The possibility of determining the age of ... - Wiley Online Library

Nezi; Phytol. (1989), 112, 577-584

The possibility of determining the age of colonies of clonally propagating herbaceous species from historic records: the case of Aster novi-belgii L. (first recorded as A. salignus Willd.) at Wicken Fen Nature Reserve, Cambridgeshire, England BY D. B R I G G S , M.

BLOCK

AND S.

JENNINGS

Botany School, Downing Street, Cambridge, UK, CB2 3EA {Received 31 March 1989; accepted 10 April 1989) SUMMARY For a number of species, population biologists have estimated the age of apparent clones. In studying a colony of naturalized Aster novi-belgii L. (first recorded as Aster salignus Willd.) growing at Wicken Fen Nature Reserve, Cambridgeshire, England, vve have attempted to determine from a considerable body of historic records, its age, structure and development. While it is highly likely that the records refer to the colony in its present position on the Fen, there is uncertainty about its age and conflicting information about its position. A. novi-belgii is a self-incompatible species. Plants of the Wicken colony exhibit little variation and preliminary tests show that their achenes are sterile. As a working hypothesis, for further testing, we suggest that all the plants may be of a single clone. Population biologists, who are interested in determining the age and development of clones of plants, are likely to be disappointed both by the extent and the vagueness of historic records. This situation is understandable as the information was recorded for taxonomic purposes. The hope is expressed that the intensive studies now being nnade of populations of plants will result in the long-term survival in the public domain of detailed records and maps, which will enable future generations to study the age and development of clones of herbaceous species. Key words: Aster iiuvi-belgii, Asler salignus, Wicken Fen, age of clones.

INTRODUCTION

Oinonen (1967a, 6), studying field populations, . , \ . r

estimated the size of apparent clones in relation to There is much current interest in the population site history and concluded that clones may be matiy biology of clonally propagating plant species (Jackhundreds of years old. son, Buss & Cook, 1985; EUstrand & Roose, 1987; In a field survey of a patch of Box-huckleberry Watkinson, 1988): including studies of growth form [Gaylussacia brachycerium (Michx.) Gray] growing of clones (Menges, 1987; Cain & Cook, 1988; Cook, in Perry County, Pennsylvania, USA the uniformity 1988): the foraging of vegetatively reproducing of the plants over an 8 acre site was noted, and it was plants (Slade & Hutchings 1987a,6): the effects of suggested, but without direct evidence, that this disease (Parker, 1987): and the composition and clone was of great age, perhaps of the order of 13 000 interaction of genetically different individuals in years (Wherry, 1972). vegetation (Worthen & Stiles, 1986; Reinartz & On the evidence of aerial photographs and field Popp, 1987; Evans & Turkington, 1988). The studies Kemperman & Barnes (1976), considered question of the age of clones has also received some that large clones are produced by North American attention. Aspens (Popu/us). No direct evidence of the age of In bracken [Pteridium aquilinum (L.) Kuhn.] specific clones is available, but it has been suggested establishment from spores is a rare event, being that the largest clones may have originated in the late associated with gross habitat disturbance and fire. Pleistocene (8000-10000 years B.P.).

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D. Briggs, M. Block and S. Jennings

