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© Oxford University Press 2008
An investigation to determine variation in marsh orchid (Dactylorhiza) populations at Moses Gate Country Park, Bolton
University of Bolton, Bolton, UK
* Corresponding author: 58 Lakeside Avenue, Bolton BL3 2HY, UK. Tel: +44 01204 399460. Email: crompton462{at}btinternet.com
Supervisor: Frank Goodridge, University of Bolton, Bolton, UK.
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Abstract |
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In June 2006, two populations of Dactylorhiza were examined at Moses Gate Country Park, in Greater Manchester, to determine whether variation exists between the two populations. Careful measurements of orchid characteristics were taken at both sites, in addition to soil pH recordings, and the results compared and tested for significance using one-way ANOVA and Chi-square significance tests.
Descriptive statistics and box-plots showed that there were indeed differences in orchid height, leaf width and leaf number between the two populations, with one-way ANOVA confirming their significance as P < 0.001 for all the variables. Further analyses using frequency data and Chi-square tests also showed that there were significant variations in spur size, leaf type, labellum shape and petal colour between the two sites with P < 0.001 for all these characteristics. Soil pH data were also analysed and tested using one-way ANOVA which showed that there were significant variations in soil pH levels at both sites with P < 0.001 for this data.
It was concluded that there were indeed significant differences between the two populations of Dactylorhiza at Moses Gate Country Park, therefore the null hypothesis was rejected. It was suggested that further investigations could be undertaken at this site, using similar methods, over a number of years, to support this study and to provide further constructive information on the status of the two populations of orchids, which may increase the conservation value of the site.
Key words: Dactylorhiza, marsh, orchid, variation, Manchester
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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According to Stace,1 eight main species of Dactylorhiza can be found growing in Britain, however, Dactylorhiza are notoriously difficult to identify due to extreme variation in colour and morphology within each species and because hybridization occurs readily between the species, leading to many sub-species. Only the rare Dactylorhiza lapponica, (The Lapland marsh orchid) is included in Schedule 8 of the Wildlife and Countryside Act of 1981,2 but all the Dactylorhiza orchids could be considered endangered because many of the species have declined in recent years, due to land drainage and agricultural improvements.
Because of the complex variation within the Dactylorhiza genus, plant scientists are increasingly interested in studying the patterns of diversity within Dactylorhiza, in order to set conservation priorities for these orchids. Most studies focus on: identifying populations using morphological data3 or allozyme data;4 comparing abundant and threatened populations;5 studying Dactylorhiza reproductive strategies6 and identifying the optimal survival conditions for these orchids.7
The preferred habitats of Dactylorhiza are calcareous fens and marshes in wet meadows on alkaline soils. It avoids dry or acidic soils, but is capable of colonizing waste ground and abandoned industrial sites. Pollination occurs via insects such as the Cuckoo bee, beetles (Dascillus cervinus), Skipper butterflies and the female Red-tailed bumblebee. Seed-set is efficient or moderately efficient and plants divide vegetatively to form clumps.8
In the Greater Manchester area, Dactylorhiza can often be found growing in abandoned industrial sites or in regenerated Local Nature Reserves. One such reserve, Nob End (grid reference is given in the Methods section), can be found in Moses Gate Country Park in Bolton. Nob End was designated as a Site of Special Scientific Interest (SSSI) in 2000 because of its unique wildlife. The site is a regenerated industrial area that has a very high pH waste alkali deposit from the Leblanc process, the production of alkali, which was used in soap making. These processes have created an environment rich in flora, not usually found in the Greater Manchester area. One of the many taxa found in this area is the genus Dactylorhiza including the northern marsh orchid (Dactylorhiza purpurella), the early marsh orchid (D. incarnata), the southern marsh orchid (D. praetermissa) and the common spotted orchid (D. fuchsii).9
After liaising with the Park Rangers at Moses Gate it was revealed that for unknown reasons, the Dactylorhiza orchids growing in the Nob End area have been in decline for several years. However, recently, a second, rather abundant population has colonized an area known as Red Bridge (grid reference is given in the Methods section). The Rangers are unsure as to why this has happened because the area is not part of an industrial waste tip, but it has been suggested that building work in the area disturbed the soil a few years ago, altering the conditions of the soil at the site.
