INVESTIGATING THE DISTRIBUTION OF FLOWERING SPIKES OF VIOLET HELLEBORINE IN A SUFFOLK WOOD

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INVESTIGATING THE DISTRIBUTION OF FLOWERING SPIKES OF VIOLET HELLEBORINE EPIPACTIS PURPURATA IN A DECIDUOUS SUFFOLK WOODLAND IN RELATION TO ADJACENT DITCHES AND DIFFERENCES IN HEIGHT ABOVE THE BASE OF THE DITCH, SOIL MOISTURE AND PH DENNIS AND ANNE KELL Introduction This project originated from a chance remark by Dr Stephen Clarkson, East Anglian Branch Secretary of the Wild Flower Society. Whilst looking for Violet Helleborines in Wolves Wood, he commented that they could be found by following the ditches in a particular compartment. Personal observations supported this and the following report forms the basis of an investigation undertaken as part of an OU module during the summer of 2014. Preparatory work was also undertaken in 2013.

Epipactis purpurata Violet Helleborine Epipactis purpurata Sm. (Plate 14) is an herbaceous longlived perennial orchid, most commonly found in deciduous woodland dominated by Beech Fagus, Hornbeam Carpinus or Hazel Corylus, tolerating deep shade (Ellenberg classification of 2). (BSBI/BRC 2014) It is a non-bulbous geophyte (perennial plant with buds below ground during dormant periods) with a vertical rhizome from which roots descend vertically to 1∙2 m. It is wasp-pollinated and reproduction is entirely by seed, with no evidence of vegetative spread. It is late-flowering (July – September) with long-lived, older plants producing several flower spikes. (Harrap and Harrap 2009). It is mostly associated with soils such as clay with flints overlying chalk bedrock, but can tolerate acid soils. (Harrap and Harrap 2009).

Wolves Wood, Suffolk.

The site has been owned and managed by RSPB since 1972. It has been designated as an SSSI (Site of Special Scientific Interest.) and is typical of East Anglian ancient deciduous wet-woodland, lying on boulder clay above chalk, with many ponds and ditches (Plate 15). (Rackham, 1971) It covers 37 ha, is surrounded by arable land and active management of water levels is taking place. (Nowers et al., 2012). The main woodland type is Oak/Ash/Hazel with Aspen managed by coppice rotation.

Hornbeam Carpinus betulus is not currently included in the coppice rotation. One compartment covering approximately 1∙5 ha has been uncut for over 100 years (Rackham, 1971) and this supports the colony of E. purpurata.

The old coppice stools have developed several trunks, causing some to collapse. The canopy is dense with virtually no understorey or ground cover.

E. purpurata faces negligible competition from other herbaceous plants.

However, flowering spikes have been grazed during 2014 and there is evidence of both deer and brown hare using the compartment.

Preliminary Investigation A survey was conducted in August 2013, identifying positions of plants, marking them (white numbered plastic markers) and measuring shortest distances from the plant to the centre of the nearest ditch. 123 plants were found.

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Results suggest a normal distribution with a modal distance of 4–5 m between plant and ditch (Fig. 1). 52% of plants grew between 3–6 m of the ditch suggesting a selective pressure resulting in a realised niche (that part of its niche occupied by a species after competition) showing ecological specialisation in adult plants.

25

Number of plants

20

15

10

5

0

Distance from centre of ditch/m

Figure 1. Results of preliminary investigation. Number of Epipactis purpurata plants with distance from nearest ditch in August 2013.

This prompted further investigation into the distribution. Markers were left in place to provide additional information and in case plants produced few flowering spikes in 2014.

Methodology Based on literature searches, abiotic factors likely to affect the distribution of orchids include soil moisture, soil pH, organic content and carbon:nitrogen ratio. In addition to establishing if an association with the ditches appears to exist, soil moisture and pH have been investigated, but organic content and carbon:nitrogen ratio were beyond the scope of this project.

