Diversity and Distributions, (Diversity Distrib.) (2004) 10, 147–151 Blackwell Publishing, Ltd.
BIODIVERSITY RESEARCH
Alien species reflecting history: medieval castles in Germany Katharina Dehnen-Schmutz
Institut für Ökologie, Technische Universität Berlin, Rothenburgstraße 12, D 12165 Berlin, Germany
Present address: Environment Department, University of York, Heslington, York YO10 5DD, UK. Tel.: +44 1904 434072. Fax.: +44 1904 432998. E-mail:
[email protected]
ABSTRACT
Ninety-seven alien plant species were found in habitats provided by rocks and walls around 56 castles in Germany. Compared to Central European agriophytes (i.e. alien species naturalised in natural vegetation), the flora adjacent to castles had more species introduced before 1500. More alien species introduced earlier were found at castles built earlier compared to castles built later. Fifty percent of the species introduced before and during the Middle Ages were usable plants at that time, compared to 20% of usable plants among the native species in the same habitats. Species introduced earlier were mainly used for medication and nutrition, whereas later introductions were used for ornamental purposes. Compared to the total alien flora of Germany, there were more useable species at the castles, nearly the same percentage of ornamentals and fewer plants without use. These results imply that the species composition of alien species growing in the vicinity of medieval castles today may be traced back to the historical reasons for their introduction to these places. Keywords Alien plants, archaeobotany, biological invasions, human influence, middle ages.
INTRODUCTION Biological invasions are closely linked to historical and current human activities; the alien species composition of a country reflects historical as well as recent processes. The number of alien plant species in the 48 contiguous states of the USA was shown to be positively correlated to the duration of European settlement (McKinney, 2001). Caneva et al. (2003) found that the change in the floristic composition at the Roman Coliseum was linked to the history and abandonment of the site over the past four centuries. For long-lived species, single plants can be linked to the historical reasons for their planting in certain localities, such as Taxus baccata at abbeys in England over several hundred years (Bevan-Jones, 2002). While studying the alien species of rocks and walls of medieval castles (Dehnen-Schmutz, 1998), the question arose of whether it would be possible to explain the occurrence of alien plants on these sites with historical reasons for their introduction there. Medieval castles seem to be suitable objects for this question. Founded in the 9th to 15th century, they are among the oldest buildings in Central Europe and have changed much less over the centuries than towns or settlements. After cloisters, castles were the first places in Central Europe to have gardens (Janssen, 1986) and where alien species may have been planted. The hypothesis that the flora around castles reflects human activity cannot be examined directly, since this would require historical data to verify the occurrence of species at the castles centuries ago. Although there are records of single species at © 2004 Blackwell Publishing Ltd www.blackwellpublishing.com/ddi
some castles in historical floras, there are no comprehensive historical listings of the plant species at castles. An archaeobotanical investigation of a castle built in the lowlands of Western Germany (Janssen & Knörzer, 1971) confirmed the presence of alien species at the castle in the Middle Ages but could not differentiate between plants cultivated there from those consumed but not cultivated. Discarded plant waste could have contained propagules that resulted in the establishment of some species. No other castles have been studied and it might be more difficult to find archaoebotanical material at castles on rocky ground than at castles in the lowlands, where wet soils increase the probability that these materials are conserved. So the aim of this paper is to search for indirect evidence relating the alien species found at castles today to the history of these castles since their foundation in the Middle Ages. METHODS Fifty-six castles in Southern and Southeast Germany were studied that had similar geology of base-rich parent rocks and soils. The castles were built from base rich rock material, usually taken from the same region. The study focused on alien and native plant species of the natural or seminatural open rock vegetation and the xerothermic shrub vegetation of these habitats. The vegetation of the castle walls was also included as this habitat type is regarded as comparable to natural rock habitats (Kowarik, 1987). The reason for the exclusion of other habitats was that the study was first designed to analyse the degree of naturalisation of alien 147