On this basis and in order to determine whether the Dactylorhiza population at Nob End is similar in species composition to the Dactylorhiza population at Red Bridge, an investigation was initiated in June 2006. Similar ecological comparisons of threatened and abundant Dactylorhiza orchid populations were undertaken in Finland in 1994 and the results used to identify the conditions that were affecting the orchids; these included the effects of modern forestry and land drainage.5 For the purposes of this study data were collected to test the following hypothesis:
There will be no variation between the population of Dactylorhiza at Red Bridge and the population of Dactylorhiza at Nob End, therefore the two populations will be made up of similar species with similar traits.
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Materials and methods |
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In June 2006, data were collected from Dactylorhiza populations at Red Bridge (Ordnance Survey Grid Ref: SD745 067) and Nob End (Ordnance Survey Grid Ref: SD749 064) within the park. Several hundred morphological measurements were taken from each site using the criteria set out by Stace.1 These included qualitative data such as spur size, leaf type and labellum shape, which are all indicators of species type. Petal colour was determined using Dulux paint charts FV6, RV6, RR1 and WR3 collected from DIY stores in May 2006. Although colours are usually cross-referenced to British Standards (BS381C, 1996), time did not allow for this. Quantitative data such as plant height, leaf number and leaf width data were also collected and both sets of data were used to identify any similarities or differences within and between the two populations. Soil pH recordings were also taken at both sites to determine whether there were any similarities or differences in soil pH between the two sites. Labellum shape was determined using illustrations taken from Stace,1 and used to identify similarities in the labellum shapes of orchids at both sites and to infer species composition. The data were then recorded on a data collection sheet.
The practical recordings commenced at the Red Bridge site which was measured out and divided into seven sections measuring 14.5 m x 10 m. It was decided that 20 orchid plants and 2 soil pH recordings from each section would provide enough data for experimental purposes.
The area at Nob End is much larger than at Red Bridge, but similar sized sections were used and the number of orchid and soil pH samples taken from each section was the same for this site.
The data were analysed using descriptive and statistical tests to determine whether the similarities or differences between and within the sites are statistically significant.
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Results |
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Results from descriptive statistics showed that mean orchid height at Red Bridge was 29.8 cm compared to 20.5 cm at Nob End, a mean difference of 9.3 cm (Table 1). Thus, the orchids at Red Bridge were taller than those at Nob End. Results from one-way ANOVA showed that the difference in height within and between the two sites is statistically significant (F = 56.9, df = 1, 254, P < 0.001). In addition there were slightly more leaves on the orchids at Red Bridge, 7.3 compared to 5.5 at Nob End, a mean difference of 1.8 leaves. However, leaf number appears to be related to height (Table 1). Results from one-way ANOVA showed that the difference in leaf width within and between the two sites was also statistically significant (F = 64.6, df = 1, 254, P < 0.001). The leaves at Red Bridge were also twice as wide as the leaves at Nob End, 20.8 cm compared to 10.1 cm (Table 1). Again one-way ANOVA showed that the difference in leaf widths is statistically significant (F = 193.7, df = 1, 254, P < 0.001).
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The majority of orchids at Red Bridge have spurs greater than 2 mm, whereas the majority of orchids at Nob End have spurs less than 2 mm (Fig. 1). Chi-square significance tests showed that these results are highly significant (At 1 df, Chi Sq. = 58.98, P < 0.001).
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Results also showed that there were differences in the numbers of spotted and unspotted orchids at both sites. At Nob End there were more spotted orchids than unspotted, but at Red Bridge there were more unspotted orchids than spotted orchids (Fig. 2). Chi-square significance tests showed that these results are also highly significant (At 1 df, Chi Sq. = 26.73, P < 0.001).
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Comparisons of orchid labella showed that the orchids at Nob End were similar to only two species of Dactylorhiza, whereas the orchids at Red Bridge were similar to four species, with a few unknown samples (Fig. 3). At Nob End the most common orchid found was similar to D. fuchsia, whereas at Red Bridge the most common orchid found was similar to D. incarnata. Again Chi-square significance tests showed that these results are highly significant (At 4 df, Chi Sq. = 68.95, P < 0.001).
