Flowering patterns and synchronicity of Green-winged Orchid (Anacamptis morio) at Martins’ Meadows

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FLOWERING PATTERNS AND SYNCHRONICITY OF GREEN-WINGED ORCHID (ANACAMPTIS MORIO) AT MARTINS’ MEADOWS PAUL CHAPMAN Martins’ Meadows Martins’ Meadows is in the parish of Monewden, near Woodbridge and is owned and managed by the Suffolk Wildlife Trust (SWT). It consists of three meadows (the most important of which in terms of both floristic diversity and abundance is known as ‘First Church Meadow’) and two orchard areas, totalling an area of 3.74 ha (approx 9 acres).

The National Vegetation Classification (NVC) scheme puts the site in the MG5 group (Cynosaurus cristatus-Centaurea nigra grassland) of mesotrophic grassland communities.

Already designated an SSSI Grade 1 status reserve by Natural England, Martins’ Meadows became Plantlife’s ‘Coronation Meadow for Suffolk’ in 2013. Notable species of meadow plants include Snake’s-head Fritillary (Fritillaria meleagris), Meadow Saffron (Colchicum autumnale), Dyer’s Greenweed (Genista tinctoria), Pepper Saxifrage (Silaum silaus), Adder’s-tongue Fern (Ophioglossum vulgatum), Sulphur Clover (Trifolium ochroleucon), and several regularly occurring orchid species including Early Purple (Orchis mascula), Pyramidal (Anacamptis pyramidalis), Twayblade (Listera ovata) and Green-winged (Anacamptis morio). Great Crested newts (Triturus cristatus) have been recorded in a pond on site, while the two orchard areas contain traditional and often local varieties of fruit trees.

A map made by Thomas Fuller in 1656, now in the Suffolk Records Office, shows all the current area of the reserve as meadowland, forming part of a more extensive farmstead. Further historical records are provided by a tithe map (1838), an auctioneer’s map (1914), and various Ordnance Survey maps of the twentieth century.

There is no evidence that the meadows have been ploughed since the mid seventeenth century. Current management consists of a mid-July hay cut followed by sheep grazing from mid-September until December. Any nutritional supplementation for livesock is carefully managed to ensure there is no nutrient increase to the soil.

The Green-winged Orchid (Anacamptis morio Plate 14) Anacamptis morio reproduces mainly through sexual reproduction, with little or no vegetative reproduction. Tubers formed annually during the flowering period act as food reserves fuelling growth the following year. It is a wintergreen species with leaves appearing in autumn and persisting until after the flowering period in May. Like most orchids, the seeds of A. morio are produced in great numbers. They are light, having a large internal air space, which gives them the capacity to travel long distances and colonise new areas. The seeds contain very little stored food and after germination a small underground organ, the protocorm, is produced. To develop further, the protocorm must obtain requisite nutrients from external sources. For orchids of open habitats such as A. morio, protocorms obtain nutrient from symbiotic association with saprophytic basidiomycetes (fungi) of several types, collectively known as Rhizoctonia. These mycorrhizal associates are known to include the species Epulhoriza repens and Moniliopsis solani. Once the protocorm has developed Trans. Suffolk Nat. Soc. 52 (2016)

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sufficiently below ground (a process that usually takes at least a year), the plant will produce leaves above ground which are capable of photosynthesis, allowing the orchid to sustain itself during subsequent growth.

Jersáková and Malinová (2007) investigated dispersal in a range of orchid species using sticky Petri dishes placed at various distances and directions from a plant. Their research showed that, despite possessing the capacity to travel great distances, the vast majority of the seed ‘rain’ of A. morio fell within a radius of 0.5 to 1.0 m from the parent plant. The authors also considered the concept of ‘safe sites’, which are areas with the specific conditions that allow a seedling to emerge successfully from the soil and develop into an adult reproductive plant. In addition to factors such as soil organic matter content, nutrient content, acidity and moisture, orchids also require the presence of the mycorrhizal symbionts for the early stages of development as mentioned above. Investigations have shown that the mycorrhizae are not distributed evenly across a site, but occur in localised patches with existing orchids already in association. The ‘safe site’ for an orchid seedling usually lies near to the parent.