K. Dehnen-Schmutz species in natural or seminatural vegetation (Dehnen-Schmutz, 2000). Rocks within the castle area and directly adjacent to the castles (i.e. the whole castle rock) were investigated. From 1994 to 1997 all castles were visited at least twice and at different times in the growing season. Both native and alien plants in these habitats were recorded. In this study only the presence or absence of the species, irrespective of the habitat type, was evaluated. Alien species were defined as species whose introduction or immigration resulted from deliberate or involuntary human activities (Richardson et al., 2000). They are divided into archaeophytes (invading before 1500 ) and neophytes (invading after 1500 ). Information on the time of introduction, area of origin and the use of the plants was collated from the literature (mainly Fischer-Benzon, 1894; Fischer, 1929; Willerding, 1986, 1992; Rothmaler, 1988; Schlosser et al., 1991; Düll & Kutzelnigg, 1992; Hegi, 1906 – 98; Sebald et al., 1992, 1993, 1996, 1998). These data were analysed separately for medieval uses of native and alien plants (archaeophytes only) and for uses without provable reference to the Middle Ages for all alien plants. In the first analysis, uses were taken from historical documents from the Middle Ages (Fischer-Benzon, 1894; Fischer, 1929) or from archaeobotanical results from excavations (Willerding, 1992). Potential uses which are limited to the native range of the alien plants were not considered. For each castle, the area investigated was measured from maps. The castles were characterised by their distance from the next settlement (more than 200 m away from the edge of the next settlement, adjacent to the edge of a settlement or in a settlement) and their current use (uninhabited or inhabited). Both factors have been shown to influence the number of alien species at the castles (Dehnen-Schmutz, 1998). They are included in this analysis to test for effects correlating coincidentally with the age of the castles. The only historical date available for all 56 castles is the year of foundation, i.e. the earliest year for that a castle was mentioned in any historic document. These data were taken from Dehio (1964), Kunstmann (1971/72), Appel et al. (1987), Schwineköper (1987), Schmitt (1988–93), Goetze (1989), Patze & Aufgebauer (1989), Krahe (1994). The botanical nomenclature follows Wisskirchen & Haeupler (1998). There is no single dataset on the time of introduction and the uses of alien plants in Germany which could be used for comparison with the results here. The recent analysis of the alien flora of Germany by Kühn & Klotz (2002) gives information on the different modes of introduction, including the uses of plants, and was therefore used for comparison with the proportions of useable plants in this study. The list of 279 agriophytes (i.e. alien plants naturalised in natural and seminatural vegetation) by Lohmeyer & Sukopp (1992, 2001) was used to compare the time of introduction of the species found at the castles to a dataset covering the entire spectrum of natural and seminatural vegetation types in Germany. The Lohmeyer & Sukopp list was complemented by information on the time of introduction using the data sources mentioned above. Chi-square tests were used to compare the proportions of species with different periods of introduction and different uses. 148
The relationship between the number of species at the castles and the variables characterising the castles were analysed by a correlation analysis. Spearman’s rank correlation coefficients were used because most of the variables were non-normally distributed or categorical. RESULTS 371 plant species were recorded on the rocks and the walls of the castles, 97 of which were alien (65 archaeophytes and 32 neophytes; Table 1). The comparison with the 245 species listed by Lohmeyer & Sukopp (1992, 2001) shows a higher frequency of species introduced in the Medieval Ages and a lower frequency of species introduced in the 19th and 20th Century at the castles. This discrepancy is significant (P < 0.01). The next step was finding the correlation between the year of foundation of the castles, the stock of alien species occurring at the castles today and other variables. The results of the correlation analysis (Table 2) show that the only variable correlating with that date is the number of archaeophytes found at the castles. The negative sign of the correlation coefficient implies a decreasing number of archaeophytes with a later year of foundation. Table 2 also gives correlations between the number of archaeophytic, neophytic and native species, the use and altitude of the castle and the size of the area studied. Neophytic species do not correlate with native species, but are significantly more common at inhabited castles. Increasing altitude of the castles is associated with a decrease of alien species.