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In addition to the differences in species composition there was also more colour variation in the orchids at Nob End than at Red Bridge where the orchids were similar to only two paint charts—FV6 and RV6 (Fig. 4). Most of the orchids at Nob End were similar to FV6, while at Red Bridge the majority were similar to RV6. Chi-square significance tests showed that these results are highly significant (At 4 df, Chi Sq. = 71.10, P< 0.001)
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Descriptive statistics showed that there were further differences in mean soil pH between the two sites. At Red Bridge soil pH is neutral at 6.73 compared to Nob End where soil pH is more alkaline at 7.72. One-way ANOVA showed that the differences in soil pH within and between the two sites are statistically significant (F = 1072.1, 1 df, 254, P < 0.001)
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Discussion |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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Preliminary data using plant height, leaf number and leaf width showed that there are significant differences between the two populations of Dactylorhiza. The most obvious difference being that apart from one or two outliers, the orchids at Red Bridge appear to be taller with a greater number of leaves that tend to be wider than the orchids at Nob End. Thus initial findings would indicate that the two populations are not similar. This was confirmed using one-way ANOVA with P < 0.001 for all the variables. Therefore using quantitative data only, it is possible to reject the hypothesis that the two populations are similar.
Further analysis using qualitative data such as spur size, leaf type, labellum shape and petal colour were also used to validate this and to help with the identification of the orchids at both sites. Also Dactylorhiza studies usually involve the use of several orchid characteristics when studying distribution and variation between populations.10
According to Stace,1 spur size is often used to identify Dactylorhiza species. Orchids with spurs greater than 2 mm could belong to one of six species: D. incarnata, D. lapponica, D. traunsteineri, D. majalis, D. purpurella and D. praetermissa. Orchids with spurs less than 2 mm could belong to one of two species: D.fuchsii or D. maculata. Figure 1 shows that at Red Bridge the frequency of orchids with spurs greater than 2 mm is greater than at Nob End where the frequency of orchids with spurs less than 2 mm is greater. If there is an association between the site and spur size the observed percentage of Dactylorhiza with spur sizes less than 2 mm or greater than 2 mm should be similar to the expected frequencies of orchids with spurs less than 2 mm and greater than 2 mm at both sites, however, the results showed no evidence of this and statistical analysis established that the observed differences in spur size at both sites is highly significant with P < 0.001. Thus the hypothesis that there is no association between the site and the spur sizes of orchids at both sites is rejected. There are indeed significant differences between the spur sizes of orchids at Red Bridge and Nob End, which means that the orchids may belong to the species suggested by Stace.1
Further differences were found in the frequencies of spotted and unspotted orchids between the two sites (Fig. 2). This character could also be used to identify species type. Spotted Dactylorhiza usually belong to one of two species—D. maculata and D.fuchsii—whereas unspotted orchids usually belong to one of six species: D. incarnata, D. lapponica, D. traunsteineri, D. majalis, D. purpurella and D. praetermissa. This would suggest that 68.5% of the orchid population at Nob End could belong to D. maculata or D.fuchsii, whereas 64.1% of the orchid population at Red Bridge could belong to the other six species. However hybridization readily occurs between spotted and unspotted Dactylorhiza which give rise to spotted hybrids of orchids belonging to species that are not usually spotted.9 For example, D. praetermissa (unspotted) x D.maculata (spotted) = D. hallii (spotted) therefore interpreting these results in this way may be misleading. However, statistical analysis showed that the observed differences between spotted and unspotted orchids at the two sites were statistically significant with P < 0.001. Therefore the hypothesis that there is no association between the site and a spotted or unspotted orchid is rejected, which means that there are significant differences between the spotted and unspotted orchids at both sites.