Data were collected from the colony of Epipactis purpurata in the compartment of old hornbeam coppice at Wolves Wood, Suffolk, during the flowering stage (the only above-ground stage) of the plant’s life cycle in July/ August 2014, providing the largest sample available. Regular monitoring during late summer determined the most effective recording period.

Most data were collected during one season at one site only. Orchids do not produce flowering spikes every year. These data give a snap-shot of the current distribution of flowering spikes and cannot therefore represent longterm trends. Similarly, climate data cannot be used with this data to compare trends over longer periods.

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Current management is also affecting water levels. This may influence soil moisture in this compartment, but its influence on long-term trends cannot be assessed with these data.

Based on results from the preliminary investigation (see Fig. 1) datacollection was in two parts: a survey of all plants located in the compartment and two transects taken through the colony. Figure 2 shows the approximate locations of larger groups of plants and positions of transects.

Figure 2. Sketch map of the compartment at Wolves Wood, Suffolk, showing approximate positions of larger groups of Epipactis purpurata and transects.

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The compartment was systematically surveyed and the position of each spike of Epipactis purpurata was marked using numbered, coloured plastic markers (blue in 2014) ensuring all plants were later recorded. Having marked all plants found, the shortest distance to the centre of the nearest ditch was recorded along with the height of the base of the plant above the base of the ditch. At a depth of 10 cm, soil moisture and soil pH were recorded beside each marker. Readings were taken as close as practical to the plant, ensuring that it was not damaged.

The same measurements were also recorded for plants that had flowered in 2013 and were marked during the preliminary investigation, but had produced no flowering spikes in 2014, if the coloured, numbered tags were still in place.

Two belt transects were identified. These passed through sufficient plants to enable analysis, crossed a ditch and extended beyond the main group of plants.

In each 1 m section, the number of plants, pH, soil moisture and the height of the section at the midpoint above the base of the ditch were also recorded.

Results Distance of flowering plants from adjacent ditches Seventy three plants producing flowering spikes in 2014 and 69 sites where flowering spikes were relocated from 2013, but produced no flowers in 2014, were surveyed. The results are shown in Figure 3 below.

Figure 3. Distance of plants flowering in 2014 and those flowering in 2013 but not 2014, from adjacent ditches.

The range of the two distributions was similar. The mean distance was 5∙7 m in 2013 and 4∙9 m in 2014. However, when compared using a T-test, a significant statistical difference (P = 0∙03) was revealed. 56% of flowering spikes were between 3–6 m from the ditch in 2014 compared to 45% in 2013, suggesting that flowering spikes were generally found closer to the ditch in 2014. No spikes were recorded more than 12 m from the nearest ditch or closer than 1 m.

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Distances from nearest ditches for flowering spikes recorded in transects are shown in Figure 4. In transect 1, 61% were growing between 3–6 m, compared to 42% in transect 2. Overall, 50% of the flowering spikes were growing between 3–6 m from the nearest ditch.

Figure 4. Distance of plants from adjacent ditches in transects.

Height above the base of adjacent ditches Height above the base of the nearest ditch was recorded at the base of each plant flowering in 2014 and at positions marked in 2013. The results are shown in Figure 5.

Figure 5. Plants flowering in 2013 and 2014 and height above base of ditch.

When the data for each year were compared using a T-test, no significant difference was found. (P = 0∙43). Both sets of data suggest normal distributions. 78% of plants were growing between 0∙3 and 0∙45 m above the base of ditches.

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Soil moisture Soil moisture was recorded at each plant flowering in 2014 and at positions marked in 2013. A comparison of the two years using T-test showed no significant difference. (P = 0∙31) 35.0

2014

2013

30.0

Number of plants

25.0 20.0 15.0

10.0 5.0 0.0

Soil moisture (%)

Figure 6. Comparing plants flowering in 2013 and 2014 against moisture.

The results (Fig. 6) suggest normal distributions with 89% of the plants recorded between 9 and 18% soil moisture.