Table 1 Comparison of the observed and expected number of species introduced at different times for the 97 alien plant species found at the castles and the 245 agriophytes listed by Lohmeyer & Sukopp (1992, 2001). Expected values are calculated by assuming the frequency of species introduced in different periods is similar for the castles species and the agriophytes. To fulfil the conditions for the chi-square test the categories ‘Bronze Age’ and ‘Iron Age’ are combined. The distribution of the castle species compared to the agriophytes is significantly different (chi-square = 24.459; d.f. = 8; P = 0.002) Castles Time Archaeophytes
Neophytes
Neolithic Age Bronze Age Iron Age Roman Age Medieval Age Unknown 16th Century 17th Century 18th Century 19th Century 20th Century Unknown
Agriophytes
Observed
Expected
Observed
20 6 8 8 14 9 8 5 5 12 1 1
18.1
49 10 10 14 19 — 15 12 25 60 31 —
8.9 5.8 8.6 — 6.0 4.5 7.9 18.9 8.4 —
Diversity and Distributions, 10, 147–151, © 2004 Blackwell Publishing Ltd
Alien species at medieval castles Table 2 Spearman’s correlation coefficients between the number of alien (archaeophyte and neophyte) and native plants, the year of foundation of the castles, use (1 = uninhabited, 2 = inhabited), position (1 = more than 200 m away from the edge of the next settlement, 2 = adjacent to the edge of a settlement, 3 = in a settlement) area investigated and the altitude of the castle
Archaeophytes Neophytes Natives Year Use Position Area Altitude
Archaeophytes
Neophytes
Natives
Year
Use
Position
Area
Altitude
1.000 0.592** 0.487** − 0.306* 0.300* − 0.096 0.456** − 0.451**
0.592** 1.000 0.057 − 0.215 0.505** 0.260 0.242 − 0.681**
0.487** 0.057 1.000 − 0.100 − 0.199 − 0.389** 0.542** 0.090
− 0.306* − 0.215 − 0.100 1.000 − 0.082 − 0.007 − 0.227 0.082
0.300* 0.505** − 0.199 − 0.082 1.000 0.234 0.123 − 0.581**
− 0.096 0.260 − 0.389** − 0.007 0.234 1.000 − 0.169 − 0.322*
0.456** 0.242 0.542** − 0.227 0.123 − 0.169 1.000 − 0.173
− 0.451** − 0.681** 0.090 0.082 − 0.581** − 0.322* − 0.173 1.000
*Correlation is significant at the .05 level (2-tailed). **Correlation is significant at the .01 level (2-tailed).
Table 3 The number of native and alien archaeophytic species found at the castles, used during the Middle Ages and classified by their use. Multiple uses of species are counted separately for each category, so the total number of species used does not equal the sum of all categories
Table 4 Comparison of the potential uses of archaeophytes and neophytes at castles. (absolute number and percentage). Multiple uses of some species are not included. Information about uses from Düll & Kutzelnigg (1992), Fischer-Benzon (1894), Fischer (1929), Hegi (1906,98), Schlosser et al. (1991), Willerding (1992)
Use
Native
Alien (Archaeophytes)
Use
Archaeophytes
Medicinal Food Ornamental Spice Industrial Magical Number of species used Number of species not used
52 11 3 3 1 1 58 215
22 10 8 3 4 2 33 32
Medicinal Food Forage Industrial Ornamental Without use
24 7 1 4 8 21
Consider next the possible use of plants found at the castles. The analysis of medieval uses of native and alien plants indicates that altogether 92 species were usable plants during the Middle Ages, 33 of them archaeophytes. This means that of 65 archaeophytes occurring at the castles 50% had a possible use at that time. The percentage of usable native plants is much lower at 21% (58 species). Table 3 shows the plants were most commonly medicinal plants, often with other applications. Archaeophytes to neophytes are compared in Table 4. This time uses that had not been verified for the Middle Ages were included, which increases the number of usable archaeophytes. As above, most of the archaeophytes were used as medicinal plants. In contrast, most of the neophytes were used as ornamentals (24 of 31 species). For calculating chi-square the first four categories were combined in one. The difference between archaeophytes and neophytes was highly significant (Chi-square 43.25; d.f. = 2; P < 0.001). Comparing these counts with the total alien flora (Table 5) requires combining medicinal, food, forage and industrial uses into one category of ‘useful plants’ so as to have the same three categories used by Kühn & Klotz (2002) in their analysis. Alien castle species had nearly twice as many useable plants as expected assuming the same proportions as in the total alien flora, a Diversity and Distributions, 10, 147–151, © 2004 Blackwell Publishing Ltd