A. morio is a food deceptive species that produces no nectar. It is thought that pollinating insects (typically queen bumble-bees) attracted to the flower spike investigate just a few flowers before the lack of nectar reward causes them to fly elsewhere. Although this may be advantageous in reducing self-pollination, it does so by limiting all pollination, and thus negatively impacts on seed production. Ruth, Neiland and Wilcock’s 1998 literature survey for various orchid species provides a figure of 21% for capsule set from potential flower numbers in A. morio growing in Portugal and Sweden. Although there could be thousands of seeds per capsule, the amount that survive to germinate and then continue to grow successfully into new recruits does not seem to have been studied to any great extent.

There is some controversy over the plant’s longevity. Summerhayes (1951) states that A. morio is monocarpic (dying after setting seed): ‘The development of the greenwinged orchid from seed is exceptionally rapid, the first leaf appearing in the spring of the second year, and the first tuber in the same year... Flowering follows after a few years’ vegetative growth, after which the plant usually dies.’ This is contradicted by several authors, including Wells, Rothery & Bamford (1998), who carried out a long term study between 1978 and 1995 at Upwood Meadows, near Huntingdon, Cambridgeshire. Recording individual plants in a 5 × 4 m permanent plot, they found that some individuals from the first cohort in 1978 survived until 1995 and flowered every year of the 17-year study. However, other individuals died or flowered only sporadically, existing in a vegetative state for the rest of the time either as a rosette of leaves above ground or as an underground tuber with no aerial organs. Wells et al.

(1998) mention the considerable interest there has been in the plant’s cost of reproduction, arguing that ‘the short-term benefits of heavy flowering and consequent high fruit production may be outweighed by the long-term cost to the plant’. A plant that flowers in one year may enter a non-flowering state for one or more subsequent years in order that resources can be dedicated to building up reserves, which eventually could allow a further cycle of flower initiation, fruiting and

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seed set. An example of survival in a non-flowering state is provided by Sanford (1991), a population of A. morio growing at Iron Latch Meadow in Essex. The site had been neglected and become overgrown with scrub. Once this was cleared, the orchids began to bloom again - the plants had survived, almost leafless, in the dense shade for about 30 years! Presumably there was no seedling recruitment during this time and these long-lived plants were surviving in a solely vegetative state.

When discussing orchid populations in general, Rasmussen (1995) suggests that mycorrhizal fungi also play a significant role in maintaining an orchid population in a particular site. She argues that if the substrate becomes unsuitable for the mycorrhizae, for example by exhaustion of nutrients required for fungal growth, then the site may no longer be suitable for establishment of orchid seedling recruits: ‘Typically the highest increase in population size occurs shortly after initial invasion; after a span of years the population may be declining because of low seedling recruitment... Some of the population that we observe today may in fact be senile rather than stable’.

Recording Since 1979, SWT wardens have compiled annual records of the number and approximate location of several flowering plants at Martins’ Meadow. The data comprises counts of flowering spikes for three orchid species, Orchis mascula, Anacamptis pyramidalis and Anacamptis morio, as well as the number of flowers for the Snake’s-head Fritillary, Fritillaria meleagris. The original concept was to provide an insight into the variation of flower numbers from year to year, tracking the long term success or decline of each species. By concentrating on highly distinctive flower spikes, records could readily be produced by volunteers with little botanical experience. Each species dataset is almost complete apart from two years where personal circumstances led to incomplete or no data capture (1994 and 2006).

Recording takes place on just one of the three meadows, First Church Meadow, which is almost rectangular in outline. The recorders use marked strings attached to fixed positions to demarcate a grid of 5 m squares. Recorders then record the total flowering spikes in each square. Results are collated on a Microsoft Excel spreadsheet.

