive years that surveys have occurred has ranged from 0 to 96 with a median of 42 (Figure 1). The best model (Table 3) indicates that over time the number of flowering individuals increased, after an initial decline, until the late 1990’s, after which it fluctuated slightly with with peaks every 5 to 6 years (Figure 2a). However, these peaks are not statistically significant at the 95% confidence level. The number of flowering individuals decreased as the number of nights ≤ -4oC increased (Figure 2b).

Figure 1 The number of flowering P. petilum plants found during annual monitoring between 1991 and 2015. The dotted line indicates the median value of 42 flowering individuals over the 25 years.

0

10

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30

40

50

60

70

80

90

100

1990 1995 2000 2005 2010 2015

Flow

erin

g In

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dual

s

Year


Figure 2 The partial plots for the number of flowering P. petilum individuals over 25 years with time (a) and the number of nights ≤ -4oC in the preceding year (b). Dotted lines indicate the standard error and values have been back-transformed to the original scale.

Table 3 Summary of the model predicting the number of flowering individuals at the Hall Cemetery. The model used a poisson distribution with a log link.

Formula: Flowering Individuals ~ s(Year ) + s(Nights ≤ -4oC, k=5) Parametric coefficients Estimate SE P Intercept 3.58777 0.03622 <2e-16 Smooth terms edf ref.df P Year 8.778 8.974 3.37E-14 Nights ≤ -4oC 2.62 3.137 2.00E-16 R Squared (adjusted) = 0.279 N=25

0

10

20

30

40

50

60

70

80

90

100

1991 1994 1998 2001 2005 2008 2011 2015

Flow

erin

g In

divi

dual

s

Year

a

0

10

20

30

40

50

60

70

80

90

100

1 5 9 12 16 20 24 28

Flow

erin

g In

divi

dual

s

Nights ≤ -4

b

a

a


3.2 Total flowering individuals over 21 years by patch One patch was removed from the analysis as there were only observations from 2010, and it was deemed an insufficient period of time to analyse temporal changes. The highest number of flowering P. petilum individuals found within a given patch over the 21 years was 81 (Appendix 1). However, the maximum number of flowering individuals within a given patch in any year tended to be less than 20. The best model (Table 4) indicates that nights ≤ -4oC, patch and survey year (fitted by patch) are significant predictors of the number of flowering individuals. The mean number of flowering individuals, and the fitted splines varied significantly between patches (Figure 4). Most patches have experienced a decline in the number of flowering individuals, with the exceptions of patch 1 and patch 3_4 which have both increased (Figure 3). The modelled number of flowering individuals declined with an increasing number of nights ≤ -4oC (Figure 3), a trend consistent with the analysis of the total population over the 25 year period (Figure 2).

Figure 3 The partial plot for the decline in the number of flowering P. petilum individuals over 21 years as the number of nights ≤ -4oC in the preceding year increases. Dotted lines indicate the standard error and values have been back-transformed to the original scale.

0.0

0.5

1.0

1.5

2.0

2.5

1 3 6 8 11 13 16 18 21 23 26 28

Flow

erin

g in

divi

dual

s

Nights ≤ -4oC


Figure 4 The partial plots for the number of flowering P. petilum individuals over time for each individual patch within the Hall Cemetery. The mean values for each patch have been incorporated in to the fitted splines, dotted lines indicate the standard error and values have been back-transformed to the original scale.

0

5

10

15

20

25

30

1995 1998 2001 2003 2006 2009 2012 2015

Flow

erin

g In

divi

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s

Year (Patch 1)

a

0

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30

1995 1998 2001 2003 2006 2009 2012 2015

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b

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1995 1998 2001 2003 2006 2009 2012 2015

Flow

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Year (Patch 3_4)

c

0

5

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30

1995 1998 2001 2003 2006 2009 2012 2015

Flow

erin

g In

divi

dual

s

Year (Patch 5)

d

0

5

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15

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30

1995 1998 2001 2003 2006 2009 2012 2015

Flow

erin

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divi

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s

Year (Patch 6)

e

0

5

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30

1995 1998 2001 2003 2006 2009 2012 2015

Flow

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Year (Patch 7)

f

0

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1995 1998 2001 2003 2006 2009 2012 2015

Flow

erin

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Year (Patch 8)

g


Table 4 Summary of the model predicting the number of flowering individuals at the Hall Cemetery by patch. The model used a poisson distribution with a log link.