Several different lines of investigation have been note that there was an earlier record, the plant employed in other studies. Following cultivation having been 'found by Mr Brown of Cambridge, on experiments on field samples and crossing experi- Wicken Fen in 1864, and given to the Professor of ments with Festuca ruhra L., Harberd (1961) Botany (C. C. Babington); but it remained unnamed concluded that a certain clone in the Pentland Hills, until after the reading of this paper'. Babington Scotland extended over 220 m and might be more (1867), no doubt prompted by Hiern's discovery, provided further information on Brown's specimen, than 1000 years old. As a result of morphological studies, aerial pho- which is also in the University herbarium. tography, counting of annual rings, radiocarbon dating and investigation of patterns of isozymes, apparent clones of great age (perhaps as old as Early viezvs on the identity and status of the Aster 11 700) years) have been described in Creosote bush Both Hiern and Babington identified the plant as [Larrea tridentata (Sesse & Moc. ex DC) Cov.J, Aster salignus Willd. In his brief note Hiern (1867) growing in the Mojave desert, California (Vasek, appears to favour the view that the plant is native 1980). rather than introduced, for he writes that it was Here we consider whether it might be possible to found growing in 'an apparently wild state on the discover the age, and follow the development of a Fen... It grows wild in Germany and Denmark, in colony of a clonally propagating herbaceous species many places by the banks of rivers, and, therefore, from direct historical evidence. For such an attempt might probably occur in Britain in such a locality as to succeed it is necessary to discover appropriate Wicken Fen. It is not a plant in ordinary cultivation, records. and could not, therefore, easily escape from a Our attention has been drawn to the wealth of garden.' In the slightly longer report of his paper to information about the vegetation at Wicken Fen, the British Association, Miern seems less certain of Cambridgeshire, Fngland (Cirid reference: T L 55 its status, considering that it could be native or 70), which is a reserve of the National Trust. While perhaps introduced. the Trust's first holdings were acquired in 1899, After reviewing the available evidence, Babington biological records date back to the 1850s (Rowell, (1867) comes to a firm conclusion. ' As it appears that 1983; Rowell & Harvey, 1988). this plant is not a native of America, but of the In this paper we consider the case of an introduced European continent, where it grows by the sides of variant of Aster novi-belgii L., a rhizomatous perrivers and in swamps, we may reasonably suppose ennial species, to discover whether it is possible to that it is also a native of Great Britain.' Aster date the arrival of the plant in Wicken Fen and to salignus, which was also detected in a Scottish locality follow the subsequent history of its spread. in the 1860s, now took its place, briefiy, as a native species of the British Bora. n^hus, a picture emerges from these papers of a SOURCES OF F.VlDF.NCi; hitherto undetected plant, native to the British flora. We have gathered evidence irom the following Moreover, its a'leged native status naturally sugprimary sources; published papers; the records in gested that it was a longstanding member of the fen the archives of Wicken Fen Nature Reserve; unpubvegetation. lished lists of localities and annotations in Floras (in the Botany School library collections); maps (in the University Library, Cambridge, and in the Cambridge Collection of the City Library); comments Reassessirient of the identity and status of the Wicken Aster and notes on herbarium specimens (in the University Herbarium, International herbarium code: CGF); Babington continued to use the name Aster salignus and aerial photographs in the collections of Cam- throughout his life. But in the Botanical Exchange bridge University Department of Aerial Photogra- Club Report for 1897, page 551, is a note by J. A. phy. Wheldon, in which we are given the view of the celebrated American botanist Professor Asa Gray, who considered that the Wicken plant was wrongly RESULTS AND DISCUSSION named and should be called Aster novi-belgii L., a First records of the Aster plant from eastern North America widely naturalized The first published record is that of Hiern (1867). in central and north-west Europe. His material, dated 25 August 1867, is preserved as Another view was taken by Dr Thellung, who a herbarium specimen in CGE. Hiern's note is a identified a plant collected by G. Goode at Wicken summary of a paper given at the British Association Fen on 30 August 1892, as Aster novimeeting at Dundee in September of that year. In the belgii'? x salignus (Wheldon, 1919). Transactions of the Association (1868) we find a In 1972, Dr P. F. Yeo, studying the herbarium fuller account of his finding of the Aster, and also a material in CGE, decided that the material was all

Aster at Wicken Fen referable to A. novi-belgii (Crompton, 1976; Merxmiiller, Schrieber & Yeo, 1976). Concerning the status of the plant in the British Flora, Babington changed his \iews. In his own annotated copy of the sixth (1867) edition of his Manual of British Botany (first edition published in 1 843) and in the text of the seventh edition (1874), he notes that Aster salignus is an alien. Botanists now agree with the views of I'erring et al. (1964), in A Flora of Catnbridgesliire, that the plant at Wicken is 'presumably a naturalized garden escape'. Evidence for the date of introduction T'be recognition of the fact that the Aster is an introduced plant suggests that it might be possible to determine the date of its first arrival on the Fen, for, according to his diaries, Babington (1897) made seven visits to the Fen in the period 1851-9 (Rowell, 1983) before publishing his Elora of Cambridgeshire in 1860. In Appendix No. VIII of the flora he notes that, ' A s the kind of vegetation whicb formerly occupied the Great Level of the Fens is very little known to botanists, to most of whom the Fens are nearly a "terra incognita", it seems desirable to give a complete list (our italics) of the plants which have been recently found growing in Wicken Fen.' Aster is not included in the list of 130 species. Thus, it seems possible that it could have established itself in the early 1860s, just before Brown discovered it. Given the aim of this investigation, it seems, at first sight, that we have succeeded, within narrow limits, in establishing a probable date of arrival of the plant at Wicken. However, such a conclusion may be unwarranted as Babington (1867), ofTers a convincing explanation of why the plant might have been overlooked on his various visits, drawing attention to 'the extreme wildness of the unreclaimed fen which it inhabits, and the late time of its flowering (August), when most of the naturalists of Cambridge are away from home'. From the evidence at present available it cannot safely be concluded that the plant was introduced in tbe 1860s. In considering the earliest possible date of the arrival of Aster at Wicken, we may note that Asters were introduced from eastern North America from 1633 onwards, with Aster novi-belirii being brought into cultivation about 1710 (CJreen, 1974). The location and number of Aster colonies In order to assess the ease with which introduction to tbe Fen from a garden might be possible, it is necessary to know the position of the original colony on the Fen. There is conflicting evidence on this point. Hiern (1868) notes that the Aster was found 'growing in company with Cladiuin niariscus (L.) Pohl., Thalictrum flavutn L., Peucedanum palustre