Each 5 m square in the field is represented by a cell in the spreadsheet for that year.

Figure 1 (overleaf) shows results of the 2015 survey. For example, the square which is the third from the top in row 32 in the field is represented by cell B5 on the spreadsheet and has 36 flowering spikes. Henceforth, for ease of reference, each square of the field will be identified by its cell reference on the spreadsheet.

Data Analysis Annual Flowering Spike Totals Unsurprisingly, an important measure of a species’ success in a particular year is the total flower spikes produced over the whole meadow. This can easily be obtained from each spreadsheet; the results for A. morio are shown graphically in Figure 2.

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Figure 1. Spreadsheet showing numbers of flowering spikes for Green-winged Orchid A. morio in 2015. Darker shading corresponds to a greater number of flowering spikes. The numbered rows from 32 to 1 along the bottom are used at the time of recording.

Once transferred to a spreadsheet it is easier to reference the rows by the letters - so row 32 becomes row B. Each 5 x 5 metre square can then be referenced by a letter and number e.g. the square represented by cell B5 has 36 flowering spikes. The numbers on the far right are the totals for each row e.g. row 3 contains 17 flowering spikes. The total for the year is 3,396 flowering spikes.

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Figure 2. The total number of flowering spikes of A. morio in First Church Meadow, 1979–2015. The straight line is a linear trend line and is fairly constant over the time period at around 2000 individuals. (No records were taken in 1994) Figure 2 shows there are intervals of considerable variation, where the number of flower spikes increases for several years (usually about six), reaches a peak, and then decreases over subsequent years. The causes of these fluctuations are as yet unknown. However, the fact that the trend line over the whole period is fairly constant shows that the population of A. morio as a whole seems to be stable.

Dispersal mechanisms: a clumping effect Each year’s spreadsheet can also be used to give a graphical display of the distribution of flowering individuals across the whole meadow, as shown in Figure 1. Flowering spikes were very unevenly distributed in 2015 with several squares containing more than 50 individuals, whilst others contained far fewer, or none. This ‘clumping’ pattern of dispersal was widespread over the meadow and reflects neither random dispersal (which would result in unpredictable spacing where each individual seems completely independent), nor regular dispersal (where individuals are uniform and evenly spaced). Instead, the clumping effect (also known as ‘contagious dispersal’) suggested a negative binomial model of dispersal. The model was tested using observed results for 2015 and following the method described by Fowler, Cohen & Jarvis (2005). Figure 3 shows the results plotted as a histogram. The close fit between the model and observed results is striking.

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Figure 3. Frequency distribution of number of flowering spikes per 5 m square for 2015. The histogram shows the observed frequency of flowering spikes while the line represents frequencies expected from a negative binomial model.

Each annual spreadsheet was analysed to determine the ten most clumped squares (equivalent to the 2.5% of cells containing the greatest numbers of flowering spikes each year). Over the 35-year period of data collection, more than 80 different 5 m squares were identified. Table 1 represents those that fell into the top 2.5% for 10 or more years of the whole recording period. One group (cells O5, O6, P5, P6 and Q5) had consistently high numbers of flowering spikes over an extended period (cell O6 was in this category for 25 years) but elsewhere the areas of highest density changed position each year. It seems that clumping, or contagious dispersal, is a feature of the distribution of A. morio over First Church Meadow, but the location of squares containing most flowering spikes can vary annually.

Synchronous Patterns of Flowering The fact that squares O5, O6, P5, P6 and Q5 represent a consistent cluster of flower spikes over a number of years (see shaded area in Table 1) suggests that the clumping effect may be spread over several contiguous squares, representing an area of 10 × 15 m in the field. This raises the question of synchronicity within this group and with other squares across the Meadow: if flowering spikes in one square increased or decreased in a particular year, was this matched by similar changes in other squares, either immediately adjacent or more widely spread across the meadow?