Formula: Flowering Individuals ~ s(Year, by = Patch, k = 3) + s(Nights ≤ -4oC, k=3) + Area Parametric coefficients Estimate SE P Intercept 0.2796 0.2516 0.2685 Patch 2 -2.6319 1.0612 0.0144 Patch 3_4 1.4248 0.2789 1.13e-06 Patch 5 0.3575 0.3299 0.2806 Patch 6 -3.1801 1.4089 0.0257 Patch 7 -0.3280 0.3853 0.3962 Patch 8 3.0652 0.2566 < 2e-16 Smooth terms edf ref.df P Year (Patch 1) 1.927 1.927 3.63e-05 Year (Patch 2) 1.000 1.000 0.00133 Year (Patch 3_4) 1.978 1.978 3.01e-10 Year (Patch 5) 1.000 1.000 7.60e-05 Year (Patch 6) 1.000 1.000 0.03087 Year (Patch 7) 1.000 1.000 0.02408 Year (Patch 8) 1.895 1.895 0.01320 Nights ≤ -4oC 1.000 1.000 3.16e-15 R Squared (adjusted) = 0.877 N=25 Scale estimate = 1.5455

3.3 Frequency of flowering in individuals over 21 years The final analysis examined the probability of a known individual flowering in response to time climate and patch. Three patches were excluded from the analysis due to discrepancies in the tagging of individuals or an insufficient number of survey years. Two hundred and thirty-nine individual plants were tagged over 21 years (Appendix 2). The longest interval between flowering observed in an individual was 16 years (13 years was observed in two other individuals). Since all tagged plants have flowered at least once in the past 16 years, none were considered to now be dead. The time since an individual was first tagged was the only parameter in the best model (Table 5). The likelihood of a given plant flowering within a given year decreased with increasing time since it was first tagged (Figure 5). The analysis shows the probability of flowering declined from 0.9 to less than 0.1 within the first three years.


Figure 5 The predicted decline in the probability of an individual P. petilum flowering with years since it was first tagged. Dotted lines indicate the standard error and values have been back-transformed to the original scale.

Table 5 Summary of the model predicting the probability of flowering within individual plants at the Hall Cemetery. The model used a binomial distribution with a logit link.

Formula: Probability of Flowering ~ s(Time Since First Tagged, k = 4) Parametric coefficients Estimate SE P Intercept -1.38335 0.07268 <2e-16 Smooth terms edf ref.df P Time Since First Tagged 2.898 2.898 <2e-16 R Squared (adjusted) = 0.278 N= 2315 Scale estimate = 0.89248

4 Discussion Twenty five years of monitoring data were analysed to determine how the number of P. petilum individuals has changed over time, and what might be causing these changes. To do this, survey year and climate variables were used to predict the change in the number of flowering individuals across the entire Hall Cemetery, the number of flowering individuals within different parts of the Hall Cemetery, and the probability of an individual plant flowering.

4.1 Warm winters favour flowering The number of nights ≤ -4oC in the preceding calendar year negatively affected flowering (Figure 2 and Figure 3). Frost damage associated with a loss of protection due to early snow melt has been attributed to fewer flowering individuals in Prasophyllum tadgellianum

0.0

0.1

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Prob

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Years Since First Tagged


(Gallagher et al. 2009) and other herbaceous flowering plants (Inouye et al. 2002, Inouye 2008). Wang et al. (2015) suggest that frost may adversely impact orchids that only produce leaves during the winter months. The association between lower minimum temperatures and flowering support the postulation that frost may influence flowering. The inflorescence of P. petilum forms inside the leaf, which establishes at the end of autumn (Department of Environment 2010). The occurrence of nights ≤ -4oC is likely to occur after leaves have sprouted, ruling out the possibility that it may affect sprouting from tubers. An increase in the number of nights ≤ -4oC is expected to increase the likelihood that the leaf containing the developing inflorescence of a P. petilum will be damaged due to freezing, preventing flowering. However, the authors acknowledge that a mechanism has not been demonstrated, and that the associated between P. petilum and nights ≤ -4oC requires further research.

4.2 Complex temporal variation In contrast to the consistent effect of minimum temperature on flowering, the change in flowering over time differed between analyses. Over the 25 years of monitoring, the total number of flowering P. petilum individuals tended to increase before stabilising in the late 1990’s with minor fluctuations (Figure 2). However, when the data was analysed by patch within the Hall Cemetery, various trends occurred. The patch with highest number of flowering individuals (patch 8) remained relatively stable, but most other patches showed slight declines in the number of individuals over time (Figure 3). In contrast, patch 3_4, and to a lesser extent patch 1, experienced a decrease in the number of individuals before increasing. These two patches are located on the northern boundary of the cemetery, and are sheltered by Box-Gum Grassy Woodland which surrounds the cemetery. Blennow et al. (1998) find that microsites with less canopy cover experience lower minimum winter temperatures 20 cm above the ground. There has been a general increase in the severity of minimum winter temperatures over the monitoring period (unpublished data). This change may explain the slight decline in the more open parts of the Hall Cemetery, that is not being experienced in patch 3_4 and patch 1, which has greater shelter. However, this explanation must be regarded with caution, and further evidence is required to substantiate it. The probability of a given plant flowering declined rapidly with the number of years since it was first tagged. Inference of this trend representing the life cycle of P. petilum is limited, as it is not known if a plant has ever flowered prior to being tagged. However, it does indicate that there is not a clear pattern in the frequency of flowering, other than being more likely within two years of the last flowering event. Thus, flowering appears more likely to be influenced by external factors, such as climate variability. As outlined earlier, the management history of P. petilum at the Hall Cemetery varies greatly and may explain some of the observed variation. During several of the earlier surveys, it was