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(L.) Moench., Cirsium dissectum (L.) Hill. (Carduus pratensis Huds.), Agrostis canina L., Thelypteris palustris Schott. [Lastrea Thelypteris (L.) Bory], and several salices... The spot where the Aster grows is in the midst of sedge, and no house is near it' (our italics). In contrast there is a note on the herbarium specimen collected by Brown. It states 'One large patch in Wicken Fen, Cambridgeshire (not far from the houses) John Brown 1864.' In preparing his Flora of Cambridgeshire Babington made three quarto v'olumes of records. These manuscripts are now in the collection of historic material in the Botany Sehool Library. Out of taxonomie sequence, at the end of volume 3, is a note under the name of Aster salignus, 'A large patch in Wicken Fen near the upper end of the lode. 1865.' Presumably this is a reference to Wicken Lode (Fig. \a). A final piece of evidence is provided by a sketch in Babington's hand. In a letter to Burkill (Babington, 1897) Babington refers to the existence of a sketch but does not seem to be able to remember its location. He suggests 'You had better look into the interleaved volumes of the "Manual" [Manual of British Botany'] for there you may(}) find a plan of the ground.' In a postscript he adds ' Look also in the Interleaved "Flora", and the quarto notes concerning it.' The sketch in question is in Babington's own annotated copy of the Flora of Cambridgeshire. There are no sketches in his annotated copy of the sixth edition of the Manual or in the quarto notes. Babington's copy of the Flora came into the possession of R. L Lynch, Curator of the Botanie Ciarden (1879-1919), and is now in the Botany School library. The undated thumbnail sketch (Fig. 2) may be interpreted as showing the end of Wicken Lode and that part of the Sedge Fen nearest to the village by the present entrance to the reserve. The location of the Aster [which inexplicably he calls A. saticinus (um)] is indicated on the map by a small square, which is a little to the west of the present-day position of the colony. With the evidence available, and there is a surprising quantity of information from the 1860s, there are difl^culties in interpretation. Are the different observers referring to the same patch ? How do we evaluate the two opposing statements about the distance of the pateh from nearby houses ? The comments of Brown and Babington could be taken to refer to the patch in its present position. While this is highly probable, there is insufficient evidence to be completely certain. Hiern's finding of a plant with 'no house near it', may refer to a different patch. Alternatively, they may have been sampling at the same point, but because Hiern thought about the possible native status of the plant he sought to give the impression that it was a wild plant. The possibility of there being more than one patch of Aster must therefore be taken seriously. AM' 11 -

.S80

D. Briggs, M. Block and S. Jennings (a)

Sedge

tb)

Aster at IVicken Fen

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Figure 2. In his own personal, interleaved, annotated, copy of Flora of Cambridgeshire, on a portion of the interleaf opposite page 118, Babington records the site of the Aster colony. The sketch, which lacks date, scale, orientation and labelling of fixed points is intcrpretable as showing that portion of VVicken Sedge I'"en bounded to the left by the end of the na\ igable portion of Wicken Lode and on the right by what is now called Gardiner's Drove.

We have no direct evidence on the mode of introduction of the Aster, but there are two possibilities. It has been suggested by Evans (1939) that there were gardens on the Fen. He writes that Hiern (1867; p. 306) 'was the first to record this Aster from the village end of Wicken Fen, then used as cottage gardens ' (our italics). There is no evidence of gardens on the Fen in maps we have studied (Fig. 1 a, b). Furthermore, Hiern in his accounts makes no mention of any garden on the Fen proper. Indeed, as we have seen, his paper to the British Association gives details of the fen community in which the Aster was growing, stating that the plant was found in the midst of sedge with no house near it. Babington also saw the plant growing at Wicken, for he notes in his letter to Burkill ' I brought a root away which is now growing in . le south west corner of our kitchen