Information given by English Nature suggests that the orchids at Nob End belong to four species of Dactylorhiza: D. fuchsii, D. incarnata, D. purpurella and D. Praetermissa.9 From Fig. 3 it would appear that the orchid labella examined at Nob End are similar to only two species: D. incarnata and D.fuchsii, while at Red Bridge the orchid labella appear to be similar to all the four species suggested by English Nature. Thus the data are not consistent with the information given by English Nature for Nob End. It is possible that these inconsistencies may be due to the differences in the timing of data collection between the two sites. The Red Bridge data were collected between 6 June 2006 and 19 June 2006, whereas the Nob End data were collected slightly later between 26 June 2006 and 7 July 2006. However, information about the flowering periods of the four species of Dactylorhiza given by English Nature8 suggests that all the species would have been flowering during these dates so timing may not be responsible for the inconsistencies after all. Indeed it is possible that differences in site composition may be influencing species composition at both sites. Statistical analysis of the labellum shape data showed that P < 0.001, therefore the hypothesis that there is no association between the site and labellum shape is rejected. The observed differences in labellum shape between the two sites are highly significant.
The frequencies of orchids with similar petal colours at Red Bridge and Nob End show that orchid petal colour at Red Bridge appear to be similar to two shade cards FV6 (37.8%) and RV6 (62.2%) which are shades of lilac and purple. At Nob End, 66.9% of the orchids were similar to card FV6—shades of lilac; 14.5% were similar to RV6—shades of purple; and the rest 18.6% were similar to RR1—red to dark pink; and WR3—dark pink to light pink and white. These results are quite surprising given that when comparing labellum shape, the orchids at Nob End appear to be similar to only two species of Dactylorhiza, whereas the orchids at Red Bridge appear to be similar to the four species suggested by English Nature.9 However, the population at Nob End is much older than the population at Red Bridge which may explain the variation in petal colour at Nob End. Indeed, studies of orchid differentiation often show that morphological variation is greater and more pronounced in older populations and these variations are more pronounced in the analysis of floral morphology than in any other morphology.11 Therefore population age could explain why there is more colour variation at Nob End than at Red Bridge. Statistical analysis of petal colour data showed that P < 0.001, which means that these results are highly significant. Thus, the null hypothesis can be rejected and it may be assumed that site composition may also be influencing petal colour.
Differences in mean soil pH were also found at both sites with statistical analysis confirming that these differences were significant with P < 0.001. At Red Bridge mean soil pH was 6.73 compared to Nob End where mean soil pH was 7.72. For Nob End, which is calcareous grassland, this result is to be expected as calcareous soils tend to have pH values around or above 7.12 However, the soil at Red Bridge appears to be more acidic than at Nob End and although Dactylorhiza tend to avoid acidic soils, the opposite appears to be true with the Red Bridge site producing a greater abundance of better performing orchids than at Nob End. Nevertheless, Dactylorhiza are able to tolerate a wide range of soils,9 and soil pH values of between 6.5 and 7.0 usually provide the most favourable conditions for absorbing elements from the soil.13
Thus, statistical analyses have shown that there is indeed a significant difference between the two populations of Dactylorhiza at Nob End and Red Bridge. The main differences being that the population at Red Bridge is made up of all the four species suggested by English Nature9 compared to only two of the suggested species at Nob End. The orchids growing at Red Bridge also appear to be taller with a greater number of leaves that are wider than those at Nob End. Soil pH is also lower at this site and the area is generally boggy compared to Nob End, where the ground is much drier with excess scrub. The frequency of mowing and scrub clearing also differs between the sites with scrub clearing occurring in early March at Nob End and mowing only occurring after the orchids have flowered in August at Red Bridge. Other studies have shown that the frequency and timing of mowing and scrub clearing can have a major effect on the performance of Dactylorhiza.7 However, it would be unwise to suggest that two of the suggested species have permanently disappeared from the Nob End site using the evidence from this study alone, further studies are required in subsequent years to determine whether this is the case or not. For the purposes of this study the Null Hypothesis is rejected, the two populations of Dactylorhiza at Moses Gate Country Park are significantly different. These results are consistent with studies undertaken by Andersson11 who showed that patterns of floral morphology differ in older populations and by Kuitunen and Kuitunen5 who showed that Dactylorhiza populations are very sensitive to changes in surroundings and land drainage.