noted that mowing had recently occurred and may have influenced the number of individuals counted. A change of management after 2002 meant that mowing is unlikely to have affected any results since. There have also been changes in surveyors over the 25 years of monitoring, and one change of organisation running the surveys. Additionally, Sulphur-Crested Cockatoos (Cacatua galerita) have repeatedly been observed digging in the cemetery. None of these disturbances have been reliably or quantifiably recorded and could therefore not be included in the analysis.

4.3 Implications and further research The number of flowering P. petilum plants are monitored at Hall Cemetery so as to gain an indication of the population – the assumption being that flowering and the actual population size are positively correlated. The analyses of these data indicate the population of P. petilum at Hall Cemetery is relatively stable, and there is no need for an urgent change in management. However, if frost is more likely in parts of the cemetery with less canopy cover, the lack of recruitment of the few trees within the cemetery may become an issue. There is also an issue with persistent canopy decline in the Eucalyptus blakleyi (Blakley’s Red Gum) trees in and around the Cemetery. If this trend continues there could be a substantial loss of canopy cover and associated frost protection. To avoid further habitat degradation, land management practises that enable the persistent of elevated vegetation around the cemetery are encouraged. It is also recommended that adequate regeneration is allowed to gradually replace the few trees within the cemetery as they inevitably senesce. Minimum temperatures experienced by individual P. petilum plants may also be worse where the surrounding grass height is lower. Mowing is permitted at the Hall Cemetery when P. petilum is dormant (late summer/early autumn). In light of this evidence, we suggest a trial of not mowing certain patches of P. petilum to determine if taller grass cover favours flowering. Little is known about how the surrounding environment influences P. petilum, and consequently, the research questions the study aimed to address were very broad. However several research questions have arisen due to this analysis:

1. How are minimum winter temperatures affecting P. petilum, and does microsite variation influence this effect? To address this question, temperature loggers could be placed across the different patches at Hall Cemetery, in addition to mapping out the extent of frost.

2. Is surrounding vegetation associated with patterns in flowering? The dominant ground cover varies both spatially and temporally at the Hall Cemetery and is considered to affect flowering, however no quantitative data is yet available to validate this hypothesis. It is recommended that botanical and structural descriptions of the vegetation associated with each patch be recorded during monitoring, so that these data can be analysed.

3. Does soil moisture influence P. petilum flowering? The species is known to occur in moist depressions, and rainfall has been suggested as a possible influence on


flowering. Although rainfall was not significant predictor in these analysis, localised soil moisture might be influential. It is recommended that measuring soil moisture across different parts of the Hall Cemetery during winter and/or during flowering to address this question.

4. Do other populations respond in the same way? Conducting similar studies on other populations of P. petilum will help to validate the conclusions of this study. Genetic analysis both within and across populations may also provide more answers.

4.4 Conclusion Praophyllum petilum is a poorly understood species, persisting in only a few fragmented populations. To identify trends in the fluctuations and possible causes monitoring data from the population located at the Hall Cemetery was analysed. The number of flowering individuals – a proxy for the size of the population – appears to have increased slightly before stabilising over the 25 years of monitoring. However, within the site a variety of trends are occurring within different patches. The cause of the fluctuations in the number of flowering individuals appears to be the number of nights ≤ -4oC in the preceding year. In light of these findings we see no reason to changes the management of Hall Cemetery. These findings do however highlight the need to ensure the persistence of elevated vegetation in and around the Hall Cemetery, so as to avoid frequent and severe frost.

Acknowledgments The authors would like to thank Sarah Sharp for reviewing this report and providing valuable feedback. We also wish to thank all of the Conservation Research Staff and David Jones for their contributions to the annual P. petilum surveys at the Hall Cemetery.

References ACT Government, 2003. ACT Lowland Woodland Conservation Strategy. Action Plan no 27, Environment ACT, Canberra

Blennow, K., Lang, A.R.G., Dunne, P. and Ball, M.C., 1998. Cold-induced photoinhibition and growth of seedling snow gum (Eucalyptus pauciflora) under differing temperature and radiation regimes in fragmented forests. Plant, Cell & Environment, 21(4), pp.407-416.