Neophytes 36% 11% 2% 6% 12% 33%
1 0 0 0 24 7
3% — — — 78% 19%
Table 5 Comparison of alien plants found at the castles with the 916 species of the total alien flora of Germany (Kühn & Klotz, 2002), by use. Expected values for the castles species are calculated by assuming the frequency of species in the three categories is similar for the castles species and the total alien flora. The distribution of the castle species compared to the total alien flora is significantly different (Chi-square = 19.141; d.f. = 2; P < 0.001) Castles
Total Alien Flora
Observed number Expected number Observed Useful plant 37 Ornamental 30 Without use 28
22.0 27.3 45.7
197 261 458
slightly higher number of ornamentals and fewer plants without any uses. These differences are highly significant (Chi-square = 19.141; d.f. = 2; P < 0.001). DISCUSSION From indirect evidence, the species composition of alien plant species growing around medieval castles today may be traced 149
K. Dehnen-Schmutz back to the historical reasons for their introduction there. Species introduced at different times correspond with different uses of the castles over the centuries. In the Middle Ages castles were built and used for protection and for the demonstration of power (Biller, 1993). In the castle area there were stables, working areas and gardens. People living in the castles also had to work in the fields. Plants used then were mostly plants useful for daily life in the castles. The alien species introduced in or before the Middle Ages were used for such purposes. With the end of the Middle Ages the function of castles changed because of social and economic changes in the society and improved cannon technologies, against which many castles did no longer offer enough protection. Many castles were abandoned and dilapidated, some were used as prestigious residential buildings. Now ornamental plants became more important for the inhabitants of the castles. This could explain why neophytes (introduced after the Middle Ages) at the castles are mostly ornamental plants (24 of 31 species). However, it is likely that more neophytes were introduced for ornamental reasons than archaeophytes but there is no dataset separating the potential uses of native, archaeophytic and neophytic species that could be used for comparison. The results also show that castles built earlier are likely to have had more species introduced earlier than castles built later. This implies that the species composition is affected not only by the duration of human influence but also by the historical period of this influence. Compared with cities and rural settlements, castles are distinguished by a higher percentage of archaeophytes. In cities, the percentage of neophytes is higher (Kowarik, 1995; Pysek, 1998), and in rural settlements their numbers are nearly equal (Kowarik, 1995; Otte & Mattonet, 2001), but the total percentage of alien species is in both cases higher than at castles. Limiting this study to plant species recorded in the natural and near natural rock and wall vegetation might be thought to bias the results. However, less natural habitats are more intensely affected by current human activities and have probably changed much more since the foundation of the castles than the natural and near natural habitats, which might therefore be more likely to preserve past influences. The only other type of natural vegetation occurring at castles on hilltops