To answer this question, data on the total flowering spikes in each square for every year of recording was compared using the ‘correlation’ function in Microsoft Excel. This produces a table of correlation coefficients, ranging between -1 and +1. If two datasets are exactly the same, then a value of +1 is assigned. If there is no correlation then the value would be 0 and if one dataset was exactly the opposite of another then the value would be -1.

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GREEN-WINGED ORCHIDS AT MARTINS’ MEADOWS N15 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2007 2008 2009 2010 2011 2012 2013 2014 2015 Total

O5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

1

O6 1 1 1 1 1 1 1 1 1 1 1 1 1

P5 1 1 1 1 1 1 1 1 1 1 1 1

P6

1

1 1 1 1 1

Q5 1

Q15

1 1 1 1 1 1 1

1 1

1

1

1 1 1 1 1 1

1 1

1 1 1

1

1 1 1 1 1 1 1 1

AB8

1

1 1 1 1

1 1

1 1 1

1 1 1 1 1 1 1 1 1

1

1 1

1 1 1 1

1 1 1

1 1

1 1

1 1 1 1

1 1 1 1

1

AC7 1 1 1

1

1 1 1 1 1 1 1 1 1 1

X12

1 1 1 1 1

1

1 1

1 1 22

25

` 21

10

17

10

16

13

17

Table 1. Squares with the greatest number of flowering spikes in each year (representing the top 2 to 3% of all squares).

A ‘correlation map’ was prepared for the meadow (Fig. 4). Data for each square over the period 1979–2015 was compared to that of its immediate neighbours: for example, D3 was compared with the square immediately above (D2), below (D4), to the left (C3) and to the right (E3). The total correlation value for D3 was calculated by summing these four values, the maximum possible value being +4. Where a square was on the edge with just two or three neighbouring squares a correction factor was applied so that all cells could have a possible maximum of +4.

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Figure 4. Correlation map of A. morio. The darker shading shows cells with higher correlation values to those around them. Numbers within each cell show the sum of the correlations of each cell with its four neighbours - the maximum possible value being 4. The darkest cells are those with a value of 3 or more.

There were some areas with high levels of correlation between the number of flowerings spikes in adjacent cells. 20 cells had a correlation value greater than 3, i.e. the average correlation of each of these squares with each one of their neighbours was 0.75 or more. Other areas showed far weaker correlation (particularly towards the bottom right of the spreadsheet, representing the most easterly part of First Church Meadow).

Data for the top 20 squares from Figure 4 were then drawn as individual line graphs. The results showed an unexpected division into two distinct groups. Ten of the line graphs showed high numbers of flowering spikes in the early years of recording (1981–1987) with a remarkable consistency of annual increase and decrease in other years, hereafter referred to as Group 1 (Fig. 5). The other ten showed high numbers in the later years (2009–2015) with a similarly consistent pattern in population numbers (Fig. 6), hereafter referred to as Group 2. Though there were several peaks common to both groups e.g. 1991, 2004, 2011 and 2015, the differences in the overall shape of the two graphs suggested that the two groups were very distinct.

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Figure 5. Chart representing flower spike numbers for Group 1 squares, 1979–2015.

Note the wide spread of cells (E13 to Q8). The mean is calculated only from those cells on the spreadsheet with values > 0.

Figure 6. Chart representing flower spike numbers for Group 2 squares, 1979–2015.

Note the wide spread of cells (C9 to Z10). The mean is calculated only from those cells on the spreadsheet with values > 0.

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Table 2. Correlation of the two Groups represented in Figures 5 and 6. The two sets are shaded differently for clarity.

The correlation between these 20 squares was then tested using the same correlation function as before. The results (Table 2) show strong correlation within groups but little or no correlation between the two groups. The significance was tested on the lowest correlated pair in each of the two groups using the Pearson Correlation Coefficient (r) together with a p–value for significance. For Group 1 (high flowering 1981–1987) this was significant - r(33) = 0.48, p <0.05). Group 2 (high flowering 2009–2015) also showed highly significant correlation (r(33) = 0.62, p <0.001).