garden. ' It seems unlikely that one of the foremost botanists of his age would have published the record as a species new to Britain if the material had been found growing in a garden, either cultivated or neglected. There is evidence (Farren, 1926) that there were several cottages and an orchard associated with the Wicken brickyard, to the north-north-west of the Aster colony (Fig. l a , site C), but the development of the site, for the manufacture of bricks, post-dated the first finding of the Aster plants (Rowell, 1983). The balance of evidence suggests that the plant established itself in fen vegetation. Fstablishment by seed into the very tall closed community on the Sedge Fen seems unlikely. However, glass has been found on the nearby Poors' Fen (G. Crompton, personal communication). This suggests the possi-

Figure 1. (a) Sketch map of Wicken Village and Sedge Fen showing the present day location of the Aster colony (A); the probable position of the colony as recorded in Babington's sketch map (B) (see Fig. 2); the position of the Wicken Brickworks (C); and the limit of navigation of Wicken lode (D). (h) A black-and-white plan of Wicken area dated 1835 provides e\ idence that houses and gardens were present in Lode Lane near to the Sedge Fen some time before Babington's visits and the finding of the Aster colony in 1864. This plan - MS 19 in the Map Collections of the University Library, Cambridge - lacks scale, orientation and the names of fixed points. As an aid to interpretation, we have added the names of certain features in the study area.

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bility that rubbish, perhaps including rhizomes of Aster, could have been taken on to the Fen from the gardens of nearby cottages (Fig. 1 h). Ecological factors influencing the Aster colony The Sedge Fen has been subject to several management practices which could bave affected tbe Aster once it bad become established (Rowell, 1983; Rowell & Harvey, 1988). Until the early nineteenth century, sedge was cut every 4 years to provide material for thatching. Then, regular cutting was neglected as the market for sedge declined. In the twentieth century areas were cut for litter, and as part of the management of the area within the nature reserye. The chief effect of the management regimes on the Aster has been the disturbance associated with the frequent and sometimes regular cutting of the plants resulting in the decapitation of plants before possible seed set. Moreover, even if seed has been set occasionally, the tall (c. 1 m) high closed vegetation of the area is likely to have made seedling establishment very difficult. Thus, it is supposed that vegetative spread from the original introduction has been of the utmost importance. The development of the colony There are a few pieces of evidence about the colony from the end of the nineteenth century. First, Babington's letter to Burkill introduces an element of uncertainty about the continued existence of the colony. Having directed Burkill to look for the sketch 'of the ground where the Aster grew', Babington then continues ' 1 say grew, for I am far from sure that it is there now. It has never been again gathered there, and it has been looked for unsuccessfully by me and others', as for example in 1868 when Babington and Mudd (Curator of the Botanic Garden) visited Wicken. Babington (1897, p. 209) notes in his journal, 'we did not find Aster salignus, from a mistake'. In his letter to Burkill he suggests another possibility ' I fear that it may have been carefully removed by the farmer as a troublesome weed' (Babington, 1897). C3n receiving Babington's letter (dated 23 July 1894), Burkill wasted no time in looking for the plant, and it appears that Babington's view was incorrect, for, on 17 August of that year Burkill and A. S. Shrubbs (an Assistant in the Botany School) successfully found the Aster, noting on their herbarium sheet that 'the plant now occupies a considerable area on Wicken Sedge Fen'. Moreover, other botanists had detected the plant in the early 189()s and there are herbarium specimens in CGF collected in 1891 (W. A. Dutt), 1892 and 1893 (A. Bennett). There are three herbarium specimens in CC;E for 1894 (one collected by A. S. Shrubbs,