is woods. Investigations of the woods adjacent to castles have shown the influence of edaphic factors on the native tree species composition (Siegl, 1998) but only a few alien species were recorded. Moreover, woodlands in Central Europe are generally known to have only a few alien species whereas rock vegetation is the second richest habitat for naturalised alien species (Lohmeyer & Sukopp, 1992). This shows that an inclusion of more habitat types would not have resulted in an improved dataset for this study. Castles and their ruins are known to be places of high species diversity (Lohmeyer, 1975) and are therefore of nature conservation interest (Eicke, 1998). In this study, 28 of the plant species recorded, including 7 archaeophytes, are listed in Red Data Books (Dehnen-Schmutz, 2000). The alien species, by reflecting the history of the castles, represent a heritage that justifies their conservation as well. There may also be concerns about possible negative impacts of alien species on native biodiversity. However, 150
at the castles studied only a few species might cause problems. Syringa vulgaris and Lycium barbarum built up dense shrub vegetation with a herbal layer very poor in species. At most castles in this study this is not seen as a problem. A combined effort in the conservation of both biodiversity and historical monuments is necessary to keep alive the memory of medieval history represented not only in the walls and towers of the castles but in the plant species growing in their vicinity as well. ACKNOWLEDGEMENTS I thank Herbert Sukopp for his helpful support during the study. Mark Williamson kindly improved the English and commented on the manuscript. I am also grateful to four anonymous referees for valuable comments. REFERENCES Appel, B., Rischert, H. & Zecherle, K. (1987) Burgen und Schlösser. Kreis Eichstätt. Hercynia-Verlag, Kipfenberg. Bevan-Jones, R. (2002) The ancient yew. A history of Taxus Baccata. Windgather Press, Macclesfield, Cheshire. Biller, T. (1993) Die Adelsburg in Deutschland. Deutscher Kunstverlag, München. Caneva, G., Pacini, A., Celesti Grapow, L. & Ceschin, S. (2003) The Colosseum’s use and state of abandonment as analysed through its flora. International Biodeterioration and Biodegradation, 51, 211–219. Dehio, G. (1964) Handbuch der Deutschen Kunstdenkmäler. Baden-Württemberg. Deutscher Kunstverlag, München. Dehnen-Schmutz, K. (1998) Medieval castles as centers of spread of non-native plant species. Plant invasions: ecological mechanisms and human responses (eds U. Starfinger, K. Edwards, I. Kowarik and M. Williamson), pp. 307–312. Backhuys, Leiden. Dehnen-Schmutz, K. (2000) Nichteinheimische Pflanzen in der Flora Mittelalterlicher Burgen. J. Cramer, Berlin. Düll, R. & Kutzelnigg, H. (1992) Botanisch-Ökologisches Exkursionstaschenbuch, 4th edn. Quelle & Meyer, Heidelberg. Eicke, L. (1998) Anliegen des Naturschutzes bei der Sanierung von historischer Bausubstanz. Naturschutz und Denkmalpflege: Wege zu einem Dialog im Garten (eds I. Kowarik, E. Schmidt and B. Sigel), pp. 293–307. vdf Hochschulverlag ETH Zürich, Zürich. Fischer, H. (1929) Mittelalterliche Botanik. Reprint 1967. Georg Olms, Hildesheim. Fischer-Benzon, R., (1894) Altdeutsche Gartenflora — Untersuchungen über die Nutzpflanzen des deutschen Mittelalters, ihre Wanderung und ihre Vorgeschichte im klassischen Altertum. Lipsius & Tischer, Kiel. Goetze, J. (1989) Burgen im Neckartal. Brausdruck, Heidelberg. Hegi, G. (1906 – 98) Illustrierte Flora von Mitteleuropa, Vol. I to VI, partly, 3rd edn. Lehmann, München and Parey, Berlin. Janssen, W. (1986) Mittelalterliche Gartenkultur. Nahrung und Rekreation. Mensch und Umwelt im Mittelalter (ed. B. Herrmann), 2nd edn, pp. 224–243. Deutsche Verlags-Anstalt, Stuttgart. Janssen, W. & Knörzer, K.H. (1971) Die Frühmittelalterliche Diversity and Distributions, 10, 147–151, © 2004 Blackwell Publishing Ltd
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