The correlation coefficient and regression between soil moisture and height above base of ditch for both transects are statistically significant.

Therefore, as height increases, soil moisture decreases.

Soil pH Soil pH was recorded at 46 plants flowering in 2014 and at 56 positions marked in 2013. A comparison of the two years using T-test showed no significant difference. (P = 0∙18) The results (Fig, 7) suggest normal distributions with 76% of the plants recorded between 6∙3 and 7∙1 soil pH. The correlation coefficient and regression between soil moisture and soil pH for both transects are statistically significant. Therefore, as soil moisture increases, soil pH increases.

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2013

20 18 16

Number of plants

14 12 10 8

6 4 2 0 5.7-5.99

6.0-6.29

6.3-6.59

6.6-6.89 Soil pH

6.9-7.19

7.2-7.49

7.5-7.79

Figure 7. Comparing plants flowering in 2013 and 2014 against pH. Presence or absence of plants Using the complete set of data from 2014, it was possible to separate sites where no plants were growing from those where plants were found. These sites were compared using a T-test to see if any significant difference existed between sites and the height of the ground or soil moisture. (Table 1) It was not possible to compare soil pH. Table 1. Comparing sites with plants in 2014 against sites with no plants in 2014 using T-test. (**= P<0∙01; NS = Not Significant) Statistic

Height above base of ditch

Soil Moisture

P value Significance

P = 0∙02 **

P = 0∙14 NS

The data for height above the base of the ditch shows a significant difference suggesting that plants with flowering spikes are found in significantly higher ground than sites with no flowers.

Discussion The results suggest that Epipactis purpurata occupies a well-defined realised niche with relation to the ditches in Wolves Wood. Data from both the preliminary study in 2013 and the flowering season in 2014 suggest that plants show a preference for areas between 3–6 m from ditches (Fig. 3) at a height of between 0∙3–0∙45 m above the base of ditches. (Fig. 5) The profile of the ditches suggests this zone may have developed from spoil being deposited when ditches were dug or cleared. Such practise would raise ground height adjacent to ditches. It may also change the organic content of the soil by adding partially decomposed material to the surface layer, or expose soil from below the surface horizons if spoil is inverted when dug out. Former RSPB warden Russell Leavett explained that it was usual practice for woodsmen to clear the ditches surrounding

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compartments as they were coppiced, to improve drainage and make extraction easier. Rackham (1971) describes the network of watercourses as “…intricate and irregular” agreeing that drainage was one purpose for creating these ditches. He suggests coppicing ceased at least 100 years ago and it would be expected that the profile has eroded during this period.

However, the presence of plants producing multiple spikes suggests plants may be over 100 years old and therefore likely to have been present when this work was carried out. (Harrap and Harrap, 2009) No soil profiles were dug, but it might be assumed that the higher ground also implies a greater depth of soil. The vertical rhizome of E. purpurata produces vertical roots that may descend as much as 1∙2 m. (Harrap and Harrap 2009). Summerhayes noted in 1985 “… a feature common to nearly all habitats is the considerable depth of soil, shallow soils being quite unsuitable.” Harrap and Harrap (2009) also comment that a considerable thickness of soil is required. It is possible that the build-up of spoil alongside ditches might provide such deeper soils. Suitable cores might help investigate this further.

There is strong correlation between height of plants above the base of the ditch and soil moisture. Flowering spikes were growing in the range 9–18% soil moisture, at the time of recording. No flowering spikes were found closer than 1 m from, or less than 0∙24 m above the base of the ditch. During recording, soil moisture at the base of the ditch was above 20% and during winter, may contain standing water, showing evidence of waterlogging.