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Conclusion |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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Preliminary data using descriptive statistics showed that there were real differences between the populations of orchids at Red Bridge and Nob End, with one-way ANOVA confirming that the differences in height, leaf width and leaf number were statistically significant. Further analyses using frequency tables and Chi-square tests showed that the observed differences in spur size, leaf type, labellum shape and petal colour between the two sites are highly significant. The study also showed that only two of the species suggested by English Nature could be identified at the Nob End Site, but further studies are required before this can be confirmed as accurate. Comparisons of mean soil pH at both sites showed that mean soil pH at Red Bridge is 0.99 lower than at Nob End, where the soil is more alkaline. One-way ANOVA confirmed that these results are also highly significant; therefore the hypothesis that there is no variation between the two populations of Dactylorhiza at Moses Gate Country Park is rejected. It is possible that the variation between the two populations is due to the differences in soil composition and the frequency of scrub clearing at both sites. These results are similar to studies undertaken by Andersson11 and Kuitunen and Kuitunen.5
Since this study is the first of its kind at Moses Gate, these results may prove useful to the managing body of Moses Gate Country Park, as it may provide some insights as to why the population at Red Bridge appears to be flourishing when the population at Nob End is declining. In order to support this study and to determine whether the two species D. purpurella and D. praetermissa are still present in the population at Nob End it is recommended that further studies using similar data are undertaken in future years, which will provide English Nature and the managing body of Moses Gate Country Park with further constructive information about the status of the orchids at Nob End and Red Bridge. This may help to obtain more grants and further action to bring the site into favourable condition, thus increasing the conservation value of the two sites.
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Acknowledgements |
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Grateful thanks are offered to the following people: Dr Ruth Hall, Lecturer, Psychology and Life Sciences, University of Bolton; Dr Frank Goodridge, Lecturer, Psychology and Life Sciences, University of Bolton; Alan Crawshaw, Senior Technician, University of Bolton; Mr Phil Sharples, Park Ranger at Moses Gate Country Park, whose knowledge and advice was invaluable for initiating this study.
English Nature for allowing me to make practical recordings of the orchids at Nob End which is a protected site of special scientific interest (SSSI). Finally, special thanks are offered to Mr Wilfrid Bailey, BA (Hons) Community Studies, University of Bolton, for helping me to collect the data necessary for this study.
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References |
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- Stace C. New Flora of the British Isles (1997) 2nd edn. Cambridge: Cambridge University Press. 973–979.
- Joint Nature Conservation Committee—Advisor to the Government. (2007) http://www.jncc.gov.uk/page-1785/1816 [accessed 25 January 2007].
- Andersson E. On the identity of orchid populations: A morphometric Study of the Dactylorhiza traunsteineri complex in eastern Sweden. Nordic J Bot (1994) 14:269–275.
- Pederson H. Dactylorhiza majalis s. l. (orchidaceae) in acid habitats: variation taxonomy and evolution. Nordic J Bot (2004) 22:641–658.
- Kuitunen M, Kuitunen T. Ecological comparison of a threatened and an abundant orchid species (Dactylorhiza incarnate and D. maculata) in Finland. Aquilo Ser Bot (1994) 33:63–68.
- Koivisto AM, Vallius E, Salonen V. Pollination and reproductive success of two colour variants of a deceptive orchid, Dactylorhiza maculate (Orchidaceae). Nordic J Bot (2002) 22:53–58.
- Janeckova P, Wotavova K, Schoedelbaurova I, et al. Relative effects of management and environmental conditions on performance and survival of Dactylorhiza majalis. Biol Conserv (2006) 129:40–49.[CrossRef]
- English Nature—‘Britain's Orchids’. (2006) www.britainsorchids.fieldguide.co.uk [accessed 3 May 2006].
- English Nature—Special Sites. (2007) www.english-nature.org.uk [accessed 25 January 2007].
- Jonsell B. Dactylorhiza incarnata and D. traunsteineri in Northernmost Uppland, Central Sweden. Svensk Botanisk Tidskrift (1982) 76:103–111.
- Andersson E. Age related morphological differentiation among populations of Dactylorhiza traunsteineri in Eastern Sweden. Nordic J Bot (1995) 15:127–137.
- Fitter AH, Hay RKM. Environmental Physiology of Plants (1995) 2nd edn. Academic Press: London. 228–229.
- Mauseth JD. Botany: An Introduction to Plant Biology (2003) 3rd edn. London: Jones and Bartlett Publishers. 387.
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