Further analysis was done to see if this pattern of synchronicity appeared in other parts of First Church Meadow. The data for each cell was compared with a typical square from Group 1 (E13) and Group 2 (C9). If a cell showed a correlation value of 0.5 or more with either Group 1 or 2, this was mapped onto a plan of the meadow (Fig. 7). There was only one cell which showed a correlation of more than 0.5 with both groups.

Figure 7 shows that both Group 1 (typified by E13) and Group 2 (typified by C9) were distributed widely across First Church Meadow. The cells showing the strongest correlation occur towards the left i.e. between rows 32 to 24 (this is the south western edge of the meadow) and this is true for both groups. Figure 7 clearly shows that the two very distinctive patterns of historical flowering occur throughout the meadow and that cells with very strong correlation to one group can be found only a short distance from cells with equally strong correlation to the other group.

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Figure 7. The two groups of flowering patterns in First Church Meadow.

The left hand side shows Group 1 (closely correlated to E13) and the right hand side Group 2 (closely correlated to C9). The deeper the shading, the greater the correlation.

Note both the clustering of each group in distinct areas, and the way in which both types are found throughout the field. Unshaded areas are those squares that showed no correlation value above 0.5 to either group.

Discussion Conclusions relating to annual flowering spike numbers Some factors appear to affect the entire population of A. morio, reducing flower numbers in both groups. For example, Figures 2, 5 and 6 reveal that 1989 was the poorest year for flower spike numbers in First Church Meadow over the entire period 1979–2015. Wells et al. (1998: 41), noted a similar decline in flowering spike numbers at Upwood Meadows, Cambs. in the same year. The authors note: ‘A high proportion of Orchis morio plants flowered each year, exceeding 40% in all years except for 1989 when, for unknown reasons, only 14% flowered.’

The weather records for this period show that the winter of 1988/89 was exceptionally mild and very dry, being one of the warmest since 1659. The following May was also one of the driest, sunniest and warmest on record. It is possible that this combination of factors may have influenced flower spike numbers across a wide area of eastern England. To date, the lack of availability of local weather records for the last 30 years has made it impossible to investigate whether other peaks and troughs of flowering can be correlated to weather conditions.

Conclusions relating to dispersal mechanisms and longevity ‘Clumping’ or ‘contagious dispersal’ is often found in plants that propagate by vegetative means (a classic example is the runners produced by strawberry, Fragaria).

However, while A. morio does produce tubers in the spring, these are not thought to

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be used for vegetative reproduction but solely as a nutrient store, fuelling vegetative growth and production of flowers and seeds in the following year. The Online Atlas of British and Irish Flora states that there is ‘little or no vegetative spread in A. morio’. It is therefore surprising to find this pattern of dispersal in this orchid.

In First Church Meadow the ‘clumps’ may represent young plants of around the same age, grown from seed shed close to the parent plant (as described by Jersáková & Malinová, 2007), developing at a similar rate and reaching first flowering in synchrony. However, they may also represent established, long-lived plants entering the next flowering phase after a period of ‘recovery’ and vegetative growth (as mentioned by Wells et al., 1998). It is difficult to draw any conclusion concerning longevity without further investigation to determine the age of the individuals in a clump.

Conclusions relating to correlated groups The data showed two groups with distinct patterns of flowering behaviour. Group 1 (Fig. 5) was composed of squares that had significant numbers of flowering spikes in the earlier years of recording. A comparison with the mean values for each year shows these areas greatly exceeded the average number of flower spikes between 1982 and 1987, and fell below this figure in many other survey years. Group 2 (Fig. 6) behaved in almost the opposite way, with values below the mean before 2000, and then exceeding it thereafter. During their peak flowering years, squares from both groups were represented in the top 2.5% of squares.