These results are consistent with published Ellenberg values. (BSBI/BRC, 2014) Epipactis purpurata is classified as 5 for moisture (Moist-site indicator, mainly on fresh soils of average dampness). Annual precipitation is classified as 728 mm. Historical data from nearby RAF Wattisham (15 km) shows the totals in 2012/13 as 509 mm and 788 mm respectively. (Tutiempo, 2014) Soil moisture was recorded at 0∙1 m depth. This was consistent throughout data collection and a practical depth at which to compare soil moisture and soil pH using the equipment available. However, as mentioned above, rooting depth of E. purpurata is much greater. Whilst data can be used for comparison, it may not reflect the actual soil moisture levels available to the plants. 9–18% soil moisture in a clay loam would be past the permanent wilting point (Conway et.al, 2008). In fact, all plants seemed quite healthy so it must be assumed that rooting depth is an important feature in enabling plants to grow in this area. Bateman (1981) commented that it was the only orchid to be increasing in Hertfordshire after the cessation of coppicing. In this Hornbeam compartment, coppice stools have produced several trunks that have two significant effects on the habitat. Firstly, the dense shade of the canopy reduces light levels considerably. Second, increased canopy will also increase evapotranspiration and interception reducing soil moisture levels. These two variables contribute to the realised niche E. purpurata is able to exploit.

Height measurements were compared with the base of the ditches.

Periodic comparisons, suggested that ditch bases were similar heights and data can be used for comparative purposes. No standing water was observed in the ditches at the time of data-collection. If wells could be installed in the

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Transect 2

5.6

5.6

5.4

5.4

5.2

5.2

5

5

Soil pH

Soil pH

63

4.8

4.8

4.6

4.6

4.4

4.4

4.2

4.2

4

4 0

10 20 Soil moisture (%)

30

0

10 20 Soil moisture (%)

30

Figures 8 and 9. Transects 1 and 2. Comparing soil moisture and pH. area, using the water table as a base-line for height might be a more accurate and consistent measure.

Analysis of the pH data is more difficult. pH is actually recorded on a logarithmic scale and tests used are designed for linear data. Recording was made using a Lutron PH-220S Soil pH Meter. Unfortunately, the fragile probe was broken after 102 sites had been surveyed. The remaining 40 sites had no pH data recorded. A replacement probe was used to record all transect data.

Both probes were calibrated using manufacturer’s instructions, but a clear difference exists between the two sets. Individual survey data is consistently higher (mean 6∙7) than transect data (mean 5∙0). Whilst it is not appropriate to use data to give absolute values, it can be used for comparative purposes.

Data suggests that Epipactis purpurata occupies a niche in relation to pH with a range of no more than 1∙8. (Fig. 7). For Transect 1 data, pH correlates significantly with height above the base of the ditch, which appears to influence the position of spikes. Soil moisture was also strongly correlated with soil pH, (Figs 8 and 9) again suggesting that it may influence the positions of flowering spikes. Ellenberg values for reaction (soil pH) classify E. purpurata as 8 (Between an indicator of weakly acid to weakly basic and an indicator of basic reaction). (BSBI/BRC, 2014) However, Harap and Harrap (2009) state that it can tolerate acid soils. This is consistent with pH recorded in this survey that were all 7 or below.

Data comparing sites with plants flowering in 2014 against those having no flowering spikes in either 2013 or 2014 shows a significant difference in height above the base of the ditch, supporting earlier findings (Table 1). No significant difference was shown between sites when compared for soil moisture. It was not possible to compare sites for pH as the data was combined and therefore included results from the two different pH probes and as discussed earlier, these showed inconsistency in recording between transect and survey data. Some uncertainty remains with this result as the two sample sizes were uneven (41 non-flowering; 73 flowering) even though adequate numbers of observations were included. Furthermore, transect data came from selected areas whereas survey data was chosen more randomly by the presence or absence of flowers. A more comprehensive investigation comparing entirely random sites within the compartment, or

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systematically sampling the whole compartment might provide more robust data for this analysis.

Given the suggestion made by McCormick and Jacquemyn (2014), that adult plants may reflect hotspots for mycorrhizal fungal partners, the identification of differences in abiotic factors between sites showing the presence or absence of flowering spikes may also reflect sites most suitable for mycorrhizae to grow. Significant associations established between soil moisture, soil pH and heights support the importance of the abiotic factors.