another by Burkill and a third collector unknown). There is also herbarium material collected at later dates; 1898 (G. Goode), 1901 (S. H. Bickham), 1901 (R. H. Lock), 1914 (collector unknown), 1961 (P. D. Sell), and 1965 (S. M. Walters and P. D. Sell). The Fen Aster is mentioned in an account of Wicken Fen prepared by Gardiner (1928) and noted in the list of Wicken plants published by Evans (1923). In no case is there sufficient detailed information on herbarium sheets to allow us to determine, or infer, the exact location or extent of the colony (ies) or the position of individual plants. However, some information of interest is provided by Evans (1939). He notes that the plant 'has increased to fill a space of twenty or thirty yards square' adding, with no information as to source, 'though there were at first only two or three clumps, which had hardly increased by 1877'. Studies of aerial photographs reveal that, unfortunately, plants of Aster cannot themselves be discerned. Such photographs confirm, however, that the area in which they grow has frequently been cut since the 1950s, and was even the site of an experiment on the effect of various cutting treatments carried out by Rowell (1983). In our preliminary survey in 1988 we found Aster in one area of the Sedge Fen (Fig. 1 a). Two very diffuse patches were discovered. The larger patch was c 17 8 X 10 m and the smaller patch t. 11 -5 x 7 m. At the present time, as part of the management of the Fen as a nature reserve, the area containing the larger patch of Aster is cut annually in early summer. The adjacent area containing the smaller patch is cut biennially at the same season (T. Bennett, personal communication). Variability in Aster A number of lines of evidence are available which suggest a working model of the genetical structure of the population for future study. Herbarium specimens of Aster in CGE reveal a uniformity of morphology consistent with the notion that all the material could be part of a single clonal patch. East (1940) reports that Asters, including Aster novibelgii, are completely self-sterile. Only if several genotypes are present in a population might viable achenes be produced. Achenes collected from the Aster colony in 1986 proved to be empty and incapable of germination. This evidence supports the idea that only one clone is present. It might be considered that the scattered distribution of the plants at the present time might be inconsistent with such a view. However, Asters quickly exhaust the soil on which they grovy (Green, 1974) and instead of yielding a symmetrical hollow ring. Brown's original 'one large patch', which has been subject to continual disturbance, could have produced the diffuse patches at present found on the Sedge Fen.

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Aster at Wicken Een Before this model is accepted, further studies of the population are necessary, for East (1940) noted that some cultivars of Aster produced a few achenes when individual plants were isolated. Also, further examination of the viability of achenes is necessary. In 1986 almost all the Aster plants had been cut before fruiting and we were only able to harvest a small sample of achenes, which was perhaps unrepresentative of the potential behaviour of the plants in the colony.

exist for another class of plants, namely, those native and exotic species which have been deliberately planted. In conclusion, we express the hope that the detailed population studies of the past decades, including introductions and reintroductions, will result in the survival in the public domain of maps of sufficient detail for botanists working in the future to study the age, structure and development of colonies of plants.

CONCLUDING HV. M ARKS

.\ C K N O W L !•: U G E M F, N T S

Field botanists in the m i d - n i n e t e e n t h century were, for t h e most part, interested in the distribution iif p l a n t s , in particular the finding of new or interesting taxa in new or interesting places. F o r new records to b e accepted a h e r b a r i u m specimen was necessary, w h i c h traditionally was labelled with only brief details of the locality. M a p s are only likely to be found in u n p u b l i s h e d diaries, field note-books, etc. It is clear from these c o m m e n t s that the historic r e c o r d s were collected to serve specific purposes and t h a t generally there will be little detailed information a b o u t exactly where, and in what n u m b e r s , plants w e r e to be found. W e were very interested, therefore, to discover such an unusually large n u m b e r of historic records for the Wicken Aster. At first sight it would appear possible to date the introduction, b u t as we have shown there are m a n y unresolved issues and it has not proved possible to d e t e r m i n e the age of the colony with certainty. T h e r e is also uncertainty about the position and s t r u c t u r e of the colony (ies). T h e sketch of Babington is interpretable, even t h o u g h it lacks a date and the labelling of fixed points. It is highly likely that m o r e t h a n 120 years ago Babington was referring to the patch of Aster which still exists, flowever, the vague confiicting statements of Brown and Hiern about the distance from the houses suggest that there m a y have been m o r e than one colony. N o n e of the records provide information on the seed fertility of the Aster, which would enable us to deduce the most likely genetic s t r u c t u r e of the patches. W e have considered o u r example in considerable detail. T h e Wieken Aster is of more than parochial interest, for it p r o m p t s us to assess the likelihood of d e t e r m i n i n g age of colonies and clones from the historic records for other species. F r o m our own experience, and from discussions with a n u m b e r of botanists, we consider that population biologists are likely to be disappointed both by the quality and q u a n t i t y of evidence which may be discovered about t h e history of populations of herbaceous plants. H o w e v e r , we feel that records of other longstanding n a t u r e reserves should be studied to see if our view is justified. N o t only should information about accidentally introduced taxa be investigated, b u t it m i g h t also be interesting to examine such records as

In the preparation of this account we have had very helpful advice from Mr T . J. Bennett, Mrs G. Crompton, Dr S. M. Walters, and Dr P. I'. Yeo. In particular we thank Dr T . A. Rowell, who drew our attention to Babington's sketch map. We are also grateftil to L. C. Nicol and .\. Clarke for valuable assistance.

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