Bureau of Meteorology (BOM), 2015. Climate Data Online, Bureau of Meteorology. Available at: http://www.bom.gov.au/climate/data/.

Burnham, K.P. and Anderson, D., 2003. Model selection and multi-model inference. A Pratical informatio-theoric approch. Sringer.

Coates, F., Lunt, I.D. and Tremblay, R.L., 2006. Effects of disturbance on population dynamics of the threatened orchid Prasophyllum correctum DL Jones and implications for


grassland management in south-eastern Australia. Biological Conservation, 129(1), pp.59-69.

Department of Environment, Climate Change and Water (NSW) 2010. National Recovery Plan for Prasophyllum petilum, Department of Environment and Climate Change and Water (NSW), Hurstville.

Environment and Planning, Conservation Research (ACT) 2016, Prasophyllum petilum – 2015 survey, Environment and Planning (ACT), Canberra.

Gallagher, R.V., Hughes, L. and Leishman, M.R., 2009. Phenological trends among Australian alpine species: using herbarium records to identify climate-change indicators. Australian Journal of Botany, 57(1), pp.1-9.

Inouye, D.W., 2008. Effects of climate change on phenology, frost damage, and floral abundance of montane wildflowers. Ecology, 89(2), pp.353-362.

Inouye, D.W., Morales, M.A. and Dodge, G.J., 2002. Variation in timing and abundance of flowering by Delphinium barbeyi Huth (Ranunculaceae): the roles of snowpack, frost, and La Nina, in the context of climate change. Oecologia, 130(4), pp.543-550.

Jones, D.L., 1988. Native Orchids of Australia. Reed Books, Sydney.

Jones, D.L., Egan, J. and Wood, T., 2008. Field guide to the orchids of the Australian Capital Territory. National Parks Association of the ACT.

NSW Office of Environment and Heritage (NSW OEH) (2012). Tarengo Leek Orchid - profile. [Online]

R Core Team (2015). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/.

Wang, H.H., Wonkka, C.L., Treglia, M.L., Grant, W.E., Smeins, F.E. and Rogers, W.E., 2014. Species distribution modelling for conservation of an endangered endemic orchid. AoB PLANTS, 7.

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Appendix 1 The number of flowering P. petilum plants found in each patch during annual monitoring between 1995 and 2015. Patch 10 was excluded.

Year

Flow

erin

g In

divi

dual

s

20

40

60

801

1995 2000 2005 2010 2015

2 3_4

5 6

20

40

60

807

20

40

60

80

1995 2000 2005 2010 2015

8


Appendix 2 The presence or absence of flowering (indicated by a value of one or zero respectively) in each P. petilum tagged since 1995 plotted against the time since the plant was first tagged. Plants tagged in Patch 2, 6 and 10 were excluded.

Time S

ince First Tagged

Flowering

0.01.0

100

05

10

100H101

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10

101H102

05

10

102H103

05

10

103H104

05

10

104H105

05

10

105H106

05

10

106H107

05

10

107H

108108H

109109H

10H110

110H111

111H112

112H112H

a113

113H114

0.01.0

114H

0.01.0

115H116H

117H118H

119H11H

120H122H

124H125H

126H127H

128H129H

12H130H

132H133H

134H135H

136H138H

138HC

139H139H

a13H

140H140H

a141H

141Ha

142H0.01.0

142Ha

0.01.0

143H143H

a144H

144Ha

145H146H

147H148H

149H14H

150H152H

153H153H

C154H

154HC

155H156H

156HC

157H158H

159H15H

160H161H

161Ha

162H163H

164H165H

166H0.01.0

167H

0.01.0

168H169H

16H170H

171H172H

173H174H

175H177H

178H179H

17H17H

B17H

C180H

181H182H

183H184H

185H186H

187H188H

189H18H

190H191H

192H193H

194H0.01.0

195H

0.01.0

196H197H

198H199H

19H1H

200H201H

202H203H

204H205H

206H207H

208H209H

20H210H

211H212H

213H21H

22H23H

24H25H

26H275H

276H27H

28H0.01.0

29H

0.01.0

2H30H

31H32H

33H34H

35H36H

37H38H

39H3H

40H41H

42H43H

44H45H

46H47H

48H49H

4H50H

51H52H

53H54H

55H56H

57H0.01.0

58H

0.01.0

59H5H

60H61H

62H63H

64H65H

66H67H

68H69H

6H70H

71H72H

73H74H

75H76H

77H78H

79H7H

80H81H

82H83H

84H85H

86H0.01.0

87H

0.01.0

88H89H

8H90H

91H92H

93H94

94H95

95H96

96H97

97H98

05

10

98H99

05

10

99H9H

05

10

H261

H279

05

10

0.01.0

H280

Factors influencing the flowering of the Tarengo Leek ...

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Transcript of Factors influencing the flowering of the Tarengo Leek ...