Since the development of DNA sequencing, more fungal associates have been identified. Among plants surveyed, some had practically no chlorophyll but were thriving and producing flowers. With very limited ability to photosynthesise and being in deep shade, it must be assumed that most of the plant’s carbon was obtained from fungal associates. Similar examples are quoted by Harrap and Harrap (2009) who also note that some Epipactis species are associated with ectomycorrhizal fungi. These are normally associated with temperate and high latitude woody plants. This suggests that E. purpurata may share fungal associations with trees. Light and MacConaill (2006) also considered the ecological implications of trees in sharing mycorrhizal associations, suggesting that the presence of large trees is critical to the persistence of the mycorrhizae and hence to the survival of the orchids, especially in their hypogeal (underground) state. Data on the relationship to trees was not considered in this investigation, but may be useful in exploring biotic and abiotic conditions further.

Conclusion The results of this investigation suggest that Epipactis purpurata occupies a specific realised niche in relation to the ditches in Wolves Wood, with the majority of flowering spikes found between 3–6 m from ditches and 0∙3–0∙45 m above the base of the ditch. Soil moisture at 0∙1 m depth in this area was 9–18% at the time of recording. Significant associations were established between soil moisture, soil pH and heights above the base of ditches. Plants were found growing on significantly higher ground than where no plants were growing.

Implications of the results to habitat management for E. purpurata at Wolves Wood Wolves Wood is managed by coppice rotation but the hornbeam compartment is currently excluded from this. Bateman (1981) commented that E. purpurata was the only species of orchid to be increasing in Hertfordshire, possibly as a result of the cessation of coppicing. This strategy would therefore appear appropriate.

However, since coppicing has not taken place for over 100 years (Rackham, 1971) the old hornbeam coppice stools are now supporting several trunks, becoming less secure. Left, many will eventually fall.

Management of this compartment has been discussed. Re-coppicing after such a long break may be unsuccessful and if management is considered urgent, it might be better to consider singling trees (reducing trees to one pole) rather than coppicing. (Green, 1981) Maintaining the shade and canopy with single trees might be more suitable for the E. purpurata colony than

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re-coppicing the area. Left unmanaged, Green (1981) suggests that coppice stools will self-single, but create â&#x20AC;&#x153;very ragged woodlandâ&#x20AC;?.

A second consideration to future management concerns soil moisture.

Wolves Wood is surrounded by drained arable land and has been drained in the past to facilitate coppice extraction. Despite the reinstatement of coppice rotation, RSPB did not record increases in target nesting bird species e.g. nightingale. To address this, a series of dams were installed in selected ditches during 2010 retaining soil moisture in summer, increasing the invertebrate population and therefore increasing nesting bird populations.

(Nowers et al., 2012) Given the results that E. purpurata has specific soil moisture requirements, long-term monitoring of the population alongside soil moisture should be encouraged.

Further investigation This colony of Epipactis purpurata is one of only five recorded in Suffolk and close to the north-eastern edge of its UK range. A longer term study might enable more details of the population and its specific condition requirements to be understood.

Monitoring the population over a period of years would provide data on how frequently individual plants produced flowering spikes and how many. It would also be possible to record new individuals recruited to the population and those that disappeared, giving an indication of germination success.

Similarly, careful monitoring of abiotic factors where plants grow, would enable comparison with climate data, especially precipitation. Using the water table as a base line, rather than the base of ditches, would provide robust data on the depth of water in the soil. Simple wells would need to be installed in the compartment, providing a three dimensional picture of the water table.

Systematic or random sampling within the compartment of an equal number of sites where no plants are growing could provide data to identify niche preferences.

To facilitate this, accurate recording of plant position would be essential.

Simple GPS recorders proved too inaccurate to separate individual plants during this investigation. The use of a Total Station System could improve accuracy and distinguish individual spikes from separate plants, as used by Dodd in studying a population of Orchis morio (Green-winged Orchid).