It is difficult to explain the spatial distribution of these two groups. While some banding effect was observable, the groups were both widespread across First Church Meadow, with cells from each group lying almost adjacent to each other (as shown in Fig. 7). They would have been exposed to very similar conditions with respect to weather and climate, availability of soil nutrients and water, and numbers of pollinating insects. Why should some cells in one group show significant increases in numbers in certain years, whilst others in the second group and present in much the same area show a more modest increase or even no increase at all?

It is possible that the groups represent two long-lived, possibly ‘senile’ populations, as described by Rasmussen (1995). Low levels of recruitment would help to explain stability of the flowering pattern within each group, and would suggest that each comprises long-lived plants that only flower sporadically. Perhaps the first group had high recruitment and flowering in the 1980s, followed by a long and continuing period of sporadic flowering amongst a lower number of individuals. The second group, with high flowering in recent years, may also be composed of long-lived individuals that flowered in a period before recording began. Loss of vigour due to the ‘reproductive cost’ of this earlier flowering could explain their absence from the records in earlier years, when plants would have been in a non-flowering, vegetative state, building up resources. If so, the some form of triggering action occurred, causing them to flower (perhaps enough time had passed to allow them to build up sufficient resources to do so). This would explain why plants in Group 2, which is discontinuous and widely spaced across the whole meadow, flowered at more or less

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the same time. Such a trigger effect has parallels with the example given by Sanford of a population existing in a vegetative state for a prolonged period and then coming into flowering due to changing conditions, although in that case the trigger was much more obvious than anything affecting First Church Meadow.

Further research into the age structure of the population (whether new recruits or longer-lived plants) is required to understand these patterns. Are the peaks showing us the first flowering of new recruits or are they showing existing long-lived plants that have been able to flower again by after building up their reserves?

Final Note The surveys show clumping in the pattern of flowering across the site and two distinct groups of squares, with different patterns of flowering behaviour. However, the method used, i.e. recording just the total flowering spikes in each square, provides limited evidence to explain why these patterns occur.

To provide more insight into just what is affecting the ‘clumping’ and synchronicity observed it would be necessary to follow individual plants in smaller sample areas to determine both the degree of recruitment of new individuals and the longevity of existing plants. This could be achieved by using an approach like that of Wells et al.

(1998) in suitable sample squares.

References BSBI/BRC Online Atlas of the British and Irish Flora. [online] Available at: http://www.brc.ac.uk/plantatlas/index.php?q=plant/orchis-morio Accessed 09/01/2016.

Fowler, J., Cohen, L. & Jarvis, P. (2005). Practical Statistics for Field Biology. England: Wiley.

Jersáková, J. & Malinová, T. (2007). Spatial aspects of seed dispersal and seedling recruitment in orchids. The New Phytologist 176: 237–241.

Rasmussen, H. (1995). Terrestrial orchids, from seed to mycotrophic plant.

Cambridge: Cambridge University Press.

Ruth, M., Neiland, M. & Wilcock, C. (1998). Fruit set, nectar reward and rarity in the Orchidaceae. American Journal of Botany 85: 1657–1671.

Summerhayes, V. S. (1951). Wild Orchids of Britain. Collins.

Sanford, M. (1991). The Orchids of Suffolk. Suffolk Naturalists’ Society.

Wells, T. C. E., Rothery, P., Cox, P., & Bamford, S. (1998). Flowering dynamics of Orchis morio L. and Herminium monorchis (L.) R.Br. at two sites in eastern England.

Botanical Journal of the Linnean Society 126: 39–48.

Paul Chapman 20 Thanet Road Ipswich IP4 5LB All annual records and background information relating to Martins’ Meadows is available at http://www.paulechapman.free-hoster.net/

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P. Chapman

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Plate 14: Single flowering spike of Green-winged Orchid (Anacamptis morio) with nine flowers. This would be recorded as one flowering spike. (p. 43).

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