(Gillman, 2008) Acquiring data that will enable associations between biotic and abiotic factors to be identified and differences between sites where plants grow or do not grow, whilst monitoring changes in population and relating these to climate data, could provide information to make informed judgements about the conservation of Epipactis purpurata.

Acknowledgements We should like to sincerely acknowledge the assistance given in completing this project. Firstly, permission to conduct this project in Wolves Wood was kindly granted by RSPB through Rick Vonk and the reserve warden, Shirley Boyle, who has continued to show interest and support throughout the last year.

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The Suffolk Naturalists’ Society have kindly agreed to provide a bursary to cover costs of equipment in purchasing coloured plant markers, laser level, pH meter and some assistance with travelling. Colin Hawes, from the Suffolk Naturalists’ Society, having read the original bursary application, has kindly loaned a moisture meter for the duration of the fieldwork.

Martin Sanford from the Suffolk Biological Records Centre who has provided records and edited this paper.

Open University tutor Jo Davis has been extremely encouraging and supportive throughout the module and her feedback has been invaluable in planning and developing the project.

References Bateman, R. M. (1981). The Hertfordshire Orchidaceae. Transactions Hertfordshire Natural History Society 28(4): 56–79.

BSBI/BRC (2014). Online Atlas of the British and Irish Flora. [online] Available at: http://www.brc.ac.uk/plantatlas/index.php?q=node/1339 Accessed 18.08.14.

BSBI (2014). BSBI Vascular Plant Records – Tetrad Data for GB and Ireland. [online] Available from: http://www.bsbimaps.org.uk/tetradmaps/ Accessed 19.08.14.

Conway, A., Reynolds, R., Dise, N., Dubbin, B. & Gagan, M. (2008). S216 Block 2 Air and Earth. The Open University.

Gillman, M. (2008). S216 Topic 11. Biological Conservation. Milton Keynes, The Open University.

Green, B. H. (1981). Countryside Conservation. George Allen and Unwin.

Harrap, A. & Harrap, S. (2009). Orchids of Britain and Ireland a Field and Site Guide. A & C Black.

Light, M. H. S. & MacConaill, M. (2006). Appearance and disappearance of a weedy orchid, Epipactis helleborine. Folia Geobotanica 41: 77–93. [online] Available from: http://eds.a.ebscohost.com.libezproxy.open.ac.uk/ehost/pdfviewer/ pdfviewer?vid=3&sid=11378278-10e8-4a26-b51c-b0d70f577587% 40sessionmgr4004&hid=4213 Accessed 20.08.14.

McCormick, M. K. & Jacquemyn, H. (2014). What constrains the distribution of orchid populations? New Phytologist 202: 392–400. [online] Available from: http://onlinelibrary.wiley.com.libezproxy.open.ac.uk/enhanced/ doi/10.1111/nph.12639/ Accessed 20.08.14.

Nowers, M., Self, M. & White, G. (2012). Re-wetting Wolves Wood. [online] Available from: http://www.rspb.org.uk/Images/rspbreserves2012_tcm9326414.pdf#page=46 Accessed 21.08.14.

Rackham, O. (1971). Wolves Wood. A provisional assessment. Unpublished report held by SBRC. Summerhayes, V. S. (1985). Wild Orchids of Britain. Collins.

Tutiempo (2014). Historical climate data Climate Wattisham 1974–2013 [online] Available from: http://www.tutiempo.net/en/Climate/Wattisham/35900.htm Accessed 18.08.14.

Dennis & Anne Kell, 9 Pheasant Rise, Copdock, Ipswich, Suffolk. IP8 3LF

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A. Kell

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Plate 14: Violet Helleborine Epipactis purpurata growing in Wolves Wood, Suffolk. August 2013 (p. 55).

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Plate 15. Ditch and wet area passing through a compartment in Wolves Wood, Suffolk. August 2014 (p. 55).

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